Stomatal Responses to Water Stress and Light in Plants Grown in Controlled Environments and in the Field 1

Experiments were performed to investigate the water relations of plants grown in controlled environments and in the field. Cotton ( Gossypium hirsutum cv. ‘McNair 511’) and soybeans ( Glycine max cv. ‘Ransom’), were grown from seed in pots in a phytotron growth chamber, an air‐conditioned greenhouse, and in a field plot. All plants were well‐watered but minimum midday water potentials were lower in field‐grown plants than in chamber‐ or greenhouse‐grown plants, and lower in cotton than in soybean. Predawn‐ (in the field and greenhouse) and “before lights on‐” (in the chamber) water potential (ψ) levels were consistently lower in cotton than in soybean. In both soybean and cotton, adaxial stomata were more sensitive than abaxial stomata to decreasing leaf water potential. Stomatal sensitivity to decreasing leaf water potential and leaf water content (RWC) was related follows: Chamber‐grown plants> greenhouse‐grown> plants> field‐grown plants. There were differences in the ψ/RWC relationships of the two species and in soybeaus, the ψ/RWC relationship differed between chamber‐ and field‐grown plants. Adaxial stomata of both species were considerably more sensitive to low light intensity than were abaxial stomata. In soybeans, both abaxial and adaxial stomata of chamber‐grown plants were more sensitive to low light intensity than were respective abaxial and adaxial stomata of greenhouse‐ or field‐grown plants. In cotton, stomata of chamber‐ and greenhousegrown plants behaved similarly and were considerably more sensitive to low light intensity than were stomata of field‐grown plants. The effect of plant growth conditions may not be uniform for all species. Considerable care should be exercised in making comparisons among species or varieties grown in the field or in different types of controlled environments.