Physiological Responses and Tolerance Evaluation of Different Cupressus gigantea Populations under Drought Stress

Abstract

: The selection of drought-tolerant tree species is crucial for successful afforestation in the Tibetan Plateau of China. However, the drought tolerance of Cupressus gigantea , a rare and endangered native tree species, remains poorly understood. In this study, two-year-old seedlings from three natural populations of C. gigantea in the Tibetan Plateau, including Bayi District (BD), Milin County (MC), and Lang County (LC), were subjected to drought stress treatments under normal watering (control, CK), light drought (LD), moderate drought (MD), and severe drought (SD). We evaluated population-level differences in drought tolerance based on physiological and biochemical responses. The results showed that the LC population exhibited the strongest drought tolerance, which could maintain high instantaneous water-use efficiency (WUE), antioxidant enzyme activities, and greater accumulation of proline (Pro) and soluble sugars (SS). The MC population displayed intermediate drought tolerance, mainly through maintaining relatively high WUE, increasing SS accumulation, and Pro accumulation. Meanwhile, the BD population showed lower WUE and antioxidant enzyme activities under drought stress. Overall, drought tolerance varied significantly among the three populations, ranking with LC > MC > BD. The superior drought tolerance of the LC population provides valuable insights for the conservation and restoration of C. gigantea and suggests its potential suitability for future afforestation programs in the Tibetan Plateau.