Nutrient uptake, physiological responses and growth of tobacco (Nicotiana tabacum L.) in soil under composite salt stress

High soil salinity imposes osmotic stress and ion toxicity in plants, leading to substantial crop yield loss worldwide. Understanding of the quantitative and dynamic physiological responses to composite soil salt stress is limited and needs to be expanded. In this study, physiological, nutritional, and biomass yield parameters of tobacco (Nicotiana tabacum L.) grown in soil with five levels of composite soil salinity (CSS), basal CSS level (control, CK) and 3 (T1), 6 (T2), 9 (T3), and 12 (T4) times the basal CSS level, under greenhouse were determined at days 30, 60, and 90 after transplanting. Leaf dry biomass significantly (P < 0.05) increased at the low salinity levels applied (T1 and T2) at all three time points, whereas it progressively declined as the CSS level further increased. The leaf physiological and photosynthetic responses were more adversely affected by CSS at the early growth stage (day 30). A path coefficient analysis demonstrated that leaf proline content had the largest direct effect (−0.66), and leaf Cu content had the most significant indirect effect (0.49) on leaf dry biomass of plants. The results suggest that lower CSS levels (T1 and T2) could stimulate tobacco growth (leaf biomass yield, in particular), and higher leaf proline and Cu levels at the early growth stage may potentially increase the ability of tobacco plants to withstand the adverse effects of salinity, which could be considered for future research and development of salinity management strategies.