Mycorrhizal Fungi Influence Soil Structure

Abstract

A series of closely related processes is presented, by which arbuscular mycorrhizal (AM) fungi contribute to the formation of relatively stable aggregate structures. Fibrous roots and AM fungal hyphae can be viewed as a “sticky-string bag” that contributes to the entanglement and enmeshment of soil particles to form macroaggregates, a basic building block of soil structure. Furthermore, AM fungi produce a glycoprotein, glomalin, that is deposited on their outer hyphal walls and on adjacent soil particles. Glomalin appears to be a rather stable hydrophobic glue that might reduce macroaggregate disruption during wetting and drying events by retarding water movement into the pores within the aggregate structure. Examples from various soil types are used to demonstrate the contributions of AM fungi to soil aggregation and its subsequent stabilization. Over a wide range of soil types, these contributions depend largely on broad textural characteristics and whether the soil’s structure is hierarchical in construction, among other factors.