Bacillus pumilus AD14: A Saline-Alkali-Tolerant Plant Growth-Promoting Bacterium for Enhancing Soybean Tolerance and Ameliorating Saline-Alkali Soil

According to an FAO report, the total area of saline-alkali land worldwide is approximately 954 million hectares, accounting for about 20% of global cultivated land. Saline-alkali stress significantly reduces soybean (Glycine max L.) yield and quality, and saline-alkali-tolerant plant growth-promoting bacteria (PGPB) have shown important application value for soybean planting in such farmlands. In this study, 15 strains of saline-alkali-tolerant bacteria were isolated from saline-alkali soil in Anda City, Heilongjiang Province, China, and identified morphologically, belonging to the genera Enterobacter, Bacillus, Chryseobacterium, Acinetobacter, Enterococcus, and Pseudomonas. Through tests for nitrogen fixation, phosphorus solubilization, potassium solubilization, hydrolase production (including pectinase, amylase, and protease), and germination promotion assays, Bacillus pumilus AD14 was identified as having the best growth-promoting effect on soybean seedlings. Pot experiments in saline-alkali soil showed that AD14 significantly promoted soybean seedling growth, increasing plant height by 5.63–6.37 cm and root length by 3.58–3.99 cm compared to the control. AD14 also enhanced saline-alkali tolerance by improving the activity of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) and increasing soluble sugar and protein contents. Meanwhile, soil pH decreased by 10.94–12.15% and soluble salt content decreased by 9.59–13.39% after planting, and soil enzyme activities (including urease, sucrase, and catalase) increased markedly. These results demonstrate the great potential of AD14 for soybean planting in saline-alkali soil. This study provides a relevant reference for enriching the resources of saline-alkali-tolerant PGPB and developing new biological agents suitable for soybean planting in saline-alkali soils.