Understanding how climate change alters biotic interactions is important to predicting community and ecosystem responses to global change. Fungal symbionts, ubiquitous inhabitants of plant above- and belowground tissues, can play important roles in mediating plant responses to climate variability, potentially buffering their hosts against warming and drought. However, if fungi and plants differ in their physiological or phenological responses to climate, their distributions may become decoupled, with important, potentially negative consequences for plant hosts. Plants that experience climate-induced range shifts may leave behind original symbionts and encounter novel ones. Plants that retain their initial distributions could experience shifts in their symbiont assemblage.
This study tested the potential for disruption of plant-fungal symbioses under climate-induced range shifts along replicated altitudinal gradients and in a long-term warming experiment at the Rocky Mountain Biological Laboratory (RMBL, CO, USA). Root and leaf samples from three grass species (Achnatherum lettermanii, Festuca thurberi, and Poa pratensis) were collected from 44 sites along eight altitudinal gradients, as well as from heated and non-heated plots in the warming experiment. We used microscopy and Illumina MiSeq amplicon sequencing to examine how symbiont colonization and composition changed with elevation and experimental warming.
Results/Conclusions
Along altitudinal gradients, fungal symbiont composition varied with elevation (R2 = 0.050), host species (R2 = 0.182), and gradient (R2 = 0.123), and the effect of elevation depended on host species identity (R2 = 0.050). We also found trends in fungal colonization with temperature change that differed among host species and symbiont groups. For example, for A. lettermanii, as temperature decreased with altitude, there was a decrease in colonization of leaves by horizontally transmitted endophytes. However, colonization of F. thurberi leaves by vertically transmitted endophytes in the genus Epichloë was lower under experimental warming relative to control plots. In contrast, for A. lettermanii, colonization of roots by arbuscular mycorrhizal fungi (AMF) was higher under warming, but trends in AMF colonization with warming were not present for the other two grass species. Our work suggests that climate change may have differential effects on plant-fungal symbioses that depend on host plant identity and fungal functional group, with some associations weakened or disrupted and others affected less strongly by climate warming. Our results shed light on how ecologically important interactions may be affected by climate shifts, helping to elucidate the role of symbionts in mediating plant community and ecosystem responses to global change.