Identifying Plant Healthy Indicators of Five Tropical Perennials Using Certain Leaf Physiological Traits During Drought Stress and Re-Watering

Perennials improve soil strength and stabilize the slope. However, they are very prone to drought stress (DS). To identify plant health indicators, this study investigated the responses of five tropical perennials commonly grown in Singapore’s slope to DS and re-watering (RW) in the greenhouse. The durations for mild, intermediate, and severe DS defined as T1, T2, and T3, respectively, before RW were based on the extents of reduced Fv/Fm ratio (maximal quantum efficiency of PSII) and the levels of wilting. After RW, soil water content (SWC) increased until field capacity in all DS soil, although they were significantly lower than in well-watered (WW) soil. Overall, the Fv/Fm ratios and leaf water content (LWC) decreased significantly in all DS plants compared to those of WW plants, but all increased to the similar level as WW plants after RW. Nitrogen deficiency did not occur in any plants during DS. There were clear positive correlations of SWC with Fv/Fm ratios, LWC, effective quantum yield of PSII (∆F/Fm’), electron transport rate (ETR), and photochemical quenching (qP) for all species. To monitor plant health, it would recommend using both non-destructive measurements such as SWC and Fv/Fm ratios and destructive parameters like LWC, ∆F/Fm’, ETR, and qP.