Responses of Calligonum leucocladum to Prolonged Drought Stress Through Antioxidant System Activation, Soluble Sugar Accumulation, and Maintaining Photosynthetic Homeostasis

Desert shrubs play an important role in the stability of arid and fragile desert ecosystems. However, despite their significant ecological importance, limited research has been performed on shrub drought tolerance strategies at the morphological, physiological, and molecular levels. Therefore, this study focused on the typical desert shrub, <i>Calligonum leucocladum</i>, and analyzed its morphology, physiology, and protein expression under two different habitats: moist low-salt and arid low-salt. The results indicate that drought stress inhibited the growth of <i>C. leucocladum</i>, leading to significant reductions in its plant height, base diameter, and crown width by 14.93%, 49.57%, and 48.49%, respectively. Drought stress triggered a 30% decline in stomatal conductance, whereas homeostasis was observed in net photosynthesis, intercellular CO₂, and transpiration. The soluble sugar content significantly increased by 13.43%, while the starch, soluble protein, and proline content significantly decreased by 20.32%, 10.67%, and 55.61%, respectively. In addition, under drought stress, membrane peroxidation products, reactive oxygen species metabolites, and antioxidant enzyme activities significantly increased. Weighted gene co-expression network analysis revealed 40 proteins that were significantly enriched in the photosynthesis and oxidative phosphorylation pathways through KEGG enrichment analysis. In addition, <i>C. leucocladum</i> maintains photosynthetic homeostasis by enhancing PSII repair (PsbE, PsbL, PsbH) and electron transfer chain efficiency (PetD, nad 2, nad 9), thereby compensating for the insufficient carbon dioxide supply caused by stomatal limitation. This study integrated multidimensional data from morphology, physiology, and proteomics to reveal that <i>C. leucocladum</i> drives a coupled network of photosynthesis, antioxidant, and carbon metabolism through chloroplast translation reprogramming. It maintains photosynthetic homeostasis and osmotic balance under a 30% decrease in stomatal conductance, elucidating the cross-scale regulatory strategy of desert shrubs adapting to extreme drought.