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 (Gossypium hirsutum) and pima (G. barbadense) cotton were analyzed during a drought cycle. While both species decreased net CO2 assimilation rate (P-N) to a similar extent under drought, in pima cotton rewatering rapidly restored PN, the stomatal conductance (g(s)), the maximum carboxylation rate (V-cmax), and the maximum electron transport rate above the control level. Meanwhile, the response of leaf intrinsic WUE (WUEi) to drought and recovery was different between the two cotton species, which was mainly co-regulated by V-cmax and g(s). In conclusion, pima and upland cotton exhibit different response patterns of P-N and WUEi during the whole process of drought and recovery.