PARENT SESSION
Oral Session #35: Carbon and Nitrogen Cycling.
Presiding: D. Rothstein
Tuesday, August 6. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.
Biogeochemical consequences of resource and environmental manipulation in shortgrass steppe.
Burke, Ingrid*,1, Lowe, Petra1, Lauenroth, William1, Mosier, Arvin2, Sala, O5, Aguiar, M5, 1 Colorado State University, Fort Collins, CO2 Colorado State University, Fort Collins, CO5 Department of Ecology, AR
ABSTRACT- Human alterations to ecosystems both directly and indirectly alter ecosystem resource availability. Anthropogenic effects include increases in nitrogen availability, potential changes in seasonality and mean annual water availability, and increases in temperature associated with radiative forcing. The interactions of resource alterations for different ecosystem types are not well understood, with much work focusing primarily on the response of net primary production, and much less on trace gas fluxes from soil. We manipulated resource availability in shortgrass steppe, a strongly water-limited ecosystem, by increasing temperature, adding nitrogen, and increasing rainfall, alone and in combination. Combined water and nitrogen additions had the largest effects on both carbon dioxide (25%) and nitric oxide efflux (400%) and on net nitrogen mineralization (300%). Increase in temperature alone had the most dramatic effects on methane uptake, which was 30% higher than in the control treatments, and on nitrous oxide flux, which doubled under increased temperatures. All treatments had the largest effects in the spring and early summer, when substrate availability was high. With the exception of methane uptake, the net result of nearly all treatments alone and in combination was to increase volatile losses of both C and N from soils, but only the temperature treatment resulted in a net decrease in the balance of N. Our results suggest that increases in water and nitrogen availability increase greenhouse gas fluxes from shortgrass steppe, while potentially increasing N capital.
KEY WORDS: trace gas flux, shortgrass steppe, resource availability, warming