Abstract
The relationships between salinity and mineral nutrition are extremely complex and may change depending on many factors in soil-plant system. We investigated the contribution of silicon (Si at 50 mg kg−1 soil) and potassium (K at 40 and 60 mg K2O kg−1 soil) to improve salt tolerance in sunflower grown with 100 mM sodium chloride (NaCl). The experimental design was factorial based on a completely randomized design with five replications. Added NaCl increased sodium ion (Na+) accumulation by 966 percent in shoots and 1200 percent in roots but reduced shoot potassium ion (K+) concentration by 49 percent, root K+ 51 percent, and shoot K+/Na+ ratio 95 percent. However, Si and K application effectively reduced Na+ accumulation and increased K+ concentration and K+:Na+ ratio, with a significant improvement in plant growth and yield. Among all treatments, greater alleviative effects of Si and K were observed for 50 mg Si + 60 mg K2O kg−1 soil, which decreased shoot Na+ concentration by 67 percent, root Na+ 18 percent, and shoot Na+/root Na+ ratio 60 percent and increased shoot K+ by 198 percent, shoot K+/Na+ ratio 812 percent, membrane stability index (MSI) 35 percent, relative water content (RWC) 26 percent, and seed weight head−1 86 percent compared to salt-stressed plants without supplemental Si and K. Most of the plant growth parameters were negatively correlated with Na+ accumulation but positively correlated with K+ and K+/Na+ ratio. This study suggests that Si and K mediated reduction in Na+ accumulation, and increase in K+ concentration, K+/Na+ ratio, RWC, and MSI are the main factors contributing to improved adaptation capability of sunflower to NaCl stress.