Mycorrhizal fungi mediation of terrestrial ecosystem responses to global change: mini-review

Mycorrhizal fungi are responsible for most nutrient uptake by the majority of land plants. As such, mycorrhizas are increasingly recognized as important drivers of terrestrial ecosystem processes, and may mediate ecosystem responses to environmental change. Here we review published studies that explicitly address the role of mycorrhizal influence on ecosystem responses such as biogeochemical fluxes and pools, ecosystem productivity, and dominant vegetative growth responses to global change. We find that most studies are of limited duration (≤1 yr) and geographical distribution. A strong bias in the literature regarding the location of studied ecosystems, with large parts of the globe, such as highly-weathered soil systems in the tropics, subtropics and warm temperate biomes, accounting for ∼30 % of the global land base, greatly under-investigated. In terms of mediating ecosystem responses to global change, mycorrhizal-plant symbioses exhibit conflicting responses although some generalities do exist. Plants often shift carbon allocation belowground and the activities of mycorrhizal associates are frequently enhanced at elevated atmospheric CO2 conditions, but the direct effects for ecosystem dynamics are less clear. Mycorrhizal associations reduce plant stress under drought conditions. How mycorrhizal root colonization responds to nitrogen deposition depends on the type of mycorrhizas and background levels of soil nitrogen and phosphorus. The capacity of mycorrhizas for mediating plant and ecosystem responses to warming are varied, but over 60 % of these studies found increased mycorrhizal abundance and decreased mycorrhizal activity with warmer temperatures. This review suggests the role mycorrhizal fungi play in ecosystems responding to global change is not well understood. We emphasize the need for more research in this emerging field, as such responses and ecosystem feedbacks to Earth's climate system are of concern to multiple scientific disciplines and society.