Biochar Increased Plant Growth-Promoting Hormones and Helped to Alleviates Salt Stress in Common Bean Seedlings

Salinity seriously disrupts the growth and physiology of plants, whereas phytohormones play an important role in regulating plant responses to salinity stress. Biochar is attracting increasing attention in recent years as a potential soil amendment under stress condition. This study addressed the use of biochar to mitigate salt-stressed soil and evaluated the levels of some phytohormones in bean (Phaseolus vulgaris L.) seedlings. A pot experiment was conducted in a climate-controlled greenhouse with three biochar ratios (control, 10, and 20% mass), three salt stress treatments (non-saline, 6, 12 dS m(-1) NaCl), and four replications. The results indicated that sodium (Na) concentration, polyamine oxidase (PAO) activity, the contents of polyamines (putrescine, spermidine, and spermine), abscisic acid (ABA), 1-aminocyclopropane-1-carboxylic acid (ACC), jasmonic acid (JA), and salicylic acid (SA) in bean leaf and root increased under salt stress. However, endogenous indole-3-acetic acid (IAA) content was decreased by salinity compared to the non-saline treatment. On the other hand, we observed decreases of Na concentration, PAO activity, polyamines, ABA, ACC, and JA contents in plants treated by biochar. In contrast, biochar enhanced IAA content and the growth of roots and shoots. As a result, the effectiveness of 20% biochar was superior to the 10% treatment in terms of polyamine contents, especially under saline conditions. Interestingly, there were no considerable changes in phytohormone contents by use of biochar under non-saline conditions. Overall, biochar alleviated the negative effects of salt stress on bean seedlings by reduction of Na concentration, endogenous stress hormones, and improvement of growth hormones.