Nitrogen and drought effects on the tree-soil interaction of ECM and AM temperate trees

树木不仅通过吸收水分和养分与土壤环境相互作用，而且还通过释放根系分泌物与土壤环境相互作用，根系分泌物增加矿物养分的溶解度，为土壤生物群提供基质，并刺激土壤有机质释放养分。树木和土壤之间的这种反馈是由共生根协会介导的。在中欧森林中的两种主要类型的根协会是丛枝菌根和外生菌根，这改变了重要的根功能和根际过程，如资源获取，凋落物质量和营业额，启动根际微生物和森林土壤中的碳封存。虽然单一的，易于培养的根联营公司对磷吸收的影响已被广泛接受，生态系统水平的微生物群落的影响仍然研究不足，但可能是必不可少的，因为它们驱动碳的保留和损失的土壤有机质（SOM）从森林土壤。了解根和hyphosphere SOM动态将是至关重要的预测如何在森林土壤中的碳储存在重要的中欧树种将响应上升的N沉降和夏季droughts.The拟议的研究项目调查共生菌根根协会的主要根功能的影响，应用一种新的技术，在原位渗出测量，微型roizotron成像和15 N-标记。从温带树木植物群中选取了4种外生菌根树种（森林山毛榉、栎、椴树、桦鹅耳枥）和4种丛枝菌根树种（细叶白蜡、悬铃木、悬铃木、稠李）作为研究对象。我们将调查受土著森林微生物感染的树木，以研究不同的微生物群落如何影响根系寿命，分泌和吸收过程。我们测试了三个假设的组合（i）在德国中部的一个混合林中的8个树种的成熟树木的根际动态的实地调查与夏季干旱的自然发生和（ii）在Göttingen Rhizolab中，对干旱胁迫下这8个树种的幼树中土著微生物群落对根系功能和根际动态的影响进行了实验分析，相关的蒸渗仪。在主要的全球变化因素中，我们将重点关注N的可用性增加和夏季干旱强度的影响，通过共生根协会调解树木-土壤反馈。

Trees interact with their soil environment not only by the uptake of water and nutrients, but also by the release of root exudates, which increase the solubility of mineral nutrients, provide substrates for soil biota and stimulate the release of nutrients from soil organic matter. This feedback between trees and soil is mediated by symbiotic root associations. Among the two main types of root associations in Central European forests are arbuscular mycorrhizae and ectomycorrhizae, which alter important root functions and rhizosphere processes like resource acquisition, litter quality and turnover, priming of rhizosphere microbes, and carbon sequestration in forest soils. While the influence of single, easy to culture root associates on P uptake has been widely accepted, ecosystem-level influences of microbial communities are still understudied, but may be essential, since they drive carbon retention and loss of soil organic matter (SOM) from forest soils. Understanding rhizo- and hyphosphere SOM dynamics will be critical to predicting how the carbon storage in forest soils under important Central European tree species will respond to rising N deposition and summer droughts.The proposed research project investigates the effect of symbiotic mycorrhizal root associations on major root functions, applying a novel technique for in situ exudation measurement, mini-rhizotron imaging and 15N-labeling. Four ectomycorrhizal (Fagus sylvatica, Quercus robur, Tilia cordata, Carpinus betulus) and four arbuscular mycorrhizal (Fraxinus excelsior, Acer pseudoplatanus, Acer platanoides, Prunus avium) tree species will be selected as examples from the temperate tree flora. We will investigate trees infected by indigenous forest microbes in order to examine how diverse microbial communities influence root longevity, exudation and absorption processes. We test three hypotheses with a combination of (i) field investigations of the rhizosphere dynamics in mature trees of the eight tree species in a mixed stand in Central Germany with natural occurrence of summer droughts and (ii) an experimental analysis on the influence of indigenous microbial communities for root functions and rhizosphere dynamics in young trees of these eight species under controlled drought stress in the Göttingen Rhizolab and associated lysimeters. Among the major global change factors we will focus on the influence of increasing N availability and intensity of summer droughts for the mediation of the tree-soil feedback by symbiotic root associations.