Estimating the Morphological and Physiological Plasticity of Ligustrum obtusifolium Seedlings in Response to Drought Stress and Subsequent Rewatering

Drought resistance and post drought recovery strategy and ability are important parameters to measure adaptation of plants to heterogeneous water environments; in addition, they are very important to study costs and benefits of plasticity. We compared the differences in multiple traits of Ligustrum obtusifolium seedlings under four water conditions, well-watered, light drought, moderate drought, and severe drought, for 30 days, as well as under rewatering conditions for 7, 14, and 21 days in the greenhouse. We observed increased levels of malondialdehyde content, antioxidant activity, and osmotic adjustment substances and significantly decreased stem height, leaf area, specific leaf area, aboveground biomass, total biomass, and chlorophyll content in response to drought stress. The root biomass and root–shoot ratio reached maximum values under moderate drought conditions. The seedlings subjected to light and moderate drought recorded physiological parameters that were similar to control levels after 21 days of rewatering. However, the seedlings under severe drought treatment did not show such recovery and only carotenoids content returned to the control levels. In conclusion, the extent of plants recovery after rewatering depends on drought stress severity and rewatering time. The early drought experience may not be harmful immediately, but it can induce active biochemical responses, to support morphological, biomass, and photosynthetic physiological traits responses under subsequent rewatering.