湿季极端降雨对热带季雨林土壤甲烷通量的影响及微生物机制研究

Tropical seasonal dry forests are important sinks for atmosphere methane (CH4), yet their response to changes in precipitation patterns remain unknown. According to climate models and measured data, tropical seasonal dry forest will suffer a “more extreme precipitation events in wet season” precipitation pattern in East Asia region. However, limited studies have been conducted to test the impact of this precipitation pattern on the dynamic change of CH4 flux of forests, due to the difficulty in simulating atmospheric rainfall at the field scale. In this study, I will conduct a precipitation manipulation experiment simulating a “more extreme precipitation events in wet season” in the tropical seasonal dry forests in Southern China to study 1) whether this precipitation pattern change has short-term effects on soil CH4 flux and how this effect impacts the whole-year CH4 flux, and 2) to infer how the dynamic pattern of CH4 flux will change under “more extreme precipitation events in wet season” conditions as related to the underlying microbial mechanisms. In addition, I will conduct a laboratory experiment by incubating soils under different soil moisture conditions to quantify the response of methanotrophs and methane oxidation potential to “more extreme precipitation events in wet season” conditions. This study will provide parameter testing and model verification for simulating and predicting the response of tropical forest ecosystems to changes in precipitation patterns, and contribute knowledge to the development of effective greenhouse gas abatement measures.

热带季雨林生态系统是重要的甲烷（CH4）汇，但其对降雨格局改变如何响应尚不清楚，这也是全球变化生态学研究的重要科学问题之一。气候模型及经验观测数据均表明，在东亚热带季雨林会出现“湿季极端降雨增加”的降雨格局。然而，由于对大气降雨的大规模调控很难实现，因此湿季极端降雨增加对热带季雨林生态系统土壤CH4通量的影响尚未明晰。本项目拟以热带海岸带季雨林为研究对象，基于野外大型降雨控制试验平台，研究湿季极端降雨对CH4通量影响的动态变化特征及微生物驱动机制。同时，通过室内模拟控制实验，探索湿季极端降雨处理下，土壤CH4氧化能力及微生物过程对土壤湿度变化的敏感性差异。本研究将为模拟和预测热带森林生态系统，对降雨格局改变的响应提供参数检验与模型验证，并有助于制定有效的温室气体减排措施。

热带季雨林具有较强的甲烷吸收能力，但在未来降雨格局改变背景下其甲烷汇功能是否会发生改变仍不清楚。本项目依托中国科学院华南植物园热带海岸带野外定位站的大型野外降雨控制实验平台，布设了降雨格局改变对热带季雨林土壤甲烷通量的影响及其机制研究实验。我们的研究表明雨季推迟使甲烷的吸收速率提高了，为对照的1.64倍，其中，干季土壤湿度增加及土壤酶活活性增强导致干季甲烷吸收速率明显增加。湿季降雨增加同样使干季甲烷吸收速率提高了，主要与土壤温度，养分状况及酶活的变化有关。再者，我们发现甲烷氧化菌丰度对湿度的响应存在季节差异：在干季，其与湿度成正相关，而在湿季，相关关系为负。我们的结果还发现，该森林生态系统甲烷吸收速率的最适孔隙度为 0.45 m3 m-3。我们的研究结果表明在未来雨季推迟的降雨格局下，热带季雨林的甲烷吸收功能将显著增加。研究结果为准确评估和预测未来降雨格局改变下热带季雨林土壤甲烷通量的变化提供理论基础。