Tree diversity effects on rhizodeposition and rhizosphere priming: the role of the mycorrhizal colonization in coupling C and N cycles in diverse tree stands

大多数温带树种主要与丛枝菌根（AM）或外生菌根（ECM）真菌结合，它们为宿主提供矿物质营养以换取碳。由于两种菌根类型在营养经济方面存在根本差异，因此建议提供与森林碳(C)循环和养分保持相关的生物地球化学转化的综合指数。然而，人们对菌根类型在树木多样性-生态系统功能关系中的群体特异性作用知之甚少。本研究项目的中心目的是确定不同AM和ECM林分之间根际碳通量和土壤氮循环的功能群差异。在关键的生物地球化学过程中，我将重点关注根系渗出和分解，这代表了微生物启动效应刺激土壤有机质养分释放的因果关系。基于对ECM林分有机养分经济的假设，作者假设增加根系渗出是ECM林分维持生产力的主要机制，而不同AM林分主要依赖于落叶对土壤过程的影响。为了实现这个项目的目标，我将把一个已经建立的树木多样性实验与创新和超越最先进的生态和生态生理学方法结合起来，并辅以三维激光消融断层扫描、固态13C-CPMAS核磁共振波谱和代谢组学。该项目将完善一个关于菌根类型在树木多样性对土壤功能影响中的作用的概念模型，以便纳入全球模拟模型。

The majority of temperate tree species associates predominantly with either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi, which provide mineral nutrients to their host in exchange for carbon. Since the two mycorrhizal types differ fundamentally in their nutrient economy they were suggested to provide an integrated index of biogeochemical transformations relevant to carbon (C) cycling and nutrient retention in forests. Yet little is known about the group-specific role of the mycorrhizal type in the tree diversity–ecosystem functioning relationship. The central aim of this research project is to determine functional group differences in rhizosphere C fluxes and soil nitrogen cycling between diverse AM and ECM tree stands. Among the key biogeochemical processes I will focus on root exudation and decomposition, which represent cause and effect of the microbial priming effect to stimulate nutrient release from soil organic matter. On the basis of the assumed organic nutrient economy of ECM stands, I hypothesize that increased root exudation is a primary mechanism by which ECM trees sustain productivity in diverse stands, while diverse AM stands mainly depend on leaf litter effects on bulk soil processes. To achieve the objectives of this project I will combine an established tree diversity experiment that manipulates mycorrhizal type abundances with innovative and beyond state-of-the-art ecological and ecophysiological methods that are complemented by 3-D laser ablation tomography, solid-state 13C-CPMAS nuclear magnetic resonance spectroscopy, and metabolomics. This project will refine a conceptual model on the role of the mycorrhizal type in tree diversity effects on soil functions for the incorporation in global simulation models.