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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">Lowering N<sub>2</sub>O emissions from soils using eucalypt biochar: the importance of redox reactions</title><author><name sortKey="Quin, P" sort="Quin, P" uniqKey="Quin P" first="P" last="Quin">P. Quin</name><affiliation><nlm:aff id="a1"><institution>University of New England</institution>, Armidale, NSW 2351,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a2"><institution>Wollongbar Primary Industries Institute, NSW Department of Primary Industries</institution>, 1243 Bruxner Highway, Wollongbar, NSW 2477,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Joseph, S" sort="Joseph, S" uniqKey="Joseph S" first="S" last="Joseph">S. Joseph</name><affiliation><nlm:aff id="a3"><institution>School of Materials Science and Engineering, University of New South Wales</institution>, NSW 2052,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a6"><institution>Discipline of Chemistry, University of Newcastle</institution>, Callaghan NSW 2308,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a7"><institution>Department of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong</institution>, Wollongong NSW, 2522,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Husson, O" sort="Husson, O" uniqKey="Husson O" first="O" last="Husson">O. Husson</name><affiliation><nlm:aff id="a4"><institution>CIRAD, UPR AIDA, TAB 115/02 Avenue Agropolis 34398 Montpellier Cedex 5, France and AfricaRice Centre</institution>, 01 BP 2031 Cotonou,<country>Bénin</country></nlm:aff></affiliation></author><author><name sortKey="Donne, S" sort="Donne, S" uniqKey="Donne S" first="S" last="Donne">S. Donne</name><affiliation><nlm:aff id="a6"><institution>Discipline of Chemistry, University of Newcastle</institution>, Callaghan NSW 2308,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Mitchell, D" sort="Mitchell, D" uniqKey="Mitchell D" first="D" last="Mitchell">D. Mitchell</name><affiliation><nlm:aff id="a5"><institution>Electron Microscopy Center, AIIM, University of Wollongong</institution>, Wollongong NSW, 2522,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Munroe, P" sort="Munroe, P" uniqKey="Munroe P" first="P" last="Munroe">P. Munroe</name><affiliation><nlm:aff id="a3"><institution>School of Materials Science and Engineering, University of New South Wales</institution>, NSW 2052,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Phelan, D" sort="Phelan, D" uniqKey="Phelan D" first="D" last="Phelan">D. Phelan</name><affiliation><nlm:aff id="a8"><institution>Electron Microscope and X-Ray Unit, University of Newcastle</institution>, Callaghan NSW 2308,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Cowie, A" sort="Cowie, A" uniqKey="Cowie A" first="A" last="Cowie">A. Cowie</name><affiliation><nlm:aff id="a9"><institution>NSW Department of Primary Industries, University of New England</institution>, Armidale, NSW 2351,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Van Zwieten, L" sort="Van Zwieten, L" uniqKey="Van Zwieten L" first="L" last="Van Zwieten">L. Van Zwieten</name><affiliation><nlm:aff id="a1"><institution>University of New England</institution>, Armidale, NSW 2351,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a2"><institution>Wollongbar Primary Industries Institute, NSW Department of Primary Industries</institution>, 1243 Bruxner Highway, Wollongbar, NSW 2477,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a10"><institution>Southern Cross Plant Science, Southern Cross University</institution>, Military Road, East Lismore NSW 2480,<country>Australia</country></nlm:aff></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">26615820</idno><idno type="pmc">4663753</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4663753</idno><idno type="RBID">PMC:4663753</idno><idno type="doi">10.1038/srep16773</idno><date when="2015">2015</date><idno type="wicri:Area/Pmc/Corpus">000812</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">000812</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">Lowering N<sub>2</sub>O emissions from soils using eucalypt biochar: the importance of redox reactions</title><author><name sortKey="Quin, P" sort="Quin, P" uniqKey="Quin P" first="P" last="Quin">P. Quin</name><affiliation><nlm:aff id="a1"><institution>University of New England</institution>, Armidale, NSW 2351,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a2"><institution>Wollongbar Primary Industries Institute, NSW Department of Primary Industries</institution>, 1243 Bruxner Highway, Wollongbar, NSW 2477,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Joseph, S" sort="Joseph, S" uniqKey="Joseph S" first="S" last="Joseph">S. Joseph</name><affiliation><nlm:aff id="a3"><institution>School of Materials Science and Engineering, University of New South Wales</institution>, NSW 2052,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a6"><institution>Discipline of Chemistry, University of Newcastle</institution>, Callaghan NSW 2308,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a7"><institution>Department of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong</institution>, Wollongong NSW, 2522,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Husson, O" sort="Husson, O" uniqKey="Husson O" first="O" last="Husson">O. Husson</name><affiliation><nlm:aff id="a4"><institution>CIRAD, UPR AIDA, TAB 115/02 Avenue Agropolis 34398 Montpellier Cedex 5, France and AfricaRice Centre</institution>, 01 BP 2031 Cotonou,<country>Bénin</country></nlm:aff></affiliation></author><author><name sortKey="Donne, S" sort="Donne, S" uniqKey="Donne S" first="S" last="Donne">S. Donne</name><affiliation><nlm:aff id="a6"><institution>Discipline of Chemistry, University of Newcastle</institution>, Callaghan NSW 2308,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Mitchell, D" sort="Mitchell, D" uniqKey="Mitchell D" first="D" last="Mitchell">D. Mitchell</name><affiliation><nlm:aff id="a5"><institution>Electron Microscopy Center, AIIM, University of Wollongong</institution>, Wollongong NSW, 2522,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Munroe, P" sort="Munroe, P" uniqKey="Munroe P" first="P" last="Munroe">P. Munroe</name><affiliation><nlm:aff id="a3"><institution>School of Materials Science and Engineering, University of New South Wales</institution>, NSW 2052,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Phelan, D" sort="Phelan, D" uniqKey="Phelan D" first="D" last="Phelan">D. Phelan</name><affiliation><nlm:aff id="a8"><institution>Electron Microscope and X-Ray Unit, University of Newcastle</institution>, Callaghan NSW 2308,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Cowie, A" sort="Cowie, A" uniqKey="Cowie A" first="A" last="Cowie">A. Cowie</name><affiliation><nlm:aff id="a9"><institution>NSW Department of Primary Industries, University of New England</institution>, Armidale, NSW 2351,<country>Australia</country></nlm:aff></affiliation></author><author><name sortKey="Van Zwieten, L" sort="Van Zwieten, L" uniqKey="Van Zwieten L" first="L" last="Van Zwieten">L. Van Zwieten</name><affiliation><nlm:aff id="a1"><institution>University of New England</institution>, Armidale, NSW 2351,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a2"><institution>Wollongbar Primary Industries Institute, NSW Department of Primary Industries</institution>, 1243 Bruxner Highway, Wollongbar, NSW 2477,<country>Australia</country></nlm:aff></affiliation><affiliation><nlm:aff id="a10"><institution>Southern Cross Plant Science, Southern Cross University</institution>, Military Road, East Lismore NSW 2480,<country>Australia</country></nlm:aff></affiliation></author></analytic><series><title level="j">Scientific Reports</title><idno type="eISSN">2045-2322</idno><imprint><date when="2015">2015</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><p>Agricultural soils are the primary anthropogenic source of atmospheric nitrous oxide (N<sub>2</sub>O), contributing to global warming and depletion of stratospheric ozone. Biochar addition has shown potential to lower soil N<sub>2</sub>O emission, with the mechanisms remaining unclear. We incubated eucalypt biochar (550 °C) – 0, 1 and 5% (w/w) in Ferralsol at 3 water regimes (12, 39 and 54% WFPS) – in a soil column, following gamma irradiation. After N<sub>2</sub>O was injected at the base of the soil column, in the 0% biochar control 100% of expected injected N<sub>2</sub>O was released into headspace, declining to 67% in the 5% amendment. In a 100% biochar column at 6% WFPS, only 16% of the expected N<sub>2</sub>O was observed. X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N<sub>2</sub>O and the biochar surfaces. We have shown increases in -O-C = N /pyridine pyrrole/NH<sub>3</sub>, suggesting reactions between N<sub>2</sub>O and the carbon (C) matrix upon exposure to N<sub>2</sub>O. With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents. Evidence suggests that biochar has taken part in redox reactions reducing N<sub>2</sub>O to dinitrogen (N<sub>2</sub>), in addition to adsorption of N<sub>2</sub>O.</p></div></front><back><div1 type="bibliography"><listBibl><biblStruct><analytic><author><name sortKey="Butterbach Bahl, K" uniqKey="Butterbach Bahl K">K. Butterbach-Bahl</name></author><author><name sortKey="Baggs, E M" uniqKey="Baggs E">E. M. Baggs</name></author><author><name sortKey="Dannenmann, M" uniqKey="Dannenmann M">M. Dannenmann</name></author><author><name sortKey="Kiese, R" uniqKey="Kiese R">R. Kiese</name></author><author><name sortKey="Zechmeister Boltenstern, S" uniqKey="Zechmeister Boltenstern S">S. Zechmeister-Boltenstern</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Clough, T J" uniqKey="Clough T">T. J. Clough</name></author><author><name sortKey="Sherlock, R R" uniqKey="Sherlock R">R. R. Sherlock</name></author><author><name sortKey="Rolston, D E" uniqKey="Rolston D">D. E. Rolston</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Heincke, M" uniqKey="Heincke M">M. Heincke</name></author><author><name sortKey="Kaupenjohann, M" uniqKey="Kaupenjohann M">M. Kaupenjohann</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Mukherjee, A" uniqKey="Mukherjee A">A. Mukherjee</name></author><author><name sortKey="Lal, R" uniqKey="Lal R">R. Lal</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Sanchez Garcia, M" uniqKey="Sanchez Garcia M">M. Sánchez-García</name></author><author><name sortKey="Roig, A" uniqKey="Roig A">A. Roig</name></author><author><name sortKey="Sanchez Monedero, M A" uniqKey="Sanchez Monedero M">M. A. Sanchez-Monedero</name></author><author><name sortKey="Cayuela, M L" uniqKey="Cayuela M">M. L. Cayuela</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Cayuela, M L" uniqKey="Cayuela M">M. L. Cayuela</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Cayuela, M L" uniqKey="Cayuela M">M. L. Cayuela</name></author><author><name sortKey="Jeffery, S" uniqKey="Jeffery S">S. Jeffery</name></author><author><name sortKey="Van Zwieten, L" uniqKey="Van Zwieten L">L. Van Zwieten</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Lin, X" uniqKey="Lin X">X. Lin</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Davidson, E A" uniqKey="Davidson E">E. A. Davidson</name></author><author><name sortKey="Chorover, J" uniqKey="Chorover J">J. Chorover</name></author><author><name sortKey="Dail, D B" uniqKey="Dail D">D. B. Dail</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Clough, T J" uniqKey="Clough T">T. J. Clough</name></author><author><name sortKey="Condron, L M" uniqKey="Condron L">L. M. Condron</name></author><author><name sortKey="Kamman, C" uniqKey="Kamman C">C. Kamman</name></author><author><name sortKey="Muller, C" uniqKey="Muller C">C. Müller</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Van Zwieten, L" uniqKey="Van Zwieten L">L. Van Zwieten</name></author><author><name sortKey="Lehmann, J" uniqKey="Lehmann J">J. Lehmann</name></author><author><name sortKey="Joseph, S" uniqKey="Joseph S">S. Joseph</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Shcherbak, I" uniqKey="Shcherbak I">I. Shcherbak</name></author><author><name sortKey="Robertson, G P" uniqKey="Robertson G">G. P. Robertson</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Quin, P R" uniqKey="Quin P">P. R. Quin</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Sun, Z" uniqKey="Sun Z">Z. Sun</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Harter, J" uniqKey="Harter J">J. Harter</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Joseph, S D" uniqKey="Joseph S">S. D. Joseph</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Cornelissen, G" uniqKey="Cornelissen G">G. Cornelissen</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Cayuela, M L" uniqKey="Cayuela M">M. L. Cayuela</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Klupfel, L" uniqKey="Klupfel L">L. Klüpfel</name></author><author><name sortKey="Keiluweit, M" uniqKey="Keiluweit M">M. Keiluweit</name></author><author><name sortKey="Kleber, M" uniqKey="Kleber M">M. Kleber</name></author><author><name sortKey="Sander, M" uniqKey="Sander M">M. Sander</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Joseph, S" uniqKey="Joseph S">S. Joseph</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Melton, E D" uniqKey="Melton E">E. D. Melton</name></author><author><name sortKey="Swanner, E D" uniqKey="Swanner E">E. D. Swanner</name></author><author><name sortKey="Behrens, S" uniqKey="Behrens S">S. Behrens</name></author><author><name sortKey="Schmidt, C" uniqKey="Schmidt C">C. Schmidt</name></author><author><name sortKey="Kappler, A" uniqKey="Kappler A">A. Kappler</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Hirsch, W" uniqKey="Hirsch W">W. Hirsch</name></author><author><name sortKey="Fried, V" uniqKey="Fried V">V. Fried</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Zimmerman, A R" uniqKey="Zimmerman A">A. R. Zimmerman</name></author><author><name sortKey="Gao, B" uniqKey="Gao B">B. Gao</name></author><author><name sortKey="Ahn, M Y" uniqKey="Ahn M">M.-Y. Ahn</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Luo, Y" uniqKey="Luo Y">Y. Luo</name></author><author><name sortKey="Durenkamp, M" uniqKey="Durenkamp M">M. Durenkamp</name></author><author><name sortKey="De Nobili, M" uniqKey="De Nobili M">M. De Nobili</name></author><author><name sortKey="Lin, Q" uniqKey="Lin Q">Q. Lin</name></author><author><name sortKey="Brookes, P C" uniqKey="Brookes P">P. C. Brookes</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Fang, Y" uniqKey="Fang Y">Y. Fang</name></author><author><name sortKey="Singh, B P" uniqKey="Singh B">B. P. Singh</name></author><author><name sortKey="Singh, B" uniqKey="Singh B">B. Singh</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Butterbach Bahl, K" uniqKey="Butterbach Bahl K">K. Butterbach-Bahl</name></author><author><name sortKey="Sutton, M" uniqKey="Sutton M">M. Sutton</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Hansen, H C B" uniqKey="Hansen H">H. C. B. Hansen</name></author><author><name sortKey="Koch, C B" uniqKey="Koch C">C. B. Koch</name></author><author><name sortKey="Nancke Krogh, H" uniqKey="Nancke Krogh H">H. Nancke-Krogh</name></author><author><name sortKey="Borggaard, O K" uniqKey="Borggaard O">O. K. Borggaard</name></author><author><name sortKey="S Rensen, J" uniqKey="S Rensen J">J. Sørensen</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Ramsay, A J" uniqKey="Ramsay A">A. J. Ramsay</name></author><author><name sortKey="Bawden, A D" uniqKey="Bawden A">A. D. Bawden</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Singh, B R" uniqKey="Singh B">B. R. Singh</name></author><author><name sortKey="Kanehiro, Y" uniqKey="Kanehiro Y">Y. Kanehiro</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Mcnamara, N P" uniqKey="Mcnamara N">N. P. McNamara</name></author><author><name sortKey="Black, H I J" uniqKey="Black H">H. I. J. Black</name></author><author><name sortKey="Beresford, N A" uniqKey="Beresford N">N. A. Beresford</name></author><author><name sortKey="Parekh, N R" uniqKey="Parekh N">N. R. Parekh</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Cheng, C H" uniqKey="Cheng C">C.-H. Cheng</name></author><author><name sortKey="Lehmann, J" uniqKey="Lehmann J">J. Lehmann</name></author><author><name sortKey="Thies, J E" uniqKey="Thies J">J. E. Thies</name></author><author><name sortKey="Burton, S D" uniqKey="Burton S">S. D. Burton</name></author><author><name sortKey="Engelhard, M H" uniqKey="Engelhard M">M. H. Engelhard</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Point, S" uniqKey="Point S">S. Point</name></author><author><name sortKey="Minea, T" uniqKey="Minea T">T. Minea</name></author><author><name sortKey="Bouchet Fabre, B" uniqKey="Bouchet Fabre B">B. Bouchet-Fabre</name></author><author><name sortKey="Granier, A" uniqKey="Granier A">A. Granier</name></author><author><name sortKey="Xps, Turban G" uniqKey="Xps T">Turban G. XPS</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Ravishankara, A R" uniqKey="Ravishankara A">A. R. Ravishankara</name></author><author><name sortKey="Daniel, J S" uniqKey="Daniel J">J. S. Daniel</name></author><author><name sortKey="Portmann, R W" uniqKey="Portmann R">R. W. Portmann</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Lin, Y" uniqKey="Lin Y">Y. Lin</name></author><author><name sortKey="Munroe, P" uniqKey="Munroe P">P. Munroe</name></author><author><name sortKey="Joseph, S" uniqKey="Joseph S">S. Joseph</name></author><author><name sortKey="Kimber, S" uniqKey="Kimber S">S. Kimber</name></author><author><name sortKey="Van Zwieten, L" uniqKey="Van Zwieten L">L. Van Zwieten</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Aylward, G H" uniqKey="Aylward G">G. H. Aylward</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Carabineiro, S A" uniqKey="Carabineiro S">S. A. Carabineiro</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Avdeev, V I" uniqKey="Avdeev V">V. I. Avdeev</name></author><author><name sortKey="Ruzankin, S F" uniqKey="Ruzankin S">S. F. Ruzankin</name></author><author><name sortKey="Zhidomirov, G M" uniqKey="Zhidomirov G">G. M. Zhidomirov</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Husson, O" uniqKey="Husson O">O. Husson</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Li, Y" uniqKey="Li Y">Y. Li</name></author><author><name sortKey="Yu, S" uniqKey="Yu S">S. Yu</name></author><author><name sortKey="Strong, J" uniqKey="Strong J">J. Strong</name></author><author><name sortKey="Wang, H" uniqKey="Wang H">H. Wang</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Chao, T T" uniqKey="Chao T">T.-T. Chao</name></author><author><name sortKey="Kroontje, W" uniqKey="Kroontje W">W. Kroontje</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Alowitz, M J" uniqKey="Alowitz M">M. J. Alowitz</name></author><author><name sortKey="Scherer, M M" uniqKey="Scherer M">M. M. Scherer</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Dhakal, P" uniqKey="Dhakal P">P. Dhakal</name></author><author><name sortKey="Matocha, C J" uniqKey="Matocha C">C. J. Matocha</name></author><author><name sortKey="Huggins, F E" uniqKey="Huggins F">F. E. Huggins</name></author><author><name sortKey="Vandiviere, M M" uniqKey="Vandiviere M">M. M. Vandiviere</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Klupfel, L" uniqKey="Klupfel L">L. Klüpfel</name></author><author><name sortKey="Piepenbrock, A" uniqKey="Piepenbrock A">A. Piepenbrock</name></author><author><name sortKey="Kappler, A" uniqKey="Kappler A">A. Kappler</name></author><author><name sortKey="Sander, M" uniqKey="Sander M">M. Sander</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Sang, C" uniqKey="Sang C">C. Sang</name></author><author><name sortKey="Kim, B H" uniqKey="Kim B">B. H. Kim</name></author><author><name sortKey="Lund, C R F" uniqKey="Lund C">C. R. F. Lund</name></author></analytic></biblStruct><biblStruct></biblStruct><biblStruct><analytic><author><name sortKey="Krull, E S" uniqKey="Krull E">E. S. Krull</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Van Zwieten, L" uniqKey="Van Zwieten L">L. Van Zwieten</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Rangott, G" uniqKey="Rangott G">G. Rangott</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Hunt, C" uniqKey="Hunt C">C. Hunt</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Downie, A" uniqKey="Downie A">A. Downie</name></author><author><name sortKey="Crosky, A" uniqKey="Crosky A">A. Crosky</name></author><author><name sortKey="Munroe, P" uniqKey="Munroe P">P. Munroe</name></author><author><name sortKey="Lehmann, J" uniqKey="Lehmann J">J. Lehmann</name></author><author><name sortKey="Joseph, S" uniqKey="Joseph S">S. Joseph</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Daly, M J" uniqKey="Daly M">M. J. Daly</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Van Gerwen, S J C" uniqKey="Van Gerwen S">S. J. C. van Gerwen</name></author><author><name sortKey="Rombouts, F M" uniqKey="Rombouts F">F. M. Rombouts</name></author><author><name sortKey="Van Riet, K" uniqKey="Van Riet K">K. Van’t Riet</name></author><author><name sortKey="Zwietering, M H" uniqKey="Zwietering M">M. H. Zwietering</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Zelles, L" uniqKey="Zelles L">L. Zelles</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Clarke, J M" uniqKey="Clarke J">J. M. Clarke</name></author><author><name sortKey="Gillings, M R" uniqKey="Gillings M">M. R. Gillings</name></author><author><name sortKey="Altavilla, N" uniqKey="Altavilla N">N. Altavilla</name></author><author><name sortKey="Beattie, A J" uniqKey="Beattie A">A. J. Beattie</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Rayment, G E" uniqKey="Rayment G">G. E. Rayment</name></author><author><name sortKey="Lyons, D J" uniqKey="Lyons D">D. J. Lyons</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Fiedler, S" uniqKey="Fiedler S">S. Fiedler</name></author><author><name sortKey="Vepraskas, M J" uniqKey="Vepraskas M">M. J. Vepraskas</name></author><author><name sortKey="Richardson, J L" uniqKey="Richardson J">J. L. Richardson</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Glinski, J" uniqKey="Glinski J">J. Glínski</name></author><author><name sortKey="Ste Pniewski, W" uniqKey="Ste Pniewski W">W. Stępniewski</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Pidello, A" uniqKey="Pidello A">A. Pidello</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Joseph, S" uniqKey="Joseph S">S. Joseph</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Puigdomenech, I" uniqKey="Puigdomenech I">I. Puigdomenech,</name></author></analytic></biblStruct></listBibl></div1></back></TEI><pmc article-type="research-article"><pmc-dir>properties open_access</pmc-dir>
<front><journal-meta><journal-id journal-id-type="nlm-ta">Sci Rep</journal-id><journal-id journal-id-type="iso-abbrev">Sci Rep</journal-id><journal-title-group><journal-title>Scientific Reports</journal-title></journal-title-group><issn pub-type="epub">2045-2322</issn><publisher><publisher-name>Nature Publishing Group</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="pmid">26615820</article-id><article-id pub-id-type="pmc">4663753</article-id><article-id pub-id-type="pii">srep16773</article-id><article-id pub-id-type="doi">10.1038/srep16773</article-id><article-categories><subj-group subj-group-type="heading"><subject>Article</subject></subj-group></article-categories><title-group><article-title>Lowering N<sub>2</sub>O emissions from soils using eucalypt biochar: the importance of redox reactions</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>Quin</surname><given-names>P</given-names></name><xref ref-type="aff" rid="a1">1</xref><xref ref-type="aff" rid="a2">2</xref><xref ref-type="author-notes" rid="n1">*</xref></contrib><contrib contrib-type="author"><name><surname>Joseph</surname><given-names>S</given-names></name><xref ref-type="aff" rid="a3">3</xref><xref ref-type="aff" rid="a6">6</xref><xref ref-type="aff" rid="a7">7</xref><xref ref-type="author-notes" rid="n1">*</xref></contrib><contrib contrib-type="author"><name><surname>Husson</surname><given-names>O</given-names></name><xref ref-type="aff" rid="a4">4</xref></contrib><contrib contrib-type="author"><name><surname>Donne</surname><given-names>S</given-names></name><xref ref-type="aff" rid="a6">6</xref></contrib><contrib contrib-type="author"><name><surname>Mitchell</surname><given-names>D</given-names></name><xref ref-type="aff" rid="a5">5</xref></contrib><contrib contrib-type="author"><name><surname>Munroe</surname><given-names>P</given-names></name><xref ref-type="aff" rid="a3">3</xref></contrib><contrib contrib-type="author"><name><surname>Phelan</surname><given-names>D</given-names></name><xref ref-type="aff" rid="a8">8</xref></contrib><contrib contrib-type="author"><name><surname>Cowie</surname><given-names>A</given-names></name><xref ref-type="aff" rid="a9">9</xref></contrib><contrib contrib-type="author"><name><surname>Van Zwieten</surname><given-names>L</given-names></name><xref ref-type="corresp" rid="c1">a</xref><xref ref-type="aff" rid="a1">1</xref><xref ref-type="aff" rid="a2">2</xref><xref ref-type="aff" rid="a10">10</xref></contrib><aff id="a1"><label>1</label><institution>University of New England</institution>, Armidale, NSW 2351,<country>Australia</country></aff><aff id="a2"><label>2</label><institution>Wollongbar Primary Industries Institute, NSW Department of Primary Industries</institution>, 1243 Bruxner Highway, Wollongbar, NSW 2477,<country>Australia</country></aff><aff id="a3"><label>3</label><institution>School of Materials Science and Engineering, University of New South Wales</institution>, NSW 2052,<country>Australia</country></aff><aff id="a4"><label>4</label><institution>CIRAD, UPR AIDA, TAB 115/02 Avenue Agropolis 34398 Montpellier Cedex 5, France and AfricaRice Centre</institution>, 01 BP 2031 Cotonou,<country>Bénin</country></aff><aff id="a5"><label>5</label><institution>Electron Microscopy Center, AIIM, University of Wollongong</institution>, Wollongong NSW, 2522,<country>Australia</country></aff><aff id="a6"><label>6</label><institution>Discipline of Chemistry, University of Newcastle</institution>, Callaghan NSW 2308,<country>Australia</country></aff><aff id="a7"><label>7</label><institution>Department of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong</institution>, Wollongong NSW, 2522,<country>Australia</country></aff><aff id="a8"><label>8</label><institution>Electron Microscope and X-Ray Unit, University of Newcastle</institution>, Callaghan NSW 2308,<country>Australia</country></aff><aff id="a9"><label>9</label><institution>NSW Department of Primary Industries, University of New England</institution>, Armidale, NSW 2351,<country>Australia</country></aff><aff id="a10"><label>10</label><institution>Southern Cross Plant Science, Southern Cross University</institution>, Military Road, East Lismore NSW 2480,<country>Australia</country></aff></contrib-group><author-notes><corresp id="c1"><label>a</label><email>lukas.van.zwieten@dpi.nsw.gov.au</email></corresp><fn id="n1"><label>*</label><p>These authors contributed equally to this work.</p></fn></author-notes><pub-date pub-type="epub"><day>30</day><month>11</month><year>2015</year></pub-date><pub-date pub-type="collection"><year>2015</year></pub-date><volume>5</volume><elocation-id>16773</elocation-id><history><date date-type="received"><day>09</day><month>07</month><year>2015</year></date><date date-type="accepted"><day>20</day><month>10</month><year>2015</year></date></history><permissions><copyright-statement>Copyright © 2015, Macmillan Publishers Limited</copyright-statement><copyright-year>2015</copyright-year><copyright-holder>Macmillan Publishers Limited</copyright-holder><license license-type="open-access" xlink:href="http://creativecommons.org/licenses/by/4.0/"><pmc-comment>author-paid</pmc-comment>
<license-p>This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit <ext-link ext-link-type="uri" xlink:href="http://creativecommons.org/licenses/by/4.0/">http://creativecommons.org/licenses/by/4.0/</ext-link></license-p></license></permissions><abstract><p>Agricultural soils are the primary anthropogenic source of atmospheric nitrous oxide (N<sub>2</sub>O), contributing to global warming and depletion of stratospheric ozone. Biochar addition has shown potential to lower soil N<sub>2</sub>O emission, with the mechanisms remaining unclear. We incubated eucalypt biochar (550 °C) – 0, 1 and 5% (w/w) in Ferralsol at 3 water regimes (12, 39 and 54% WFPS) – in a soil column, following gamma irradiation. After N<sub>2</sub>O was injected at the base of the soil column, in the 0% biochar control 100% of expected injected N<sub>2</sub>O was released into headspace, declining to 67% in the 5% amendment. In a 100% biochar column at 6% WFPS, only 16% of the expected N<sub>2</sub>O was observed. X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N<sub>2</sub>O and the biochar surfaces. We have shown increases in -O-C = N /pyridine pyrrole/NH<sub>3</sub>, suggesting reactions between N<sub>2</sub>O and the carbon (C) matrix upon exposure to N<sub>2</sub>O. With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents. Evidence suggests that biochar has taken part in redox reactions reducing N<sub>2</sub>O to dinitrogen (N<sub>2</sub>), in addition to adsorption of N<sub>2</sub>O.</p></abstract></article-meta></front><body><p>It is well established that soils are the dominant source of atmospheric nitrous oxide (N<sub>2</sub>O), though a full understanding of the complex biotic and abiotic factors governing N<sub>2</sub>O production and consumption remains to be achieved<xref ref-type="bibr" rid="b1">1</xref><xref ref-type="bibr" rid="b2">2</xref><xref ref-type="bibr" rid="b3">3</xref>. Amendment of soil with biochar can lead to a reduction of N<sub>2</sub>O emissions, though under some circumstances biochar amendment has resulted in an increase in N<sub>2</sub>O emissions<xref ref-type="bibr" rid="b4">4</xref><xref ref-type="bibr" rid="b5">5</xref>. A review of literature published from 2007 to 2013 found that biochar reduced soil N<sub>2</sub>O emissions by a mean 54 ± 6% (95% confidence interval)<xref ref-type="bibr" rid="b6">6</xref>. Herbaceous- and wood-based biochars were most effective in reducing emissions, while the mean effect of those made from manure was negligible. Cayuela, Jeffery<xref ref-type="bibr" rid="b7">7</xref> found that the biochars with a molar H:C<sub>org</sub> (organic C) ratio of <0.3, indicative of a high degree of aromatic condensation, were more effective in lowering N<sub>2</sub>O emissions than those with a molar H:C<sub>org</sub> ratio of >0.5. A study by Lin, Spokas<xref ref-type="bibr" rid="b8">8</xref> found that biochar application reduced N<sub>2</sub>O production in three soils, apparently through the reaction of the biochar with various N forms (nitrate, nitrite, or N<sub>2</sub>O) and possibly catalytic involvement of iron (Fe). They concluded that biochar reduced N<sub>2</sub>O production in these soils through abiotic (chemodenitrification) mechanisms, and hypothesised that Fe-rich biochar can stimulate the abiotic transformation of nitrate/nitrite/N<sub>2</sub>O to N<sub>2</sub><xref ref-type="bibr" rid="b8">8</xref>. Others have also proposed that Fe(II), and perhaps manganese (Mn)(II), play a key role as a catalyst in the abiotic reduction of nitrate (NO<sub>3</sub><sup>−</sup>) in soils<xref ref-type="bibr" rid="b9">9</xref>. The variability in response to biochar amendment is well recognised, as are the considerable knowledge gaps that exist in understanding the precise mechanisms through which biochar influences soil nitrogen (N) transformations<xref ref-type="bibr" rid="b4">4</xref><xref ref-type="bibr" rid="b5">5</xref><xref ref-type="bibr" rid="b6">6</xref><xref ref-type="bibr" rid="b10">10</xref><xref ref-type="bibr" rid="b11">11</xref>.</p><p>Diffusion of N<sub>2</sub>O through soil is influenced by soil structural characteristics and moisture content. Soil water impedes gas diffusion and the high water solubility of N<sub>2</sub>O may play a significant role in retarding its movement in the soil<xref ref-type="bibr" rid="b3">3</xref><xref ref-type="bibr" rid="b12">12</xref>. Biochar application can alter soil structure and thus affect soil functions, enhancing porosity and pore connectivity<xref ref-type="bibr" rid="b13">13</xref>, water retention, air-filled porosity and gas transport<xref ref-type="bibr" rid="b14">14</xref>. While biochar is found to affect the N-cycling microbial community, with consequential impacts on microbial N<sub>2</sub>O production<xref ref-type="bibr" rid="b15">15</xref>, it is also suggested that abiotic factors, specifically adsorption or redox reactions on biochar surfaces, may influence N<sub>2</sub>O emissions<xref ref-type="bibr" rid="b16">16</xref><xref ref-type="bibr" rid="b17">17</xref>. Biochar has considerable aromatic C content which, in spite of its high stability, has redox activity and mainly functions as a reducing agent<xref ref-type="bibr" rid="b16">16</xref>. Cayuela, Sánchez-Monedero<xref ref-type="bibr" rid="b18">18</xref> propose that biochar can act as an “electron shuttle” and Klüpfel, Keiluweit<xref ref-type="bibr" rid="b19">19</xref> found biochars to be redox-active, reversibly accepting and donating up to 2 mmol electrons per gram of biochar. Those produced at highest treatment temperatures (HTTs) of 400–700 °C showing greater activity than those of lower HTTs. It has been noted that Fe minerals may be influential in some of these redox reactions<xref ref-type="bibr" rid="b16">16</xref><xref ref-type="bibr" rid="b20">20</xref> and Melton, Swanner<xref ref-type="bibr" rid="b21">21</xref> observed that discerning whether biotic or abiotic processes control Fe redox chemistry is a major challenge.</p><p>Nitrous oxide was injected into columns containing soil/biochar mixes, 100% biochar and sterilised sand (as a system control) to examine the effect of both water content and biochar amendment on diffusion of N<sub>2</sub>O gas and to determine the importance of adsorption and redox reactions.</p><sec disp-level="1"><title>Results</title><sec disp-level="2"><title>Analysis of N<sub>2</sub>O data</title><p>For each of the 0, 1 and 5% biochar additions to soil, water-filled pore space (WFPS) values of 12 (0.48), 39 (0.47) and 54 (0.50) % were established, hereafter termed low (L), medium (M) and high (H) WFPS (standard error of the mean (s.e.m.) in parentheses, <italic>n</italic> = 3). Moisture contents of the 100% biochar (BC100%) and sand were estimated to be 6 and 3% WFPS respectively. At the end of the sampling periods (tmax) the change in estimated total quantity of N<sub>2</sub>O in air-filled pore space (AFPS) and headspace and dissolved N<sub>2</sub>O in WFPS, divided by the estimated quantity of N<sub>2</sub>O injected (∆N<sub>2</sub>O/inj.N<sub>2</sub>O) for all 0% biochar and acid-washed sand treatments was close to unity (<xref ref-type="table" rid="t1">Table 1</xref>). Treatments of 1 and 5% biochar had mean values (across all WFPS) of ∆N<sub>2</sub>O/inj.N<sub>2</sub>O at tmax of 0.91 and 0.67 respectively. This suggested that some injected N<sub>2</sub>O was intercepted by these treatments. Treatments were injected with a mean of 22.2 nmol N<sub>2</sub>O (s.e.m. = 1.23 nmol, <italic>n</italic> = 6). When compared with the mean N<sub>2</sub>O intercepted by 0% biochar treatments (−25 pmol), the 1 and 5% biochar treatments significantly lowered N<sub>2</sub>O emitted, by 2.14 and 7.97 nmol respectively (<italic>p</italic> = 0.0094 and <italic>p</italic> = 5.6 × 10<sup>−8</sup>). Although there were differences in ∆N<sub>2</sub>O/inj.N<sub>2</sub>O at tmax between treatments of differing mean WFPS at the same biochar content (<xref ref-type="table" rid="t1">Table 1</xref>), only that between the 39 and 54% WFPS treatments with 5% biochar was significant (<italic>p</italic> = 0.018). For the BC100% treatments, ∆N<sub>2</sub>O/inj.N<sub>2</sub>O at tmax was only 0.16 (<xref ref-type="table" rid="t1">Table 1</xref>). The apparent loss of N<sub>2</sub>O within the sampling periods for any treatments containing biochar suggests that some of this gas might have been adsorbed, at least temporarily, or decomposed. <xref ref-type="fig" rid="f1">Figure 1</xref> shows the mean change in headspace N<sub>2</sub>O (injected mol N<sub>2</sub>O)<sup>−1</sup> for each treatment. For soil/biochar columns the associated (<xref ref-type="fig" rid="f1">Fig. 1</xref>) caption includes the significance of differences at tmax between treatments of 0, 1 and 5% biochar, based on both headspace N<sub>2</sub>O (injected mol N<sub>2</sub>O)<sup>−1</sup> and estimated ∆N<sub>2</sub>O/inj.N<sub>2</sub>O. Estimated from headspace N<sub>2</sub>O concentration ([N<sub>2</sub>O]) at tmax, the mean unaccounted N<sub>2</sub>O from headspace and AFPS (injected N<sub>2</sub>O)<sup>−1</sup> (i.e. N<sub>2</sub>O injected that was ‘missing’ from the combined volume of headspace and estimated AFPS) for 1% and 5% biochar composites was significantly greater than for BC100% treatments per unit weight of biochar (<italic>p</italic> = 0.044 and 0.015 respectively). For treatments of 1% biochar this measure of unaccounted N<sub>2</sub>O was 8.7 (s.e.m. = 1.7, <italic>n</italic> = 3) times greater than the mean for BC100% treatments, and the comparable ratio for treatments of 5% biochar was 4.0 (s.e.m. = 0.37, <italic>n</italic> = 3).</p><p>The time to peak headspace [N<sub>2</sub>O] (injected N<sub>2</sub>O)<sup>−1</sup> was determined for each treatment, with some slight decline expected thereafter due to continued sample removal alone. These values (see <xref ref-type="supplementary-material" rid="S1">Supplementary Table S2</xref> online) reflect the trends seen in <xref ref-type="fig" rid="f1">Fig. 1</xref>, namely that the rate of increase in headspace [N<sub>2</sub>O] (injected N<sub>2</sub>O)<sup>−1</sup> generally slowed with increase in both biochar content and WFPS. However, the times determined for treatments of medium WFPS, particularly those with 0 and 1% biochar, were somewhat anomalous, being less than the corresponding times for treatments of low WFPS, though not significantly. These differences had parallels in the higher values seen in ∆N<sub>2</sub>O/inj.N<sub>2</sub>O for treatments of medium WFPS than the corresponding treatments of low WFPS, though again the differences being of minor significance for treatments of 0, 1 or 5% biochar (<italic>p</italic> = 0.33, 0.062 and 0.075 respectively). The diffusion coefficient of N<sub>2</sub>O in water is about four orders of magnitude smaller than in air<xref ref-type="bibr" rid="b3">3</xref>, so increased water content would be expected to retard diffusion. It is surmised that these time-related and headspace [N<sub>2</sub>O] effects, though only minor, could have been an artefact related to the repacking of moist soil, possibly leading to creation of some larger channels in the porespace of those soils than in the soils of low WFPS, so allowing a freer passage of injected N<sub>2</sub>O to the column headspaces. Any such effect would appear to have been overcome by the higher water content of the corresponding soils with high WFPS, where the mean time to reach peak headspace [N<sub>2</sub>O] was greater than for the corresponding drier soils.</p><p>There was no increase in headspace [N<sub>2</sub>O] detected in the BC100% treatments until 120 min after N<sub>2</sub>O injection, and little further increase thereafter (<xref ref-type="fig" rid="f1">Fig. 1</xref>). The mean increase in headspace [N<sub>2</sub>O] at tmax in BC100% was only 16.1% of that anticipated from the injected N<sub>2</sub>O (<xref ref-type="table" rid="t1">Table 1</xref>). Amendment of Ferralsol with 5% biochar has been shown to significantly increase soil porosity, pore connectivity and mean pore radius<xref ref-type="bibr" rid="b13">13</xref>. Each of these changes would be expected to increase the rate of gas diffusion. Yet, for soils of similar WFPS there was no increase in the rate of headspace N<sub>2</sub>O accumulation with the addition of biochar. On the contrary, as shown in <xref ref-type="fig" rid="f1">Fig. 1</xref>, the rate of and nett change in headspace [N<sub>2</sub>O] (injected N<sub>2</sub>O)<sup>−1</sup> decreased as % biochar and WFPS increased. These significant differences, and the low headspace [N<sub>2</sub>O] detected in the BC100% treatments, suggest that adsorption and/or decomposition of injected N<sub>2</sub>O is likely to have occurred.</p></sec><sec disp-level="2"><title>Modelling of N<sub>2</sub>O data</title><p>Modelling of the effects of N<sub>2</sub>O permeation through, and reaction with, a soil sample as a function of WFPS and biochar content can provide insight into the interactions between N<sub>2</sub>O, biochar and soil.</p><p>To begin, first assume that there is no interaction at all between the N<sub>2</sub>O and the soil/biochar composite. Under these conditions the processes being observed in the columns can best be regarded as an effusion experiment, where the N<sub>2</sub>O is permeating through the porous structure of the soil/biochar compact as a result of a pressure differential. This process can be modelled based on effusion of gases, which is described by the exponential relationship</p><p><disp-formula id="eq1"><inline-graphic id="d33e740" xlink:href="srep16773-m1.jpg"></inline-graphic></disp-formula></p><p>where Δ<italic>N</italic> is the number of gas molecules having moved from one side of the porous medium to the other at time <italic>t</italic>, Δ<italic>N</italic><sub>o</sub> is the total number of molecules in the system, <italic>A</italic> is the porous area in the solid composite, <inline-formula id="d33e757"><inline-graphic id="d33e758" xlink:href="srep16773-m2.jpg"></inline-graphic></inline-formula> is the average speed of the gas molecules, and <italic>V</italic> is the volume of N<sub>2</sub>O gas before effusion starts<xref ref-type="bibr" rid="b22">22</xref>. Therefore, the process of effusion is exponential in nature. Equation <xref ref-type="disp-formula" rid="eq1">(1)</xref> can be adapted to the following form, using the equivalent terms assessed in this study:</p><p><disp-formula id="eq3"><inline-graphic id="d33e774" xlink:href="srep16773-m3.jpg"></inline-graphic></disp-formula></p><p>where [N<sub>2</sub>O] is the concentration of N<sub>2</sub>O in the column headspace, A and B are fitting constants, where A–B is the maximum N<sub>2</sub>O concentration change, and k<sub>1</sub> is the rate constant for effusion. Here k<sub>1</sub> is related to the terms in the exponential in the previous expression.</p><p>Equations <xref ref-type="disp-formula" rid="eq1">(1</xref>) and (<xref ref-type="disp-formula" rid="eq16">2</xref>) exclude interactions between the N<sub>2</sub>O and the soil/biochar composite through which the N<sub>2</sub>O is effusing. Two possible interactions will now be considered: the dissolution of N<sub>2</sub>O into the water occupying the pores within the soil/biochar composite, and the reaction of N<sub>2</sub>O with the solid components (soil and/or biochar), leading to its decomposition.</p><p>The dissolution of N<sub>2</sub>O into the water present in the composite can best be considered as a quasi-equilibrium process where the kinetics of dissolution are much faster than any of the other processes ongoing in the chamber. Given the duration of the experiments, this is a realistic assumption. As such, the total amount of gas phase N<sub>2</sub>O will be lowered by an amount dictated by the solubility of N<sub>2</sub>O in water and the availability of water in the system.</p><p>In terms of reaction between the N<sub>2</sub>O and soil/biochar composite little is known about the reaction kinetics, in particular the order of the reaction. Therefore, we have assumed that this is a first order process dependent on the partial pressure of gas phase N<sub>2</sub>O in the system. That is:</p><p><disp-formula id="eq4"><inline-graphic id="d33e834" xlink:href="srep16773-m4.jpg"></inline-graphic></disp-formula></p><p>where k<sub>2</sub> is the rate constant for decomposition, and C is the initial concentration of N<sub>2</sub>O.</p><p>Combining all terms together, the resultant expression is:</p><p><disp-formula id="eq5"><inline-graphic id="d33e848" xlink:href="srep16773-m5.jpg"></inline-graphic></disp-formula></p><p>This was then fitted to the experimental data using linear least squares regression (see <xref ref-type="supplementary-material" rid="S1">Supplementary Table S4</xref>). A good fit was found between the measured headspace [N<sub>2</sub>O] values and those predicted from the modelling expression, and there was also a fairly close correspondence of times to peak headspace [N<sub>2</sub>O] with those modelled (see <xref ref-type="supplementary-material" rid="S1">Supplementary Table S5</xref>). These outcomes offer support to the concepts of diffusion and that adsorption and/or decomposition of injected N<sub>2</sub>O is likely to have occurred.</p></sec><sec disp-level="2"><title>pH and Eh</title><p>In the soil/biochar composites pH increased with increases in both soil water and biochar content (<xref ref-type="table" rid="t2">Table 2</xref>). These changes are consistent with decreased soil [H<sup>+</sup>] with increasing water content, and the strong acid-neutralising capacity of the biochar. Values of Eh<sub>pH7</sub> decreased with increasing WFPS, independent of biochar content, probably due to low oxygen diffusion in water. On the contrary, Eh<sub>pH7</sub> (Eh corrected to pH = 7) increased with increasing biochar content, most particularly at low WFPS (<xref ref-type="table" rid="t2">Table 2</xref>). This could lead to the conclusion that biochar addition led to reduction of N<sub>2</sub>O, taking electrons from the composite media and thus increasing its redox potential. However, it is unlikely that the small quantity of N<sub>2</sub>O injected (22 nmol) would be sufficient to promote such significant changes in ~200 g of composite. Initial rapid mineralisation of biochar C and the priming of mineralisation of native soil organic C following addition of biochar have been observed<xref ref-type="bibr" rid="b23">23</xref><xref ref-type="bibr" rid="b24">24</xref><xref ref-type="bibr" rid="b25">25</xref>. One or both of these processes, which would be increasingly handicapped by increasing WFPS, would seem to be more likely responsible for the changes seen in Eh<sub>pH7</sub> with increased biochar rate, and would also account for freeing of electrons that might be used in any reduction of N<sub>2</sub>O to N<sub>2</sub>.</p><p>The Pourbaix diagram (<xref ref-type="fig" rid="f2">Fig. 2</xref>) shows that NH<sub>4</sub><sup>+</sup> would not be expected to be the dominant form of N in any of the treatments, and that NO<sub>3</sub><sup>−</sup> would dominate, especially in the 5% biochar treatment at low WFPS. Yet this was clearly not the case, with NH<sub>4</sub><sup>+</sup>-N dominant in all soil/biochar treatments. Nevertheless, as anticipated, NH<sub>4</sub><sup>+</sup>-N increased substantially with increasing WFPS (<xref ref-type="table" rid="t2">Table 2</xref>). NH<sub>4</sub><sup>+</sup>-N, relative to pre-packed soil (44 mg kg<sup>−1</sup>), had increased in all medium and high WFPS treatments but decreased at low WFPS. In all soils NO<sub>3</sub><sup>−</sup>-N had decreased markedly (from 23 mg kg<sup>−1</sup>) to <2 mg kg<sup>−1</sup> (<xref ref-type="table" rid="t2">Table 2</xref>). Increased NH<sub>4</sub><sup>+</sup>-N would not be likely to result from dissimalatory NO<sub>3</sub><sup>−</sup> reduction to NH<sub>4</sub><sup>+</sup>, as this is catalysed by bacteria under anaerobic conditions<xref ref-type="bibr" rid="b26">26</xref>. Likewise, the abiotic reduction of NO<sub>3</sub><sup>−</sup> to NH<sub>4</sub><sup>+</sup> involving green rust compounds [Fe<sup>II</sup><sub>4</sub>Fe<sup>III</sup><sub>2</sub>(OH)<sub>12</sub>SO<sub>4</sub> • <italic>y</italic>H<sub>2</sub>O], as proposed by Hansen, Koch<xref ref-type="bibr" rid="b27">27</xref>, is also only favoured in anoxic environments. The γ-irradiation of soil has been shown to produce an up to 30-fold increase of NH<sub>4</sub>-N<sub>2</sub><xref ref-type="bibr" rid="b28">28</xref> and up to 100% decrease of NO<sub>3</sub>-N<sub>2</sub><xref ref-type="bibr" rid="b29">29</xref>. This would appear to be the most likely explanation for the changes observed, and the heightened effect of γ-irradiation on NH<sub>4</sub>-N with higher soil moisture<xref ref-type="bibr" rid="b30">30</xref> very strongly supports this conclusion.</p></sec><sec disp-level="2"><title>X-ray photoelectron spectroscopy</title><p>Results of the analysis of the C and N surface functional groups of the unincubated (original non-irradiated biochar without injected N<sub>2</sub>O – see Method) and aged biochars are presented in <xref ref-type="table" rid="t3">Table 3</xref> and <xref ref-type="table" rid="t4">Table 4</xref>. There was a substantial change in both the concentration of the C functional groups on the surfaces of the biochar pooled from the low, medium and high WFPS 5% treatments (known as LMH5%) and a smaller reduction on BC100%. For LMH5% the concentration of aromatic/aliphatic C = C/C-C/C-H and shake up peaks are much lower, and the BC100% lower, than for the unincubated biochar. The carboxylic and the C-O content had increased for both treatments compared with the unincubated biochar. However an increase in the C = O groups was only measured in the LMH5%. Carbonates were also detected on the surface of the LMH5% from the soil but not on the unincubated biochar or the BC100% treatment. These findings for the biochar from the soil are consistent with those of<xref ref-type="bibr" rid="b16">16</xref><xref ref-type="bibr" rid="b31">31</xref> who measured the oxidation of the surface of the biochar after addition to soil. A large increase in the -O-C = N /pyridine pyrrole/NH<sub>3</sub> was measured in the LMH5%, and a much smaller increase in the BC100%, when compared with the unincubated biochar. A new N group for the LMH5% was detected at 402.56 eV which is often associated with the Pyridine/N-O/Chemisorbed ammonia (NH<sub>3</sub>) and/or the formation of a conjugated N-C-N configuration<xref ref-type="bibr" rid="b32">32</xref>.</p><p><xref ref-type="table" rid="t4">Table 4</xref> reveals considerable differences between the mineral content on the surface of the unincubated biochar and the BC100% and the LMH5%. Iron was present on the surface at 1.3% and silicon (Si) and aluminium (Al) at approximately 7.3% in the LMH5%, whereas no Fe was measured in the unincubated biochar or the BC100%. Silicon and Al were not detected on the surface of the unincubated biochar and only a small amount was detected on the BC100%. Total surface N was increased from approximately 0.9% in the unincubated biochar to 1% in BC100%, and to 1.1% in LMH5%.</p></sec><sec disp-level="2"><title>Scanning transmission electron and transmission electron microscopy: examination of the surface and internal structure of aged eucalypt biochar</title><p>The structure of the biochar before application to soil is shown in <xref ref-type="supplementary-material" rid="S1">Supplementary Fig. S2</xref>. It can be seen that the internal and external C surfaces are typical of a woody biochar that has high C content and a very low mineral content. There were no significant structural or compositional differences noted between the incubated BC100% and the unincubated biochar.</p><p><xref ref-type="fig" rid="f3">Figure 3</xref> characterises some of the changes that have occurred on the surfaces of the LMH5%. Some of the internal pores have a layer of organic molecules that are rich in Ca and Mg (<xref ref-type="fig" rid="f3">Fig. 3b</xref>: energy dispersive x-ray (EDS)) and some of the pores have filled with organic matter and mineral matter that is high in Al/Si/O, Fe/O /, Ca/C/O and Ti/O compounds (<xref ref-type="fig" rid="f3">Fig. 3c</xref>). <xref ref-type="fig" rid="f3">Figure 3d</xref> illustrates the range of different mineral phases observed on the surface of the biochar. The EDS data mirrors the survey analysis carried out using x-ray photoelectron spectroscopy (XPS).</p><p>Scanning transmission electron microscope (STEM) images and x-ray mapping reveal a nanostructure that is highly heterogeneous. <xref ref-type="fig" rid="f4">Figure 4</xref> shows a high angle annular dark field (HAADF) STEM image of a section of the biochar particle that has interacted with the soil organic and mineral matter. The associated EDS spectra (<xref ref-type="fig" rid="f4">Fig. 4</xref>) demonstrate the considerable organic content of the mineral phases (see also <xref ref-type="supplementary-material" rid="S1">Supplementary Figure S3</xref>). Electron energy loss spectrometry (EELS) of the regions showed strong Fe signals but of varying oxidation state (<xref ref-type="fig" rid="f5">Fig. 5</xref>) with some of the Fe/O phases having an oxidation state of 3 + (haematite) and others a mixed oxidation state of 2+/3+ (possibly magnetite). Transmission electron microscopy (TEM) imaging with selected area electron diffraction indicated that these nanophases could be a mixture of haematite, magnetite and possibly goethite (see <xref ref-type="supplementary-material" rid="S1">Supplementary Figure S4</xref>). <xref ref-type="fig" rid="f6">Figure 6</xref> is an analysis of another interface between a biochar region and a region that has a number of nanophase minerals. On the biochar boundary there are nanophase particles rich in Si/O (probably SiO<sub>2</sub>) and also Fe/O phases that have a mixed (II-III) Fe oxidation state (probably magnetite). In the organomineral phase adjacent to the biochar there are various Al/Si/Ca/Fe/C/S/O nanophase minerals.</p></sec></sec><sec disp-level="1"><title>Discussion</title><p>In columns containing soil/biochar composites and 100% biochar, nett headspace [N<sub>2</sub>O] was significantly lowered when N<sub>2</sub>O was injected into the profile. This has important consequences for global mitigation options for this greenhouse gas, which also depletes stratospheric ozone<xref ref-type="bibr" rid="b33">33</xref>. This observation is consistent with studies showing that biochars can lower N<sub>2</sub>O emissions from the soil surface<xref ref-type="bibr" rid="b6">6</xref>. These previous studies have paid little attention to the different mechanisms involved<xref ref-type="bibr" rid="b10">10</xref><xref ref-type="bibr" rid="b14">14</xref>. We have shown definitively that that abiotic consumption and/or adsorption of N<sub>2</sub>O is an important mechanism in the studied system.</p><p>The interception of N<sub>2</sub>O was not related to soil/biochar moisture content, in the range approx. 12–54% WFPS. Diminishing N<sub>2</sub>O emissions were observed with increasing biochar content in the soil. Cornelissen, Rutherford<xref ref-type="bibr" rid="b17">17</xref> examined the sorption properties of a range of softwood biochars. Two, with comparable BET surface areas (176 and 286 m<sup>2</sup> g<sup>−1</sup>) to the eucalypt biochar, had Langmuir maximum sorption capacities for N<sub>2</sub>O of 47 and 55 cm<sup>3</sup> g<sup>−1</sup> respectively at 20 °C under anhydrous conditions, equivalent to 1.95 and 2.29 mmol g<sup>−1</sup>. The BC100% treatments contained a mean 72.7 g of biochar in a close to anhydrous state. It thus seems highly probable that the apparent ‘loss’ of 84% of the mean injected 22.2 nmol of N<sub>2</sub>O from BC100% treatments (<xref ref-type="table" rid="t1">Table 1</xref>), as calculated from headspace [N<sub>2</sub>O], could be attributed to adsorption. Comparing BC100% with unincubated biochar, there was a small increase from 0.40 to 0.49 atom % of -O-C = N/pyridine pyrrole/NH<sub>3</sub> revealed by XPS, possibly as a consequence of reaction with (consumption of) N<sub>2</sub>O. The XPS results of the LMH 5% samples indicated that there had been a considerable increase in the -O-C = N /pyridine pyrrole/NH<sub>3</sub>, to 0.77 atom %, and appearance of pyridine/N-O/chemisorbed NH<sub>3</sub> and/or possibly the formation of a conjugated N-C-N configuration<xref ref-type="bibr" rid="b32">32</xref> (<xref ref-type="table" rid="t3">Table 3</xref>). It is apparent from these increases in N-C/H-N –O-C = N groups that N<sub>2</sub>O had been adsorbed onto the surface of the biochar and could have undergone reactions both with the C and some of the mineral elements (especially Fe nanophase particles identified by TEM) in the biochar. A similar finding re adsorption of N<sub>2</sub>O was reported by Cornelissen, Rutherford<xref ref-type="bibr" rid="b17">17</xref>. The significantly greater unaccounted N<sub>2</sub>O per unit weight of biochar from headspace and AFPS in soil/biochar treatments than from BC100% also suggests that additional mechanisms may have been responsible for this loss than for that in the BC100%.</p><p>The increase in the COOH content (<xref ref-type="table" rid="t3">Table 3</xref>) and Fe/Al/Si content (<xref ref-type="table" rid="t4">Table 4</xref>) of the LMH5% is consistent with the findings of Joseph, Camps Arbestain<xref ref-type="bibr" rid="b16">16</xref> and Lin, Munroe<xref ref-type="bibr" rid="b34">34</xref> who measured the changes to poultry manure/sawdust, greenwaste and paper sludge biochars after 2 years, and poultry manure/sawdust and paper sludge biochars after 3 months respectively in the same Ferralsol used in this study. The latter study found biochars in Ferralsol formed oxidised C surfaces and reacted with soil organic matter. The formation of a porous organomineral layer resulting in the appearance of Fe compounds with Fe<sup>2+</sup>/Fe<sup>3+</sup> oxidation state indicated that redox reactions<xref ref-type="bibr" rid="b20">20</xref> between the N<sub>2</sub>O and the Fe cations may have taken place.</p><p>N<sub>2</sub>O is a very strong oxidant. It has a standard reduction potential of 1.77 V, which makes it stronger than O<sub>2</sub> (1.23 V) and Fe(III) (0.77 V)<xref ref-type="bibr" rid="b35">35</xref>. Thus it was expected that the 100% biochar would have acted as a catalytic surface to promote the reduction of N<sub>2</sub>O. Our data indicate that biochars will not significantly reduce N<sub>2</sub>O without formation of either redox active organic compounds or organomineral phases high in Fe and other transition metals on their surface. This is consistent with the findings of Carabineiro, Fernandes<xref ref-type="bibr" rid="b36">36</xref> who noted that catalysts are required on the surface of activated C to speed up N<sub>2</sub>O reduction reactions at low temperatures.</p><p>Reaction of N<sub>2</sub>O might occur with either redox active water soluble organic molecules on the surface of the biochar and/or organic molecules that are deposited from the soil as the organomineral layer is formed during the biochar ageing process. Avdeev, Ruzankin<xref ref-type="bibr" rid="b37">37</xref> reported that a range of aromatic and aliphatic compounds are oxidized by N<sub>2</sub>O. They hypothesised that an O atom is transferred through the 1,3-dipolar cyclo-addition of N<sub>2</sub>O to the C = C bond with the resulting intermediate decomposing to yield a ketone and N<sub>2</sub>. Biochars contain a range of aromatic and non-aromatic compounds on their internal and external surfaces. The XPS data presented here, showing substantial increase in ketonic groups in LMH5% (<xref ref-type="table" rid="t3">Table 3</xref>), indicate that this reaction has taken place.</p><p>It is also consistent with the recent research related to the role of Fe<sup>2+</sup>/Fe<sup>3+</sup> cycling, Eh/pH with N release dynamics and formation and reduction of N<sub>2</sub>O<xref ref-type="bibr" rid="b38">38</xref>. It should be noted that the soil contains NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>−</sup> and these can exist in solution within the water filled pores and from there bind to the surfaces of the biochar. With the injection of N<sub>2</sub>O the following sequence of reactions could take place.</p><p><disp-formula id="eq6"><inline-graphic id="d33e1291" xlink:href="srep16773-m6.jpg"></inline-graphic></disp-formula></p><p><disp-formula id="eq7"><inline-graphic id="d33e1294" xlink:href="srep16773-m7.jpg"></inline-graphic></disp-formula></p><p><disp-formula id="eq8"><inline-graphic id="d33e1297" xlink:href="srep16773-m8.jpg"></inline-graphic></disp-formula></p><p><disp-formula id="eq9"><inline-graphic id="d33e1300" xlink:href="srep16773-m9.jpg"></inline-graphic></disp-formula></p><p>(hypothesised by Li, Yu<xref ref-type="bibr" rid="b39">39</xref>)</p><p><disp-formula id="eq10"><inline-graphic id="d33e1308" xlink:href="srep16773-m10.jpg"></inline-graphic></disp-formula></p><p>Results of the XPS and the examination of the aged biochar surfaces indicated that there had been significant reactions. Iron has already been reported as a vital key for orchestrating N-transformations<xref ref-type="bibr" rid="b27">27</xref><xref ref-type="bibr" rid="b40">40</xref><xref ref-type="bibr" rid="b41">41</xref><xref ref-type="bibr" rid="b42">42</xref>. Li, Yu<xref ref-type="bibr" rid="b39">39</xref> have shown that reduction and oxidation of N compounds are enhanced when Fe and organic matter are also oxidized or reduced. They refer to this as the “FeIII–FeII redox wheel”. A similar mechanism was found in anoxic environments by Klüpfel, Piepenbrock<xref ref-type="bibr" rid="b43">43</xref>. Reactions between Fe<sup>2+</sup> and either NO<sub>3</sub><sup>−</sup> or NO<sub>2</sub><sup>−</sup> to produce N<sub>2</sub> (reduced species) are energetically favourable resulting in the formation of iron (oxy-)hydroxide<xref ref-type="bibr" rid="b40">40</xref>. The addition of amorphous Fe(III)hydroxide (HFO) and, to a lesser extent magnetite, greatly accelerated rates of reaction compared to systems containing Fe<sup>2+</sup> alone<xref ref-type="bibr" rid="b40">40</xref>. If N<sub>2</sub>O is adsorbed onto the surfaces of these nanoparticles or if soluble N<sub>2</sub>O surrounds the nanoparticles, catalytic reduction of N<sub>2</sub>O is likely. Sang, Kim<xref ref-type="bibr" rid="b44">44</xref> proposed the following reaction mechanism as being the most likely to fit their experimental data for the reduction of N<sub>2</sub>O on Fe exchanged zeolites. This reaction mechanism may also be occurring in the organomineral phases and in the pores of the biochars where there is a concentration of nanophase Fe.</p><p><disp-formula id="eq11"><inline-graphic id="d33e1358" xlink:href="srep16773-m11.jpg"></inline-graphic></disp-formula></p><p><disp-formula id="eq12"><inline-graphic id="d33e1361" xlink:href="srep16773-m12.jpg"></inline-graphic></disp-formula></p><p><disp-formula id="eq13"><inline-graphic id="d33e1364" xlink:href="srep16773-m13.jpg"></inline-graphic></disp-formula></p><p><disp-formula id="eq14"><inline-graphic id="d33e1367" xlink:href="srep16773-m14.jpg"></inline-graphic></disp-formula></p><p><disp-formula id="eq15"><inline-graphic id="d33e1370" xlink:href="srep16773-m15.jpg"></inline-graphic></disp-formula></p><p>It is true that the system used in this study was not natural, lacking biological activity. Nonetheless, there have been numerous studies investigating the influence of biochar on biological aspects associated with changes to N<sub>2</sub>O emissions from soil, and not all of these changes could be easily explained and indeed, the importance of abiotic reactions has been highlighted in numerous works, e.g. Van Zwieten, Kammann<xref ref-type="bibr" rid="b11">11</xref>, and Cayuela, Sánchez-Monedero<xref ref-type="bibr" rid="b18">18</xref>. This work was designed to investigate abiotic reactions following a moderate degree of aging between the biochar and the soil. There is no information on the impact of γ-irradiation on biochar, so this may have impacted the results obtained showing biochar retarded N<sub>2</sub>O movement through the soil profile. However, we deemed it necessary to sterilise the matrix in this way, as other methods (i.e. autoclaving, oven, etc.) could be equally influential in changing properties of biochar.</p><p>In summation, eucalypt biochar was shown to lower emissions of injected N<sub>2</sub>O via abiotic mechanisms. In the 100% biochar treatment, the decline in [N<sub>2</sub>0] may be solely the result of adsorption. Given the small quantities of N<sub>2</sub>O injected this could explain why the nett N<sub>2</sub>O in the headspace is substantially less for the 100% biochar than for the soil/biochar treatments, or indeed the sand column system control. The significantly greater decline seen in the composite treatments per unit of biochar, combined with the changes revealed by XPS in biochar from the 5% treatments and changes in Eh<sub>pH7</sub>, suggest very strongly that redox reactions have occurred, reducing a proportion of the intercepted N<sub>2</sub>O to N<sub>2</sub>. There remains much to understand about the importance of abiotic and redox properties in altering soil GHG emissions following biochar addition, yet this offers a significant opportunity to address a globally important issue.</p></sec><sec disp-level="1"><title>Materials and Methods</title><sec disp-level="2"><title>Soil and Biochar</title><p>A Ferralsol<xref ref-type="bibr" rid="b45">45</xref> from Wollongbar (28<sup>o</sup>50’S, 153<sup>o</sup>25’E) in north-eastern New South Wales was sieved to ≤2 mm. The soil was rich in Fe sesquioxides (clay content 44.1%; total organic C 4.39%)<xref ref-type="bibr" rid="b46">46</xref>, with total Fe 8.4%, total Mn 350 mg kg<sup>−1</sup>, total C 4.9%, total N 0.47% and pH of 4.2 in CaCl<sub>2</sub><xref ref-type="bibr" rid="b47">47</xref>, NH<sub>4</sub><sup>+</sup>-N and NO<sub>3</sub><sup>−</sup>-N contents of 44 and 23 mg kg<sup>−1</sup> respectively, with NO<sub>2</sub><sup>−</sup>-N < 0.10 mg kg<sup>−1</sup> (analytical laboratory accredited to ISO17025). Biochar was obtained from Pacific Pyrolysis, made from the woody residue of <italic>Eucalyptus polybractea</italic> after steam extraction of eucalypt oil. It was produced using a semi-continuous 40 kg h<sup>−1</sup> pilot unit at a highest treatment temperature (HTT) of 550 <sup>o</sup>C and heating rate of 5–10 °C min<sup>−1</sup>. Residence time at HTT was 45 min. Measured prior to application the biochar had a pH of 8.65 in CaCl<sub>2</sub>, an acid neutralising capacity of 8.8 (%CaCO<sub>3</sub> eq.), electrical conductivity of 1.5 dS m<sup>−1</sup>, total C of 70% and total N of 0.81%, NH<sub>4</sub><sup>+</sup>-N and NO<sub>3</sub><sup>−</sup>-N contents of 0.49 and <0.2 mg kg<sup>−1</sup> respectively, Fe content of 0.24% and Mn of 300 mg kg<sup>−1</sup>, and CEC of 17 cmol(<sup>+</sup>)/kg C<xref ref-type="bibr" rid="b48">48</xref>, a molar H:C<sub>org</sub> ratio of 0.48 and BET specific surface area of 269 m<sup>2</sup> g<sup>−1</sup><xref ref-type="bibr" rid="b46">46</xref>. The ash content was 11.6%, containing 9,900 and 5,400 mg kg<sup>−1</sup> of Fe and Mn respectively<xref ref-type="bibr" rid="b49">49</xref>. (All chemical properties determined by ultimate and proximate analysis using the Australian Standard methods AS 1038.5, AS 1038.6.1 and AS 1038.3).</p></sec><sec disp-level="2"><title>Sample packing and irradiation</title><p>Air dried soil was sieved to ≤2 mm and biochar to between 250 μm and 2 mm to enhance homogeneity of mixing into small soil volumes. Biochar dosing rates into the columns were 0, 1, 5 and 100% (w/w, dry) biochar, while a system (method check) control of acid-washed sand was also utilized. The columns were 300 mm tall PVC tubes of 37 mm internal diameter, fitted with airtight base and top caps. Each column had a sampling port in the top cap and an injection port in the base cap comprising butyl rubber septa (see <xref ref-type="supplementary-material" rid="S1">Supplementary Figure S1</xref>). Soil and soil/biochar mixtures were repacked in 3 equal sections to a depth of 200 mm. Components for each section were individually weighed and distilled water added (by weight) during mixing to homogeneity for the three levels of soil moisture, being 12, 39 and 54% WFPS (<italic>n</italic> = 3) (see <xref ref-type="supplementary-material" rid="S1">Supplementary Table S1</xref> online). Unamended soils were repacked to field bulk density (BD) of 1.02 g cm<sup>−3</sup>. Composites of 1 and 5% biochar were repacked to BDs of 1.00 and 0.93 g cm<sup>−3</sup> respectively, to account for the lower BD of the biochar (see <xref ref-type="supplementary-material" rid="S1">Supplementary Method online</xref>). Columns of 100% biochar and system controls of acid-washed sand were both repacked using gentle tapping (neither with additional moisture) to respective BDs of 0.34 and 1.65 g cm<sup>−3</sup> (<italic>n</italic> = 3).</p><p>The porosities of the soil, 1 and 5% biochar composites and sand were 61.5, 61.9, 63.4 and 37.7% respectively, and that of the biochar from its BD and the density of its solid C fraction<xref ref-type="bibr" rid="b50">50</xref> to be between 75 and 80% (see <xref ref-type="supplementary-material" rid="S1">Supplementary Method</xref> online). The WFPS of each set of replicate columns was determined as the volumetric water content (see <xref ref-type="supplementary-material" rid="S1">Supplementary Table S1</xref>) divided by the relevant porosity.</p><p>After repacking, a muslin covered non-absorbent cotton wool plug was inserted into the top of each column to secure the test matrix, and top caps fitted and sealed, enabling the columns to be shipped in an upright position without any disturbance of the packed contents. All columns were weighed and γ-irradiated, using a minimum dose of 25 kGy in order to render the contents abiotic<xref ref-type="bibr" rid="b51">51</xref><xref ref-type="bibr" rid="b52">52</xref>. The packing was removed from each column inside a UV sterilized biological safety cabinet and the column resealed in the same abiotic environment. Each column was then re-weighed to determine any loss in moisture (none detected). The columns were then incubated at 23 °C for 4 months before N<sub>2</sub>O injection. They were later tested for biological activity (see below). At all stages care was taken to avoid disturbance of the contents.</p></sec><sec disp-level="2"><title>Injection of N<sub>2</sub>O and headspace sampling</title><p>Injection mixtures (IMs) of N<sub>2</sub>O (>99.8% pure) diluted in N<sub>2</sub> (99.999% pure) were prepared in 500 mL Tedlar<sup>®</sup> bags. Samples (<italic>n</italic> = 3) of each IM were injected into pre-evacuated 12 mL Exetainer<sup>®</sup> vials for later analysis. A 2 mL sample of the IM was injected through the base port using a gas-tight glass syringe with Teflon plunger and a 23G × 1¼” needle inserted to be centre of the column. Immediately prior to injection, and at specific post-injection intervals (see <xref ref-type="supplementary-material" rid="S1">Supplementary Table S3</xref>), 2 mL samples of headspace gas were withdrawn through the top port. A tap connected through a side port immediately above the column contents (see <xref ref-type="supplementary-material" rid="S1">Supplementary Figure S1</xref>) was opened only during sample withdrawals to maintain atmospheric pressure in the headspace.</p><p>Gas samples were analysed according to Van Zwieten, Kimber<xref ref-type="bibr" rid="b47">47</xref> (see also <xref ref-type="supplementary-material" rid="S1">Supplementary Method</xref>). The rate of diffusion and any abiotic adsorption or degradation of N<sub>2</sub>O gas injected at the base was measured by its accumulation in the column headspace. Pre-injection headspace [N<sub>2</sub>O] was assumed to be in equilibrium with that of air-filled pore space (AFPS [%] = 100 - WFPS), itself assumed to be in equilibrium with N<sub>2</sub>O dissolved in WFPS. From headspace [N<sub>2</sub>O] an estimate was made of the quantity of N<sub>2</sub>O dissolved in WFPS (see <xref ref-type="supplementary-material" rid="S1">Supplementary Method</xref>). Total gas pressure within both the headspace of the columns and soil air was assumed to be atmospheric. Dissolved N<sub>2</sub>O was assumed to be in equilibrium with N<sub>2</sub>O in AFPS at the time corresponding to maximum headspace [N<sub>2</sub>O]. For each column the total quantity of N<sub>2</sub>O in headspace, AFPS and WFPS prior to injection was deducted from the same total at diffusive equilibrium, the difference being divided by the quantity of N<sub>2</sub>O injected.</p><p>At the end of the experiment, 3 g of substrate was carefully removed from the upper surface of the columns, within the biological safety cabinet, and the columns resealed (see <xref ref-type="supplementary-material" rid="S1">Supplementary Method</xref>). These samples were analysed for microbial activity by fluorescein diacetate (FDA) hydrolysis<xref ref-type="bibr" rid="b53">53</xref>. A range of 0.17–0.34 μg sodium fluorescein (g dry matrix)<sup>−1</sup> min<sup>−1</sup> confirmed insignificant microbial activity. The small quantity detected may have resulted from residual enzyme activity<xref ref-type="bibr" rid="b54">54</xref>.</p></sec><sec disp-level="2"><title>pH and Eh</title><p>All soil/biochar composites and the BC100% were analysed at the completion of the incubation and gas sampling for NH<sub>4</sub><sup>+</sup>-N and NO<sub>3</sub><sup>−</sup>-N content, pH (in H<sub>2</sub>O) by the method of<xref ref-type="bibr" rid="b55">55</xref>, and redox potential (Eh)<xref ref-type="bibr" rid="b56">56</xref> using a hand held ORP meter (Hanna HI 98160) with platinum electrode (<xref ref-type="table" rid="t2">Table 2</xref>). Redox potentials were transformed<xref ref-type="bibr" rid="b57">57</xref><xref ref-type="bibr" rid="b58">58</xref> to correct the Eh to pH = 7 (Eh<sub>pH7</sub>), referenced to the standard hydrogen electrode through the following equation:</p><p><disp-formula id="eq16"><inline-graphic id="d33e1683" xlink:href="srep16773-m16.jpg"></inline-graphic></disp-formula></p><p>where R is the ideal gas constant (8.31447 J K<sup>−1</sup> mol<sup>−1</sup>), F the Faraday constant (96485.34 C mol<sup>−1</sup>), and T the temperature (in K).</p><p>All Eh measurements were recorded at 25 °C, where</p><p><inline-formula id="d33e1698"><inline-graphic id="d33e1699" xlink:href="srep16773-m17.jpg"></inline-graphic></inline-formula>, with Eh expressed in V.</p></sec><sec disp-level="2"><title>Examination of the biochar after adsorption of N<sub>2</sub>O</title><p>To help determine the possible mechanisms that resulted in the reduction in N<sub>2</sub>O, biochar was studied using a range of electron microscopy and x-ray photoelectron spectroscopy (XPS) techniques. Biochar pieces from different water content columns using the 5% soil/biochar matrix were separated<xref ref-type="bibr" rid="b16">16</xref><xref ref-type="bibr" rid="b34">34</xref> and crushed to pass a 0.1mm sieve. Representative samples of the BC100% treatments, and the unincubated biochar (original non-irradiated biochar stored frozen in a sealed container and without injected N<sub>2</sub>O), were also crushed and sieved. Surface functional groups and major mineral elements of the unincubated biochar, the biochar extracted from the soil and the BC100% treatment were measured by XPS analysis (Thermo Scientific ESCALAB250Xi), using a 500 micron diameter beam of monochromatic Al-Kα radiation (photon energy = 1486.6 eV) at a pass energy of 20 eV. The core level binding energies (BEs) were aligned with respect to the C1s BE of 285.0 eV. Examination of over 50 biochar pieces was carried out using a Zeiss Sigma scanning electron microscope (SEM) fitted with a Bruker energy dispersive x-ray analyser as described in Joseph, Graber<xref ref-type="bibr" rid="b59">59</xref>. To provide detailed microstructural, crystallographic and microchemical analysis both transmission electron microscopy (TEM) and scanning transmission electron microscopy (SEM) was undertaken using JEOL ARM200F aberration corrected TEM fitted with an electron energy loss spectrometer and JEOL EDS detector. To help determine the crystal structure of the mineral phases selected area electron diffraction was carried out in TEM mode (see <xref ref-type="supplementary-material" rid="S1">Supplementary Method</xref> for further details of sample preparation and conditions of both TEM and SEM examination).</p></sec><sec disp-level="2"><title>Statistical analysis</title><p>All statistical comparisons of two groups of data used a two-tailed Welch’s t-test, on account of its suitability for mean values with unequal variance. Unless otherwise stated, any significant difference is based on a 95% confidence level.</p></sec></sec><sec disp-level="1"><title>Additional Information</title><p><bold>How to cite this article</bold>: Quin, P. <italic>et al.</italic> Lowering N<sub>2</sub>O emissions from soils using eucalypt biochar: the importance of redox reactions. <italic>Sci. Rep.</italic><bold>5</bold>, 16773; doi: 10.1038/srep16773 (2015).</p></sec><sec sec-type="supplementary-material" id="S1"><title>Supplementary Material</title><supplementary-material id="d33e44" content-type="local-data"><caption><title>Supplementary Information</title></caption><media xlink:href="srep16773-s1.pdf"></media></supplementary-material></sec></body><back><ack><p>We gratefully acknowledge Joseph Horvats, Stephen Kimber, Yun Lin, Ben Pace and Sara Taherymoosavi for their input.</p></ack><ref-list><ref id="b1"><mixed-citation publication-type="journal"><name><surname>Butterbach-Bahl</surname><given-names>K.</given-names></name>, <name><surname>Baggs</surname><given-names>E. M.</given-names></name>, <name><surname>Dannenmann</surname><given-names>M.</given-names></name>, <name><surname>Kiese</surname><given-names>R.</given-names></name> & <name><surname>Zechmeister-Boltenstern</surname><given-names>S.</given-names></name><article-title>Nitrous oxide emissions from soils: how well do we understand the processes and their controls?</article-title><source>Philos. T. Roy. Soc. B</source><volume>368</volume>, <fpage>1621</fpage>, <pub-id pub-id-type="doi">10.1098/rstb.2013.0122</pub-id> (<year>2013</year>).</mixed-citation></ref><ref id="b2"><mixed-citation publication-type="journal"><name><surname>Clough</surname><given-names>T. J.</given-names></name>, <name><surname>Sherlock</surname><given-names>R. R.</given-names></name> & <name><surname>Rolston</surname><given-names>D. E.</given-names></name><article-title>A Review of the Movement and Fate of N<sub>2</sub>O in the Subsoil</article-title>. <source>Nutr. Cycl. Agroecosyst.</source><volume>72</volume>, <fpage>3</fpage>–<lpage>11</lpage> (<year>2005</year>).</mixed-citation></ref><ref id="b3"><mixed-citation publication-type="journal"><name><surname>Heincke</surname><given-names>M.</given-names></name> & <name><surname>Kaupenjohann</surname><given-names>M.</given-names></name><article-title>Effects of soil solution on the dynamics of N<sub>2</sub>O emissions: a review</article-title>. <source>Nutr. Cycl. Agroecosyst.</source><volume>55</volume>, <fpage>133</fpage>–<lpage>157</lpage> (<year>1999</year>).</mixed-citation></ref><ref id="b4"><mixed-citation publication-type="journal"><name><surname>Mukherjee</surname><given-names>A.</given-names></name> & <name><surname>Lal</surname><given-names>R.</given-names></name><article-title>The biochar dilemma</article-title>. <source>Soil Res.</source><volume>52</volume>, <fpage>217</fpage>–<lpage>230</lpage> (<year>2014</year>).</mixed-citation></ref><ref id="b5"><mixed-citation publication-type="journal"><name><surname>Sánchez-García</surname><given-names>M.</given-names></name>, <name><surname>Roig</surname><given-names>A.</given-names></name>, <name><surname>Sanchez-Monedero</surname><given-names>M. A.</given-names></name> & <name><surname>Cayuela</surname><given-names>M. L.</given-names></name><article-title>Biochar increases soil N<sub>2</sub>O emissions produced by nitrification-mediated pathways</article-title>. <source>Front. Environ. Sci.</source><volume>2</volume>, <fpage>25</fpage>, <pub-id pub-id-type="doi">10.3389/fenvs.2014.00025</pub-id> (<year>2014</year>).</mixed-citation></ref><ref id="b6"><mixed-citation publication-type="journal"><name><surname>Cayuela</surname><given-names>M. L.</given-names></name><italic>et al.</italic><article-title>Biochar’s role in mitigating soil nitrous oxide emissions: A review and meta-analysis</article-title>. <source>Agr. Ecosyst. Environ.</source><volume>191</volume>, <fpage>5</fpage>–<lpage>16</lpage> (<year>2014</year>).</mixed-citation></ref><ref id="b7"><mixed-citation publication-type="journal"><name><surname>Cayuela</surname><given-names>M. L.</given-names></name>, <name><surname>Jeffery</surname><given-names>S.</given-names></name> & <name><surname>Van Zwieten</surname><given-names>L.</given-names></name><article-title>The molar H:C<sub>org</sub> ratio of biochar is a key factor in mitigating N<sub>2</sub>O emissions from soil</article-title>. <source>Agr. Ecosyst. Environ.</source><volume>202</volume>, <fpage>135</fpage>–<lpage>138</lpage> (<year>2015</year>).</mixed-citation></ref><ref id="b8"><mixed-citation publication-type="journal"><name><surname>Lin</surname><given-names>X.</given-names></name><italic>et al.</italic><article-title>Assessing Microbial Contributions to N<sub>2</sub>O Impacts Following Biochar Additions</article-title>. <source>Agron.</source><volume>4</volume>, <fpage>478</fpage>–<lpage>496</lpage> (<year>2014</year>).</mixed-citation></ref><ref id="b9"><mixed-citation publication-type="journal"><name><surname>Davidson</surname><given-names>E. A.</given-names></name>, <name><surname>Chorover</surname><given-names>J.</given-names></name> & <name><surname>Dail</surname><given-names>D. B.</given-names></name><article-title>A mechanism of abiotic immobilization of nitrate in forest ecosystems: the ferrous wheel hypothesis</article-title>. <source>Global Change. Biol.</source><volume>9</volume>, <fpage>228</fpage>–<lpage>236</lpage> (<year>2003</year>).</mixed-citation></ref><ref id="b10"><mixed-citation publication-type="journal"><name><surname>Clough</surname><given-names>T. J.</given-names></name>, <name><surname>Condron</surname><given-names>L. M.</given-names></name>, <name><surname>Kamman</surname><given-names>C.</given-names></name> & <name><surname>Müller</surname><given-names>C.</given-names></name><article-title>A Review of Biochar and Soil Nitrogen Dynamics</article-title>. <source>Agron</source><volume>3</volume>, <fpage>275</fpage>–<lpage>293</lpage> (<year>2013</year>).</mixed-citation></ref><ref id="b11"><mixed-citation publication-type="journal"><name><surname>Van Zwieten</surname><given-names>L.</given-names></name>, <italic>et al.</italic> In <source>Biochar for Environmental Management: Science, Technology and Implementation</source> 2nd edn (eds <name><surname>Lehmann</surname><given-names>J.</given-names></name>, <name><surname>Joseph</surname><given-names>S.</given-names></name>) Ch. 17, <fpage>489</fpage>–<lpage>520</lpage> Routledge (<year>2015</year>).</mixed-citation></ref><ref id="b12"><mixed-citation publication-type="journal"><name><surname>Shcherbak</surname><given-names>I.</given-names></name> & <name><surname>Robertson</surname><given-names>G. P.</given-names></name><article-title>Determining the Diffusivity of Nitrous Oxide in Soil using <italic>In Situ</italic> Tracers</article-title>. <source>Soil Sci. Soc. Am. J. J</source><volume>78</volume>, <fpage>79</fpage>–<lpage>88</lpage> (<year>2014</year>).</mixed-citation></ref><ref id="b13"><mixed-citation publication-type="journal"><name><surname>Quin</surname><given-names>P. R.</given-names></name><italic>et al.</italic><article-title>Oil mallee biochar improves soil structural properties—A study with x-ray micro-CT</article-title>. <source>Agr. Ecosyst. Environ.</source><volume>191</volume>, <fpage>142</fpage>–<lpage>149</lpage> (<year>2014</year>).</mixed-citation></ref><ref id="b14"><mixed-citation publication-type="journal"><name><surname>Sun</surname><given-names>Z.</given-names></name><italic>et al.</italic><article-title>Direct and Indirect Short-term Effects of Biochar on Physical Characteristics of an Arable Sandy Loam</article-title>. <source>Soil Sci.</source><volume>178</volume>, <fpage>465</fpage>–<lpage>473</lpage> (<year>2013</year>).</mixed-citation></ref><ref id="b15"><mixed-citation publication-type="journal"><name><surname>Harter</surname><given-names>J.</given-names></name><italic>et al.</italic><article-title>Linking N<sub>2</sub>O emissions from biochar-amended soil to the structure and function of the N-cycling microbial community</article-title>. <source>ISME J.</source><volume>8</volume>, <fpage>660</fpage>–<lpage>674</lpage> (<year>2014</year>).<pub-id pub-id-type="pmid">24067258</pub-id></mixed-citation></ref><ref id="b16"><mixed-citation publication-type="journal"><name><surname>Joseph</surname><given-names>S. D.</given-names></name><italic>et al.</italic><article-title>An investigation into the reactions of biochar in soil</article-title>. <source>Aust. J. Soil Res.</source><volume>48</volume>, <fpage>501</fpage>–<lpage>515</lpage> (<year>2010</year>).</mixed-citation></ref><ref id="b17"><mixed-citation publication-type="journal"><name><surname>Cornelissen</surname><given-names>G.</given-names></name><italic>et al.</italic><article-title>Sorption of Pure N<sub>2</sub>O to Biochars and Other Organic and Inorganic Materials under Anhydrous Conditions</article-title>. <source>Environ. Sci. Technol.</source><volume>47</volume>, <fpage>7704</fpage>–<lpage>7712</lpage> (<year>2013</year>).<pub-id pub-id-type="pmid">23758057</pub-id></mixed-citation></ref><ref id="b18"><mixed-citation publication-type="journal"><name><surname>Cayuela</surname><given-names>M. L.</given-names></name><italic>et al.</italic><article-title>Biochar and denitrification in soils: when, how much and why does biochar reduce N<sub>2</sub>O emissions?</article-title><source>Sci. Rep.</source><volume>3</volume>, <fpage>1732</fpage>, <pub-id pub-id-type="doi">10.1038/srep01732</pub-id> (<year>2013</year>).<pub-id pub-id-type="pmid">23615819</pub-id></mixed-citation></ref><ref id="b19"><mixed-citation publication-type="journal"><name><surname>Klüpfel</surname><given-names>L.</given-names></name>, <name><surname>Keiluweit</surname><given-names>M.</given-names></name>, <name><surname>Kleber</surname><given-names>M.</given-names></name> & <name><surname>Sander</surname><given-names>M.</given-names></name><article-title>Redox Properties of Plant Biomass-Derived Black Carbon (Biochar)</article-title>. <source>Environ. Sci. Technol.</source><volume>48</volume>, <fpage>5601</fpage>–<lpage>5611</lpage> (<year>2014</year>).<pub-id pub-id-type="pmid">24749810</pub-id></mixed-citation></ref><ref id="b20"><mixed-citation publication-type="journal"><name><surname>Joseph</surname><given-names>S.</given-names></name><italic>et al.</italic><article-title>The Electrochemical Properties of Biochars and How They Affect Soil Redox Properties and Processes</article-title>. <source>Agron.</source><volume>5</volume>, <fpage>322</fpage> (<year>2015</year>).</mixed-citation></ref><ref id="b21"><mixed-citation publication-type="journal"><name><surname>Melton</surname><given-names>E. D.</given-names></name>, <name><surname>Swanner</surname><given-names>E. D.</given-names></name>, <name><surname>Behrens</surname><given-names>S.</given-names></name>, <name><surname>Schmidt</surname><given-names>C.</given-names></name> & <name><surname>Kappler</surname><given-names>A.</given-names></name><article-title>The interplay of microbially mediated and abiotic reactions in the biogeochemical Fe cycle</article-title>. <source>Nat. Rev. Micro.</source><volume>12</volume>, <fpage>797</fpage>–<lpage>808</lpage> (<year>2014</year>).</mixed-citation></ref><ref id="b22"><mixed-citation publication-type="journal"><name><surname>Hirsch</surname><given-names>W.</given-names></name> & <name><surname>Fried</surname><given-names>V.</given-names></name><article-title>Gas effusion - A relaxation process</article-title>. <source>J. Chem. Educ.</source><volume>57</volume><bold>(10)</bold>, <fpage>706</fpage> (<year>1980</year>).</mixed-citation></ref><ref id="b23"><mixed-citation publication-type="journal"><name><surname>Zimmerman</surname><given-names>A. R.</given-names></name>, <name><surname>Gao</surname><given-names>B.</given-names></name> & <name><surname>Ahn</surname><given-names>M.-Y.</given-names></name><article-title>Positive and negative carbon mineralization priming effects among a variety of biochar-amended soils</article-title>. <source>Soil. Biol. Biochem.</source><volume>43</volume>, <fpage>1169</fpage>–<lpage>1179</lpage> (<year>2011</year>).</mixed-citation></ref><ref id="b24"><mixed-citation publication-type="journal"><name><surname>Luo</surname><given-names>Y.</given-names></name>, <name><surname>Durenkamp</surname><given-names>M.</given-names></name>, <name><surname>De Nobili</surname><given-names>M.</given-names></name>, <name><surname>Lin</surname><given-names>Q.</given-names></name> & <name><surname>Brookes</surname><given-names>P. C.</given-names></name><article-title>Short term soil priming effects and the mineralisation of biochar following its incorporation to soils of different pH</article-title>. <source>Soil. Biol. Biochem.</source><volume>43</volume>, <fpage>2304</fpage>–<lpage>2314</lpage> (<year>2011</year>).</mixed-citation></ref><ref id="b25"><mixed-citation publication-type="journal"><name><surname>Fang</surname><given-names>Y.</given-names></name>, <name><surname>Singh</surname><given-names>B. P.</given-names></name> & <name><surname>Singh</surname><given-names>B.</given-names></name><article-title>Temperature sensitivity of biochar and native carbon mineralisation in biochar-amended soils</article-title>. <source>Agr. Ecosyst. Environ.</source><volume>191</volume>, <fpage>158</fpage>–<lpage>167</lpage> (<year>2014</year>).</mixed-citation></ref><ref id="b26"><mixed-citation publication-type="journal"><name><surname>Butterbach-Bahl</surname><given-names>K.</given-names></name>, <italic>et al.</italic> In <source>The European Nitrogen Assessment: Sources, Effects and Policy Perspectives</source> (eds. <name><surname>Sutton</surname><given-names>M.</given-names></name>, <italic>et al.</italic>) Ch. 6, <fpage>99</fpage>–<lpage>125</lpage> Cambridge University Press (<year>2011</year>).</mixed-citation></ref><ref id="b27"><mixed-citation publication-type="journal"><name><surname>Hansen</surname><given-names>H. C. B.</given-names></name>, <name><surname>Koch</surname><given-names>C. B.</given-names></name>, <name><surname>Nancke-Krogh</surname><given-names>H.</given-names></name>, <name><surname>Borggaard</surname><given-names>O. K.</given-names></name> & <name><surname>Sørensen</surname><given-names>J.</given-names></name><article-title>Abiotic Nitrate Reduction to Ammonium: Key Role of Green Rust</article-title>. <source>Environ. Sci. Technol.</source><volume>30</volume>, <fpage>2053</fpage>–<lpage>2056</lpage> (<year>1996</year>).</mixed-citation></ref><ref id="b28"><mixed-citation publication-type="journal"><name><surname>Ramsay</surname><given-names>A. J.</given-names></name> & <name><surname>Bawden</surname><given-names>A. D.</given-names></name><article-title>Effects of sterilization and storage on respiration, nitrogen status and direct counts of soil bacteria using acridine orange</article-title>. <source>Soil. Biol. Biochem.</source><volume>15</volume>, <fpage>263</fpage>–<lpage>268</lpage> (<year>1983</year>).</mixed-citation></ref><ref id="b29"><mixed-citation publication-type="journal"><name><surname>Singh</surname><given-names>B. R.</given-names></name> & <name><surname>Kanehiro</surname><given-names>Y.</given-names></name><article-title>Effects of gamma irradiation on the available nitrogen status of soils</article-title>. <source>J. Sci. Food Agr.</source><volume>21</volume>, <fpage>61</fpage>–<lpage>64</lpage> (<year>1970</year>).</mixed-citation></ref><ref id="b30"><mixed-citation publication-type="journal"><name><surname>McNamara</surname><given-names>N. P.</given-names></name>, <name><surname>Black</surname><given-names>H. I. J.</given-names></name>, <name><surname>Beresford</surname><given-names>N. A.</given-names></name> & <name><surname>Parekh</surname><given-names>N. R.</given-names></name><article-title>Effects of acute gamma irradiation on chemical, physical and biological properties of soils</article-title>. <source>Appl. Soil. Ecol.</source><volume>24</volume>, <fpage>117</fpage>–<lpage>132</lpage> (<year>2003</year>).</mixed-citation></ref><ref id="b31"><mixed-citation publication-type="journal"><name><surname>Cheng</surname><given-names>C.-H.</given-names></name>, <name><surname>Lehmann</surname><given-names>J.</given-names></name>, <name><surname>Thies</surname><given-names>J. E.</given-names></name>, <name><surname>Burton</surname><given-names>S. D.</given-names></name> & <name><surname>Engelhard</surname><given-names>M. H.</given-names></name><article-title>Oxidation of black carbon by biotic and abiotic processes</article-title>. <source>Org. Geochem.</source><volume>37</volume>, <fpage>1477</fpage>–<lpage>1488</lpage> (<year>2006</year>).</mixed-citation></ref><ref id="b32"><mixed-citation publication-type="journal"><name><surname>Point</surname><given-names>S.</given-names></name>, <name><surname>Minea</surname><given-names>T.</given-names></name>, <name><surname>Bouchet-Fabre</surname><given-names>B.</given-names></name>, <name><surname>Granier</surname><given-names>A.</given-names></name> & <name><surname>XPS</surname><given-names>Turban G.</given-names></name><article-title>and NEXAFS characterisation of plasma deposited vertically aligned N-doped MWCNT</article-title>. <source>Diam. Relat. Mater.</source><volume>14</volume>, <fpage>891</fpage>–<lpage>895</lpage> (<year>2005</year>).</mixed-citation></ref><ref id="b33"><mixed-citation publication-type="journal"><name><surname>Ravishankara</surname><given-names>A. R.</given-names></name>, <name><surname>Daniel</surname><given-names>J. S.</given-names></name> & <name><surname>Portmann</surname><given-names>R. W.</given-names></name><article-title>Nitrous Oxide (N<sub>2</sub>O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century</article-title>. <source>Science</source><volume>326</volume>, <fpage>123</fpage>–<lpage>125</lpage> (<year>2009</year>).<pub-id pub-id-type="pmid">19713491</pub-id></mixed-citation></ref><ref id="b34"><mixed-citation publication-type="journal"><name><surname>Lin</surname><given-names>Y.</given-names></name>, <name><surname>Munroe</surname><given-names>P.</given-names></name>, <name><surname>Joseph</surname><given-names>S.</given-names></name>, <name><surname>Kimber</surname><given-names>S.</given-names></name> & <name><surname>Van Zwieten</surname><given-names>L.</given-names></name><article-title>Nanoscale organo-mineral reactions of biochars in ferrosol: an investigation using microscopy</article-title>. <source>Plant Soil</source><volume>357</volume>, <fpage>369</fpage>–<lpage>380</lpage> (<year>2012</year>).</mixed-citation></ref><ref id="b35"><mixed-citation publication-type="journal"><name><surname>Aylward</surname><given-names>G. H.</given-names></name>, <source>Findlay TJV. <italic>SI Chemical Data</italic>,</source> 5th edn, John Wiley & Sons Australia (<year>2002</year>).</mixed-citation></ref><ref id="b36"><mixed-citation publication-type="journal"><name><surname>Carabineiro</surname><given-names>S. A.</given-names></name><italic>et al.</italic><article-title>N<sub>2</sub>O reduction by activated carbon over iron bimetallic catalysts</article-title>. <source>Catal. Today</source><volume>133–135</volume>, <fpage>441</fpage>–<lpage>447</lpage> (<year>2008</year>).</mixed-citation></ref><ref id="b37"><mixed-citation publication-type="journal"><name><surname>Avdeev</surname><given-names>V. I.</given-names></name>, <name><surname>Ruzankin</surname><given-names>S. F.</given-names></name> & <name><surname>Zhidomirov</surname><given-names>G. M.</given-names></name><article-title>Molecular mechanism of direct alkene oxidation with nitrous oxide: DFT analysis</article-title>. <source>Kinet. Catal.</source><volume>46</volume>, <fpage>177</fpage>–<lpage>188</lpage> (<year>2005</year>).</mixed-citation></ref><ref id="b38"><mixed-citation publication-type="journal"><name><surname>Husson</surname><given-names>O.</given-names></name><article-title>Redox potential (Eh) and pH as drivers of soil/plant/microorganism systems: a transdisciplinary overview pointing to integrative opportunities for agronomy</article-title>. <source>Plant Soil</source><volume>362</volume>, <fpage>389</fpage>–<lpage>417</lpage> (<year>2013</year>).</mixed-citation></ref><ref id="b39"><mixed-citation publication-type="journal"><name><surname>Li</surname><given-names>Y.</given-names></name>, <name><surname>Yu</surname><given-names>S.</given-names></name>, <name><surname>Strong</surname><given-names>J.</given-names></name> & <name><surname>Wang</surname><given-names>H.</given-names></name><article-title>Are the biogeochemical cycles of carbon, nitrogen, sulfur, and phosphorus driven by the “FeIII–FeII redox wheel” in dynamic redox environments?</article-title><source>J. Soils Sediments</source><volume>12</volume>, <fpage>683</fpage>–<lpage>693</lpage> (<year>2012</year>).</mixed-citation></ref><ref id="b40"><mixed-citation publication-type="journal"><name><surname>Chao</surname><given-names>T.-T.</given-names></name> & <name><surname>Kroontje</surname><given-names>W.</given-names></name><article-title>Inorganic Nitrogen Transformations Through the Oxidation and Reduction of Iron1</article-title>. <source>Soil. Sci. Soc. Am. J.</source><volume>30</volume>, <fpage>193</fpage>–<lpage>196</lpage> (<year>1966</year>).</mixed-citation></ref><ref id="b41"><mixed-citation publication-type="journal"><name><surname>Alowitz</surname><given-names>M. J.</given-names></name> & <name><surname>Scherer</surname><given-names>M. M.</given-names></name><article-title>Kinetics of Nitrate, Nitrite, and Cr(VI) Reduction by Iron Metal</article-title>. <source>Environ. Sci. Technol.</source><volume>36</volume>, <fpage>299</fpage>–<lpage>306</lpage> (<year>2002</year>).<pub-id pub-id-type="pmid">11871541</pub-id></mixed-citation></ref><ref id="b42"><mixed-citation publication-type="journal"><name><surname>Dhakal</surname><given-names>P.</given-names></name>, <name><surname>Matocha</surname><given-names>C. J.</given-names></name>, <name><surname>Huggins</surname><given-names>F. E.</given-names></name> & <name><surname>Vandiviere</surname><given-names>M. M.</given-names></name><article-title>Nitrite Reactivity with Magnetite</article-title>. <source>Environ. Sci. Technol.</source><volume>47</volume>, <fpage>6206</fpage>–<lpage>6213</lpage> (<year>2013</year>).<pub-id pub-id-type="pmid">23662623</pub-id></mixed-citation></ref><ref id="b43"><mixed-citation publication-type="journal"><name><surname>Klüpfel</surname><given-names>L.</given-names></name>, <name><surname>Piepenbrock</surname><given-names>A.</given-names></name>, <name><surname>Kappler</surname><given-names>A.</given-names></name> & <name><surname>Sander</surname><given-names>M.</given-names></name><article-title>Humic substances as fully regenerable electron acceptors in recurrently anoxic environments</article-title>. <source>Nat. Geosci.</source><volume>7</volume>, <fpage>195</fpage>–<lpage>200</lpage> (<year>2014</year>).</mixed-citation></ref><ref id="b44"><mixed-citation publication-type="journal"><name><surname>Sang</surname><given-names>C.</given-names></name>, <name><surname>Kim</surname><given-names>B. H.</given-names></name> & <name><surname>Lund</surname><given-names>C. R. F.</given-names></name><article-title>Effect of NO upon N<sub>2</sub>O Decomposition over Fe/ZSM-5 with Low Iron Loading†</article-title>. <source>J. Phys. Chem. B</source><volume>109</volume>, <fpage>2295</fpage>–<lpage>2301</lpage> (<year>2005</year>).<pub-id pub-id-type="pmid">16851222</pub-id></mixed-citation></ref><ref id="b45"><mixed-citation publication-type="journal">International Union of Soil Sciences Working Group. <source>World reference base for soil resources 2006: A framework for international classification, correlation and communication.</source> FAO (<year>2006</year>).</mixed-citation></ref><ref id="b46"><mixed-citation publication-type="other"><name><surname>Krull</surname><given-names>E. S.</given-names></name><italic>et al.</italic> From Source to Sink: A National Initiative for Biochar Research. Department of Agriculture. Fisheries and Forestry, Australia (2012).</mixed-citation></ref><ref id="b47"><mixed-citation publication-type="journal"><name><surname>Van Zwieten</surname><given-names>L.</given-names></name><italic>et al.</italic><article-title>Influence of biochars on flux of N<sub>2</sub>O and CO<sub>2</sub> from Ferrosol</article-title>. <source>Aust. J. Soil Res.</source><volume>48</volume>, <fpage>555</fpage>–<lpage>568</lpage> (<year>2010</year>).</mixed-citation></ref><ref id="b48"><mixed-citation publication-type="journal"><name><surname>Rangott</surname><given-names>G.</given-names></name><source>Char Analysis Report. Diagnostic and Analytical Services Environmental Laboratory.</source> Department of Primary Industry (<year>2010</year>).</mixed-citation></ref><ref id="b49"><mixed-citation publication-type="journal"><name><surname>Hunt</surname><given-names>C.</given-names></name><source>Char Analysis Report-Ash. Diagnostic and Analytical Services Environmental Laboratory.</source> Department of Primary Industry (<year>2015</year>).</mixed-citation></ref><ref id="b50"><mixed-citation publication-type="journal"><name><surname>Downie</surname><given-names>A.</given-names></name>, <name><surname>Crosky</surname><given-names>A.</given-names></name> & <name><surname>Munroe</surname><given-names>P.</given-names></name> In <source>Biochar for Environmental Management: Science and Technology</source> (eds <name><surname>Lehmann</surname><given-names>J.</given-names></name>, <name><surname>Joseph</surname><given-names>S.</given-names></name>) Ch. 2, <fpage>13</fpage>–<lpage>32</lpage> Earthscan (<year>2009</year>).</mixed-citation></ref><ref id="b51"><mixed-citation publication-type="journal"><name><surname>Daly</surname><given-names>M. J.</given-names></name>, <italic>et al.</italic><article-title>Accumulation of Mn(II) in, Deinococcus radiodurans facilitates gamma-radiation resistance</article-title>. <source>Science</source><volume>306</volume>, <fpage>1025</fpage>–<lpage>1028</lpage> (<year>2004</year>).<pub-id pub-id-type="pmid">15459345</pub-id></mixed-citation></ref><ref id="b52"><mixed-citation publication-type="journal"><name><surname>van Gerwen</surname><given-names>S. J. C.</given-names></name>, <name><surname>Rombouts</surname><given-names>F. M.</given-names></name>, <name><surname>Van’t Riet</surname><given-names>K.</given-names></name> & <name><surname>Zwietering</surname><given-names>M. H.</given-names></name><article-title>A data analysis of the irradiation parameter D-10 for bacteria and spores under various conditions</article-title>. <source>J. Food Protect.</source><volume>62</volume>, <fpage>1024</fpage>–<lpage>1032</lpage> (<year>1999</year>).</mixed-citation></ref><ref id="b53"><mixed-citation publication-type="journal"><name><surname>Zelles</surname><given-names>L.</given-names></name><italic>et al.</italic><article-title>Microbial activity measured in soils stored under different temperature and humidity conditions</article-title>. <source>Soil. Biol. Biochem.</source><volume>23</volume>, <fpage>955</fpage>–<lpage>962</lpage> (<year>1991</year>).</mixed-citation></ref><ref id="b54"><mixed-citation publication-type="journal"><name><surname>Clarke</surname><given-names>J. M.</given-names></name>, <name><surname>Gillings</surname><given-names>M. R.</given-names></name>, <name><surname>Altavilla</surname><given-names>N.</given-names></name> & <name><surname>Beattie</surname><given-names>A. J.</given-names></name><article-title>Potential problems with fluorescein diacetate assays of cell viability when testing natural products for antimicrobial activity</article-title>. <source>J. Microbiol. Meth.</source><volume>46</volume>, <fpage>261</fpage>–<lpage>267</lpage> (<year>2001</year>).</mixed-citation></ref><ref id="b55"><mixed-citation publication-type="journal"><name><surname>Rayment</surname><given-names>G. E.</given-names></name> & <name><surname>Lyons</surname><given-names>D. J.</given-names></name><source>Soil Chemical Methods - Australasia.</source> CSIRO Publishing (<year>2010</year>).</mixed-citation></ref><ref id="b56"><mixed-citation publication-type="journal"><name><surname>Fiedler</surname><given-names>S.</given-names></name>, <name><surname>Vepraskas</surname><given-names>M. J.</given-names></name> & <name><surname>Richardson</surname><given-names>J. L.</given-names></name><article-title>Soil Redox Potential: Importance, Field Measurements, and Observations</article-title>. <source>Adv. Agron.</source><volume>94</volume>, <fpage>1</fpage>–<lpage>54</lpage> (<year>2007</year>).</mixed-citation></ref><ref id="b57"><mixed-citation publication-type="journal"><name><surname>Glínski</surname><given-names>J.</given-names></name> & <name><surname>Stępniewski</surname><given-names>W.</given-names></name><source>Soil aeration and its role for plant</source> s. CRC Press (<year>1985</year>).</mixed-citation></ref><ref id="b58"><mixed-citation publication-type="journal"><name><surname>Pidello</surname><given-names>A.</given-names></name><article-title>Environmental Redox Potential and Redox Capacity Concepts Using a Simple Polarographic Experiment</article-title>. <source>J. Chem. Educ.</source><volume>80</volume>, <fpage>68</fpage> (<year>2003</year>).</mixed-citation></ref><ref id="b59"><mixed-citation publication-type="journal"><name><surname>Joseph</surname><given-names>S.</given-names></name>, <italic>et al.</italic><article-title>Shifting paradigms: development of high-efficiency biochar fertilizers based on nano-structures and soluble components</article-title>. <source>Carbon Manag.</source><volume>4</volume>, <fpage>323</fpage>–<lpage>343</lpage> (<year>2013</year>).</mixed-citation></ref><ref id="b60"><mixed-citation publication-type="other"><name><surname>Puigdomenech,</surname><given-names>I.</given-names></name> (2009–2011) Medusa software, available at: <ext-link ext-link-type="uri" xlink:href="https://sites.google.com/site/chemdiagr/">https://sites.google.com/site/chemdiagr/</ext-link>(Accessed: 17th June 2015).</mixed-citation></ref></ref-list><fn-group><fn><p><bold>Author Contributions</bold> P.Q., S.J. and L.V.Z. conducted principal research. P.Q., S.J., O.H. and S.D. wrote the main manuscript text with assistance from L.V.Z., D.M. and A.C. Figures were prepared by P.Q., S.J., O.H., D.M., P.M. and D.P. All authors reviewed the manuscript.</p></fn></fn-group></back><floats-group><fig id="f1"><label>Figure 1</label><caption><p>The change in mean headspace N<sub>2</sub>O (injected N<sub>2</sub>O)<sup>−1</sup> for mean soil water contents of, (<bold>a</bold>) 12% WFPS; (<bold>b</bold>) 39% WFPS; (<bold>c</bold>) 54% WFPS; and also, (<bold>d</bold>) 100% biochar and acid-washed sand (error bars represent ± s.e.m., <italic>n</italic> = 3). At tmax for 12% WFPS the significance of difference in mean nett headspace N<sub>2</sub>O (injected N<sub>2</sub>O)<sup>−1</sup> between 0 and 1%, 0 and 5% and 1 and 5% biochar was <italic>p</italic> = 0.10, 0.0058 and 0.018 respectively. For 39% WFPS the corresponding values were <italic>p</italic> = 0.31, 0.0054 and 0.016, and for 54% WFPS were <italic>p</italic> = 0.020, 0.00022 and 0.00079. Accounting for N<sub>2</sub>O in WFPS and AFPS, at tmax for 12% WFPS the significance of difference in mean nett (column) total N<sub>2</sub>O content (injected N<sub>2</sub>O)<sup>−1</sup> between 0 and 1%, 0 and 5% and 1 and 5% biochar was <italic>p</italic> = 0.12, 0.0069 and 0.021 respectively. For 39% WFPS the corresponding values were <italic>p</italic> = 0.34, 0.00076 and 0.018, and for 54% WFPS were <italic>p</italic> = 0.022, 0.00024 and 0.00092.</p></caption><graphic xlink:href="srep16773-f1"></graphic></fig><fig id="f2"><label>Figure 2</label><caption><title>Pourbaix diagram of N representing its various forms in a 100 μM solution at 25 °C as a function of Eh (in V) and pH (diagram drawn using <italic>Medusa software</italic><xref ref-type="bibr" rid="b60">60</xref>).</title></caption><graphic xlink:href="srep16773-f2"></graphic></fig><fig id="f3"><label>Figure 3</label><caption><p>(<bold>a</bold>) SEM image of xylem in the biochar after interaction with soil; (<bold>b</bold>) Internal surfaces of the xylem of the biochar coated in an organomineral film containing significant amounts of Ca and Mg; (<bold>c</bold>) external surface of the biochar and a pore coated with a range of minerals, and (<bold>d</bold>) the EDS spectrum of (<bold>c</bold>).</p></caption><graphic xlink:href="srep16773-f3"></graphic></fig><fig id="f4"><label>Figure 4</label><caption><p>(<bold>a</bold>) HAADF image showing an organomineral layer (bright) coating an external surface of a biochar particle; (<bold>b</bold>) Phase map of (<bold>a</bold>) derived from x-ray microanalysis spectrum imaging, showing three distinct phases; Average EDS spectra of: (<bold>c</bold>) red (biochar) phase in (<bold>b</bold>) containing C and O only; (<bold>d</bold>) yellow (clay) phase in (<bold>b</bold>) containing mainly C, O, Al and Si; (<bold>e</bold>) blue (Fe-rich) phase in (<bold>b</bold>). Both mineral phases [(<bold>c,d</bold>)] have a considerable organic content.</p></caption><graphic xlink:href="srep16773-f4"></graphic></fig><fig id="f5"><label>Figure 5</label><caption><p>(<bold>a</bold>) STEM HAADF image of biochar with organomineral layer; (<bold>b</bold>) Fe-L<sub>2,3</sub> EELS spectra (background stripped) were obtained from the points marked in (<bold>a</bold>). The EELS 1 spectrum is characteristic of haematite (Fe III). The spectrum from EELS 2 (red line) shows a pronounced low energy shoulder, suggesting a mixed (II–III) valence state. Note: peak maxima aligned at 709 eV for comparison.</p></caption><graphic xlink:href="srep16773-f5"></graphic></fig><fig id="f6"><label>Figure 6</label><caption><p>(<bold>a</bold>) STEM HAADF image of edge of biochar showing organomineral phase formed by reaction with soil; (<bold>b</bold>) EDS spectrum of Fe-rich mineral phase (EDS 1); (<bold>c</bold>) EDS spectrum of Si-rich phase (EDS 2); (<bold>d</bold>) Fe-L<sub>2,3</sub> EELS spectrum (background stripped) at EELS 1 showing a pronounced low energy shoulder on the Fe-L<sub>3</sub> edge at around 708 eV, characteristic of a mixed (Fe II–III) valence state such as found in magnetite.</p></caption><graphic xlink:href="srep16773-f6"></graphic></fig><table-wrap position="float" id="t1"><label>Table 1</label><caption><title>The nett increase in total N<sub>2</sub>O content in column air and water relative to N<sub>2</sub>O injected, measured at tmax: 300 minutes for acid-washed sand, 100% biochar and 12% WFPS; 360 minutes for 39 and 54% WFPS (s.e.m. in parentheses, <italic>n</italic> = 3).</title></caption><table frame="hsides" rules="groups" border="1"><colgroup><col align="left"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col></colgroup><thead valign="bottom"><tr><th rowspan="3" align="left" valign="top" charoff="50">% biochar (w/w soil)</th><th colspan="5" align="center" valign="top" charoff="50">Mean WFPS (%)<hr></hr></th></tr><tr><th align="center" valign="top" charoff="50">L (12)</th><th align="center" valign="top" charoff="50">M (39)</th><th align="center" valign="top" charoff="50">H (54)</th><th align="center" valign="top" charoff="50">3</th><th align="center" valign="top" charoff="50">6</th></tr><tr><th align="center" valign="top" charoff="50"> </th><th align="center" valign="top" charoff="50"> </th><th align="center" valign="top" charoff="50">∆N<sub>2</sub>O/inj.N<sub>2</sub>O(mol/mol)</th><th align="center" valign="top" charoff="50"> </th><th align="center" valign="top" charoff="50"> </th></tr></thead><tbody valign="top"><tr><td align="left" valign="top" charoff="50">0</td><td align="center" valign="top" charoff="50">0.958 (0.085)</td><td align="center" valign="top" charoff="50">1.020 (0.026)</td><td align="center" valign="top" charoff="50">1.025 (0.115)</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td></tr><tr><td align="left" valign="top" charoff="50">1</td><td align="center" valign="top" charoff="50">0.837 (0.054)</td><td align="center" valign="top" charoff="50">0.970 (0.070)</td><td align="center" valign="top" charoff="50">0.914 (0.040)</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td></tr><tr><td align="left" valign="top" charoff="50">5</td><td align="center" valign="top" charoff="50">0.614 (0.081)</td><td align="center" valign="top" charoff="50">0.772 (0.088)</td><td align="center" valign="top" charoff="50">0.652 (0.029)</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td></tr><tr><td align="left" valign="top" charoff="50">100</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">0.161 (0.012)</td></tr><tr><td align="left" valign="top" charoff="50">Acid-washed sand</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">1.056 (0.113)</td><td align="center" valign="top" charoff="50"> </td></tr></tbody></table></table-wrap><table-wrap position="float" id="t2"><label>Table 2</label><caption><title>Nitrate- and ammonium-N concentrations, pH and Eh of soil/biochar mixtures after incubation, with Eh values corrected to pH = 7 (s.e.m. in parentheses, <italic>n</italic> = 3).</title></caption><table frame="hsides" rules="groups" border="1"><colgroup><col align="left"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="left"></col></colgroup><thead valign="bottom"><tr><th align="left" valign="top" charoff="50">Biochar (%)</th><th colspan="3" align="center" valign="top" charoff="50">0<hr></hr></th><th colspan="3" align="center" valign="top" charoff="50">1<hr></hr></th><th colspan="3" align="center" valign="top" charoff="50">5<hr></hr></th><th align="center" valign="top" charoff="50">100</th></tr><tr><th align="left" valign="top" charoff="50">WFPS (%)</th><th align="center" valign="top" charoff="50">12</th><th align="center" valign="top" charoff="50">39</th><th align="center" valign="top" charoff="50">54</th><th align="center" valign="top" charoff="50">12</th><th align="center" valign="top" charoff="50">39</th><th align="center" valign="top" charoff="50">54</th><th align="center" valign="top" charoff="50">12</th><th align="center" valign="top" charoff="50">39</th><th align="center" valign="top" charoff="50">54</th><th align="center" valign="top" charoff="50">6</th></tr></thead><tbody valign="top"><tr><td align="left" valign="top" charoff="50"><bold>NH<sub>4</sub></bold><sup><bold> + </bold></sup><bold>-N</bold> (mg kg<sup>−1</sup>)</td><td align="center" valign="top" charoff="50">24.7 (0.33) a<xref ref-type="fn" rid="t2-fn1">*</xref>c<xref ref-type="fn" rid="t2-fn1">****</xref></td><td align="center" valign="top" charoff="50">72.5 (1.50) a<xref ref-type="fn" rid="t2-fn1">*</xref>b<xref ref-type="fn" rid="t2-fn1">*</xref></td><td align="center" valign="top" charoff="50">95.3 (0.67) b<xref ref-type="fn" rid="t2-fn1">*</xref>c<xref ref-type="fn" rid="t2-fn1">****</xref>j<xref ref-type="fn" rid="t2-fn1">*</xref></td><td align="center" valign="top" charoff="50">23.3 (0.33) d<xref ref-type="fn" rid="t2-fn1">***</xref>f<xref ref-type="fn" rid="t2-fn1">****</xref></td><td align="center" valign="top" charoff="50">73.0 (1.15) d<xref ref-type="fn" rid="t2-fn1">***</xref>e<xref ref-type="fn" rid="t2-fn1">**</xref>k<xref ref-type="fn" rid="t2-fn1">*</xref></td><td align="center" valign="top" charoff="50">94.0 (0.00) e<xref ref-type="fn" rid="t2-fn1">**</xref>f<xref ref-type="fn" rid="t2-fn1">****</xref>n<xref ref-type="fn" rid="t2-fn1">*</xref></td><td align="center" valign="top" charoff="50">24.0 (0.58) g<xref ref-type="fn" rid="t2-fn1">****</xref>h<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">77.7 (1.20) g<xref ref-type="fn" rid="t2-fn1">****</xref>k<xref ref-type="fn" rid="t2-fn1">*</xref></td><td align="center" valign="top" charoff="50">79.7 (3.18) h<xref ref-type="fn" rid="t2-fn1">**</xref>j<xref ref-type="fn" rid="t2-fn1">*</xref>n<xref ref-type="fn" rid="t2-fn1">*</xref></td><td align="center" valign="top" charoff="50"><0.3</td></tr><tr><td align="left" valign="top" charoff="50"><bold>NO<sub>3</sub></bold><sup><bold>−</bold></sup><bold>-N</bold> (mg kg<sup>−1</sup>)</td><td align="center" valign="top" charoff="50">0.2 (0.03) a<xref ref-type="fn" rid="t2-fn1">**</xref>b<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">1.2 (0.35)</td><td align="center" valign="top" charoff="50">1.9 (0.56)</td><td align="center" valign="top" charoff="50">0.5 (0.01) a<xref ref-type="fn" rid="t2-fn1">**</xref>c<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">0.9 (0.24)</td><td align="center" valign="top" charoff="50">1.7 (0.26) c<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">0.5 (0.01) b<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">1.3 (0.51)</td><td align="center" valign="top" charoff="50">0.9 (0.29)</td><td align="center" valign="top" charoff="50"><0.20</td></tr><tr><td align="left" valign="top" charoff="50"><bold>pH</bold></td><td align="center" valign="top" charoff="50">5.8 (0) a<xref ref-type="fn" rid="t2-fn1">#</xref>b<xref ref-type="fn" rid="t2-fn1">**</xref> h<xref ref-type="fn" rid="t2-fn1">#</xref>j<xref ref-type="fn" rid="t2-fn1">#</xref></td><td align="center" valign="top" charoff="50">6.0 (0) a<xref ref-type="fn" rid="t2-fn1">#</xref>n<xref ref-type="fn" rid="t2-fn1">*</xref> q<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">6.1 (0.03) b<xref ref-type="fn" rid="t2-fn1">**</xref>r<xref ref-type="fn" rid="t2-fn1">*</xref> t<xref ref-type="fn" rid="t2-fn1">****</xref></td><td align="center" valign="top" charoff="50">6.1 (0) c<xref ref-type="fn" rid="t2-fn1">*</xref>d<xref ref-type="fn" rid="t2-fn1">*</xref> h<xref ref-type="fn" rid="t2-fn1">#</xref>k<xref ref-type="fn" rid="t2-fn1">#</xref></td><td align="center" valign="top" charoff="50">6.3 (0.03) c<xref ref-type="fn" rid="t2-fn1">*</xref>n<xref ref-type="fn" rid="t2-fn1">*</xref> p<xref ref-type="fn" rid="t2-fn1">****</xref></td><td align="center" valign="top" charoff="50">6.4 (0.07) d<xref ref-type="fn" rid="t2-fn1">*</xref>r<xref ref-type="fn" rid="t2-fn1">*</xref>s<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">6.7 (0) e<xref ref-type="fn" rid="t2-fn1">**</xref>g<xref ref-type="fn" rid="t2-fn1">**</xref> j<xref ref-type="fn" rid="t2-fn1">#</xref>k<xref ref-type="fn" rid="t2-fn1">#</xref></td><td align="center" valign="top" charoff="50">7.0 (0.03) e<xref ref-type="fn" rid="t2-fn1">**</xref>f<xref ref-type="fn" rid="t2-fn1">**</xref> p<xref ref-type="fn" rid="t2-fn1">****</xref>q<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">7.4 (0.03) f<xref ref-type="fn" rid="t2-fn1">**</xref>g<xref ref-type="fn" rid="t2-fn1">**</xref> s<xref ref-type="fn" rid="t2-fn1">**</xref>t<xref ref-type="fn" rid="t2-fn1">****</xref></td><td align="center" valign="top" charoff="50">9.7 (0.1)</td></tr><tr><td align="left" valign="top" charoff="50"><bold>Eh<sub>pH7</sub></bold> (mV)</td><td align="center" valign="top" charoff="50">454 (3.8) a<xref ref-type="fn" rid="t2-fn1">**</xref>f<xref ref-type="fn" rid="t2-fn1">*</xref> g<xref ref-type="fn" rid="t2-fn1">*</xref>h<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">382 (7.0) f<xref ref-type="fn" rid="t2-fn1">*</xref></td><td align="center" valign="top" charoff="50">404 (5.8) a<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">515 (4.5) b<xref ref-type="fn" rid="t2-fn1">**</xref>c<xref ref-type="fn" rid="t2-fn1">**</xref> g<xref ref-type="fn" rid="t2-fn1">*</xref>j<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">405 (6.9) b<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">414 (11.6) c<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">621 (12.0) d<xref ref-type="fn" rid="t2-fn1">**</xref>e<xref ref-type="fn" rid="t2-fn1">***</xref> h<xref ref-type="fn" rid="t2-fn1">**</xref>j<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">428 (4.0) d<xref ref-type="fn" rid="t2-fn1">**</xref></td><td align="center" valign="top" charoff="50">429 (14.0) e<xref ref-type="fn" rid="t2-fn1">***</xref></td><td align="center" valign="top" charoff="50">499 (13.3)</td></tr></tbody></table><table-wrap-foot><fn id="t2-fn1"><p>Within rows, means accompanied by the same letter are significantly different (*<italic>p</italic> < 0.05, **<italic>p</italic> < 0.01, ***<italic>p</italic> < 0.001, ****<italic>p</italic> < 0.0001, #<italic>p</italic> = 0).</p></fn></table-wrap-foot></table-wrap><table-wrap position="float" id="t3"><label>Table 3</label><caption><title>C 1s and N 1s bonding state and their relative atomic percentage on the biochar surfaces of eucalypt biochar before addition to columns, extracted from the soil LMH5% treatments and from the 100% biochar treatment, as determined by XPS (regional scan).</title></caption><table frame="hsides" rules="groups" border="1"><colgroup><col align="left"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col></colgroup><thead valign="bottom"><tr><th colspan="4" align="center" valign="top" charoff="50">Unincubated biochar<hr></hr></th><th colspan="2" align="center" valign="top" charoff="50">Biochar from LMH5% soils<hr></hr></th><th colspan="3" align="center" valign="top" charoff="50">BC100% after addition of N<sub>2</sub>O<hr></hr></th></tr><tr><th align="left" valign="top" charoff="50">Name</th><th align="center" valign="top" charoff="50">Functional Groups</th><th align="center" valign="top" charoff="50">Peak BE(mV)</th><th align="center" valign="top" charoff="50">At. %</th><th align="center" valign="top" charoff="50">Peak BE(mV)</th><th align="center" valign="top" charoff="50">At. %</th><th align="center" valign="top" charoff="50">Functional Groups</th><th align="center" valign="top" charoff="50">Peak BE(mV)</th><th align="center" valign="top" charoff="50">At. %</th></tr></thead><tbody valign="top"><tr><td align="left" valign="top" charoff="50">C1s A</td><td align="center" valign="top" charoff="50">C = C/C-C/C-H</td><td align="center" valign="top" charoff="50">284.47</td><td align="center" valign="top" charoff="50">68.24</td><td align="center" valign="top" charoff="50">284.38</td><td align="center" valign="top" charoff="50">35.68</td><td align="center" valign="top" charoff="50">C = C/C-C/C-H</td><td align="center" valign="top" charoff="50">284.57</td><td align="center" valign="top" charoff="50">57.10</td></tr><tr><td align="left" valign="top" charoff="50">C1s B</td><td align="center" valign="top" charoff="50">C-O</td><td align="center" valign="top" charoff="50">286.57</td><td align="center" valign="top" charoff="50">6.76</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">C-O</td><td align="center" valign="top" charoff="50">286.56</td><td align="center" valign="top" charoff="50">12.11</td></tr><tr><td align="left" valign="top" charoff="50">C1s C</td><td align="center" valign="top" charoff="50">C = O</td><td align="center" valign="top" charoff="50">287.97</td><td align="center" valign="top" charoff="50">2.40</td><td align="center" valign="top" charoff="50">286.48</td><td align="center" valign="top" charoff="50">8.04</td><td align="center" valign="top" charoff="50">C = O</td><td align="center" valign="top" charoff="50">287.96</td><td align="center" valign="top" charoff="50">3.35</td></tr><tr><td align="left" valign="top" charoff="50">C1s D</td><td align="center" valign="top" charoff="50">O = C-O</td><td align="center" valign="top" charoff="50">289.17</td><td align="center" valign="top" charoff="50">0.53</td><td align="center" valign="top" charoff="50">287.88</td><td align="center" valign="top" charoff="50">2.89</td><td align="center" valign="top" charoff="50">O = C-O</td><td align="center" valign="top" charoff="50">289.16</td><td align="center" valign="top" charoff="50">3.65</td></tr><tr><td align="left" valign="top" charoff="50">C1s E</td><td align="center" valign="top" charoff="50">Shake up peaks</td><td align="center" valign="top" charoff="50">290.36</td><td align="center" valign="top" charoff="50">6.70</td><td align="center" valign="top" charoff="50">289.08</td><td align="center" valign="top" charoff="50">2.74</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td></tr><tr><td align="left" valign="top" charoff="50">C1s F</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">Shake up peaks</td><td align="center" valign="top" charoff="50">290.87</td><td align="center" valign="top" charoff="50">4.23</td></tr><tr><td align="left" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">Carbonate</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">291.21</td><td align="center" valign="top" charoff="50">1.21</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td></tr><tr><td align="left" valign="top" charoff="50">N1s A</td><td align="center" valign="top" charoff="50">-O-C = N/pyridine pyrrole/NH<sub>3</sub></td><td align="center" valign="top" charoff="50">400.42</td><td align="center" valign="top" charoff="50">0.40</td><td align="center" valign="top" charoff="50">400.47</td><td align="center" valign="top" charoff="50">0.77</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">400.93</td><td align="center" valign="top" charoff="50">0.49</td></tr><tr><td align="left" valign="top" charoff="50">N1s B</td><td align="center" valign="top" charoff="50">NH<sub>4</sub>/NH<sub>2</sub> groups</td><td align="center" valign="top" charoff="50">398.55</td><td align="center" valign="top" charoff="50">0.28</td><td align="center" valign="top" charoff="50">398.69</td><td align="center" valign="top" charoff="50">0.13</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">399.23</td><td align="center" valign="top" charoff="50">0.25</td></tr><tr><td align="left" valign="top" charoff="50">N1s C</td><td align="center" valign="top" charoff="50">Pyridine/N-O/Chemisorbed NH<sub>3</sub></td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">402.56</td><td align="center" valign="top" charoff="50">0.11</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td></tr></tbody></table></table-wrap><table-wrap position="float" id="t4"><label>Table 4</label><caption><title>XPS survey of the C, N, O and mineral elements in the three biochar samples (nd = not detected).</title></caption><table frame="hsides" rules="groups" border="1"><colgroup><col align="left"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col><col align="center"></col></colgroup><thead valign="bottom"><tr><th colspan="3" align="center" valign="top" charoff="50">Unincubated BC<hr></hr></th><th colspan="2" align="center" valign="top" charoff="50">LMH5%<hr></hr></th><th colspan="2" align="center" valign="top" charoff="50">BC100%<hr></hr></th></tr><tr><th align="left" valign="top" charoff="50">Name</th><th align="center" valign="top" charoff="50">Peak BE</th><th align="center" valign="top" charoff="50">At. %</th><th align="center" valign="top" charoff="50">Peak BE</th><th align="center" valign="top" charoff="50">At. %</th><th align="center" valign="top" charoff="50">Peak BE</th><th align="center" valign="top" charoff="50">At. %</th></tr></thead><tbody valign="top"><tr><td align="left" valign="top" charoff="50">C1s</td><td align="center" valign="top" charoff="50">284.56</td><td align="center" valign="top" charoff="50">82.38</td><td align="center" valign="top" charoff="50">284.63</td><td align="center" valign="top" charoff="50">42.77</td><td align="center" valign="top" charoff="50">285.39</td><td align="center" valign="top" charoff="50">73.72</td></tr><tr><td align="left" valign="top" charoff="50">O1s</td><td align="center" valign="top" charoff="50">532.42</td><td align="center" valign="top" charoff="50">14.39</td><td align="center" valign="top" charoff="50">532.67</td><td align="center" valign="top" charoff="50">39.40</td><td align="center" valign="top" charoff="50">533.16</td><td align="center" valign="top" charoff="50">19.20</td></tr><tr><td align="left" valign="top" charoff="50">Ca2p</td><td align="center" valign="top" charoff="50">348.08</td><td align="center" valign="top" charoff="50">1.84</td><td align="center" valign="top" charoff="50">347.70</td><td align="center" valign="top" charoff="50">0.75</td><td align="center" valign="top" charoff="50">348.66</td><td align="center" valign="top" charoff="50">2.39</td></tr><tr><td align="left" valign="top" charoff="50">Al2p</td><td align="center" valign="top" charoff="50">nd</td><td align="center" valign="top" charoff="50">nd</td><td align="center" valign="top" charoff="50">75.39</td><td align="center" valign="top" charoff="50">7.37</td><td align="center" valign="top" charoff="50">75.63</td><td align="center" valign="top" charoff="50">0.28</td></tr><tr><td align="left" valign="top" charoff="50">Si2p</td><td align="center" valign="top" charoff="50">103.44</td><td align="center" valign="top" charoff="50">0.51</td><td align="center" valign="top" charoff="50">103.78</td><td align="center" valign="top" charoff="50">7.31</td><td align="center" valign="top" charoff="50">103.89</td><td align="center" valign="top" charoff="50">0.97</td></tr><tr><td align="left" valign="top" charoff="50">Fe2p</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">712.20</td><td align="center" valign="top" charoff="50">1.32</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td></tr><tr><td align="left" valign="top" charoff="50">N1s</td><td align="center" valign="top" charoff="50">400.14</td><td align="center" valign="top" charoff="50">0.88</td><td align="center" valign="top" charoff="50">400.59</td><td align="center" valign="top" charoff="50">1.07</td><td align="center" valign="top" charoff="50">401.60</td><td align="center" valign="top" charoff="50">0.98</td></tr><tr><td align="left" valign="top" charoff="50">S2p</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">169.70</td><td align="center" valign="top" charoff="50">0.28</td></tr><tr><td align="left" valign="top" charoff="50">P2p</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">135.02</td><td align="center" valign="top" charoff="50">0.29</td></tr><tr><td align="left" valign="top" charoff="50">K2s</td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50"> </td><td align="center" valign="top" charoff="50">378.63</td><td align="center" valign="top" charoff="50">0.46</td></tr></tbody></table></table-wrap></floats-group></pmc></record>Pour manipuler ce document sous Unix (Dilib)
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