Water Relations of Cotton Plants under Nitrogen Deficiency

Nitrogen deficiency in cotton plants (Gossypium hirsutum L.) considerably increased the sensitivity of stomata to water stress. At air temperatures of 27, 35, and >/=40 C, threshold potentials for complete stomatal closure were -10, -15, and -26 bars in N-deficient plants and -20, -20, and -30 bars in high-N plants, respectively. This three-way interaction among N supply, water potential, and air temperature was similar to that exerted on leaf expansion. The effects of N supply on stomatal behavior could not be explained on the basis of either osmotic or structural considerations. Rather, effects of N deficiency on mesophyll and stomata were independent and divergent. Stomatal behavior may impart a stress avoidance type of drought resistance to N-deficient plants.