碳和氮可利用性的改变对温带草原土壤团聚体水平上的固碳影响与微生物机制

陆地生态系统中植物初级生产力主要受养分限制，而土壤中异养微生物群落主要受有机碳或能量限制，但在探讨生态系统对全球变化的响应时，普遍将植物养分限制等同于整个生态系统的养分限制，忽略了微生物的碳限制，从而限制了对土壤异养微生物在驱动生态系统碳固持中所起作用的全面理解。本项目以内蒙古温带草原为研究对象，基于运行9年的凋落物调控与氮素添加互作野外控制实验，同时改变碳和氮的可利用性，通过测定不同粒级土壤团聚体碳含量和储量，回答碳和氮可利用性的改变及其相互作用如何影响草原土壤团聚体水平上的固碳潜力；应用土壤细菌16S 真菌ITS扩增子测序和宏基因组技术，结合参与碳循环的酶活性测定，揭示土壤团聚体中微生物群落结构和固碳功能的变化；结合微生物残体的示踪物--氨基糖和土壤微生物量碳的变化，解析土壤团聚体水平上微生物与固碳的关系，阐明温带草原土壤团聚体水平上固碳的微生物学机制，为丰富生物地球化学理论提供数据。

Numerous studies have shown that plant primary productivity is limited by nutrients in most terrestrial ecosystems, while heterotrophic microbial communities in soils are primarily limited by organic carbon or energy. In the studies of the ecosystem responses to global change, however, plant nutrient limitation is often considered to equate with the nutrient limitation of the entire ecosystem, which ignores the carbon limitation in microbes and thus limits comprehensive understanding of the potential roles that soil heterotrophic microbes could play in driving ecosystem carbon sequestration. In this project, based on the long-term manipulation experiment, in which both carbon and nitrogen availability are manipulated by addition or removal of aboveground litter and nitrogen addition in a temperate grassland of Inner Mongolia, we will 1) explore how the changes in carbon and nitrogen availability affect the carbon sequestration in soil aggregates, by accessing carbon contents and storage in soil aggregates of different sizes; 2) reveal the changes of soil microbial community structure and carbon-fixing-associated functions in soil aggregates of different sizes, through 16S rRNA and ITS high-throughput sequencing techniques and metagenomics, along with carbon-cycle-associated enzyme activity assay; and 3) interpret the relationships of microbial community and carbon sequestration, and elucidate the underlying microbial mechanisms in soil aggregate carbon sequestration in temperate grasslands, by further assessing the changes in amino sugar as the tracer of microbial necromass and microbial carbon. The project is important to be considered as part of the efforts to predict the responses of ecosystems to global change, and the results will have important implications for global biogeochemical models.