Mycorrhizal Fungi: Their Habitats and Nutritional Strategies

Abstract

Mycorrhizal fungi are specialised root symbionts, engaging in intimate association with a great variety of plants. Although the association is generally assumed to be mutualistic, with bilateral nutrient exchange between the plant and fungal partners, it stretches over a wider range on the symbiotic continuum, including commensalism and antagonism. Traditionally perceived as being restricted to the root niche, mycorrhizal fungi actually thrive at the interface between two distinct habitats, host roots (a biotic habitat) and soil (an abiotic habitat). In the last decade, application of modern techniques and innovative combinations of methodological approaches has yielded valuable new insights on their functions in natural communities, and on the mechanisms underlying such processes. The fungal and plant genes, regulation of their expression, and biochemical pathways for nutrient exchange between symbiotic partners are now coming under intense study. At the same time, progress in molecular identification and characterization of fungal symbionts has provided a much more diverse and complex view of their multifunctional nature. A picture has emerged of greater than expected plasticity of these symbiotic organisms, which have therefore the potential of impacting their hosts from the molecular to the ecosystem level.