Microbial interactions and phosphorus mobilization in forest soils - effects of carbon, nitrogen and phosphorus availability

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The newly established N x P application experiment will be used to test whether nutrient addition changes fungal-fungal interactions towards higher dominance of saprotrophic fungi due to the resulting intense mycelial growth at the surface of forest soils. Fungal-fungal interactions in the nutrient addition experiment may change due to an increase in nutrients at either constant or slightly higher carbon availability (due to enhanced plant growth), but girdling decreases the C transfer from trees into the soil environment. Therefore, we will test whether a decrease in the amount of C derived from rhizodeposition reduces the importance of symbiotic P mobilization by ectomycorrhizal fungi (EMF) in soils. Since the ability to cleave high molecular organic carbon compounds is necessary for microorganisms to access N and P containing compounds bound up in complex biotic structures like roots and litter, we want to investigate the relative roles of saprotrophic and EMF during decomposition of organic compounds. The ratio of oxidative to hydrolytic enzyme activities will give us an indication whether the exclusion of EMF will modify the behaviour of the soil microbial community during decomposition of organic matter and consequently during the release of nutrients from organic matter. Metagenomic analyses of the dominant EMF in our soil-in-growth experiment will demonstrate whether EMF have the genetic potential to decompose organic matter. The addition of Mn peroxidase under lab conditions will prove whether oxidative enzymes might liberate otherwise protected organic N and P compounds for subsequent microbial decomposition. We will continue our intense collaborations with other groups within the SPP interested in interactions between plants and soil microorganisms.