Silicon and Potassium Nutrition Enhances Salt Adaptation Capability of Sunflower by Improving Plant Water Status and Membrane Stability

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 50mgkg(-1) soil) and potassium (K at 40 and 60mgK(2)Okg(-1) soil) to improve salt tolerance in sunflower grown with 100mM 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 50mg Si+60mgK(2)Okg(-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.