Physiological Responses and Salt Tolerance Evaluation of Purple-Leaf Berberis (Berberis thunbergii var. Atropurpurea) and Glacier Red-Leaf Berberis (Berberis thunbergii) Under NaCl Stress

Abstract

This study investigated the impact of various concentrations of NaCl stress treatment (0%, 0.1%, 0.2%, 0.3%, 0.4%) on the growth of one-year-old saplings of purple leaf barberry and glacier red leaf barberry. It also examined the impact on various physiological responses including plasma membrane permeability, antioxidant protective enzyme system, osmotic regulatory substance content, photosynthetic characteristics, ion content, and the ultrastructure of leaf cells using transmission electron microscopy. The goal was to determine the salt tolerance threshold and elucidate the physiological response mechanism to NaCl stress. The comprehensive assessment of salt tolerance in the two barberries was done using fuzzy membership functions. The results demonstrated that increasing concentrations of NaCl stress and longer treatment durations led to gradual decreases in sapling growth and increases in salt damage index. The salt tolerance thresholds were calculated to be 0.37% for purple leaf barberry and 0.33% for glacier red leaf barberry using the logistic curve equation. The activities of SOD and POD initially increased and then decreased in both barberries. Furthermore, MDA, free proline, and Na+ content gradually increased, while soluble protein content, chlorophyll content, net photosynthetic rate (Pn), K+ content, and K+/Na+ ratio gradually decreased. The purple leaf barberry displayed larger and deformed chloroplasts with significant separation of quality and wall, whereas the glacier red leaf barberry experienced a gradual decrease in chloroplast size and number until degradation. The membership function analysis revealed that purple leaf barberry exhibited superior resistance compared to glacier red leaf barberry.