Interaction of Nitrogen and Water Deficits on Stomatal Behavior in Cotton

Abstract

Stomata of normal and mildly N-deficient cotton plants (Gossypium hirsutum L.) reacted very differently to water stress. In N-deficient plants, stomata closed at water potentials up to 10 bars higher than in normal plants. Data presented here show: 1) stomata of both normal and N-deficient plants responded little to intercellular CO₂ concentrations (C_i) before the imposition of drought; 2) during drought, stomata became sensitive to C-_i, closing at elevated concentrations; 3) stomata of N-deficient plants began to respond to C-_i at a higher water potential than those of normal plants; 4) sensitivity to C_i was also induced by application of abscisic acid (ABA). The results strongly imply that in N-deficient plants, ABA was synthesized at higher water potentials than in normal plants.

Although the upper leaves of the plants did not visibly senesce during drought, the lower leaves rapidly yellowed and abscised. This process also occurred at higher water potentials in N-deficient plants than in normal plants. The responses to water stress of both stomatal behavior and leaf area adjustment (leaf abscission) indicate that N-deficiency promotes a “water-saving” type of drought avoidance.