AUTHOR=Liu Shurong , Schloter Michael , Hu Ronggui , Vereecken Harry , Brüggemann Nicolas 

TITLE=Hydroxylamine Contributes More to Abiotic N2O Production in Soils Than Nitrite

JOURNAL=Frontiers in Environmental Science

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2019.00047

DOI=10.3389/fenvs.2019.00047

ISSN=2296-665X

ABSTRACT=<p>Nitrite (<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula>) and hydroxylamine (NH<sub>2</sub>OH) are important intermediates of the nitrogen (N) cycle in soils. They play a crucial role in the loss of nitrous oxide (N<sub>2</sub>O) and nitric oxide (NO) from soil due to their high reactivity. In this study, we collected soil samples from three ecosystems (grassland, arable land, and forest with a riparian zone) and explored the contribution of <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> and NH<sub>2</sub>OH to N<sub>2</sub>O formation in the different soils after exposure to oxic or anoxic pre-treatment. In addition, the importance of abiotic processes on the N<sub>2</sub>O formation from the two intermediates was studied by irradiating the soil samples with γ-irradiation. Our results demonstrate that <inline-formula><mml:math id="M3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> addition induced the largest N<sub>2</sub>O production in the grassland soil, followed by the forest and arable soils. Only 9–39% of the produced N<sub>2</sub>O after <inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> addition came from abiotic processes. NH<sub>2</sub>OH addition increased N<sub>2</sub>O emissions the most from the arable soil, followed by the grassland and forest soils. The conversion of NH<sub>2</sub>OH to N<sub>2</sub>O was mostly (73–93%) abiotic. Anoxic pre-treatment decreased N<sub>2</sub>O production from NH<sub>2</sub>OH remarkably, especially for the grassland soil, while it increased N<sub>2</sub>O production from <inline-formula><mml:math id="M5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> for most of the soils. Correlation analysis showed that <inline-formula><mml:math id="M6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> effects on N<sub>2</sub>O production were strongly correlated to <inline-formula><mml:math id="M7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> content in soils with anoxic pre-treatment, while NH<sub>2</sub>OH effects on N<sub>2</sub>O production were strongly correlated to soil Mn and C content in soils with oxic pre-treatment. Our results indicate that NH<sub>2</sub>OH plays an important role for abiotic N<sub>2</sub>O formation in soils with low C and high Mn content, while the effect of <inline-formula><mml:math id="M8" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> was important mainly during biotic N<sub>2</sub>O production. Anoxic periods prior to N addition may increase the contribution of <inline-formula><mml:math id="M9" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula>, but reduce the contribution of NH<sub>2</sub>OH, to soil N<sub>2</sub>O formation.</p>