<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="6.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Marc L. Fischer</style></author><author><style face="normal" font="default" size="100%">David P. Billesbach</style></author><author><style face="normal" font="default" size="100%">William J. Riley</style></author><author><style face="normal" font="default" size="100%">Joseph A. Berry</style></author><author><style face="normal" font="default" size="100%">Margaret S. Torn</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Spatiotemporal Variations in Growing Season Exchanges of CO2, H2O, and Sensible Heat in Agricultural Fields of the Southern Great Plains</style></title><secondary-title><style face="normal" font="default" size="100%">Earth Interactions</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">agriculture</style></keyword><keyword><style  face="normal" font="default" size="100%">carbon cycle</style></keyword><keyword><style  face="normal" font="default" size="100%">carbon dioxide</style></keyword><keyword><style  face="normal" font="default" size="100%">co2 flux</style></keyword><keyword><style  face="normal" font="default" size="100%">land use</style></keyword><keyword><style  face="normal" font="default" size="100%">southern great plains</style></keyword><keyword><style  face="normal" font="default" size="100%">spatial scaling</style></keyword><keyword><style  face="normal" font="default" size="100%">wheat</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2007</style></year></dates><volume><style face="normal" font="default" size="100%">11</style></volume><pages><style face="normal" font="default" size="100%">1-21</style></pages><abstract><style face="normal" font="default" size="100%">&lt;p&gt;Climate, vegetation cover, and management create finescale heterogeneity  in unirrigated agricultural regions, with important but not  well-quantified consequences for spatial and temporal variations in  surface CO&lt;sub&gt;2&lt;/sub&gt;, water, and heat fluxes. Eddy covariance fluxes  were measured in seven agricultural fields—comprising winter wheat,  pasture, and sorghum—in the U.S. Southern Great Plains (SGP) during the  2001–03 growing seasons. Land cover was the dominant source of variation  in surface fluxes, with 50%–100% differences between fields planted in  winter–spring versus fields planted in summer. Interannual variation was  driven mainly by precipitation, which varied more than twofold between  years. Peak aboveground biomass and growing season net ecosystem  exchange (NEE) of CO&lt;sub&gt;2&lt;/sub&gt; increased in rough proportion to  precipitation. Based on a partitioning of gross fluxes with a regression  model, ecosystem respiration increased linearly with gross primary  production, but with an offset that increased near the time of seed  production. Because the regression model was designed for well-watered  periods, it successfully retrieved NEE and ecosystem parameters during  the peak growing season and identified periods of moisture limitation  during the summer. In summary, the effects of crop type, land  management, and water limitation on carbon, water, and energy fluxes  were large. Capturing the controlling factors in landscape-scale models  will be necessary to estimate the ecological feedbacks to climate and  other environmental impacts associated with changing human needs for  agricultural production of food, fiber, and energy.&lt;/p&gt;</style></abstract></record></records></xml>