Growth of soybean plants under saline conditions: the role of potassium and Bradyrhizobium japonicum inoculation

This study aimed to evaluate the effects of potassium (K) and Bradyrhizobium japonicum applications on physiological and microbial parameters in soybean plants under salt stress. The study included treatments of control, potassium (2.2 g K₂SO₄), bacteria (B), and their combinations (K + B), along with versions exposed to 100 mM NaCl salt stress. Key parameters such as leaf water content (RWC), chlorophyll (SPAD, Chlo a/b), oxidative stress indicators (H₂O₂ and MDA), proline, protein, antioxidant enzyme activities (APX, POD, and CAT), microbial biomass carbon (MBC), and CO₂ release from soil were measured. Salt stress reduced RWC in plants by 15%, while H₂O₂ and MDA levels increased by 25% and 30%, respectively. However, potassium and bacterial applications improved plant resilience against stress by increasing proline levels by 20%, reducing protein loss by 18%, and enhancing antioxidant enzyme activities to mitigate oxidative damage. In soil microbial activities, MBC increased by up to 161%, and CO₂ release increased by up to 27.7% with K + B application. Under salt stress, MBC and CO₂ release were restored by 122% and 50.8%, respectively, demonstrating the positive effects of potassium and bacterial inoculation on microbial activity. These findings suggest that potassium and Bradyrhizobium japonicum applications could be considered effective strategies for enhancing plant tolerance and soil health under salt stress conditions.