华西雨屏区天然次生林土壤呼吸对模拟氮沉降的响应

Soil respiration is constituted by components different in carbon (C) source. The potential response mechanisms of components of soil respiration may different. However, the effects of N deposition on the different components of soil respiration in forests are poorly understood. Therefore, we here hypothesized that N deposition would alter environment of root growth, properties of fine root, and soil microbial properties and enzyme activities, which in turn affect processes of rhizospheric and heterotrophic components of soil respiration. In this project, natural subtropical secondary forests in Rainy Zone of West China will be taken as subject. The response of rhizospheric and heterotrophic components of soil respiration, fine root growth and turnover, fine root chemical properties, and soil microbial properties and enzyme activities will be measured. Morever, soil temperature, soil moisture and background atmospheric N deposition of study site will also be monitored in the experimental period. We will comprehensively analyze all measuring parameters and environmental factors, and explore the underlying mechanisms of effects of N deposition on rhizospheric and heterotrophic respiration. This project may be helpful to understand the theory of C cycle of natural secondary forests, and supply a reference for assessment of effect of nitrogen deposition on natural seconday forests' C budget.

土壤呼吸由消耗不同碳源的呼吸组分构成，各组分对氮沉降的响应机制具有潜在的差异性，然而氮沉降对森林土壤呼吸不同组分的影响却缺乏相应的关注。因此，本项目基于"氮沉降的增加改变根系生长环境和细根特性，影响土壤微生物特征和土壤酶活性，进而驱动根际呼吸和异养呼吸过程发生变化"的科学假设，以华西雨屏区典型亚热带天然次生林为研究对象，拟通过外加氮的形式模拟大气氮沉降增加情景，研究天然次生林根际呼吸、异养呼吸以及与之密切相关的细根生产周转、细根特性、土壤微生物特征及土壤酶活性，结合对土壤温度、湿度和背景氮沉降的监测，揭示氮沉降对两种土壤呼吸组分的影响方式和作用机制。本项目的实施可丰富天然次生林碳循环的理论研究，为评估氮沉降对天然次生林碳收支的影响提供参考。

土壤呼吸是全球重要的碳循环过程，受到全球氮沉降增加的潜在影响。而在常绿阔叶次生林生态系统中土壤呼吸对氮沉降增加的响应机制还不十分明了。本项目以华西雨屏区典型亚热带天然次生林为研究对象，拟通过外加氮的形式模拟大气氮沉降增加情景，研究天然次生林土壤呼吸以及与之密切相关的细根生产周转、细根特性、土壤微生物特征及土壤酶活性，结合对土壤温度、湿度和背景氮沉降的监测，研究氮沉降对土壤呼吸的影响方式和作用机制。结果表明氮添加降低了土壤呼吸速率，减少了细根生物量、微生物生物量碳、微生物生物量氮和土壤pH值；氮添加处理增加了土壤铵态氮和碳态氮含量；氮处理对土壤各酶活性和其他土壤指标无显著影响。本研究揭示：在常绿阔叶次生林生态系统中，氮沉降的增加将改变根系生长环境和细根特性，影响土壤微生物特征和土壤酶活性，进而驱动土壤呼吸过程发生变化。