Background/Question/Methods Dryland ecosystems are especially susceptible to climate change, land-use change and nitrogen deposition. Frequently, studies on the effects of global change have either focused on aboveground responses, like plant diversity or on belowground impacts on soil biodiversity and ecosystem processes. However, it has been hypothesized that plants are holobionts and the soil microbiome affects the plant’s fitness and ability to respond to global change pressures. Specifically, plants have the ability to maintain high fitness under global change due to the response of their soil microbial associations. In dryland systems, which have less available water, and even small nutrient inputs can have a significant effect on plant fitness, the interactions between plants and microbes may be especially critical. Here using a greenhouse experiment we tested the hypothesis that the rhizosphere microbiome helps dryland plants adapt to global change pressures, and those interactions feedback to affect soil carbon dynamics and plant productivity. Specifically, we grew 4 plant species (Bouteloua eriopod, Gaillaridia pulchella, Yucca filaments and Cactaceae) under drought and nutrient treatments for three months. At 4, 8, and 12 weeks we characterized the bacterial and fungal community using high-throughput Illumina sequencing and quantified above and belowground plant biomass. After 12 weeks, pH, soil microbial biomass, carbon use efficiency (CUE), CN ratios, and Nitrogen mineralization were also measured. Results/Conclusions As expected, both above- and belowground plant biomass was negatively impacted by the drought treatments. However the largest responses were seen after 4 and 8 weeks, with little response by 12 weeks. Conversely, responses to the nutrient addition varied by plant species, and were not linear over time whereas negative responses were seen at 4 weeks, but a positive effect was seen at 8 and 12 weeks. Microbial community structure was also significantly impacted by both treatments, but plant species was the strongest predictor of community composition. Relative changes in the community composition were primarily dependent on plant species, and secondarily the treatment. However, there was an interaction between species and treatment type. Finally, we observed significant differences in microbial biomass and CUE between treatments. Our study suggests that development of specific microbial communities under drought can help certain plant species adapt to their changing environment, and can feedback to affect nutrient cycling.
