Role of inter-specific ectomycorrhizal fungal diversity for forest ecosystem nutrition

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The main goal of this project is to characterize the inter-specific diversity of ectomycorrhizal fungi for P uptake and tree nutrition in P acquiring and recycling ecosystems. In the first phase of this project, it was shown that the vertical distribution of P forms exhibited contrasting patterns and concentrations in different soil depths of our study sites. These findings suggest that the distribution of P is decisive for the mechanism of P supply to the vegetation. In this renewal proposal we plan to study whether and how P forms and P availability structure the taxonomic and functional composition of the fungal communities. We will address the following hypotheses:(i) the functional composition of the fungal communities (saprophytic or mycorrhizal fungi) shows a vertical gradient according to soil layers. We propose that the functional similarity is higher in the O-horizons than in A-horizons of sites with contrasting P availability. Fine roots and their associated mycorrhizas in the O layer are important for P supply at the P poor site leading to high P recycling, whereas those in the A horizon at the P rich site foster P acquisition. To test this suggestion we will study the vertical fungal profiles (metagenome analysis) and test functional differences by soil exchange experiments. For functional analyses of root associated fungi, imaging of P uptake will be applied.(ii) Changes in P availability induce taxonomic and functional changes of the fungal communities. This hypothesis will be tested by application of P, N and N x P in P-poor and P-rich forest sites. We expect that N application also influences P availability with consequence for the mycorrhizal communities.(iii) P uptake and translocation to the host is regulated by the supply of the ectomycorrhizal fungi with recent photo-assimilates. To test this hypothesis, girdling experiments will be conducted.