Symbiotic and other associations for nutrient capture

Abstract

Symbiosis between green plants and microorganisms is now known to be so widespread that the exceptions among green plants should be regarded as special cases. The basic unit of study must be conceived of as being a pair or cluster of organisms. A commonplace example is of a nodulated legume with a vesicular-arbuscular mycorrhiza. This adds a new dimension to plant physiology, agriculture and ecology. Without even considering the joint metabolic properties of symbiotic associations, we must realise that soil environmental conditions surround and influence all parts of the association. This may mean, for example, that anaerobic soil conditions may incapacitate or eliminate mycorrhizal fungi, which are obligate aerobes, more readily than a larger green plant possessing aerenchyma. Awareness of such possibilities should influence the formulation and testing of hypotheses in ecology more than it does at present. Detailed possibilities will be referred to under appropriate sub-headings. There has been a large amount of research activity and review in the area of plant-microbe symbiosis. This has concentrated on the fundamental biology of interactions and their economic importance. The ecological literature is relatively sparse. The account that follows will outline the expectations of the ecologist from each category of symbiotic interactions, referring to purely ecological material when it is available.