The Impact of Mycorrhizosphere Bacterial Communities on Soil Biofunctioning in Tropical and Mediterranean Forest Ecosystems

Mycorrhizal fungi constitute a key functional group of soil biota that greatly contribute to productivity and sustainability of terrestrial ecosystems. The benefits of mycorrhizal symbiosis to the host plant have usually been considered as a result of closed relationships between the host plant and the fungal symbiont. However, the extramatrical mycelium provides an increased area for interactions with other soil microorganisms by enhancing the development of the host plant root systems. Mycorrhizal fungi act as a bridge connecting the rhizosphere to the bulk soil and, through an active development of extraradical mycelium into the soil, this soil compartment (mycorrhizosphere) extends root–fungal interactions with soil microbial communities. Interactions within the mycorrhizosphere microbial community are of special interest because some microorganisms associated with mycorrhiza may complement mycorrhizal activities. The purpose of this chapter is to outline the mycorrhizosphere interactions between ectomycorrhizal fungi associated with forest tree species and soil microflora of potentially synergistic properties that lead to stimulation of plant growth. By focussing on the ectomycorrhizal symbiosis associated with Tropical and Mediterranean tree species, we will review the global effects of ectomycorrhizal symbiosis on the functional diversity of soil microflora and in particular, the interactions between ectomycorrhizal fungi and some plant-growth-promoting rhizobacteria. This review will focus on the interactions between ectomycorrhizal fungi and soil microflora leading to a sustainable microbial complex ecosystem with high efficiency against phosphorus mobilization and transferring phosphorus from the soil organic matter or from soil minerals to the host plant.