Rhamnolipids combined with drip irrigation as a novel strategy for promoting cotton growth by reducing salinity stress and optimizing rhizosphere microbial communities

Soil salinization is a serious issue that is being faced worldwide. This study investigated the effects of different concentrations of rhamnolipids (CK: 0 mg/L, RhaL: 100 mg/L, RhaM: 300 mg/L and RhaH: 500 mg/L) combined with drip irrigation on the rhizosphere environment of the saline soil used for cotton cultivation. Results showed that rhamnolipids reduced soil pH and soil water-soluble salts (e.g., Na+, K+, and SO42-), whereas Cl- and electrical conductivity increased in RhaM and RhaH. In addition, rhamnolipids increased the activity of alkaline phosphatase, sucrase, and CAT by 16.9-44.8%, 84.0-108.5%, and 29.6-41.9%, respectively, and decreased urease by 33.2-39.0%. In addition, the bacterial abundance in the rhamnolipid-treated group increased, whereas that of fungi decreased with increasing rhamnolipid concentrations. Moreover, co-occurrence network analysis showed that rhamnolipids improved the stability of the rhizosphere microbial communities. Furthermore, functional gene predictions indicated that rhamnolipids enhanced soil C, N, P, S, and energy cycling. Ultimately, the cotton growth and stem diameter in rhamnolipid-added treatments increased by 24.6-65.3% and 2.1-10.7%, respectively. This study provides valuable information for establishing effective strategies to meliorate saline soils and contributes to the sustainable agricultural development.