Phosphate nutrition in root- fungus interactions

Phosphate belongs to the major mineral nutrient category in plants and is a nonrenewable resource. Many natural soils are phosphate deficient, and phosphate fixation into insoluble mineral complexes limits plant growth by decreasing root uptake. Different strategies have appeared during the evolution of land plants to cope with this situation, one of which is to interact with various microbes (bacteria and fungi) located in the plant rhizosphere. This chapter will focus on three major groups of fungi that colonise the roots of most land plants: arbuscular mycorrhizal fungi (Glomeromycotina), fungi from the order Sebacinales (Basidiomycota) and the diverse form-group of dark septate endophytes (Ascomycota). Three major mechanisms of fungal contribution to plant nutrition will be discussed. First, fungi are able to solubilise phosphate from inorganic sources that are not available to plants. Second, fungican set free mineral nutrients from organic compounds/ sources. Third, fungi are able to transport phosphate along their hyphae towards the plant, thereby bridging phosphate depletion zones around the roots. In this chapter, we summarise published knowledge on this topic and present some new non- published data to complete our current model.