菌根对土壤腐生菌群落和森林凋落物分解的影响

凋落物分解是生态系统碳循环的重要过程。土壤中的腐生菌是凋落物的主要分解者，而树木的“菌根”（根系和菌根真菌形成的共生体）能通过影响腐生菌的生物量和活性，间接参与凋落物分解。以往研究发现菌根既能促进，也能抑制腐生菌群落，但对于菌根调控腐生菌以及凋落物分解的内在机制和关键影响因素，目前尚不明确。本项目以浙江天目山的常见树种为研究对象，通过菌根调控下的根、叶凋落物的原位分解实验，结合荧光定量qPCR以及高通量DNA测序等分子生物学技术，从“活根”的角度研究影响凋落物分解过程的关键因素，试图探究：1）不同树种的菌根对腐生菌群落的调控方向和调控强度的差异，以及该差异与菌根功能性状、菌根类型和菌根真菌群落结构之间的关系；2）不同树种的菌根对腐生菌群落的差异化调控将如何进一步影响凋落物分解。本项目的开展将为森林菌根功能研究开拓一个新的切入点，为全面认识菌根在生态系统碳循环中的关键作用提供重要的理论依据。

In forest ecosystems, the roots and mycorrhizal fungi (i.e. mycorrhizas) interact with saprotrophic fungal and bacterial communities that are strongly involved in litter decomposition. The live mycorrhizas can either stimulate rhizosphere saprotrophic activities through root exudates (priming effect) or compete with saprotrophs for nutrients and consequently suppress saprotrophic activities (Gadgil effect). The overall goal of this proposed study is to understand the relationship between the traits and nutrient acquisition strategies of mycorrhizas and the relative strength of priming vs. Gadgil effects across various tree species. We will conduct an in-situ litter decomposition experiment in a subtropical forest at Tianmushan National Reserve in Zhejiang, China. The absorptive roots will grow within monoculture root-bags, together with buried litter-bags filled with leaf and root litters. To study the impacts of live mycorrhizas, we apply girdling on the main transport roots to half of the root bags, which eliminates the carbon allocation to the connecting absorptive roots. We then compare the absorptive roots, mycorrhizal fungi, saprotrophic fungi, and bacteria between the disturbed and undisturbed root bags of the same tree species. Root and litter decomposition were also compared and analyzed based on the changes in microbial biomass and structures of the saprotrophic communities. This proposed study emphasizes the role of “live mycorrhizas” on dead material dynamics that contributes significantly to the soil carbon pool. Results of this study can also provide novel insights aimed at improving conceptual and analytical accuracy of terrestrial ecosystem models that link mycorrhizal traits with belowground carbon stability.