Humic Acid Promotes the Growth of Switchgrass under Salt Stress by Improving Photosynthetic Function

As a potential crop in saline-alkali land, the growth of switchgrass could also be threatened by salt stress. Promoting the growth of switchgrass under salt stress by humic acid has great significance in the utilization of saline-alkali land. In this study, a pot experiment was arranged to investigate the responses of photosynthetic and physicochemical characteristics of switchgrass to HA under salt stress. Results showed that humic acid increased the photosynthetic function of switchgrass and enhanced plant height by 41.1% and dry weight by 26.9% under salt stress. Correlation analysis showed that the membrane aquaporin gene PvPIP1, malondialdehyde, ascorbate peroxidase, abscisic acid, polyamine, and jasmonic acid were important factors affecting the photosynthetic function of switchgrass in this study. Meanwhile, HA reduced the content of malondialdehyde, indicating the alleviation of the membrane damage caused by salt stress. On the other hand, HA upregulated the relative expression of the PvPIP1 gene and activated ascorbate peroxidase, abscisic acid, polyamine, and jasmonic acid in switchgrass to resist salt stress. These improved the membrane stability and promoted the photosynthetic activity of switchgrass to enhance the plant's tolerance against salt stress and growth. Results from this study are helpful to the efficient growing of switchgrass and the sustainable development of saline-alkali land.