Rhamnolipid-modified biochar improves the microenvironment of saline soils to enhance soil productivity

Objective: This study aims to elucidate the mechanisms by which rhamnolipid-modified biochar enhances saline soil quality and increases peanut yield, while preliminarily exploring its potential ecological risks. The findings are expected to provide theoretical and technical support for the sustainable improvement of saline soils in arid regions and for the green production of peanuts. Methods: A field experiment was conducted with three treatments: a control (CK, no biochar application), biochar (BC, application of cotton stalk biochar), and modified biochar (RBC, application of rhamnolipid-modified biochar). The amelioration effects and driving mechanisms of modified biochar on saline soil were investigated by analyzing soil physicochemical properties, microbial community structure, enzyme activities, and peanut yield under different treatments. Results and discussion: The results showed that, compared with the control, the application of rhamnolipid-modified biochar significantly increased total carbon (by 30.33%-45.20%), total nitrogen (by 28.66%-55.76%), organic carbon (by 244.07%-370.10%), and moisture content (by 25.61%-42.42%) in the 0-20 cm soil layer, while significantly decreasing the total salt content (by 39.40%-56.78%). Furthermore, the RBC treatment activated the activities of soil urease, sucrase, and cellulase. Regarding the microbial community, modified biochar mitigated the inhibitory effect of unmodified biochar on bacterial diversity. It enriched nutrient-rich microbial groups such as Proteobacteria, Acidobacteria, and Firmicutes, as well as salt-tolerant functional bacteria like Neobacillus and Luteitalea, and the fungal phylum Ascomycota. Concurrently, it suppressed the abundance of pathogenic fungi such as Basidiomycota and Colletotrichum, thereby reducing the risk of soil-borne diseases. Random forest analysis identified total carbon, total organic carbon, and soil carbon loading as key environmental factors driving changes in the soil microbial community. Partial least squares path modeling further confirmed that modified biochar improved soil physicochemical properties, activated enzyme activities, subsequently regulated the fungal community, alleviated the suppression of the bacterial community, and fostered the formation of a synergistic microbial network structure. These combined effects ultimately enhanced soil quality and led to a significant 27.57% increase in peanut yield.