羊草和大针茅群落土壤微生物对CO2浓度升高的响应及其对土壤碳库的反馈影响

As plant roots and aboveground litters are the main sources of the soil organic C, elevated CO2 has an impact on both the quality and quantity of fresh soil C inputs and potential to affect soil C sequestration and efflux. The decomposition and soil C release processes were regulated by the responses and feedbacks of soil microbe which lead to a positive or negative feedback to elevated CO2. Although many studies indicate that the increasing atmospheric CO2 may hold more C in the vegetation, few data are available about how changes in the composition of the soil microbial community affect decomposition rates and its feedbacks to elevated CO2 and eventually to soil C sequestration. The research aimed to understand soil C dynamics and feedbacks of changes in microbial traits to increased soil C inputs in temperate grassland. The study objectives were achieved by conducting a field experiment in which different qualities, quantities or sources of plant litters and root were added to the two different plant communities (Leymus chinensis and Stipa grandis communities) in temperate grassland, and the litter decomposition, soil microbial community composition, soil respiration and the component of soil C were measured to distinguish and quantify the contribution of soil carbon pool and carbon cycle, as well as the soil microbial response mechanisms and their impact on soil organic carbon pool. This study will provide the responses of soil carbon dynamics in the temperate grassland ecosystems in China to future climate changes.

根系和凋落物是土壤有机碳的主要来源。CO2浓度升高改变了输入土壤有机质的量和质从而影响土壤碳库和碳循环，土壤微生物的响应和适应调控了碳库和碳循环响应和反馈。CO2浓度升高导致的草地生态系统有机碳输入改变对土壤碳库和碳循环的影响已有一些研究，但关注其对土壤微生物群落结构的影响及微生物对碳循环的反馈调控机制研究很少，限制了深入研究我国草地生态系统碳循环对全球气候变化的响应与适应机制。本项目以我国温带典型草原的羊草和大针茅群落为对象，研究高CO2浓度下有机质输入（量、质、途径）改变对土壤微生物群落结构和功能多样性的影响，区分和量化有机物输入改变对土壤碳库和碳循环的贡献，以及土壤微生物的响应与土壤有机碳库的关系。对揭示在全球变化背景下草地生态系统土壤碳库和碳循环的变化规律有重要科学意义，为预测未来全球气候变化对土壤碳贮存的影响提供科学依据。

人类活动导致的大气CO2浓度升高、N沉降会通过改变输入土壤有机质的量、质和途径，从而影响微生物介导的土壤碳氮循环，而土壤有机碳库很小幅度的变化将可能显著影响大气CO2浓度。本研究在野外自然条件下建立的6个开顶式气室（OTC）模拟大气CO2浓度升高，同时设置2个N素水平，探讨我国温带典型草原不同功能性植物种对大气CO2浓度升高、N素添加的差异性响应，以及其导致的有机质输入改变对土壤微生物群落及土壤碳氮循环产生的影响。研究发现，不同功能型植物种地上、地下生物量以及根构型均对CO2浓度升高、N素添加表现差异性响应，导致有机质输入（量、质、途径）改变对土壤有效氮及土壤微生物群落产生不同影响，CO2浓度升高和N素添加对不同土壤微生物群落组成均有显著影响，且具有显著的季节动态，但CO2浓度升高条件下土壤总N库和总有机C库并没有显著变化。本项目的研究结果对揭示在全球变化背景下草地生态系统地上地下响应机制有重要科学意义，为预测未来全球气候变化对土壤碳贮存的影响提供科学依据。