Diurnal CO2 profiles from a Zea mays L. canopy

Observations of CO2 fluxes from corn (Zea mays L.) canopies have been used to estimate the total carbon fixed during a growing season. Comparisons of carbon fixation from an open path infrared gas analyzer (IRGA) and periodic biomass and end of season yield sampling revealed an underestimate of the carbon fixed as measured by the IRGA. It has been speculated that this underestimate is due to the contribution to photosynthesis of CO2 from the soil respiration that is not detected by the IRGA located above the canopy. To determine if this is the case, CO2 profiles were monitored in a corn canopy, during the summer of 2003. Profile sampling included intakes at 5 cm above the soil surface, mid-canopy height, and the height of the IRGA above the canopy (10 m). The day light profile information from the corn canopy showed the lowest CO2 concentrations at the mid-canopy height, followed by the 5 cm height, with the highest concentrations at the IRGA height. Night profiles showed the highest concentrations at the 5 cm level, followed by the mid-canopy height, and the lowest concentrations at the IRGA level. This work will report on the canopy profiles differences observed at different times of the day, and under different atmospheric forcing conditions.