COLLABORATIVE RESEARCH: Responses of Productivity and Nutrient Dynamics to Elevated CO2 in an Intact Mojave Desert Ecosystem.

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The Nevada Desert FACE Facility (NDFF) is a long-term research project examining the responses of an intact Mojave Desert ecosystem to elevated CO2. In the first four years of NDFF operation, we found that primary production increased substantially at elevated CO2, but only in wet years, and that an exotic annual grass responded more strongly than did native shrubs and annuals. Therefore, our initial results suggest that an ecosystem type (drylands) that represents 30% of the earth's terrestrial surface area may not respond to elevated CO2 in a simple manner, as predicted by existing models of global change.In the context of these results and the long-term nature of our desert FACE experiment, we propose to address three overarching questions in this study:1. Will elevated CO2 alter community composition and structure in the Mojave Desert by continuing to stimulate a disproportionate increase in an exotic annual species?2. Will the increases in production and changes in nutrient dynamics that we have observed in response to a step-change increase in CO2 be sustained over time?3. Can we adapt proven models of desert ecosystem function to predict how this Mojave Desert ecosystem will respond to elevated CO2 in the future?The intellectual merit of this proposal lies in our conceptual approach in which we are focusing on the functional interactions between species composition and ecosystem function, tied together by an explicit modeling component. The model will be an adaptation of an established, validated desert model (PALS, the Patch Arid Lands Simulator) that will be used to develop a synthetic understanding of biotic and abiotic controls on carbon, nitrogen, and water fluxes to elevated CO2 in this arid ecosystem. The broader impact of this proposed study will be an examination of the potential invasion of an exotic species in response to elevated CO2, and how this process may impact ecosystem function, and therefore ecosystem services, in a desert environment. Through this research program, we are also forging a cohesive network between five research campuses. To date, our research group has an excellent record of training undergraduate, graduate, and postdoctoral scholars at the NDFF, including members of underrepresented groups. This study will similarly train a wide spectrum of students and postdocs, both at the NDFF and in our support laboratories.