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清除数十亿吨人为碳。被同化的C有一半分配给根，大部分通过根沉积释放到土壤中。尽管事实上，根沉积引起了土壤中微生物介导过程中最剧烈的变化，但我们对自然条件下根与微生物相互作用的相关性的理解是有限的。因此，这些相互作用很难被纳入生态系统C模型。本项目旨在建立一个预测框架，以了解北美中部阔叶林树种及其菌根伴生菌如何耦合C和营养循环。几乎所有树木的细根都是由丛枝（AM）或外生菌根（ECM）真菌定植的。与其他土壤微生物相比，菌根真菌不受C的限制，因为它们从自养宿主那里获得C作为燃料。因此，它们具有通过土壤有机质（SOM）分解在养分动员中发挥重要作用的潜力。我们的目标是获得基于过程的理解和菌根诱导的SOM分解的定量估计。我们假设SOM分解的机制和程度在AM和ECM树之间有很大差异。在这个项目中，我们将应用创新的跨学科工具（同位素方法结合微生物技术），我们将在不同的时间和空间尺度上进行研究。在微观尺度上，我们打算研究微观世界中树根与其相关真菌之间的二元联系。将分析AM和ECM真菌通过胞外酶生产直接分解SOM的能力。通过根际启动效应间接分解SOM将在根箱试验中进行研究。这些实验也将允许确定启动的大小以及机制。此外，我们将根据植物伙伴的营养吸收来量化效益。在田间尺度上，将在印第安纳州以AM和ECM树为主的阔叶林中研究菌根诱导的C和养分循环的机制和强度。这个多学科和国际项目结合了创新技术，利用了长期监测的成熟森林遗址，并改善了美国和德国学生和导师之间的科学交流。该项目将大大提高我们对根与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.