Plant-fungal symbioses play critical roles in vegetation dynamics and nutrient cycling and in doing so, modulate the impacts of global changes on ecosystem functioning. However, critical gaps remain in our understanding of biogeographic patterns of mycorrhizal associations, and our limited knowledge of the anthropogenic factors responsible for shifting plant-mycorrhizal distributions has hindered efforts to predict ecosystem feedbacks to climate change. Here, we used forest inventory data consisting of over three million trees to (i) map the tree mycorrhizal association patterns and identify underlying drivers of these observed associations, (ii) quantify the impacts of human induced global changes, primarily climate change, N deposition, and disturbance regimes, on tree mycorrhizal associations, and (iii) assess the potential feedback of mycorrhizal association shifts on soil C and nutrient dynamics.
Results/Conclusions
We show that abundances of the two dominant mycorrhizal tree groups – arbuscular mycorrhizal (AM) and ectomycorrhizal trees – are associated primarily with climate. Further, we show that anthropogenic influences, primarily nitrogen (N) deposition and fire suppression, in concert with climate changes, have increased AM tree dominance during the past three decades in the eastern US. Given that most AM-dominated forests in this region are underlain by soils that are high in N availability, our results suggest that the increasing abundance of AM trees has the potential to induce nutrient acceleration, with critical consequences for forest productivity, ecosystem carbon and nutrient retention, and feedbacks to climate change.