Cotton stomatal closure under varying temperature and vapor pressure deficit, correlation with the hydraulic conductance trait

Background Cotton (Gossypium hirsutum L.) is often grown in locations characterized by high atmospheric evaporative demand. It has been hypothesized that plants which resist hydraulic flow under this condition will limit water use and conserve soil water. Therefore, in a series of controlled environment experiments ten cotton cultivars were exposed to two different temperature and vapor pressure deficit (VPD) conditions (i.e., 38 degrees C, > 3 kPa and 32 degrees C, 1 similar to 1.5 kPa) as well as a progressive soil drying. Then, individual differences in shoot hydraulic conductance (K-shoot) was measured using a hydraulic conductance flow meter (HCFM). Physiological parameters were reported included leaf area, dry leaf weight, stomatal conductance (g(s)), and water use efficiency coefficient (WUEk). Results Differences were observed in K-shoot among cultivars under the 38 degrees C, > 3 kPa but not the 32 degrees C, 1 similar to 1.5 kPa environment. Under the 38 degrees C, > 3 kPa environment, correlations were found between K-shoot, stomatal conductance (g(s)), VPD breakpoint, WUEk, total leaf area, dry leaf weight, fraction transpirable soil water (FTSW) threshold, and slope of TR decline after FTSW threshold. Conclusion Results show that the ability of some cotton cultivars to restrict water loss under high evaporative demand through early stomatal closure is associated with the cultivars' K-shoot. The K-shoot is influential in the limitation of TR trait under high temperature and VPD.