Rhamnolipids supplement in salinized soils improves cotton growth through ameliorating soil properties and modifying rhizosphere communities

Soil salinization is a global environmental concern due to its great restriction on land use efficiencies and crop production. Rhamnolipids demonstrate great potential in ameliorating soils and improving plant growth. However, the exact performance and underlying mechanisms still remain unclear. Herein, a field-scale study was conducted to investigate the effect of rhamnolipids addition on cotton growth in soils with different degrees of salinization (i.e., slightly, moderately, and highly salinized soils). The drip-irrigated rhamnolipids solution (300 mg/L) effectively reduced the salinity in rhizosphere soils, with desalination rates of 9.7 %, 4.5 %, and 2.5 % in slightly, moderately, and highly salinized soils, respectively, and mitigated the salt stress on cotton plants. The analysis of microbial community in highly salinized soils showed that the rhizosphere community was modified by the rhamnolipids, with enriched populations of plant growth-promoting fungi and decreased abundance of plant pathogens. Further investigation of functional genes related to carbon, nitrogen, sulfur, and phosphorus cycling suggested that the rhamnolipids efficiently drove the nutrient cycling and promoted the interconnection of functional microorganisms. The ameliorated soil environment and strengthened microecological functions led to the enhanced photosynthetic process and improved cotton growth and yield (up to 24.4 %). Our study is the first to demonstrate the feasibility of applying rhamnolipids to improve cotton growth in salinized areas and disclose the underlying mechanisms.