Spatiotemporal variations in growing season exchanges of CO2, H2O,and sensible heat in agricultural fields of the Southern GreatPlains Page: 2 of 35
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Interannual and Landuse Variations in SGP
2 Climate, vegetation cover, and management create fine-scale heterogeneity in unirrigated
3 agricultural regions, with important but not well-quantified consequences for spatial and
4 temporal variations in surface CO2, water, and heat fluxes. We measured eddy covariance fluxes
5 in seven agricultural fields- comprising winter wheat, pasture, and sorghum in the U.S.
6 Southern Great Plains (SGP) during the 2001-2003 growing seasons. Land-cover was the
7 dominant source of variation in surface fluxes, with 50-100% differences between fields planted
8 in winter-spring versus fields planted in summer. Interannual variation was driven mainly by
9 precipitation, which varied more than two-fold between years. Peak aboveground biomass and
10 growing-season net ecosystem exchange (NEE) of CO2 increased in rough proportion to
11 precipitation. Based on a partitioning of gross fluxes with a regression model, ecosystem
12 respiration increased linearly with gross primary production, but with an offset that increased
13 near the time of seed production. Because the regression model was designed for well-watered
14 periods, it successfully retrieved NEE and ecosystem parameters during the peak growing
15 season, and identified periods of moisture limitation during the summer. In summary, the effects
16 of crop type, land management, and water limitation on carbon, water, and energy fluxes were
17 large. Capturing the controlling factors in landscape scale models will be necessary to estimate
18 the ecological feedbacks to climate and other environmental impacts associated with changing
19 human needs for agricultural production of food, fiber, and energy.
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Fischer, Marc L.; Billesbach, David P.; Berry, Joseph A.; Riley,William J. & Torn, Margaret S. Spatiotemporal variations in growing season exchanges of CO2, H2O,and sensible heat in agricultural fields of the Southern GreatPlains, article, June 13, 2007; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc899787/m1/2/: accessed October 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.