• Introduction

Phosphorus (P) is often the first or second element limiting aboveground net primary productivity of forests. Besides low available inorganic orthophosphate (Pi) concentrations, soil may contain high total P contents, as insoluble mineral P or as organic P. Most plants form mycorrhizal associations that improve their P nutrition. Three main hypotheses have been proposed to explain this positive effect through an increase of (1) P mobilisation from mineral P, (2) P mobilisation from organic P and (3) soil exploration and P uptake. However, the positive effect of mycorrhizal symbiosis may be variable with the fungal species forming the association. This could be due to the different abilities of mycorrhizal fungi to mobilise P and/or to take up Pi from the soil.

• Objectives

The aim of this review was to examine our current knowledge about the capacity of ectomycorrhizal fungi to release organic compounds as low-molecular-weight organic anions and phosphatases thought to have a role for mineral and organic P mobilisation, respectively. The diversity of Pi transporters among mycorrhizal species is also examined.

• Results

The main conclusion is that the study of the functional diversity of ectomycorrhizal fungi in situ is still a challenging question and could be addressed by combining different tools now available to make large-scale studies.