Effects of salt stress on physiological and biochemical characteristics as well as leaf and stem anatomical structures of seedlings from different varieties of Elaeagnus moorcroftii

【Objective】Soil salinization is a critical environmental factor limiting the sustainable development of agriculture and forestry worldwide. High salinity induces osmotic stress, ion toxicity, and oxidative damage in plants, leading to growth inhibition, metabolic disorders, and even mortality. Elaeagnus moorcroftii, a perennial tree species of the Elaeagnaceae family, exhibits strong tolerance to drought, salt, and wind erosion, making it a valuable species for vegetation restoration in arid and semiarid regions of Northwest China. While previous studies have explored its salt tolerance at the species level, systematic comparisons of salt tolerance among different varieties, integrating both physiological and anatomical responses, remain scarce. This study aims to evaluate the salt tolerance of six major cultivated varieties of E. moorcroftii by analyzing their physiological, biochemical, and anatomical responses under salt stress, thereby providing a theoretical basis for the selection and breeding of salt-tolerant genotypes and their application in saline- alkali land restoration.【Methods】One- year- old seedlings of six E. moorcroftii varieties (Jinsha, Bachu No. 1, Baishatian, Maigaiti No. 3, Celedahuang and Yafeng) were selected for the experiment. The seedlings were subjected to a gradual salt stress treatment using 500 mmol·L-1 NaCl solution, with the concentration incrementally increased every two days until a total of 2000 mL was applied. Soil electrical conductivity was monitored to maintain a target salinity level of 0.4% ± 0.1%. Control groups were irrigated with an equivalent volume of deionized water. Physiological and biochemical indicators, including malondialdehyde (MDA), soluble sugar (SS), soluble protein (SP), proline (Pro), superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), were measured at 0, 5, 10, 15, 20, 25, and 30 days after stress initiation. Leaf and stem anatomical structures were examined after 25 days of stress using paraffin sectioning and microscopic imaging. Data were analyzed using SPSS 26.0 for ANOVA and Duncan’s multiple range tests, and principal component analysis (PCA) was performed to comprehensively evaluate salt tolerance.【Results】Under salt stress, the contents of MDA and SS increased continuously across all varieties, indicating progressive membrane lipid peroxidation and osmotic adjustment. SP content and the activities of SOD and CAT showed an initial increase, followed by a decline, suggesting an early activation of defense mechanisms that weakened under prolonged stress. The proline (Pro) content showed a dynamic change of first increasing and then decreasing, with the most significant accumulation occurring at the 25th day. POD activity increased consistently throughout the stress period, highlighting its role in long- term oxidative stress mitigation. Anatomical observations revealed variety- specific structural adaptations. Yafeng exhibited well-developed palisade tissue, tightly arranged mesophyll cells, and robust xylem development. Baishatian showed a thickened lower epidermal cell wall and a wider vascular cambium. In contrast, Celedahuang had loose mesophyll tissue and underdeveloped vascular bundles. Leaf thickness and main vein thickness were significantly affected by salt stress, while upper and lower epidermal thickness remained largely unchanged. Stem anatomy also showed notable changes, with Yafeng displaying enhanced xylem and vascular bundle development, whereas Jinsha showed reductions in these traits. Principal component analysis identified SP, MDA, and SOD as the key indicators for salt tolerance evaluation. The first three principal components accounted for 84.98% of the total variance. Based on comprehensive scores derived from PCA, the salt tolerance of the six varieties was ranked as follows: Yafeng＞Baishatian＞Maigaiti No. 3＞Bachu No. 1＞Celedahuang＞Jinsha.【Conclusion】This study demonstrates that salt tolerance in E. moorcroftii is variety-specific and involves coordinated physiological, biochemical, and anatomical adaptations. The more salt- tolerant varieties, such as Yafeng and Baishatian, exhibited efficient osmotic regulation, strong antioxidant enzyme activity, and favorable anatomical traits such as dense mesophyll tissue, thickened epidermal layers, and well-developed vascular systems. In contrast, sensitive varieties like Jinsha showed weaker regulatory capacity and structural integrity under stress. The key indicators SP, MDA, and SOD effectively reflect the osmotic adjustment, membrane stability, and antioxidant capacity of the plants under salt stress. These findings provide a scientific basis for the selection and breeding of salt-tolerant E. moorcroftii varieties and support their use in the ecological restoration of saline-alkali lands.