稻田CH4产生氧化排放过程对大气CO2浓度和温度升高的响应机制

Atmospheric methane (CH4) is the second most important greenhouse gas after carbon dioxide (CO2), and rice paddy is a major source of CH4 emission. Elevated CO2 and temperature under future climate change can affect plant growth， soil environment and alter carbon and nitrogen biogeochemistry process in rice paddies, thus have a certain impact on CH4 production, oxidation and emission, leading to a feedback on climate change. However, the driving mechanisms how elevated CO2 and temperature change CH4 emission through CH4 production pathway, oxidation process and involved microbes in rice paddies remain poorly understood. To study this issue further, we propose this project to conduct field controlling experiments in situ using an open-top chamber (OTC) system and soil incubation tests in lab in a double rice cropping system. With the method of stable carbon isotope and molecular biotechnology, the effects of elevated CO2 and/or temperature on the process of CH4 production, oxidation and emission, and the abundance and composition of metahnogens and methanotrophs can be identified. Combined with the analysis of changes in rice growth and soil environment, the plant-soil-microbe mechanism affecting CH4 emission under elevated CO2 and temperature will be revealed. In conclusion, this study can provide scientific guidance for predicting CH4 emission accurately in rice paddies and illuminating the mechanisms and processes involved under the background of climate change.

CH4是大气中仅次于CO2的主要温室气体，而稻田是CH4的重要排放源。未来大气CO2浓度和温度升高会改变稻田生态系统作物生长、土壤环境及碳氮循环过程，进而影响CH4的产生、氧化及排放，对气候变暖存在一定反馈作用。现有的研究难以准确揭示大气CO2浓度和温度升高对稻田CH4排放的驱动机制，增温增CO2影响下有关CH4产生途径、氧化过程和微生物变化的机理研究仍欠缺。本项目利用开顶式气室（OTC, Open-top Chamber）进行大田原位模拟试验，辅以室内土壤培养实验，采用稳定性碳同位素及分子生物学技术，研究大气CO2浓度和温度升高对双季稻田CH4产生、氧化和排放过程以及产甲烷菌和甲烷氧化菌结构功能的影响，并结合作物生长因子和土壤环境因子，阐明增温增CO2影响稻田CH4排放的植物-土壤-微生物驱动机制，为气候变化背景下稻田CH4排放的准确评估及其过程机理解析提供科学依据。

未来大气CO2浓度和温度的升高会改变稻田生态系统作物生长、土壤环境及碳氮循环，影响作物生产力和CH4产生-氧化-排放过程。为探明水稻产量形成与CH4排放对气候变化的响应特征机制，本项目以双季稻为研究对象，利用开顶式气室开展增温增CO2大田原位模拟试验，辅以室内土壤培养实验，观测了双季稻生长、产量、甲烷产生潜力、氧化潜力、累积排放及相关土壤微生物功能基因丰度变化。研究结果表明，早稻增温一定程度抵消了增CO2对产量形成的促进效果，二者为消极的交互作用；但晚稻增温和增CO2条件下产量进一步增长，二者为协同促进的交互作用。CO2浓度和温度升高不会改变稻田CH4排放通量的季节变化规律，但会提高排放峰值，其对CH4排放通量的刺激效果主要表现在前期持续淹水阶段。单独增温或增CO2均能显著提高水稻生长季CH4排放量，二者同时升高的条件下CH4排放量进一步增长，为协同促进的交互作用，其中CO2浓度的影响占主导地位。CO2浓度和温度升高条件下，水稻生物量的增长、分蘖数的增加、土壤可溶性有机碳的提升，均有助于CH4排放的增长。增温和/或增CO2提升了稻田土壤的产甲烷潜力及甲烷氧化潜力，并提高了土壤产甲烷菌mcrA和甲烷氧化菌pmoA功能基因丰度，且对土壤甲烷氧化能力的刺激效应高于产甲烷能力, 但并未观测到CO2浓度和温度之间显著的交互作用。本项目可为准确评估未来气候变化对我国双季稻生长发育、产量形成和温室气体排放的影响提供基础数据支撑，为水稻生产适应及减缓气候变化策略的制定提供科学参考依据。