Opposing responses across latitudes drive decoupling between tree and soil fungal communities

We commonly assume that hidden belowground soil microbial communities are primarily structured by aboveground plants, leading to the hypothesis that as plant communities change in a given location, microbial communities should change similarly. Unfortunately, empirical evidence for the broad generalizability of coupled plant-fungal community change is extremely limited. The degree of coupling and decoupling between plant-microbial interactions over time and across space likely has significant implications for essential ecosystem functions. To test whether changes in plant communities over time are coupled with changes to soil fungal communities, we used tree census and soil microbiome data from the US Forest Service Forest Inventory and Analyses (FIA) Archive. We analyzed data from over 400 plots, with two measurements from each plot, taken roughly a decade apart. We found that tree and fungal communities may be decoupling over time, as tree community turnover was not correlated with fungal community turnover (p > 0.05). This decoupling was related to differential community shifts across latitudes with fungal turnover being highest at lower latitudes (p < 0.01), while tree turnover was greater at higher latitudes (p < 0.001). Decoupling between plant and fungal community change complicates predictions for the roles of plant-fungal symbiosis, confounding ecosystem responses to global change.