极端干旱影响亚热带常绿阔叶林土壤甲烷氧化能力的微生物机制

Atmospheric methane is the second greenhouse gas after carbon dioxide, contributing to approximately 25% of global warming. It has been predicted based on modeling simulation that intensity and frequency of drought will be increased due to global warming, even more extreme drought events occurring in the future. Forest ecosystems act as the largest terrestrial methane sink which is strongly regulated by a key factor, i.e., soil moisture content. Subtropical evergreen broadleaf forest is characterized by strong seasonality and sensitive to drought events. Until now, little is known about how extreme drought influence soil methane oxidation capacity of subtropical evergreen broadleaf forest and associated microbial mechanisms. On the basis of long-term extreme drought experimental site at the Tiantong national forest ecosystem observation and research station, by measuring in situ methane fluxes and analyzing soil properties such as soil moisture content, temperature, pH, inorganic N and total C and N contents as well as plant communities and methane-oxidizing bacterial communities, using 13C stable isotope probing techniques with soil genomic DNA extraction followed by PCR-DGGE, real time PCR and clone library to elucidate changes in active methane-oxidizing bacteria involved in methane uptake of forest soils, the goal of this project is (1) to elucidate response of soil methane oxidation rates and associated active methane-oxidizing bacteria to extreme drought in subtropical evergreen broadleaf forest, (2) to quantify the relative contributions of biological factors and environmental factors to methane oxidation capacity. Our results will be helpful for improving soil methane oxidation theory and for better forecasting soil methane uptake in subtropical evergreen broadleaf forest in context of extreme drought.

大气甲烷（CH4）是继CO2之后的第二大温室气体，大约贡献了全球气候变暖的25%。据模型预测，由于全球变暖，未来干旱发生的强度及频率都会增加，甚至发生极端干旱事件。森林是陆地生态系统最大的甲烷汇，水分是调节森林土壤氧化大气甲烷能力的关键因子。亚热带常绿阔叶林季节性强，对干旱敏感，但对极端干旱如何影响亚热带常绿阔叶林土壤甲烷氧化能力及其微生物机制尚缺乏研究。本项目拟以亚热带常绿阔叶林为研究对象，以浙江天童森林生态系统国家野外科学观测研究站的极端干旱样地为实验平台，通过观测甲烷通量，分析土壤理化性质、植物群落和甲烷氧化菌群落，并运用13C-CH4同位素探针技术解析土壤中活跃甲烷氧化菌的活性以及群落结构和丰度的变化，从机理上阐述亚热带常绿阔叶林土壤甲烷氧化能力对极端干旱的响应，量化生物因子和非生物因子对甲烷通量的相对贡献率。研究成果有助于完善甲烷的氧化理论和准确预测森林甲烷汇。

干旱强烈影响森林土壤氧化大气甲烷的能力，但对其微生物机制仍缺乏认识。本项目拟以亚热带常绿阔叶林为研究对象，以浙江天童森林生态系统国家野外科学观测研究站的极端干旱样地为实验平台，通过观测甲烷通量，分析土壤理化性质、植物群落和甲烷氧化菌活性及其群落结构和丰度，并运用13C-CH4同位素探针技术解析土壤中活跃甲烷氧化菌的活性以及群落结构和丰度的变化。我们发现（1）干旱降低了森林土壤可溶性碳、氮含量并改变了土壤微生物群落结构。（2）干旱显著增加了森林土壤甲烷氧化能力。（3）干旱影响土壤甲烷氧化能力有两个途径：直接途径（土壤通气性）和间接途径（诱导植物产生乙烯）；一方面干旱显著促进了乙烯的产生，显著抑制了甲烷氧化菌活性，首次验证了间接途径的重要性；另一方面干旱并没有改变甲烷氧化菌潜在活性和丰度，表明直接途径超过间接途径的作用。（4）13C-CH4培养实验结合13C-DNA同位素标记，发现土壤活跃甲烷氧化菌群落为Methylosinus属（II型甲烷氧化菌）。我们的研究结果从机理上阐述极端干旱影响亚热带常绿阔叶林土壤甲烷氧化能力的微生物机制，研究成果有助于完善甲烷的氧化理论和准确预测森林甲烷汇。