Objective The aims were to explore the effects of Jiaosu (prepared from the by-products of highland summer vegetables) on the properties of saline-alkali soil and the diversity and community structure of rhizosphere soil microorganisms, and to provide theoretical basis and practical foundation for the improvement of saline-alkali soil in arid and semi-arid areas.

Method A 100-day pot experiment of sunflower was conducted in the saline-alkali soil of Lanzhou New Area. Six treatments were set up: control (CK), 200-fold diluted Jiaosu (T1), 400-fold diluted Jiaosu (T2), 600-fold diluted Jiaosu (T3), 800-fold diluted Jiaosu (T4), and 1000-fold diluted Jiaosu (T5). Soil chemical properties were measured, and the diversity, community composition and interaction network characteristics of rhizosphere soil microorganisms were analyzed.

Result The application of Jiaosu could reduce soil salinity and alkalinity and increase soil nutrient content. Compared with the CK treatment, the soil pH in the T1 treatment decreased by 1.07%, and the available phosphorus content increased by 20.77% (P < 0.05). The soil EC value in the T3 treatment decreased by 26.40%, and the total nitrogen and organic matter contents increased by 13.92% and 23.66% (P < 0.05). The ammonium nitrogen content in the T5 treatment increased by 43.62%, and the nitrate nitrogen content in the T2 treatment decreased by 43.53% (P < 0.05). The composition and community structure of soil bacteria under different concentrations of Jiaosu were significantly different, and the fungal community was significantly different. The composition of bacterial and fungal communities was different. Compared with the CK treatment, the richness of bacterial communities in the rhizosphere soil of each treatment increased, and the diversity decreased. The T2 treatment increased the relative abundance of Proteobacteria in the rhizosphere soil, and the T4 treatment significantly increased the relative abundance of Acidobacteriota. The richness and diversity of soil fungal communities decreased, and the T2 treatment increased the relative abundance of Ascomycota in the rhizosphere soil of sunflower, and the T4 treatment increased the relative abundance of Mortierellomycota. The dilution treatment of Jiaosu increased the number of network nodes and positive correlation edges of rhizosphere soil bacteria and fungi. Redundancy analysis showed that the T3 treatment affected the community structure of rhizosphere soil bacteria by influencing soil pH and EC, and was significantly positively correlated with soil available phosphorus and organic matter content.

Conclusion The application of Jiaosu prepared from the by-products of highland summer vegetables at diluted concentrations can improve the properties of saline-alkali soil and nutrient status, and thereby affect the community structure of rhizosphere soil microorganisms. The 600-fold diluted Jiaosu treatment had the best comprehensive effect on the improvement of saline-alkali land.