Comparative Study Reveals Key Morphological, Physiological, and Biochemical Mechanisms of Drought Tolerance in Lespedeza davurica

Drought poses a significant threat to plant growth in arid and semi-arid grasslands. Lespedeza davurica (Laxm.) Schindl. exhibits higher drought tolerance than other Lespedeza species, and understanding its unique morphological and physiological mechanisms is important for the sustainable development of grassland ecosystems. To address this, a pot experiment was conducted to compare the responses of L. davurica and three other Lespedeza species (L. bicolor, L. cuneata, and L. formosa) under drought and rewatering conditions. Results demonstrated that L. davurica exhibited minimal biomass reduction, a significant decline in specific leaf area, and an elevated root-shoot ratio under drought stress. It showed higher PSII reaction center open parameter (qL), water use efficiency (WUE), and non-photochemical quenching (NPQ) than the other three species under drought stress. Under drought stress, its chlorophyll a to chlorophyll b ratio increased by 11.7–14.0%. It also maintained elevated maximal photochemical efficiency (Fv/Fm), effective quantum yield of PSII (Y(II)), and net photosynthetic rate (Pn) levels than the other three species under drought stress, and demonstrated more rapid recovery following rewatering. Furthermore, L. davurica exhibited sustained higher activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) under drought stress. The increased leaf thickness, higher capacity to sustain heightened stomatal limitation on photosynthesis, elevated NPQ and chlorophyll a to chlorophyll b ratio contribute to maintaining high photosynthetic activity of L. davurica under drought stress. Thus, the ability to maintain high photosynthetic activity, strong antioxidant capacity, and rapid recovery after rewatering are key mechanisms underlying the strong drought tolerance of L. davurica.