Climate change is predicted to cause severe and chronic stress for many organisms, and research investigating species responses to climate change typically focus on three alternative outcomes: adaption, migration, or extinction. Another mechanism for in situ persistence in the face of climate change is to form mutualistic partnerships with other organisms that ameliorate this stress. One hypothesized example of this is the ubiquitous mutualisms between plants and endophytic fungi in which these microfungal endophytes confer drought tolerance to host plants. While a great deal of work has documented context-dependency of fungal endophyte-conferred benefits, here we take a rigorous approach to this question by combining long-term field experiment (data from 2008-2016) and highly-controlled greenhouse experiments to test how endophyte presence and variation in water availability interact to affect the performance of the common native grass Festuca subverticillata.
In the greenhouse experiment, we found that the presence of endophytes increased overall biomass produced by plants, but only when plants were grown under high water conditions. Since current climate change forecasts for some areas of the Midwest predict an increase in rainfall, these results suggest an increased advantage for individuals that associate with endophytes. For the long-term field study, we again found that endophytes increased plant performance, however unlike the greenhouse study, the plants with endophytes had a greater advantage in years with higher drought conditions. Although these field results suggest that the interaction with fungal endophytes may not be as important to plant performance if rainfall does indeed increase, conferring a benefit during drought may still play an important role in plant performance because climate change predictions also call for increases in severe climatic events, under which a partnership with endophytes may result in increased survival during these times of stress.