Root associated microbes: The mediators between plants and soil

Globally, increasing human populations have either caused or accelerated several types of environmental change. Symbiotic microbes have powerful effects on plant fitness, yet little study has been done on how microbial-plant relationships are affected by environmental changes. In two different ecosystems I explore how either nitrogen (N) pollution or drought can alter root associated microbe (RAM)-plant relationships using Next Generation Sequencing. In moist-meadow alpine tundra at Niwot Ridge, CO, I examine the relative contribution of host identity, N enrichment, and plant neighborhood on RAM diversity and community composition in two co-dominant plant species; Geum rossii and Deschampsia cespitosa. In New Mexican pinon-juniper woodlands, I sampled roots from a site in which mass Pinus edulis dieback was simulated to mimic the effects of extreme drought events, which are predicted to become more frequent as climate change progresses. I examine the effect of host and neighbor identity, as well as the effect of dead P. edulis neighbors, on root associated fungi (RAF) of P. edulis and Juniperus monosperma. I also compare RAF communities between pinon-juniper woodlands and more arid juniper savanna, a good proxy for what pinon-juniper woodlands will become should these extreme drought events become more frequent.;I found that biotic assembly mechanisms (plant host and neighborhood) are important to structuring RAM communities in alpine tundra but not in pinon-juniper woodlands. In the arid southwest, abiotic factors appear to be more important in structuring RAF communities, while contrary to previous research, host identity has little effect on RAF community composition. These unusual results could be a product of the more sensitive sequencing methods, or an anomaly caused by the drought experienced by these field sites at time of sampling. In both ecosystems, plant neighborhood influenced RAM (community composition in alpine tundra, diversity in pinon-juniper woodland). In alpine tundra, both host identity and plant neighborhood mediated RAM response to N. These data emphasize the complex feedback systems between environment, plant communities, and their microbes. As a plant community becomes altered in response to the environment, the response of the microbial community to the environment will shift, making plant-microbe dynamics difficult to predict.