Background/Question/Methods With increasing temperature and changing precipitation regimes in the Midwestern United States due to climate change, temperate forest trees will have to adapt to new climatic conditions or shift ranges to track historic climates. Root associated microbes may aid tree survival and evidence suggests that temperate forest tree populations can adapt to local microbial communities. Specifically, different mycorrhizal fungal symbioses associated with forest trees may impact tree seedling success when facing a changing climate. We tested whether microbial communities sourced from locations local or foreign to tree seedling source populations influence tree seedling tolerance of drought. We grew seedlings of two species of forest trees, one an arbuscular mycorrhizal fungi (AM) associated tree, Acer negundo, and the other an ectomycorrhizal fungi (EM) associated tree, Quercus rubra, in both a greenhouse setting where temperatures and water were manipulated and in the field where precipitation was reduced. We inoculated the tree seedlings with live soil either from the same site as population of the tree seedling (local) or from five sites foreign to the tree seedling population as a novel microbial community. Results/Conclusions We measured tree seedling growth and survival to investigate how an AM and EM species respond to different microbial communities under varying climate conditions. We evaluated microbe induced tree seedling drought tolerance and local adaptation of tree seedlings to microbe populations. We found that Quercus rubra seedlings grown in the greenhouse with soil inoculum sourced from more arid climates had a higher biomass compared to seedlings grown with soil inoculum from less arid sources. Similarly, Quercus rubra seedlings grown in the field survived longer if the soil inoculum was sourced from a more arid climate. Field grown Acer negundo seedlings responded positively to soil inoculum sourced from more arid climates in both ambient and drought treatments, but this was not reflected in growth in our greenhouse experiment. Quercus rubra seedlings in the greenhouse showed maladaptation to soil inoculum sourced from their home site in drought conditions but not under well-watered conditions. Acer negundo seedlings grown in the greenhouse showed adaptation to soil inoculum local to the seedling population under well-watered conditions but not under drought conditions. Acer negundo seedlings grown in the field also showed local adaptation to microbe populations under both ambient and drought induced conditions. These results reveal the differences EM and AM associating trees may have in their responses to their local microbial communities as climates change.
