大气CO2浓度缓增对稻田硝酸盐型甲烷厌氧氧化过程的影响

硝酸盐型甲烷厌氧氧化(AOM)是控制稻田甲烷排放的一种新途径,大气CO₂浓度升高会对稻田甲烷排放产生重要影响,但有关其对硝酸盐型AOM过程的影响知之甚少。本研究依托开顶式气室组成的CO₂浓度自动调控平台,采用¹³CH₄稳定性同位素示踪技术,从甲烷氧化活性、相关功能微生物Candidatus Methanoperedens nitroreducens (M. nitroreducens)-like古菌丰度与群落组成等方面,系统研究了稻田土壤中硝酸盐型AOM过程对大气CO₂浓度缓增的响应。试验设置背景CO₂浓度和CO₂浓度缓增处理(背景CO₂浓度基础上每年增加40 μL·L^-1,直至增幅达160 μL·L^-1)。结果表明: 稻田土壤硝酸盐型AOM速率为0.7～11.3 nmol CO₂·g^-1·d^-1;定量PCR结果显示,M. nitroreducens-like古菌mcrA基因丰度为2.2×10⁶～8.5×10⁶ copies·g^-1。与对照相比,CO₂浓度缓增处理使土壤中硝酸盐型AOM速率和M. nitroreducens-like古菌mcrA基因丰度均有一定幅度提高,特别是在5～10 cm深度下两者均显著提高。CO₂浓度缓增处理未显著改变M. nitroreducens-like古菌群落结构,但使其多样性显著降低。相关性分析表明,土壤有机碳含量可能是影响硝酸盐型AOM过程的重要因子。综上,大气CO₂浓度缓增在一定程度上促进了硝酸盐型AOM反应,暗示在未来气候变化背景下其在控制稻田甲烷排放中具有积极作用。

Effect of gradual increase of atmospheric CO2 concentration on nitrate-dependent anaerobic methane oxidation in paddy soils

Nitrate-dependent anaerobic oxidation of methane (AOM) is a new pathway to reduce methane emissions from paddy ecosystems. The elevated atmospheric CO₂ concentration can affect methane emissions from paddy ecosystems, but its impact on the process of nitrate-dependent AOM is poorly known. Based on the automatic CO₂ control platform with open top chambers and the ¹³CH₄ stable isotope experiments, the responses of the activity of nitrate-dependent AOM, abundance and community composition of Candidatus Methanoperedens nitroreducens (M. nitroreducens)-like archaea to the gradual increase of CO₂ concentration were investigated in paddy fields. We set up two CO₂ concentration treatments, including an ambient CO₂ and a gradual increase of CO₂(increase of 40 μL·L^-1 per year above ambient CO₂ concentration until 160 μL·L^-1). The results showed the nitrate-dependent AOM rate of 0.7-11.3 nmol CO₂·g^-1·d^-1 in the studied paddy fields, and quantitative PCR showed the abundance of M. nitroreducens-like archaeal mcrA genes of 2.2×10⁶-8.5×10⁶ copies·g^-1. Compared to the ambient CO₂ treatment, the slow elevated CO₂ treatment enhanced the nitrate-dependent AOM rate and stimulated the abundance of M. nitroreducens-like archaea, particularly in 5-10 cm soil layer. The gradual increased CO₂ concentration treatment did not change the community composition of M. nitroreducens-like archaea, but significantly decreased their diversity. The soil organic carbon content was an important factor influencing the nitrate-dependent AOM process. Overall, our results showed that the gradual increase of CO₂ concentration could promote the nitrate-dependent AOM, suggesting its positive role in mitigating methane emissions from paddy ecosystems under future climate change.