Differential ROS Accumulation, Antioxidant Defense, and Physiological Adaptation in Two Rosa rugosa Cultivars Under Sustained Salt Stress

Salt stress is a major abiotic constraint that limits plant growth by inducing oxidative stress, disrupting photosynthetic processes, and damaging cellular membranes. Although Rosa rugosa is considered relatively tolerant to adverse environments, differences in antioxidant defense and physiological responses among its cultivars under sustained salt stress remain insufficiently understood. Comparative evaluation of these responses is important for identifying salt-tolerant germplasm and understanding stress-adaptation mechanisms. In this study, two R. rugosa cultivars, Siji and Fenghua, were subjected to irrigation treatments with solutions containing 0, 50, 100, or 150 mM NaCl for 28 days under controlled conditions. Morphological traits, salt injury, photosynthetic pigments, osmolytes, ROS accumulation, antioxidant enzyme activities, and lipid peroxidation were measured to assess cultivar-specific differences in salt-stress responses. Salt stress caused concentration-dependent growth inhibition, increased salt injury, and reduced chlorophyll content, while oxidative-stress responses differed between the two cultivars, with stronger adverse effects observed in Fenghua. Siji maintained better growth performance, higher fresh and dry mass of sampled leaves, greater chlorophyll retention, better maintenance of several osmolytes, and stronger antioxidant enzyme activities under the higher NaCl treatments. In contrast, Fenghua showed greater ROS accumulation and higher MDA under the higher NaCl treatments, which are consistent with greater oxidative stress and membrane lipid peroxidation. Exploratory correlation and principal component analyses further showed that antioxidant defense, osmotic adjustment, chlorophyll retention, and reduced oxidative damage were closely associated with salt tolerance in Siji. These results indicate that greater antioxidant capacity, osmotic adjustment, and membrane protection were associated with the superior salt-stress performance of ‘Siji’ compared with ‘Fenghua’. The study identifies Siji as a promising R. rugosa candidate for further salt-tolerance evaluation and provides useful physiological and biochemical indicators for salt-tolerance screening in ornamental rose breeding.