植物根系及其共生AM真菌对温带草原土壤有机碳动态的影响机制

Plant roots and their associated mycorrhizal fungi interact to regulate soil organic carbon dynamics. Arbuscular mycorrhizal (AM) fungi form symbiotic associations with the majority of higher plants in terrestrial ecosystems, are the dominant mycorrhizal type in grasslands, and play an important role in sustaining the ecosystem structure and function of grasslands. However, the influence of plant roots and AM fungi on soil organic carbon dynamics in temperate grassland remains poorly understood. In this project, we combine a number of state-of-the-art techniques including stable isotopic tracing, molecular microbial ecology and multivariate statistics, and conduct an in situ field manipulative experiment to investigate soil organic carbon dynamics in a temperate grassland of northern China. Specifically, we aim to 1) clarify the effects of plant roots and associated AM fungi on dynamics of organic carbon inputs from different plant sources (litter, root and root exudate); 2) quantify the relative contribution of organic carbon inputs from different plant sources to new soil organic carbon formation; and 3) reveal the mechanisms underlying the response of soil organic carbon dynamics (i.e., existing carbon decomposition and new carbon formation) to the presence of plant roots and AM fungi. This study will benefit our understanding of the processes and mechanisms of soil carbon cycling in temperate grassland of northern China.

植物根系及其共生菌根真菌对土壤有机碳的动态具有重要影响。丛枝菌根（Arbuscular mycorrhizal, AM）真菌是广泛存在于陆地生态系统中的植物共生微生物，是草地生态系统的主要菌根真菌类型，在维持草地生态系统结构和功能稳定方面具有重要作用。目前，对于植物根系及AM真菌对草原土壤有机碳库动态的影响及其内在机制尚缺乏系统研究。本项目定位于我国北方草地生态系统，综合运用稳定同位素示踪、微生物分子生态学及多元统计分析等方法，通过野外原位控制实验，试图：1）阐明植物根系及其共生AM真菌对不同植物来源有机碳（茎叶凋落物、根系残体及根系分泌物）动态的影响；2）量化不同植物来源有机碳对土壤新有机碳形成的相对贡献；3）揭示土壤有机碳动态（包括原有机碳分解和新有机碳形成）对植物根系及AM真菌响应的内在机制。本项目的实施，将有助于更深入理解我国温带草地土壤碳循环的过程与机制。

近年来，土壤有机碳动态得到学者广泛关注。植物根系及其共生丛枝菌根（AM）真菌可能在调节土壤有机碳动态中扮演重要角色。然而，目前学术界对于土壤有机碳循环的相关生物机制的认识还相对薄弱。为此，本项目结合室内盆栽实验和野外控制实验、原位土壤样品采集等方法，利用多种互补测定技术研究了北方草原生态系统土壤有机碳库对植物根系及其共生AM真菌的响应机制。结果表明， 植物根系及AM真菌的存在可能有助于土壤有机碳的积累，AM真菌对不同来源有机碳积累的影响有所差异。不同来源有机碳对土壤有机碳积累的贡献有所差异，茎叶掉落物的贡献大于根系分泌物。AM真菌对土壤有机碳动态的作用可能随着土壤养分条件的改变而发生变化。随着植物根系和AM真菌生物量的改变（不同土壤深度），土壤微生物群落的结构与功能均发生明显变化。在环境胁迫条件下，相比细菌和古菌，真菌对土壤有机碳循环的影响可能更大。此外，植物根系和AM真菌的存在，可能减少了温室气体的排放。本研究将有助于更好地解释和预测未来全球变暖背景下高寒草甸生态系统土壤有机碳库的动态变化。