Response of Photosynthetic Traits and Ion Balance to Salinity Stress in Saplings of Various Cunninghamia lanceolata Cultigens

This study investigated the response of photosynthetic traits and ion balance to salinity stress in saplings of five Cunninghamia lanceolata cultigens. Under high salinity (200 mM NaCl), the salt-tolerant cultigens ‘E Sha1’ and ‘Youshan’ maintained relatively higher chlorophyll content, photosynthesis rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), and water use efficiency (WUE), with reductions ranging from 15.3 to 30.4%. In contrast, the salt-sensitive cultigens ‘Mollifolia’ and ‘Glouca’ exhibited reductions in photosynthetic traits ranging from 28.6 to 58.1%. The salt-tolerant cultigens also maintained better ion homeostasis, with lower Na⁺ accumulation (3.2 to 3.5-fold increase) and higher K⁺, Ca²⁺, and Mg²⁺ levels (22.4 to 28.3% reduction) compared to the salt-sensitive cultigens. Correlation analysis revealed significant relationships between photosynthetic traits and ion balance parameters, suggesting their interdependence in mediating salt tolerance in C. lanceolata.