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Title: GROSS PRIMARY PRODUCTION AND LIGHT RESPONSE PARAMETERS OF FOUR SOUTHERN PLAINS ECOSYSTEMS ESTIMATED USING LONG-TERM CO2-FLUX TOWER MEASUREMENTS

Author
item GILMANOV, TAGIR - S. DAKOTA STATE UNIV
item VERMA, SHASHI - UNIV OF NEBRASKA
item Sims, Phillip
item MEYERS, TILDEN - NOAA/ARL, TENNESSEE
item Bradford, James
item BURBA, GEORGE - UNIV OF NEBRASKA
item SUYKER, ANDREW - UNIV OF NEBRASKA

Submitted to: Global Biogeochemical Cycles
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/5/2003
Publication Date: 6/20/2003
Citation: Gilmanov, T.G., Verma, S.B., Sims, P.L., Meyers, T.P., Bradford, J.A., Burba, G.G., Suyker, A.E. 2003. Gross primary production and light response parameters of four southern plains ecosystems estimated using long-term co2-flux tower measurements. Global Biogeochemical Cycles. 17(2)1071. p. 40-1 to 40-16.

Interpretive Summary: The total production of plants is one of the most important characteristics of an ecological system. At present, there are no acceptable methods to estimate total plant production plus the energy used in the production process, other than measurements of net CO2 exchange and calculations of respiration, i.e., the energy used in the process of plant growth.. Data sets from continuous CO2 flux measurements in a number of ecosystems (Ameriflux, USDA-ARS Rangeland Flux, etc.) for the first time provide an opportunity to obtain empirically based estimates of total production. In this paper, using the results of CO2 flux tower measurements during the 1997 season at four sites in Oklahoma (tallgrass prairie, mixed prairie, pasture, and winter wheat crop), we describe a method to evaluate the average daytime rate of respiration. A close linear relationship, with R**2 ranging from 0.82 to 0.98, between the predicted daytime respiration rates and directly measured corresponding nighttime respiration was found. Daily gross primary productivity can be calculated from the daytime integral of the net ecosystem CO2 exchange obtained directly from measurements minus respiration. Annual gross primary production for the sites studied in Oklahoma were: tallgrass prairie, 5223 g CO2 m**2; winter wheat, 2853 g CO2 m**2; mixed prairie, 3037 g CO2 m**2; pasture, 2333 g CO2 m**2. These values are in agreement with published estimates for non-forest terrestrial ecosystems.

Technical Abstract: Gross primary production (GPP) is one of the most important characteristics of an ecosystem. At present, no empirically based method to estimate GPP is available, other than measurements of net CO2 exchange and calculations of respiration. Data sets from continuous CO2 flux measurements in a number of ecosystems (Ameriflux, USDA-ARS Rangeland Flux, etc.) for the first time provide an opportunity to obtain empirically based estimates of GPP. In this paper, using the results of CO2 flux tower measurements during the 1997 season at four sites in Oklahoma (tallgrass prairie, mixed prairie, pasture, and winter wheat crop), we describe a method to evaluate the average daytime rate of ecosystem respiration (Rd) by estimation of the respiration term of the nonrectangular hyperbolic model of the ecosystem-scale light-response curve. Comparison of these predicted daytime respiration rates with directly measured corresponding nighttime values (Rn) after appropriate length of the night and temperature correction, demonstrated a closed linear relationship, with R**2 ranging from 0.82 to 0.98 for weekly averaged fluxes. Daily gross primary productivity (Pg) can be calculated as Pg = Pd + Rd, where Pd is the daytime integral of the net ecosystem CO2 exchange obtained directly from measurements. Annual GPP for the sites, obtained as the sum of Pg over the whole period with Pg >0 were: tallgrass prairie, 5223 g CO2 m**2; winter wheat, 2853 g CO2 m**2; mixed prairie, 3037 g CO2 m**2; pasture, 2333 g CO2 m**2. These values are in agreement with published GPP estimates for non-forest terrestrial ecosystems.