The importance of fungal-fungal and bacterial-fungal interactions for phosphorus dynamics in forest soils

Plant uptake of phosphate (P) in complex forest ecosystems relies to a great extent on microbial mineralization of P from organic and inorganic sources but the relative contributions of the microbial communities to P cycling and allocation in forest soils is not yet very well understood. Within this project we will focus on two interactions that could elucidate key processes of microbial P dynamics in forest sites. We want to clarify the importance of both fungal-fungal and bacterial-fungal interactions for P dynamics in forest soils that are transitioning from P acquiring (efficient mobilization of P from primary and secondary minerals) into P recycling systems (highly efficient cycling of P). We want to reveal furthermore the relative contributions of saprotrophic and ectomycorrhizal fungi to P cycling and allocation.

Following a hierarchical approach we want to investigate: (I) the fungal-fungal interaction between saprotrophic and ectomycorrhizal fungi at the plot scale by a systematical exclusion of ectomycorrhizal fungi in the field; (II) elucidate the P dynamics in the mycosphere at the small scale (mm to cm scale) by the use of trenching experiments. (III) investigate the regulation of bacterial as well as fungal P cycling in a microcosm experiment and evaluate the particular microbial uptake, allocation and cycling of P in the mycosphere by the use of several chemical and microbiological approaches.

The trenching experiments will be performed on the study sites: Bad Brückenau, Conventwald, Vessertal, Mitterfels and Lüss in close proximity to beech trees (Fagus sylvatica L.). The microcosm experiment will be performed under controlled conditions in the lab.