Mapping the potential mycorrhizal associations of the conterminous United States of America

Mycorrhizal associations are recognized as key symbioses in a changing world, yet our understanding of their geographic distribution and temporal dynamics remains limited. We combined data on mycorrhizal associations and historical dominant vegetation to map the pre-European Settlement mycorrhizal associations of the conterminous United States of America (USA). As a demonstration of the map's utility, we estimated changes in mycorrhizal associations due to urbanization, agriculture and the establishment of non-native species in two regions. We found that the conterminous USA was dominated by vegetation associated with arbuscular mycorrhizas, but that ∼40% of vegetation types included multiple mycorrhizal associations. Shifting land use to agriculture and the introduction of non-native species has disproportionately affected ectomycorrhizas, as did urbanization. These preliminary results set a baseline for mycorrhizal biogeography of the USA and illustrate how synthesis of available data can help us understand the impact of anthropogenic changes on an important mutualism.