The impact of elevated CO2 and global climate change on arbuscular mycorrhizas: a mycocentric approach

Arbuscular mycorrhizal (AM) symbioses are a potentially important link in t he chain of response of ecosystems to elevated atmospheric [CO2]. By promot ing plant phosphorus uptake and acting as a sink for plant carbon, they can alleviate photosynthetic down-regulation. Because hyphal turnover is likel y to be fast, especially in warmer soils, they can also act as a rapid path way for the return of carbon to the atmosphere. However, most experiments o n AM responses to [CO2] have failed to take into account the difference in growth of mycorrhizal and nonmycorrhizal plants; those that hare done so su ggest that AM colonization of roots is little altered by [CO2], although th is issue remains to be resolved. Very little is known about the effects of other factors of global environmental change on mycorrhizas. These issues n eed urgent attention. It is also necessary to understand the potential for the various AM fungal taxa to respond differentially to environmental chang es, including carbon supply and soil temperature and moisture, especially b ecause of the differential abilities of plant and fungal species to migrate in response to changing environments. Indeed, there is a need for a new ap proach to the study of mycorrhizal associations, which has been too plant-c entred. It is essential to regard the fungus as an organism itself, and to understand its biology both as an entity and as part of a symbiosis.