DIFFUSIVE RESISTANCE, TRANSPIRATION, AND PHOTOSYNTHESIS IN SINGLE LEAVES OF CORN AND SORGHUM IN RELATION TO LEAF WATER POTENTIAL

Growth chamber studies were conducted to determine the relationships between leaf water potential and diffusive resistance, transpiration rate, and photosynthesis in corn (Zea mays L.) and sorghum (Sorghum vulgare L.). Few differences were apparent between species in response to leaf water potentials above −8 to −6 bars at all light flux densities used. At lower potentials their ability to withstand water stress differed. Rapid increases in both total resistance to water vapor and mesophyll resistance to carbon dioxide within a narrow range of water potential were observed in corn with simultaneous decreases in transpiration and photosynthesis. More gradual changes occurred in sorghum, with little increase in mesophyll resistance except at the highest light flux density. Photosynthetic rate of sorghum was still 25% of maximum at −11.5 bars whereas corn was severely wilted and photosynthesis had ceased at a similar water potential.