Physiological response of selected ornamental shrubs under salinity stress

Salinity stress significantly affects plant growth, development and ornamental value, especially in coastal and peri-urban landscaping. This study evaluated the physiological and biochemical responses of four ornamental shrubs, Eranthemum pulchellum Andrews, Leucophyllum frutescens (Berland.) I.M.Johnst., Acalypha wilkesiana Müll.Arg. and Tabernaemontana divaricata (L.) R.Br. ex-Roem. & Schult. under varying levels of salinity (0, 20, 40 and 60 dS m-1) using sodium chloride (NaCl) and calcium chloride (CaCl2) in a 7 : 3 ratio under open-field conditions. Salinity significantly affected physiological and biochemical traits except leaf pH. Increasing salinity caused progressive reductions in chlorophyll a (Chl-a), chlorophyll b (Chl-b), total chlorophyll content, chlorophyll stability index (CSI), membrane stability index (MSI) and relative water content (RWC), while leaf electrical conductivity (EC) and total phenolic content (TPC) increased. Among the evaluated shrubs, L. frutescens exhibited superior salinity tolerance, maintaining total chlorophyll (0.16 mg g-1 FW), CSI (43.58 %), MSI (9.10 %) and RWC (58.64 %) at 60 dS m-1. In contrast, T. divaricata was highly susceptible, recording 96 % reduction in total chlorophyll and MSI and a 57 % reduction in RWC at 60 dS m-1. Eranthemum pulchellum and A. wilkesiana showed moderate physiological stability up to 20 dS m-1, indicating mild salinity tolerance, but exhibited substantial declines at higher salinity levels. Total phenolic content increased with salinity, reaching 1.89 mg GAE g-1 FW in P2 at 60 dS m-1, indicating enhanced antioxidant defence. Principal component analysis (PCA) revealed that the first three components explained 92.73 % of the total variation, with chlorophyll content, membrane stability and water status contributing most strongly to salinity tolerance. The study identifies L. frutescens as a highly salt-tolerant ornamental shrub suitable for coastal landscaping.