Jerry L. Hatfield and John Prueger. National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011-4420
Carbon and water exchanges above the canopy surface reveal the dynamics of the processes that govern the fluxes between the plant and the atmosphere. There are fluxes that occur within the canopy volume that provide insights into the dynamics of the plant-atmosphere coupling. However, there is little information collected on the carbon and water fluxes within canopies that help refine our understanding of these fluxes. We have developed a system to measure the CO2 and H2O vapor fluxes at multiple levels within the canopy and these systems are deployed throughout the growing season to capture the dynamics as the canopy develops and then senesces. These data have been collected within corn and soybean canopies in a production field in central Iowa as a complement to energy balance and gas flux measurements since 2003. When the canopies are small the coupling between the canopy and atmosphere is dominated by the eddy diffusivity; however, as the canopies begin to increase in leaf area and become more developed, the within canopy volume fluxes are dominated more by light penetration patterns than be eddy diffusivity. Gradient profiles of CO2 and H2O vapor within the canopy change throughout the day in fully developed canopies in response to energy availability. The implications of these findings reveal that within canopy fluxes provide insights into how canopies respond to changing C and H2O conditions and will help in development of management systems that increase C and H2O use efficiencies.