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

了解干旱胁迫下山毛榉根际微生物活动与植物生长性能之间的密切相互作用将是本项目的目的。我们推测，由于植物同化减少和次生代谢物表达增加，与未受胁迫的树木相比，渗出液的质量和数量发生了变化。这将影响根际微生物群落结构和功能，包括N转化和碳循环。我们认为，非胁迫树木根际微生物群落以高活性模式为主，以水解功能为主，能够代谢碳水化合物和氨基酸等易于降解的物质，而胁迫树木根际微生物群落则转向低活性模式，能够表达氧化酶，能够获取被困在酚类聚合物中的营养物质，如腐植酸和木质素。微生物性能的这种变化也会影响氮的周转，因为主要涉及矿化和反硝化活性的基因的表达模式会发生变化。为了研究这一假设，将使用微生物群落结构和功能的分子工具（微阵列分析）和生化酶测试。此外，将利用实时定量PCR技术研究氮循环中的特定酶。

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.