Ectomycorrhizal (EM) fungi form complex networks that link multiple tree species together belowground via mycelial connections. EM networks can involve many fungal and plant taxa and are hypothesized to have important stabilizing properties in forest ecosystems. As such, understanding the response of EM fungal networks to global change is critical to predicting future ecosystem functioning. Here, we quantify the response of EM fungal networks associated with both boreal (Pinus banksiana & Betula papyrifera) and temperate (Pinus strobus & Quercus macrocarpa) hosts to elevated temperatures and water stress at the rapidly changing boreal-temperate ecotone. The study was conducted at the B4Warmed (Boreal Forest Warming at an Ecotone in Danger) experiment in northern Minnesota, which includes a factorial combination of elevated temperatures (+0 , +3.4C above ambient) and increased water stress (ambient, water stress) treatments. EM fungal community and network structure were assessed with high-throughput sequencing.
Results/Conclusions
Elevated temperature reduced EM OTU richness (P=0.011) and altered EM fungal community composition (PERMANOVA: P=0.002), while water stress had only marginal effects on community composition (PERMANOVA: P=0.054)). Specifically, increased temperatures led to a significant decline in medium- to long-distance exploration strategy EM fungal taxa and increase in short-distance exploration strategy taxa. Under ambient conditions, EM fungal networks were well-connected, but under increased temperatures they became highly disconnected (or highly specialized). These changes in network structure were significantly correlated with changes in soil moisture (P<0.01; R2=0.89) and plant productivity (P<0.01; R2=0.72). Together, our results indicate that climate change will likely lead to the loss of EM fungal taxa important to the maintenance of mycorrhizal networks in forest ecosystems at the boreal-temperate ecotone.