Growth and Eco-Physiological Performance of Cotton Under Water Stress Conditions

A cotton cultivar Xinluzao 8 was grown under four levels of water stress treatments (normal irrigation, slight, mild and severe water stress) from the initial reproductive growth stage in Shihezi, Xinjiang, China, in 2002, to evaluate the growth and eco-physiological performances. Under water stress conditions, the transpiration ability decreased while the leaf temperature increased. Although the relative leaf water content decreased as water stress increased, the differences among the treatments were small, indicating that cotton has high ability in maintaining water in leaf. The stomatal density increased as water stress increased, while the maximum stomatal aperture reduced only in the severest stressed plants. The time of the maximum stomatal aperture was delayed in the mild and severe stressed plants. When severe stress occurred, the stomata were kept open until the transpiration decreased to nearly zero, suggesting that the stomata might not be the main factor in adjusting transpiration in cotton. Cotton plant has high adaptation ability to water stress conditions because of decrease in both stomatal conductance and hydraulic conductance from soil-to-leaf pathway. The actual quantum yield of photosystem II (PS II) decreased under water stress conditions, while the maximum quantum yield of PS II did not vary among treatments, suggesting that PS II would not be damaged by water stress. The total dry weight reduced as water stress increased.