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 hor ticultural crops increases, research into crop management practices that en hance 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 o n the drought resistance of Hibiscus rosa-sinensis L. cv. Leprechaun (Hibis cus). 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 m M K (K-10), under two irrigation regimes (drought stressed [DS] and non-dro ught stressed [non-DS]). Regular irrigation and fertigation were adopted fo r 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 la beled with Rb-86(+) to determine the percentage of post-drought stress live roots. Both K deficiency (K-0) and drought stress reduced shoot growth, bu t 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 roo ts was decreased by drought stress, K-2.5 and K-10 plants (with similar per cent live roots) had greater root survival ratio after drought treatment th an the K-deficient plants. These observations indicate that adequate K nutr ition can improve drought resistance and root longevity in Hibiscus rosa-si nensis.