Mycorhizosphere

The mycorrhizosphere is the region around a mycorrhizal fungus in which nutrients released from the fungus increase the microbial population and its activities. The roots of most terrestrial plants, including most crop plants and almost all woody plants, are colonized by mycorrhiza-forming symbiotic fungi. In this relationship, the plant roots are infected by a fungus, but the rest of the fungal mycelium continues to grow through the soil, digesting and absorbing nutrients and water and sharing these with its plant host. The fungus in turn benefits by receiving photosynthetic sugars from its host. The mycorrhizosphere consists of roots, hyphae of the directly connected mycorrhizal fungi, associated microorganisms, and the soil in their direct influence.

The mycorrhizosphere involves a community of microorganisms. There are three divisions of fungi that can form mycorrhizae, the Glomeromycota), Ascomycota, and Basidiomycota. Glomeromycota can form arbuscular mycorrhizae with angiosperms (flowering plants), gymnosperms (seed-producing plants), pteridophytes, mosses, lycopods, and Psilotales. Ascomycota fungi form ericoid mycorrhizas with plants of the order Ericales, and ectomycorrhizas with trees. Basidiomycota fungi form ecto-, orchid, monotropoid, arbutoid, and some ericoid mycorrhizae. Fungal hyphae are thinner than plant roots, which allows them to penetrate areas in the soil with moisture and nutrient that are inaccessible to roots. In some cases, mycorrhizal fungi in the mycorrhizosphere may ward off fungal plant pathogens. For example, the arbuscular mycorrhizal fungus Glomus intraradices reduces germination of the pathogen Fusarium oxysporum, but stimulates germination of a non-pathogenic fungus Trichoderma harzianum.

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