南亚热带常绿阔叶林生态系统对氮沉降的生物热力学响应

The rapid increase in nitrogen deposition and the impacts of it on the ecological balance of subtropical forests and other ecosystems along with the implications of these impacts for sustainable development are currently scientific problems of great interest, globally. Forests are the most important terrestrial ecosystems directly impacted by nitrogen deposition over a large area of the Earth. The structure, function, and efficiency reactions of forests to nitrogen deposition are attracts the interesting of many scientists. Based on a large field experiment simulating nitrogen deposition both above and below the forest canopy, this study will explore the biophysical reaction mechanisms of subtropical broadleaf evergreen forests to nitrogen loading. The effects of nitrogen loading will be examined through an integrated study of three aspects of the forest ecosystem, i.e. changes in eco-exergy of the plants and soil biotic communities, changes in the emergy flows of resources (C, N, P and H2O) absorbed and their subsequent transformations, and changes in the environmental economic and emergy-based measures of ecosystem services. The results of our study will deepen the understanding of the reaction mechanisms of forest ecosystems to nitrogen deposition. Consequently, the results of this study will be useful for the development of forest management strategies under various global change scenarios. Simultaneously, the results will also be used to test the classical hypothesis for the structural and functional self-organization of ecosystem, and developing the efficiency self-organization theory of ecosystems by examining the reaction of the forest system to disturbances. Thus, this study is expected to be significant for both practical and theoretical purposes.

氮沉降的迅速增加及其对生态环境平衡和可持续发展的影响已成为全球关注的重大环境问题。森林是陆地生态系统的最重要组分，也是氮沉降主要的直接承受者，其结构与功能对氮沉降的响应机制是众多学者关注和研究的热点。本项目借助模拟林冠和林下氮沉降野外大型对比控制实验平台的野外监测和实验分析，综合运用能值(Emergy)、生态㶲(Eco-exergy)与环境经济评价理论方法，从资源负熵(能量、物质和信息流)的摄取与转化、系统有序结构的调整、以及服务产出三个角度分析南亚热带常绿阔叶林结构、功能与效率对两种氮添加方式的响应规律；揭示森林生态系统植物、土壤生物群落结构，以及碳、氮、磷和水资源利用与转化功能对氮沉降响应特征背后的生物热力学规律；从对干扰响应的角度检验系统结构与功能自组织经典假说，发展系统效率自组织理论，为全球变化背景下森林生态系统的科学管理提供综合指导，具有重要的理论意义和实践应用价值。

中国热带和亚热带区域是当前国球氮沉降增加的热点区域。本项目利用林冠、林下氮添加野外大型控制实验平台优势，基于为期三年的森林水文（包括穿透雨、树干径流、地表径流、壤中流）监测；配合土壤种子库、优势树种幼苗生长和定居实验、土壤生物（土壤微生物、土壤动物）和两期土壤理化性状与植被群落调查分析结果，量化分析了南亚热带季风林结构、功能与服务对林冠和林下氮沉降的响应规律。结果表明，氮添加危害南亚热带森林生态系统热力学健康，并且生态㶲和结构㶲指数比传统的群落结构指数对干扰的响应更加敏感；林冠50 kg N/yr添加会增加南亚热带季风常绿阔叶林林下0-10cm土层种子库库存量，并改变土壤种子库组成结构，而林下氮添加对于南亚热带季风常绿阔叶林林下0-10cm土层种子库库存量和种子库组成结构均无显著影响；氮沉降增加在整体上会影响南亚热带常绿阔叶林优势树种幼苗的生长，且幼苗高度、基径和生物量对于林下氮添加处理的比林上氮添加处理更为敏感；传统的林下氮添加模拟方式会高估大气氮沉降增加对南亚热带常绿阔叶林优势树种幼苗生长和定居的影响；两种氮添加方式和两个氮添加浓度处理下，土壤微生物磷脂脂肪酸和其余土壤理化性质不存在显著差异。相比于对照，林冠和林下氮添加处理分别增加了树干径流中全氮的年均总输入通量273%和135%，但对于地表径流、壤中流和土壤氧化亚氮气体排放通量没有产生显著影响。氮添加处理对土壤氮库、土壤微生物氮库没有产生显著的影响。林冠氮添加下植被氮库相比对照增加了273%，其中植物群落地下根系氮库显著增加了271%。相关研究结果已发表科研论文11篇（其中SCI论文10篇），申请并获受权实用新型专利1项，全面完成预定考核指标。同时，课题执行期间培养毕业硕士1人，博士1人；项目主持人在项目执行期间当选国际能值学会（ISAER）主席。