Submitted to: Agriculture Forest Meteorology
Publication Type: Abstract Only
Publication Acceptance Date: 5/24/2002
Publication Date: 5/24/2004
Citation: Hatfield, J.L., Prueger, J.H. 2004. Seasonal interactions between carbon dioxide and water vapor flux in corn canopies [abstract]. Agriculture Forest Meteorology. American Meterology Society. p. 168-169.
Technical Abstract: Transpiration of water vapor from plant leavers into the atmosphere is critical for cooling leaves. Water vapor transfer to the atmosphere occurs through the stomata and these pores provide for the entry of carbon dioxide into the leaf. Until recent advances in measurement methods it has been impossible to develop season-long measurements of both of these gases above and within plant canopies. Microclimatic measurements consisted of net radiation, soil heat flux, soil temperature, water vapor, air temperature, windspeed, and surface temperature. Net radiation was measured at 2 m above the canopy, soil heat flux at 0.1 m below the soil surface at three positions, and soil temperature at depths of 0.01, 0.02, 0.05, 0.1, 0.2 and 0.5 m. Windspeed was measured at 0.5 and 1.25 m above the canopy along with air temperature from a shielded, aspirated Visalia humidity probe. CO2 and H2O vapor fluxes were measured at eight positions within the canopy using a multi-port LI6262 system. There was a large change in CO2 concentrations throughout the day with the highest concentration at 0600 and decreasing rapidly as sunlight began to penetrate the canopy. We observed that the profiles of both CO2 and H2O vapor changed dramatically during the day. Water vapor increased as the CO2 decreased during the day. During the nighttime the CO2 concentrations increased due to canopy and soil respiration and concentrations at the 0.5 to 1.5 m interval exceeded 700 ppm just prior to sunrise. During the early morning hours there were a wide range of shapes of the CO2 and H2O vapor profiles. Over a four-hour period there was a 50 ppm decrease in CO2 concentration and an increase of 7 mg m-2 hr-1 in H2O vapor. Combining CO2 and H2O vapor profiles provides insights into the dynamics of crop response to environmental conditions.