Photosynthetic Traits and Ion Homeostasis under Salt Stress in Seedlings of Different Artemisia selengensis Cultivars

Soil salinization poses a severe threat to the cultivation of Artemisia selengensis, a valuable medicinal and edible crop. This study elucidates the physiological and biochemical mechanisms underlying salinity tolerance by comparing three cultivars, namely ‘Chutian’, ‘Xiangli No.1’, and ‘Yunnan’, exposed to a NaCl gradient of 0 to 200 mM for 28 days. Phenotypic analyses classified ‘Chutian’ as highly salt-tolerant and ‘Yunnan’ as sensitive; under 200 mM NaCl (relative to the 0 mM control), ‘Chutian’ exhibited a total dry weight (total DW) reduction of 42.1%, compared to a 79.2% reduction in ‘Yunnan’. While stomatal closure initially limited photosynthesis in all cultivars, ‘Chutian’ uniquely preserved the integrity of its photosynthetic apparatus under severe stress, maintaining a maximum quantum yield (Fv/Fm) of 0.78 versus 0.65 in the photoinhibited ‘Yunnan’. This resilience was underpinned by superior ion regulation: ‘Chutian’ effectively restricted shoot Na+ accumulation to 53.4 mg/g DW (compared to 85.6 mg/g DW in ‘Yunnan’) and upheld a shoot K+/Na+ ratio of 0.62, more than 3-fold higher than that of the sensitive cultivar. Additionally, the tolerant cultivar deployed a robust cytoprotective strategy, evidenced by a 12-fold increase in proline for osmotic adjustment and sustained upregulation of SOD, POD, and CAT activities. Consequently, ‘Chutian’ suffered significantly lower oxidative damage, with lipid peroxidation (MDA) increasing only 1.8-fold compared to a 3.5-fold surge in ‘Yunnan’. These findings underscore the critical synergy between sodium exclusion and antioxidant defense in adaptation to salinity.