2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to use stable isotopes and related ecological methods and technologies to elucidate the role of water relations, nutrient cycling, soil biology, and plant community responses to global change, and explore management options (e.g., legume additions) or issues (e.g., weed infestation) in the analysis and development of sustainable management practices for western rangelands. 1b.Approach (from AD-416) Although we know water and N are major drivers in the functioning of semi-arid rangeland plant communities, our knowledge of how to manage these lands in order to promote their sustainability and health through these important drivers is incomplete. Further, the constantly changing environment due to global climate change is altering water and nutrient cycles, independently causing important ecosystem changes and complicating our ability to understand and manage rangeland ecosystems. The Rangeland Resources Research Unit (RRRU) will conduct CO2 enrichment, grazing management, and legume research that will explore the consequences of combined global change and management on the structure and functioning of semi-arid rangelands. RRRU scientists will collaborate with scientists in the Stable Isotope Laboratory, University of Wyoming, to use stable isotope and related ecological methods and technologies to more fully explore the consequences of global change and management effects on ecological functioning of western rangelands. The results of these investigations will provide the basis for formulating new sustainable management strategies appropriate for the changing environment due to global climate change. 3.Progress Report This report documents research conducted under the Specific Cooperative Agreement between ARS and the University of Wyoming. Additional details of research can be found in the report for the parent project 5409-11000-003-00D, Global Change: Responses & Management Strategies for Semi-Arid Rangelands. Project participants during 2006-2007 included four grad students, five undergrads and one UW tech. The Ecosystem Ecology group conducted field measurements focused on canopy-scale net ecosystem exchange of carbon dioxide (CO2) & water, soil CO2 concentrations & efflux rate, plant cover by species, & normalized difference vegetation index (NDVI). In summer 2007, stable isotope measurements of the soil CO2 efflux were initialed, and will be used to help partition soil respiration into microbial and root components. Late July soil samples in 2006 and 2007, will be subjected to analyis of organic C and N content, and C isotope composition in particulate and mineral-associated phases; inorganic carbon, pH, electrical conductivity, and potassium chloride extracts for nitrate and ammonium. 2006-2007 winter processing of soil samples and root biomass samples took place. During summer 2007, an incubation experiment was initiated to assess labile and resistant soil carbon pools and their turnover rates. The Ecophysiology Group carried out extensive leaf gas exchange and plant water relations measurements during the 2007 field season, documenting the effects of global change treatments on different species of interest, including an important invasive weed, Dalmatian toadflax. Major findings include: 1. Leaf photosynthetic activity of toadflax in 2007 was correlated with patterns of seedling mortality and treatments. Warming at present ambient CO2 concentrations caused greatest photosynthetic stress. Most favorable conditions for toadflax were conditions of high CO2 with no warming. 2. Leaf gas exchange activity in native grass and sub-shrubs was greatest under elevated CO2 with no warming in 2006 and 2007. 3. 13C discrimination was higher and leaf N lower in 2006 under elevated CO2 compared to control plots for almost all C3 plant species in native prairie plots. A poster was presented at the Soil Science Society of America Annual Meeting in Nov. 2006 titled "Patterns in Net Ecosystem Exchange: First Year Responses to Elevated CO2 and Irrigation from High Plains Global Change Experiment." A manuscript is in preparation titled "Ecosystem carbon flux responses to simulated precipitation pulses under elevated [CO2] in northern mixed-grass prairie" for submission to Oecologia. A poster was presented by a graduate student at the 2007 ESA meetings; a journal manuscript is being prepared on this material as well. To ensure accountability of funds utilized, the ADODR and his staff hold quarterly meetings with UW collaborators to discuss research and site issues; staff of both groups communicate regularly on experimental protocols, site management, and presentation of results.