Biostimulants Promote the Sedimentation of Salts to Restore Tomato Plant Growth Under Salt Stress

Soil salinization is an emerging threat to agriculture production, which results in a tremendous reduction of cultivation areas. Three commercial biostimulants with different ingredients were investigated for their effects on the sedimentation of salts and the growth of salt-stressed tomato plants. The contents of Na+ and K+ were determined using a flame photometer. The net photosynthetic rate was measured using CIRAS-3 portable photosynthesis system. The chlorophyll fluorescence and performance index on absorption basis (PIABS) were measured using FMS2+ portable pulse-modulated chlorophyll fluorometer and plant efficiency analyzer, respectively. Nuclear DNA ploidy levels were determined by flow cytometer. Biostimulants promoted the sedimentation of Na+ and K+ and reduced electrical conductivity (EC) in saline soil to various extents. Biostimulants could alleviate the limiting effects of salinity on the aboveground growth of tomato plants including promoting shoot growth, boosting leaf photosynthesis, activating antioxidant enzymes, and accelerating cell division in leaves. Biostimulants also significantly improved the root growth of tomato plants including root length, root surface area, and root volume under salt stress. Biostimulants significantly reduced Na+ content and increase K+ content in the root, stem, and leaf under salt stress. Principal component analysis based on physiological parameters revealed that the biostimulant enriched in organic matters from hydrolyzed animal epithelium had the best effects on salt sedimentation and salt stress relief. Our study illustrates the bottom-up impact of biostimulants on tomato plant growth under salt stress via ion sedimentation in soil, which provides a strategy for crop cultivation in saline soil.