Soil microorganisms improve plant fitness in the face of global change

Background/Question/Methods

Global change is challenging plant and animal populations with novel environmental conditions, including increased atmospheric CO2 concentrations, warmer temperatures, and altered precipitation regimes. In some cases, contemporary or “rapid” evolution can ameliorate the effects of global change. However, the direction and magnitude of evolutionary responses may be contingent upon interactions with other community members that also are experiencing novel environmental conditions. For example, plants often interact strongly with hyper-diverse belowground communities comprised of bacteria and fungi, and these interactions may determine how plants respond, both ecological and evolutionarily, to contemporary environmental change. In this study, we examined adaptation to drought stress in a multi-generation experiment that manipulated aboveground-belowground feedbacks between plants and soil microbial communities. We conducted a reciprocal transplant experiments to assess the importance of plant evolution and microbial dynamics for plant responses to drought stress.  In addition, we used the reciprocal transplant study to quantify the magnitude of ecological (drought) and evolutionary processes (plant adaptation) on microbial communities and soil processes (e.g., nutrient cycling). 

Results/Conclusions

Although drought stress reduced plant growth and accelerated plant phenologies, surprisingly, plant evolutionary responses to drought were relatively weak. In contrast, plant fitness in both drought and non-drought environments was linked strongly to the rapid responses of soil microbial community structure to moisture manipulations. Specifically, plants were most fit when their contemporary environmental conditions (wet vs. dry soil) matched the historical environmental conditions (wet vs. dry soil) of their associated microbial community. These findings suggest that, when faced with environmental change, plants may not be limited to “adapt or migrate” strategies; instead, they also may benefit from association with interacting species, especially diverse soil microbial communities, that respond rapidly to environmental change. Moreover, we found evidence that plant evolution can affect microbial communities and soil processes. The effects of plant evolution on the abundance and richness of soil microbial communities and soil carbon were similar in magnitude, and in some cases stronger than, the ecological effects of contemporary drought. These ecological and evolutionary interactions between plants and soil microbes set the stage for eco-evolutionary feedbacks, in which evolutionary changes by one species alter ecological conditions that drive further evolution. Such findings are important for predicting responses of soil biodiversity to global change.