Stomatal responses of five woody angiospasms to light intensity and humidity

Abstract

Stomatal responses to changes in light intensity and humidity were studied in green and chlorotic Fraxinus americana, Acer saccharum, Quercus macrocarpa, Citrus mitis, and Cercis canadensis seedlings. Stomatal closure occurred at higher light intensities in Acer than in other species. Transpiration was greater in Fraxinus and Quercus than in Citrus, Acer, or Cercis. Stomata opened faster than they closed in Fraxinus and Quercus and they closed faster than they opened in Citrus. Opening and closing rates were not significantly different from each other in Acer and Cercis. Stomata opened and closed faster in green than in chlorotic plants. In green plants, after a decrease in light intensity, species time to equilibrium of stomatal aperture was related as follows: Citrus < Acer < Quercus = Cercis < Fraxinus; and in chlorotic plants: Citrus < Acer = Quercus = Cercis < Fraxinus. After an increase in light intensity, stomatal opening time in green plants was related as follows: Citrus = Acer < Quercus < Cercis = Fraxinus. Stomatal opening in chlorotic plants was faster in Acer than in the other species, where stomata opened to equilibrium in about the same time. With changes in humidity from 20% to 80%, and the reverse, stomata of Fraxinus and Acer opened faster than they closed. Stomatal response to humidity was faster in Acer than in Fraxinus. Stomatal resistance was affected more by humidity changes at low light intensity (6500 lux) than at high intensity (32 000 lux). Postillumination CO2 bursts from leaves occurred in all species and were greater in green than in chlorotic plants. In both green and chlorotic plants, CO2 bursts varied as follows: Citrus > Quercus = Cercis > Fraxinus = Acer. Physiological responses of stomata are discussed in relation to leaf anatomy and metabolism.