Towards a predictive understanding of how mycorrhizal types influence the decomposition of soil organic matter

森林储存了大量的陆地碳(C)，每年通过光合作用从大气中去除数十亿吨人为碳。被吸收的碳有一半分配给根，大部分通过根沉积释放到土壤中。尽管根沉积在土壤中引起了微生物介导的过程中最戏剧性的变化，但我们对自然条件下根-微生物相互作用的相关性的理解是有限的。因此，这些相互作用很难纳入生态系统C模型。本项目旨在开发一个预测框架，以了解树种及其菌根如何在北美中部阔叶林中与C和养分循环相结合。几乎所有树木的细根都被丛枝菌根(AM)或外生菌根(ECM)真菌定植。与其他土壤微生物不同，菌根真菌不受碳的限制，因为它们是从自养宿主中获得碳的燃料。因此，它们有可能通过分解土壤有机质(SOM)在养分动员中发挥重要作用。我们的目标是获得一个基于过程的理解和对菌根诱导的SOM分解的定量估计。我们假设，在AM和ECM树之间，SOM分解的机制和程度有很大的不同。在这个项目中，我们将应用创新的跨学科工具(同位素方法与微生物技术相结合)，并将在各种时间和空间尺度上进行研究。在微观尺度上，我们打算在微观宇宙中研究树根及其相关真菌之间的二元联系。将分析AM和ECM真菌通过胞外酶直接分解SOM的能力。通过根际引发效应间接分解土壤有机质的研究将在根箱实验中进行。这些实验还将允许确定引爆的大小和机制。此外，我们将量化植物伙伴的养分吸收方面的好处。在田间尺度上，将在印第安纳州以AM或ECM树为主的阔叶林中研究菌根诱导C和养分循环的机制和幅度。这个多学科的国际项目允许结合创新技术，利用长期监测的成熟林地，并改善来自美国和德国的学生和导师之间的科学交流。该项目将极大地提高我们对根系-微生物相互作用的认识，从而提高我们对森林重要生态系统服务的认识，如碳储存和养分保持。

Forests store huge amounts of terrestrial carbon (C) and remove billion of tons of anthropogenic C from the atmosphere by photosynthesis every year. Half of the assimilated C is allocated to roots, and a major part thereof is released into the soil via rhizodeposition. Despite the fact that rhizodeposition provokes the most dramatic changes in microbial-mediated processes in the soil, our understanding of the relevance of root-microbial interactions under natural conditions is limited. Hence, these interactions are hardly incorporated into ecosystem C models. The present project aims to develop a predictive framework for understanding how tree species and their mycorrhizal associates couple C and nutrient cycles in central hardwood forests of North America.Nearly all fine roots of trees are colonized by either arbuscular (AM) or ectomycorrhizal (ECM) fungi. In contrast to other soil microorganisms, mycorrhizal fungi are not limited in C as they are fueled with C from their autotrophic host. Hence, they have the potential to play a major role in nutrient mobilization through soil organic matter (SOM) decomposition. We aim to gain a process-based understanding and a quantitative estimation of mycorrhizal-induced SOM decomposition. We assume that the mechanisms and the extent of SOM decomposition strongly vary between AM and ECM trees. In this project, we will apply innovative interdisciplinary tools (isotope approaches coupled with microbiological techniques), and we will conduct studies on various temporal and spatial scales. On micro-scale, we intent to investigate binary links between tree roots and their associated fungi in microcosms. The capability of the AM and the ECM fungi for direct decomposition of SOM by extracellular enzyme production will be analyzed. Indirect decomposition of SOM through rhizosphere priming effects will be studied in rhizobox experiments. These experiments will also allow to determine the magnitude of priming as well as the mechanisms. Further, we will quantify the benefit in terms of nutrient uptake for the plant partner. On field scale, the mechanisms and the magnitude of mycorrhiza-induced C and nutrient cycling will be studied in a hardwood forest in Indiana with stands dominated by either AM or ECM trees. This multidisciplinary and international project allows combining innovative techniques, taking advantage of long-term monitored well-established forests sites, and improving the scientific exchange between students and supervisors from the US and Germany. The project will significantly improve our knowledge on root-microbial interactions, and, thus, on vital ecosystem services of forests, such as carbon storage and nutrient retention.