Mycorrhiza

Abstract

Mycorrhizas are symbiotic associations between fungi in the soil and the roots of plants. Several types exist, each of which is defined by their morphological characteristics at the interface between the plant and fungus, as well as the identity of both fungal and plant partners. Mycorrhizas are the most ubiquitous terrestrial symbiosis in nature and are believed to have played an integral role in helping plants transition from aquatic to terrestrial environments c. 400 million years before present. The most recognised function of the symbiosis is the bidirectional exchange of plant growth limiting soil nutrients from the fungal partner(s) for photosynthetically derived sugars from the plant host(s). However, the function of mycorrhizal fungi extends beyond nutrient exchange, as they play other important roles for their hosts including increased resistance to pathogens and herbivory and improved plant–water relations. Key Concepts Mycorrhiza refers to the symbiotic relationship between a fungus in the soil and the root of a plant. The mycorrhizal symbiosis is the most widely distributed symbiosis on earth. Mycorrhizas are classified into different types, each of which is defined by the identity of plant and fungal partners, as well as the morphological structures, where the partners interface. The mycorrhizal symbiosis while generally considered a mutualism where both partners benefit, can fall on a continuum from parasitism to mutualism, where the direction and strength of the interaction depend upon the identity of the partners and their environmental conditions. Mycorrhizas are ubiquitous in nature, having strong influences on plant community ecology including diversity and productivity.