COS 247-3 - Soil microbiomes under climate change: effects on plant performance and symbiosis

Abstract: The impacts of climate change on soil microbial communities are important for predicting plant fitness and plant evolutionary responses to climate change, given the ubiquitous nature of symbioses between plants and microbes. While past studies have demonstrated climate can shift soil microbial communities, the actual eco-evolutionary impact of altered soil microbiomes on plants was not addressed. Climate conditions can affect microbes differently, creating new microbial competitive interactions and potentially disrupting or improving the likelihood of different symbiotic interactions and subsequent plant performance. Legumes have a close mutualism with rhizobia bacteria, making them especially good organisms to assess how symbiosis and plant performance may change. To address eco-evolutionary impacts of climate change, we first examined how a history of heat and drought affect bacterial and fungal soil community composition and symbiotic guilds, then we applied the soil to legumes in a growth chamber to test the effect of the altered microbiome on plant performance and symbiosis. Finally, in a second experiment, we tested whether drought-legacy soil had different effects on plants experiencing a drought or full water conditions.

We collected soil samples from warming array plots at the Koffler Scientific Reserve, Ontario, Canada, that have a multiyear history of being heated, droughted, heated and droughted, or left natural. Sequencing demonstrated that fungal community composition was significantly different between each climate treatment, with drought significantly decreasing observed fungal species richness while increasing parasite abundance. Additionally, bacterial community composition was significantly different due to drought, and rhizobial diversity increased in heated and droughted treatments. After applying the soils to Medicago lupulina in a growth chamber, we found that heat-legacy soil significantly reduced rhizobial symbiosis, and that drought-legacy soil significantly increased legume mortality. However, we found no effect on plant biomass. In our second experiment on condition dependence, we found drought-legacy soils did significantly decrease biomass compared to control soil and effects on performance were context dependent on water availability. Data analysis is ongoing, but preliminary results suggest that symbiosis may be disrupted and plant performance reduced when paired with microbiomes that have experienced climate change. As the frequency and severity of extreme weather events increases, understanding the eco-evolutionary dynamics between plants and microbes under climate change will be crucial to predicting plant response and mitigating negative effects on their performance.