Mycorrhizas: Symbiotic Mediators of Rhizosphere and Ecosystem Processes

Roots of most terrestrial plants form symbiotic associations with fungi. Arbuscular mycorrhizas are widespread and abundant. They are formed by bryophytes, pteridophytes, gymnosperms, and angiosperms and are ubiquitous in most temperate and tropical ecosystems including agricultural systems. Ectomycorrhizas occur in certain families of woody gymnosperms and angiosperms and are extremely important in many temperate and boreal forests. The plant order Ericales contains a natural group of closely related families with worldwide distribution. Except for orchid and monotropoid associations, mycorrhizas involve plant exchange of photosynthates in return for a fungal exchange of mineral nutrients. The convergence of so many unrelated forms of mycorrhizas is a testament for the mutual benefits of these trading partnerships. Mycorrhizal interactions influence the species composition, diversity, and stability of biotic communities. Mycorrhizal fungi co-inhabit the rhizosphere with many saprotrophic and pathogenic fungi. One of the most important functions of mycorrhizas is their role in physically structuring soils. The total effect of roots and associated mycorrhizal fungi on soil structure is related to their turnover and decomposition rates. Aerts suggested that variation in access to different nutrient pools among various types of mycorrhizal fungi leads to positive feedback between the dominant plants in an ecosystem and litter decomposition. The average global temperature has risen since the early 1980s, and it has been predicted that the land surface temperature will increase by 3.1° C by 2085. The analytical challenge of holistic studies of complex interactions among communities of rhizosphere organisms and the environment is daunting.