Physiological response mechanism of Hemsl under drought stress and rewatering.

Drought stress is a predominant environmental challenge that significantly limits plant growth and survival, particularly affecting agricultural productivity and ecological stability in arid and semi-arid regions. This study aimed to elucidate the physiological responses of one-year-old Hemsl seedlings to various degrees of drought stress, thereby aiding their cultivation and application in challenging environments. To simulate real-world drought conditions, four levels of drought stress were defined based on soil moisture content: control (80% soil moisture), mild drought (LD, 50-60% soil moisture), moderate drought (MD, 40-50% soil moisture), and severe drought (SD, 20-30% soil moisture). These thresholds were selected to represent a gradient from optimal water availability to extreme water scarcity, reflecting conditions commonly encountered in drought-prone regions. The results revealed that drought stress profoundly inhibited growth, primarily affecting plant height and reducing the number and length of new shoots. Notably, leaves under moderate and SD conditions demonstrated significant wilting and subsequent death. Photosynthetic pigment content and photosynthesis-related parameters initially increased but subsequently experienced a sharp decline as drought stress persisted. Biochemical analyses indicated elevated levels of relative conductivity and malondialdehyde, indicating extensive cell membrane damage. In the meanwhile, the activities of key antioxidant enzymes (superoxide dismutase, peroxidase, and ascorbate peroxidase) increased, alongside higher accumulations of soluble sugars, soluble protein, and proline, albeit with a sluggish recovery observed under severe stress conditions. Anatomical studies highlighted the thickening of both the upper and lower epidermis, as well as a reduction in the density of palisade and spongy tissues. Recovery following rewatering was more effective under LD and MD conditions than under SD stress, indicating that possesses strong drought tolerance but is not suitable for highly arid regions. This study elucidates the adaptive mechanisms of under drought stress and provides practical guidance for its management and cultivation in drought-prone areas, enhancing its ecological and economic viability.