Functions of mycorrhizhosphere communities under the influence of different nitrogen and water regimes in forest soils

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It will be the aim of this project to understand the close interplay between plant performance and microbial activity in the rhizosphere of drought stressed beech trees. We postulate that due to reduced assimilation of the plants and increased expression of secondary metabolites, the quality and quantity of exudates is changed compared to unstressed trees. This will affect microbial community structure and functions including N transformation and carbon cycling in the rhizosphere. We postulate that while the microbial communities in the rhizosphere of non stressed trees are characterized high activity pattern and mainly hydrolytic functions enabling them to metabolize easily degradable substances like carbohydrates and amino acids, the rhizosphere of stressed trees is shifted towards low activity and microbes which are capable to express oxidative enzymes enabling them to get access to nutrients entrapped in phenolic polymers such as humic acids and lignin. This shift changes in microbial performance will also affect nitrogen turnover, as mainly expression pattern of genes involved in mineralization and denitrification activities will be changed. To investigate this hypothesis, molecular tools (microarray analysis) of microbial community structure and function and biochemical enzymatic tests will be used. Furthermore, specific enzymes in the nitrogen cycle will be studied using real-time quantitative PCR.