Global Change and Mycorrhizal Fungi

Abstract

Mycorrhizae, due to their key position at the plant-soil interface, are impor- tant to consider in the study of ecosystem impacts of global changes.Human- induced changes in the earth’s environment are clearly multi-factorial.Exam- ples of important factors are: elevated concentrations of atmospheric gases (for example carbon dioxide or ozone), increased input of nutrients into ecosystems by atmospheric deposition (for example nitrogen), climate change (including altered precipitation and temperature regimes), invasivespecies,and increased UV-radiation.All of these components of future or pre- sent global changes can have positive or negative impacts on mycorrhizal associations. However, a more fundamental distinction has to be made between these factors, paying tribute to the fact that in the mycorrhizal sym- biosis we are dealing with two classes of organisms with partially indepen- dent biology. There are those factors that directly affect only the host plant (e.g., carbon fixation), and that only have indirect effects on mycorrhizal fungi (mycobionts) via altered carbon allocation from the host. Examples include atmospheric changes, against which soil serves largely as a buffer. Other factors can (in addition) directly affect the mycobionts, for example warming or altered precipitation. This distinction is crucial for a mechanistic understanding of the impact of global change factors, and for experimental approaches.Global change factors rarely occur in isolation.The complexity of regional combinations of global change factors further highlights the need for mechanistic studies, since direct experimental exploration of a large number of scenarios would be virtually impossible. Finally, processes and patterns at larger temporal and spatial scales have to be considered in an assessment of global change impacts on mycorrhiza.Most experiments only allow access to short-term responses,while longer-term responses are really relevant. Possi- ble approaches include the use of natural experiments, for example, CO2 springs.Large-scale processes such as shifts in the global distribution of plant communities (or their regional extinction) due to climate change would affect mycorrhiza, for example, alter the current distribution of mycorrhizal types on the globe.With potential impacts on host biodiversity,mycobiont species diversity may also be impacted at regional scales. In addition, changes in the mycorrhizal fungal community that are independent of changes in the plant community may be one of the least-understood, but potentially most impor- tant,mycorrhizal responses to global change.