温带典型草地碳增汇的微生物生态学机理及其对未来水氮耦合变化的响应

The increasing nitrogen deposition and the change of rainfall are the two important and closely related global change issues which we have to face with in the future. The effect of water and nitrogen as well as their interaction on the key processes of carbon cycle is one of the weakest links for the mechanism study of carbon cycle. As the main participant and the regulator of grassland carbon cycle, soil microorganism and soil enzymes are the important driving forces for the movement of carbon element between source and sink, and are very sensitive to the change of environmental factors such as precipitation and nitrogen deposition, but the cognition about its response to the change of water and nitrogen availability and its driving mechanism for carbon cycle are very limited up to now. In this project, the temperate typical steppe is chosen as the object of research, and through field experiments of five years, the main influencing mechanism of water-nitrogen interaction on the key processes of carbon cycle and carbon budget would be investigated systematically, and we will analyze the different responses of soil microbial characteristics to the water and nitrogen and their coupling changes quantitatively. Simultaneously, the role of soil microorganism played in the carbon cycle processes and its feedback mechanism to the global change would also be discussed, and the sensitive microbial index reflecting the response of different carbon cycle processes to the coupling change of water and nitrogen input would be put forward.The research results are of important scientific significance for revealing the interaction and feedback among the climate change, grassland carbon cycle and the microbial ecology processes, deepening the grassland study on global change and develping the coupling theory of carbon, nitrogen and water, At the same time, it is of great realistic significance to provide techanical support for effectively predicting and adjusting the carbon processes of grassland ecosystem.

氮沉降和降水变化是草地生态系统未来面临的相伴发生的两大全球变化问题，二者及其交互作用对碳循环过程的影响机理是目前碳汇机制研究最为薄弱的环节之一；土壤微生物作为草地碳循环过程的主要参与者与调节者，对于水、氮及其耦合变化有着极高的敏感性，但对其水氮响应及碳循环驱动机理的认知迄今还很有限。研究拟选择我国温带典型草原为研究对象，通过连续五年的小区水氮控制试验，深入探讨未来降水以及氮沉降变化对我国温带草地碳循环关键过程及碳收支的可能影响；定量阐述草地土壤微生物学特征对水、氮及其耦合变化的差异响应；科学揭示土壤微生物在温带草地关键碳过程中的贡献与作用机制；初步探索草地不同碳过程响应水氮耦合变化的敏感微生物学指标。研究成果有利于深入揭示气候系统、草地碳过程与草地微生物生态学过程之间的相互作用及反馈关系，深化草地全球变化研究，同时也为完善草地水、碳、氮耦合作用理论，有效预测和调控草地碳过程提供技术支持。

氮沉降和降水变化是草地未来面临的相伴发生的两大全球变化问题，二者及其交互作用对碳循环过程的影响机理是目前碳汇机制研究最为薄弱的环节之一；土壤微生物作为草地碳循环过程的主要参与者与调节者，对于水、氮及其耦合变化有着极高的敏感性，但对其水氮响应和碳循环驱动机理的认知迄今还很有限。研究选择温带典型草原为研究对象，通过四年的水、氮添加控制试验，深入比较了不同水、氮及其耦合变化对草地植被固碳、土壤碳排放、凋落物分解、碳库储量等关键碳过程的影响差异，揭示了不同水、氮情境对温带草地碳源汇特征的影响。研究指出碳汇大小总体上与施氮量呈正向增加；而单施水对碳汇的影响随年份变化表现不一致；施水对促进氮增碳汇的效应也具有不一致性。探讨了草地土壤微生物和酶活性对水、氮及其耦合变化的响应特征，发现各水、氮情境下土壤微生物变化的主控因子是10-20cm土壤有机碳，贡献率为44.3~59.3%。项目还探索了关键碳过程的微生物学与环境因子耦合驱动机制。结果显示，土壤微生物群落、水热、碳氮养分与凋落物分解、土壤呼吸、有机碳储量显著相关；凋落物分解和有机碳储量还受土壤酶活性的影响；土壤微生物与草地地上生物量相关性不显著，地上生物量仅与降水密切；驱动地下生物量的因子较为复杂，当氮水平低时，水或氮限制地下生物量；当氮水平高时，土壤可利用碳与地下生物量显著相关；增水减弱了地下生物量与环境因子的相关关系；在高氮、施水+低氮和施水+高氮处理中发现了土壤微生物群落与地下生物量之间的负相关关系。项目按计划进行，已发表资助文章27篇，其中SCI收录论文11篇，CSCD收录论文16篇。研究对于揭示草地碳过程与草地微生物生态学过程之间的相互作用及反馈关系，完善草地水碳氮耦合机制，弥补相关数据的缺乏，降低碳循环预测中的不确定性具有重要科学意义，同时对在草地有限水分和氮素营养背景下深入挖掘增产、增汇潜力，增强草地可持续能力具有较强的现实意义。