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

点击翻译按钮获取中文摘要

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.