The contributions of mycorrhizal fungi to the determination of plant community structure

While it is now widely accepted, even by ecologists, that most plants in the majority of ecosystems are infected by mycorrhizal fungi, few experiments have been designed to investigate the function of the mutualism at the community level. Those involved with mycorrhizal research have been largely preoccupied with questions of the mineral, particularly phosphorus, nutrition of individual plants, while plant community ecologists have too often found it convenient, even when acknowledging the presence of infection, to ignore its possible function in the ecosystem. This presentation examines a selected number of seminal papers written by plant community ecologists and highlights some of ‘the most striking mysteries’ which they reveal. It describes experiments designed to determine whether knowledge of the presence and activity of the mycorrhizal mycelium can help us to unravel the ‘mysteries’ which they define. It is revealed that by having direct adverse effects upon seedlings of many ‘r’ selected species, while at the same time being beneficial, if not essential, to those that are ‘K’ selected, the activities of the mycelium of VA fungi have a direct bearing upon community composition. The extent to which ‘turf compatibility’ is actually a reflection of the compatibility of plant species with the VA mycorrhizal mycelium is discussed and the possible role of the mycelium in consigning some species to the ruderal habit is considered. It is concluded that those attempting scientifically to understand, or managerially to manipulate, plant communities, without recognizing the role of the mycorrhizal mycelium, do so at their peril, and it is recommended that scientists involved in research on mycorrhiza extend their vision beyond the limited horizons which are currently so often defined by considerations of the phosphorus nutrition of individual host plants.