Global environmental change and the biology of arbuscular mycorrhizas: gaps and challenges

Our ability to make predictions about the impact of global environmental change on arbuscular mycorrhizal (AM) fungi and on their role in regulating biotic response to such change is seriously hampered by our lack of knowledge of the basic biology of these ubiquitous organisms. Current information suggests that responses to elevated atmospheric CO 2 will be largely controlled by host-plant responses, but that AM fungi will respond directly to elevated soil temperature. Field studies, however, suggest that changes in vegetation in response to environmental change may play the largest role in determining the structure of the AM fungal community. Nevertheless, the direct response of AM fungi to temperature may have large implications for rates of C cycling. New evidence shows that AM fungal hyphae may be very short lived, potentially acting as a rapid route by which C may cycle back to the atmospohere; we need, therefore, to measure the impact of soil temperature on hyphal turnover. There is also an urgent need to discover the extent to which AM fungal species are differentially adapted to abiotic environmental factors, as they apparently are to plant hosts. If they do show such an adaptation, and if the number of species is much greater than the number currently described (150), as seems almost certain, then there is the potential for several new fields of study, including community ecology and biogeography of AM fungi, and these will give us new insights into the impacts of global environmental change on AM fungi in moderating the impacts of global environmental change on ecosystems.Key words: arbuscular mycorrhiza, temperature, diversity, community structure, ecosystem, carbon cycle.