Mycorrhizas, Drought, and Host-Plant Mortality

As the Earth's climate changes, droughts are expected to become more intense, with consequences for plants and mycorrhizal fungi. We review recent studies examining the effects of drought on mycorrhizal fungi and the influence of mycorrhizal fungi on host plant-water relationships and drought tolerance. We also examine the consequences of drought-induced host mortality to mycorrhizal fungi and ecosystem processes using examples from the western United States. Mycorrhizal fungal abundance in roots and soil, as well as mycorrhizal fungal species composition, diversity, and activity are often affected by drought. Likewise both arbuscular (AM) and ectomycorrhizal (EcM) fungi increase the drought tolerance of their host plants, with more pronounced beneficial effects as drought stress increases. Host-plant mortality related to drought appears to disproportionately affect EcM plant species, with potential consequences for EcM fungi, the regeneration of plant hosts and ecosystem properties such as carbon (C) sequestration and nutrient cycling.