湿地甲烷代谢对氮输入响应的复杂性及其机制分析

氮素是影响湿地甲烷代谢过程的重要因素之一。氮输入是否影响湿地甲烷排放，增加全球气候变暖的风险，一直受到科学界的高度关注。目前关于氮输入对湿地甲烷排放影响的几篇meta-analysis文章的主要结论均为氮输入促进湿地甲烷排放，但是多篇研究性论文的结果为氮输入抑制或不影响湿地甲烷排放，由此可见氮输入对湿地甲烷排放的影响十分复杂。湿地甲烷代谢包括湿地甲烷产生、氧化和传输过程以及最终的甲烷排放，综述不同形态氮输入对水稻田、内陆湿地和滨海湿地甲烷排放通量影响的复杂性；分析湿地甲烷产生速率和途径、甲烷好氧氧化和硝酸盐/亚硝酸盐型厌氧甲烷氧化对不同形态氮输入的响应及机制。硝态氮输入对湿地甲烷产生具有抑制作用已成共识，然而其它形态氮输入对湿地土壤甲烷产生的影响具有较大的不确定性，氮输入影响湿地甲烷产生的机制主要包括电子受体-底物竞争机制、离子毒性机制、促进植物生长-碳底物供给增加机制以及pH调控机制等。氮输入对湿地好氧甲烷氧化影响的研究多集中在水稻田和泥炭湿地，影响的结果包括促进、抑制或影响不显著；氮输入促进湿地土壤硝酸盐/亚硝酸盐型厌氧甲烷氧化。着重分析氮输入对湿地甲烷代谢影响不确定性的成因，指出...

Complexity of effects of nitrogen input on methane metabolism in wetlands and mechanism analysis

Nitrogen (N) is one of the key factors that profoundly impact the global methane (CH₄) metabolism in wetlands. Whether nitrogen input would increase methane emission from wetlands and risk of global climate warming has been paid much attention. However, the magnitude and direction of methane emission rates in response to nitrogen input on a global scale are still unclear. The main study conclusion in the published meta-analysis papers was that nitrogen input increased methane emission from wetlands. But the conclusions also included nitrogen input decrease and did not affect methane emission from wetlands in lots of research papers. Nitrogen input is the driver with the most controversial effects, for which it is difficult to draw univocal patterns. Wetland methane metabolism includes methane production (methanogensis), methane oxidation, methane transport, and their final result of methane emission. This paper reviewed the complexity of effects of nitrogen input on the methane emission from paddy field, inland wetlands, and coastal wetlands. We also analyzed the responses of the rate and pathway of methane production, aerobic methane oxidation, and nitrate/nitrite-dependent anaerobic methane oxidation to nitrogen input, and their mechanism. NO^-₃-N input demonstrated inhibition on methane production, however the effects of input of other forms of nitrogen on methane production showed an uncertainty. The main controlling mechanisms of nitrogen input on methane production included ionic toxicity, promoting plant growth-increasing carbon substrate (such as plant litter, root exudates, sloughed-off cells, and roots etc.) supply, electron acceptors-carbon substrate competition, and pH regulation. The studies of nitrogen input on aerobic methane oxidation mostly focused on the rice fields and peatlands, and the effects included increase, decrease and no-effects on methane oxidations. Nitrogen input increased the nitrate/nitrite-dependent anaerobic methane oxidation. We emphatically analyzed the reasons of different influences of nitrogen input on methane metabolism, and proposed that the response of methane metabolism to nitrogen input was a biogeochemistry process at ecosystem level. We also provided a conceptual model that included microbial processes and ecosystem traits factors to predict effects of nitrogen input on methane emissions from wetlands. Finally, we proposed some basic research domains that needed to strengthen in study of effects of nitrogen input on wetland methane metabolism. Overall, our review shed light on the complexity and mechanism of effects of nitrogen input on methane metabolism in wetlands and will help improve ecosystem models for predicting wetland methane flux caused by nitrogen input.