Effects of NaHCO3 Stress on the Growth and Physiological Indexes of Pumpkin Seedlings

Few studies have investigated the alkali-based salt resistance aspect of plants. Here, we used 2 pumpkin cultivars (‘Cucurbita ficifolia Bouch.’ and ‘Chuandilong’) to study the growth and physiological response mechanisms of pumpkin to different levels of \( \text{NaHCO}_3 \) stress. After the second true leaf development, pumpkin seedlings were treated with varying levels of \( \text{NaHCO}_3 \) stress (0, 30, 60, and 90 mmol/L) during sand culture. The chlorophyll content, electrolyte leakage, malondialdehyde (MDA) contents, proline contents, soluble sugar contents, and superoxide dismutase (SOD) and peroxidase (POD) activities of both cultivars were investigated. Finally, the growth and physiological indexes of pumpkin seedlings under \( \text{NaHCO}_3 \) stress were explored. The results showed that the chlorophyll a, chlorophyll b, and total chlorophyll of both pumpkin seedlings increased with exposure to low \( \text{NaHCO}_3 \) concentrations (0-30 mmol/L) and then decreased with exposure to 30-90 mmol/L \( \text{NaHCO}_3 \), reaching their minimum values with exposure to 90 mmol/L \( \text{NaHCO}_3 \). Under the latter stress, the rate of decrease in total chlorophyll content of ‘C. ficifolia Bouch.’ was higher than that of ‘Chuandilong’. However, electrolyte leakage, MDA content, proline content, soluble sugar content, and SOD and POD activities increased with the escalation of \( \text{NaHCO}_3 \) concentration and peaked after exposure to 90 mmol/L \( \text{NaHCO}_3 \). The rates of increase in electrolyte leakage and MDA contents of ‘C. ficifolia Bouch.’ were higher than those of ‘Chuandilong’ at this \( \text{NaHCO}_3 \) concentration. These results suggested that under greater \( \text{NaHCO}_3 \) stress, these pumpkin cultivars showed significant inhibition of growth, with ‘C. ficifolia Bouch.’ being more sensitive than ‘Chuandilong’ to \( \text{NaHCO}_3 \) stress. Injury caused by \( \text{NaHCO}_3 \) stress was most likely mitigated by increasing the antioxidant activities of SOD and POD and accumulating proline and soluble sugar contents to facilitate osmotic adjustment.