Differential Stomatal Response Between C₃ and C₄ Species to Atmospheric CO₂ Concentration and Light¹

Abstract

Transpiration measurements were made on attached leaves of potted plants or on excised leaves of native plants of three C 3 species—wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L.), and dandelion ( Taraxacum officinale L.) — and three C 4 species — maize ( Zea mays L.), green foxtail ( Setaria viridis L.), and pigweed ( Amarranthus retroflexus L.) — in different CO 2 concentrations and light intensities. The experiments were begun with leaves in CO 2 ‐free air in light (0.4 cal cm −2 min −1 , 400–700 nm) to open the stomata. Stomata of C 3 species were less prone to closure than were stomata of C 4 species as the light intensity was decreased or as the CO 2 concentration was increased. The greater water use efficiency of C 4 species may be due in part to the better control of water loss because the stomata are more responsive to environmental changes than are the stomata of C 3 species.