Regulation of photosynthesis and water-use efficiency in pima and upland cotton species subjected to drought and recovery.

Photosynthesis is extremely sensitive to drought and decreases due to co-occurring stomatal, mesophyll, and biochemical limitations. Few studies have shown the effects of a drought cycle (drought-rewatering) on photosynthesis and water-use efficiency (WUE) in cotton. Here, the dynamics of photosynthesis in upland () and pima () cotton were analyzed during a drought cycle. While both species decreased net CO assimilation rate ( ) to a similar extent under drought, in pima cotton rewatering rapidly restored , the stomatal conductance ( ), the maximum carboxylation rate ( ), and the maximum electron transport rate above the control level. Meanwhile, the response of leaf intrinsic WUE (WUE) to drought and recovery was different between the two cotton species, which was mainly co-regulated by and . In conclusion, pima and upland cotton exhibit different response patterns of and WUE during the whole process of drought and recovery.