The effect of water availability on microbe-mediated interactions between native and non-native plant species
Interactions between plants and soil microbes play an important role in structuring terrestrial ecosystems by influencing plant growth and competitive ability. As such, changes in plant-microbe interactions alter plant-plant interactions, which could affect plant community composition. Investigations into the context-dependency of plant-microbe interactions have determined that abiotic conditions such as varying nutrient levels or environmental stress can alter the direction and magnitude of these interactions. Given this, it is possible that the effects of climate change, including altered water availability, could have large impacts on their outcomes, in turn affecting interactions among plant species. Furthermore, if non-native species benefit from alterations in plant-microbe interactions, climate change could exacerbate the existing threat that invasive species pose to biodiversity. We tested whether soil water availability mediated the effect of soil microbes on plant-plant interactions in the Texas coastal prairie using a controlled greenhouse experiment. To test for an interaction between water availability and soil microbes, plants were grown in either live or sterile soil and were provided average, reduced, or increased amounts of water. Within these treatments, we tested the outcome of pairwise interactions between native and non-native species by growing three plant species – the native grass Schizachyrium scoparium, the native forb Rudbeckia hirta, and the non-native forb Plantago lanceolata – in the presence of either a conspecific or a heterospecific. At the end of the experiment, above- and below-ground biomass was collected and AMF colonization quantified.
Preliminary results from companion experiments show that in the absence of interspecific competition the two native species benefit from the presence of soil microbes. Schizachyrium scoparium grew three times larger in live soil than in sterile soil. Rudbeckia hirta had a weaker response to native microbes, producing only 60% more aboveground biomass in live soil than in sterile soil. However, this benefit disappeared when R. hirta was grown in competition with non-native species. We expect that the added stress of water limitation may exacerbate this effect. The results of our study will be useful in future conservation and restoration efforts in the Texas coastal prairie by helping to identify species that are resistant and/or sensitive to changes in their interactions with the soil microbial community.