Photosynthetic Responses to CO2 and Light by Maize and Wheat Leaves Adjusted for Constant Stomatal Apertures1

Abstract

Previously we found that maize (Zea mays L.) leaf stomata were more responsive to changes in light intensity on CO2 concentration than were the stomata of wheat (Triticum aestivum L.). This study was undertaken to determine how the photosynthetic light and CO2 responses were affected by this differential stomatal sensitivity. Measurements of net photosynthesis and leaf diffusive resistances were made in various CO2 concentrations and light intensities on attached, mature leaves on 40‐ to 60‐ day‐old potted maize and wheat plants grown in a glasshouse. The data for each leaf were adjusted to a constant leaf diffusive resistance according to the diffusive equation for photosynthesis as given by Gaastra.The results showed that “apparent Km's” for CO2 response by whole maize leaves had large errors due to a changing leaf diffusive resistance as the CO2 concentration changed. The initial slope of the light response curves were greater for maize than for wheat when corrected for the changes in stomatal apertures caused by the treatment.