Interactions Between Ecto-mycorrhizal and Saprotrophic Fungi

Abstract

The microbiota of most forest soils is dominated by ecto-mycorrhizal and saprotrophic decomposer fungi which are the main organisms involved respectively in the supply of nutrients to trees and the decomposition of woody plant litter. In recognition of the pivotal role that these fungi play in plant nutrition and nutrient cycles in plantations and natural forests, the activities of their mycelial systems have been independently investigated in recent years. Such studies have revealed remarkable structural and functional similarities between these organisms, particularly in their active foraging for nitrogen and phosphorus in soils. This has highlighted the need to determine the nature and extent of interactions between the two groups of organisms. The use of radioactive tracers, time-sequence photography and digital image analysis of microcosms containing non-sterile soil in which the two groups of fungi are grown with their natural carbon resources have provided novel insights into their interactions. When mycelia of the fungi meet in soil they often interact strongly, resulting in cessation of growth or even die-back of mycelium. Such inhibition can be accompanied by loss of nutrients to the opposing fungus. This chapter reviews current evidence and presents some new data showing that interactions between the mycelial systems of mycorrhizal and saprotrophic fungi have major effects on the functioning of these organisms and upon nutrient and carbon cycling processes in temperate and boreal forest ecosystems