Actions and Interactions of Soil Invertebrates and Arbuscular Mycorrhizal Fungi in Affecting the Structure of Plant Communities

Abstract

Soil invertebrates and arbuscular mycorrhizal (AM) fungi co-occur in all ecosystems of the world. However, the interactions between these organisms are rarely studied. We present some reasons for this lack of interest and suggest that this is an area of ecology in which much useful research could be done. There are four main groups of subterranean invertebrates that can interact with AM fungi; these are the earthworms, nematodes, mites and the insects. Earthworms are likely to be beneficial to AM fungi, they aid in the dispersal of spores and hyphal fragments in soil. However, their burrowing activities may disrupt the fragile fungal mycelium. The literature regarding plant parasitic nematodes is confusing, some studies show antagonistic effects between the organisms, while others show null or positive effects. Virtually nothing is known about the effects of mycophagous nematodes on AM functioning in natural communities. Contrary to popular opinion, we suggest that the Collembola are beneficial to AM fungi, through feeding on competing fungi in the rhizosphere. The interactions between mites and AM fungi in field situations have never been studied. The meagre laboratory evidence suggests they may be selective feeders and act in a similar way to Collembola. Interactions between insects and AM fungi are variable. In a recent study we show that the effect of AM fungi on rhizophagous insects appears to be one in which single fungi reduce insect performance while colonization by more than one species has no effect. The results of a large field experiment are presented which show that the insects and fungi act and interact in determining plant community structure. A mechanism for these interactions is given and a conceptual model involving seedling establishment proposed. Much further work is required to test this model and to extend it to include the other groups of subterranean invertebrates that interact with AM fungi.