Drought stress influences leaf water content, photosynthesis, and water-use efficiency of Hibiscus rosa-sinensis at three potassium concentrations

The influence of drought stress (DS) upon whole-plant water content, water relations, photosynthesis, and water-use efficiency of Hibiscus rosa-sinensis cv. Leprechaun (Hibiscus) plants at three levels of potassium (K) nutritional status were determined after a 21-d gradually imposed DS treatment. Compared to K-deficient plants, adequate K supply improved the leaf water content (LWC) and leaf water relations of Hibiscus by decreasing the Psi(pi), and generally sustained rates of net photosynthesis (P-N) and transpiration (E), and stomatal conductance (g(s)), both in DS and non-DS plants. In K-deficient Hibiscus, LWC, turgor potential (Psi(P)), and P-N, E, and g(s) as well as instantaneous water-use efficiency, WUE (P-N/E) were consistently lower, compared to K-sufficient plants. Carbon isotope discrimination (Delta) was lower (i.e. long-term WUE was greatest) in DS than non-DS plants, but K had no effect on A during the 21-d drought treatment period under glasshouse conditions. However, the trend in the A value of DS plants suggests that A could be a useful index of the response of Hibiscus to DS under glasshouse growing conditions. Thus the incorporation of a properly controlled fertilization regime involving sufficient levels of K can improve the acclimation of P-N to low Psi(leaf), increase P-N/E of Hibiscus, and may have potential benefit for other woody plants species.