Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/23/2006
Publication Date: 11/1/2006
Citation: Gilmanov, T.G., Svejcar, A.J., Johnson, D.A., Angell, R.F., Saliendra, N.Z., Wylie, B.K. 2006. Production, respiration, and net co2 exchange in two sagebrush-steppe ecosystems. Rangeland Ecology and Management. 59(6):585-599. Interpretive Summary: Sagebrush steppe rangeland covers about 100 million acres in eight western states. In spite of it's size, relatively little is known about sagebrush steppe productivity and ability to store atmospheric CO2. We measured long-term CO2 exchange (between the ecosystem and atmosphere) at sagebrush sites in eastern Oregon and Idaho. We also evaluated the utility of satellite-based remote sensing for predicting CO2 exchange. Our results show that both sites were CO2 sinks (they took in more CO2 via photosynthesis than they released via respiration), and with appropriate modeling, remote sensing could be used to predict CO2 exchange. This information will be useful to scientists involved in global carbon modeling and climate change research.
Technical Abstract: Sagebrush-steppe ecosystems cover 36 million ha in the western U.S. and may play an important role in regional and continental carbon budgets. Long-term measurements of CO2 exchange were obtained at two locations (Burns, Oregon, 1995-2001, and Dubois, Idaho, 1996-2001) as part of the AgriFlux Network, Agricultural Research Service, United States Department of Agriculture. Net ecosystem CO2 exchange (Fc) during the growing season was continuously recorded at flux towers using the Bowen ratio-energy balance technique. Fc was partitioned into gross primary productivity (Pg) and ecosystem respiration (Re) using the light-response function method. Wintertime fluxes were measured during 1999/2000 and 2000/2001 and used to identify models to gap-fill winter fluxes in other years. Comparison of daytime respiration (Rday) from light-response analysis with nighttime measurements (Rnight) showed close correlation (r=0.79 for Burns, and r=0.86 for Dubois), with Rday being consistently higher than Rnight. Maxima of Pg and Re at Burns were both 20 g CO2 m-2 d-1 in 1998. Maxima of Pg and Re at Dubois were 37 and 35 g CO2 m-2 d-1, respectively, in 1997. Mean annual gross primary production at Burns was 1111 (range 475-1715) g CO2 m-2 yr-1 or about 30% lower than that at Dubois, which was 1602 (963-2162) g CO2 m-2 yr-1. Across the years, both ecosystems were net sinks for atmospheric CO2 with a mean net exchange of 82 g CO2 m-2 yr-1 at Burns and 253 g CO2 m-2 yr-1 at Dubois. At both sites, 10-day Pg and 10-day daytime CO2 flux (Pd) were closely correlated with 10-day composites of the normalized difference vegetation index (NDVI), with the correlation coefficient r(Pg, NDVI) consistently higher than r(Pd, NDVI). Our results suggest that Fc should be partitioned into Pg and Re components to allow prediction of seasonal and yearly dynamics of CO2 fluxes.