Nitrous oxide (N₂O) emissions from agricultural soils are an important source of greenhouse gases and are strongly influenced by fertilization practices. In this study, a field experiment was conducted from 24 June to 12 October 2024, at a saline-alkali farmland site in Binzhou, Shandong Province, China, to evaluate the effect of Bacillus subtilis biofertilizer on N₂O emissions and to explore the underlying mechanisms. Compared with conventional chemical fertilization, the Bacillus subtilis biofertilizer treatment reduced the cumulative N₂O emission flux by 39%. At the N₂O emission peak, the emission flux under the biofertilizer treatment was 40.7%, 18.2% lower than that under the CF and CBF treatments, respectively. Functional gene analysis further showed that at the N₂O emission peak, the biofertilizer treatment reduced the copy number of Bacterial-amoA by 94% and 83% relative to CF and CBF, respectively, while the hao gene abundance in the CF treatment was 7.67, 24 times higher than that in the BF and CBF treatments, indicating that the reduction in N₂O emissions was closely associated with suppression of the nitrification process. In addition, the biofertilizer treatment showed the highest plant nitrogen uptake. All fertilization treatments significantly increased crop yield compared with the control, whereas there was no significant difference in yield among BF, CF, and CBF treatments (p > 0.05). These findings indicate that B. subtilis biofertilizer can mitigate N₂O emissions from saline-alkali farmland without reducing crop yield and may represent a promising strategy for sustainable agricultural management.

Saline-alkali soils are characterized by high salt content and low organic matter, which hinders plant growth and limits their carbon sequestration capacity. Using of biofertilizer has been recognized as a promising strategy for saline-alkali soil improvement. This study evaluated the potential of biofertilizer to improve the saline-alkali soil properties and enhance carbon sequestration through field experiments, while also exploring the underlying mechanisms. The soil supplemented with 30 and 60 t·ha-1 of biofertilizer resulted into an increase in per-hectare carbon sequestration by 102 t CO2e and 144 t CO2e, respectively, in comparison to soil without biofertilizer (control). The improvement in soil properties showed an increase in Suaeda salsa biomass, enhancements in soil enzymes activities and elevation in total organic content, as evident by correlation analysis and Mantel tests. Furthermore, the metabolism of organic matter promotes an increase in total inorganic carbon. The results indicates that the use of biofertilizer is an effective strategy for improving saline-alkali soil and enhancing carbon sequestration.