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

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. The focus will be on beech as a fungal host species.

Hypothesis (i) holds that fungal assemblages of recycling and acquiring systems differ because P supply in a recycling system is expected to depend more strongly on saprotrophic properties for release of P from organic compounds and that of a P acquiring system more strongly on P release from mineral sources. To test this hypothesis the fungal communities will be determined in the organic layer, in the bulk soil, the mycorhizosphere and the roots by high throughput sequencing and annotated according to functional groups. The ectomycorrhizal communities will also be analyzed by morphotyping and Sanger sequencing of the ITS region. The fungal profiles will be recorded in relation to Pi and Porg, microbial biomass, phosphatase activities and fungal oxalate production.

(ii) The P demand of beech in relation to seasonal changes in phenology and EM assemblages is not known. We will translocate young beeches from the natural regeneration of two contrasting sites in intact soil cores to the same climatic conditions. At five phenological time points the plants will be labeled with 33P and analyzed for P uptake, P compounds, P concentrations and allocation in relation to P acquisition from their EM communities. The data will be used to develop a model linking EMF species abundance and P acquisition with plant uptake and phenology.

(iii) To investigate P uptake and flux through individual roots associated with distinct EMF, we will set up a real-time live imaging system under completely controlled conditions, which will enable us to trace the uptake and transport of P with high spatial and temporal resolution. After calibration of the systems with simple model plants (poplar), it will be adapted to beech for measure of P flux in seedlings colonized with typical natural EMF assemblages. Overall these investigations will contribute to increase our understanding of inter-specific fungal diversity for P uptake, and their role in plant P nutrition in P acquiring and recycling ecosystems.

Key-words: Ectomycorrhiza, Phosphorus nutrition, Radioisotopes, Flux analyses and Bioimaging