|Title||Physiological and environmental regulation of interannual variability in CO2 exchange on rangelands in the western United States|
|Publication Type||Journal Article|
|Year of Publication||2010|
|Authors||H. Polley W, Emmerich W, Bradford JA, Sims PL, Johnson DA, Saliendra NZ, Svejcar T, Angell R, Frank AB, Phillips RL, Snyder KA, Morgan JA|
|Journal||Global Change Biology|
|Keywords||article, climatic variability, desert, grassland, journal, leaf area, light-use efficiency, method, Bowen ratio, NEE, net ecosystem exchange of CO2, precipitation, respiration, shrubland|
For most ecosystems, net ecosystem exchange of CO2 (NEE) varies within and among years in response to environmental change. We analyzed measurements of CO2 exchange from eight native rangeland ecosystems in the western United States (58 site-years of data) in order to determine the contributions of photosynthetic and respiratory (physiological) components of CO2 exchange to environmentally caused variation in NEE. Rangelands included Great Plans grasslands, desert Shrubland, desert grasslands, and sagebrush steppe. We predicted that (1) week-to-week change in NEE and among-year-variation in the response of NEE to temperature, net radiation, and other environmental drivers would be better explained by change in maximum rates of ecosystem photorespiration at 10 °C (R10) and (2) among-year variation in the responses of NEE, Amax, and light-use efficiency to environmental drivers would be explained by changes in leaf area index (LAI). As predicted, NEE was better correlated with Amax than light-use efficiency or R10 for six of the eight rangelands. Week-to-week variation in NEE and physiological parameters correlated mainly with time-lagged indices of precipitation and water-related environmental variables, like potential evapotranspiration, for desert sites and with net radiation and temperature for Great Plains grasslands. For most rangelands, the response of NEE to a given change in temperature, net radiation, or evaporative demand differed among years because the response of photosynthetic parameters (Amax, light-use efficiency) to environmental drivers differed among years. Differences in photosynthetic responses were not explained by variation in LAI alone. A better understanding of controls on canopy photosynthesis will be required to predict variation in NEE of rangeland ecosystems.