Objective This study explored the physiological and growth response mechanisms of Pinus thunbergii seedlings under combined salt and wind stress, aiming to provide theoretical support for screening stress-tolerant germplasm for coastal shelterbelt construction.

Method A systematic study was conducted by setting four NaCl concentrations: 0 mmol/L(T0), 50 mmol/L(T1), 100 mmol/L (T2), and 150 mmol/L (T3), along with three wind speed levels: level 0 (0.0−0.2 m/s, W1), level 3 (3.4−5.4 m/s, W2), level 5 (8.0−10.7 m/s, W3), which were applied to P. thunbergii seedlings for eight weeks. Physiological and growth indices associated with the three major systems: water metabolism, photosynthetic characteristics, and oxidative defense were measured at weeks 4 and 8. Pearson correlation analysis was used to reveal the pattern of association among the various indicators. SmartPLS 4.0 was employed to construct structural equation models to elucidate the pathways through which combined stress inhibited seedling growth.

Result (1) At week 4, relative to the control (T0W1), the combined stress (T3W3) significantly reduced RWC by 30.41%, which decreased G_s and C_i, and ultimately inhibited P_n. Photosynthetic carbon assimilation was simultaneously weakened, with F_v/F_m and Rubisco activity declining. SOD and POD activities first increased and then decreased, peaking under T2W2, which led to substantial accumulation of MDA and Pro. Leaf damage area expanded to 19.84%, while stem mechanical strength was enhanced by wind but reduced by salt stress. Ultimately, height and ground diameter decreased. (2) At week 8, stress effects intensified further. In the T3W3 treatment, RWC, P_n, G_s, and C_i, decreased by 16.62%, 42.77%, 36.75%, and 17.39%, respectively, compared with week 4. F_v/F_m and Rubisco activity decreased by 6.34% and 26.78%, respectively, while SOD and POD activities decreased by 10.06% and 12.54%, respectively, indicating a reduction in antioxidant system capacity. MDA content increased, reflecting a substantial exacerbation of membrane lipid peroxidation. Leaf damage area and stem mechanical strength reached 22.83% and 15.12 N, respectively, which suppressed height and ground diameter growth. (3) Correlation analysis revealed that the growth and structural resistance of P. thunbergii seedlings were positively correlated with water status, gas exchange parameters, and photosynthetic carbon assimilation capacity, while generally negatively correlated with antioxidant enzyme activities, the level of membrane lipid peroxidation, and the accumulation of osmotic adjustment substances. (4) Structural equation modeling further revealed that combined stress synergistically affected seedling growth through water imbalance, photosynthetic carbon assimilation inhibition, and oxidative damage.

Conclusion Combined salt and wind stress affects plant growth through multiple pathways, including disruption of water balance, inhibition of photosynthetic carbon assimilation, and accumulation of oxidative damage. It is suggested that P. thunbergii germplasms with strong water regulation and antioxidant capacity should be selected for coastal shelterbelt construction.