Effect of potassium on drought resistance of Hibiscus rosa-sinensis cv. Leprechaun:: Plant growth, leaf macro- and micronutrient content and root longevity

As competition for the limited water supply available for irrigation of horticultural crops increases, research into crop management practices that enhance drought resistance, plant water-use efficiency and plant growth when water supply is limited has become increasingly essential. This experiment was conducted to determine the effect of potassium (K) nutritional status on the drought resistance of Hibiscus rosa-sinensis L. cv. Leprechaun (Hibiscus). All the treatments were fertilized with Hoagland's nutrient solution, modified to supply K as K2SO4, at 0 mM K (K-0), 2.5 mM K (K-2.5), and 10 mM K (K-10), under two irrigation regimes (drought stressed [DS] and non-drought stressed [non-DS]). Regular irrigation and fertigation were adopted for 54 days, and drought stress treatment (initiated on day 55) lasted for 21 days; while non-DS control plants continued to receive regular irrigation and fertigation. Following the 21-day drought stress period, plants were labeled with Rb-86(+) to determine the percentage of post-drought stress live roots. Both K deficiency (K-0) and drought stress reduced shoot growth, but drought stress increased root growth and thus the root:shoot ratio. At K-0, plants were K-deficient and had the lowest leaf K, Fe, Mn, Zn, Cu, B, Mo and Al, and highest Ca concentrations. Although the percentage of live roots was decreased by drought stress, K-2.5 and K-10 plants (with similar percent live roots) had greater root survival ratio after drought treatment than the K-deficient plants. These observations indicate that adequate K nutrition can improve drought resistance and root longevity in Hibiscus rosa-sinensis.