Objectives This study investigated the effects of microbial inoculants containing Bacillus subtilis as the dominant strain on maize yield and rhizosphere bacterial and fungal communities under saline-alkali conditions, to clarify the alleviating effect of the inoculants.

Methods Maize cultivars MY73, Xianyu 335 (XY335), Zhengdan 958 (ZD958), and Xundan 168 (XD168) were used as test materials in a pot experiment at the seedling stage and a field experiment throughout the whole growth period conducted at Henan Agricultural University. The pot experiment adopted a three-factor split-plot design. The main plot factor was stress treatment, including: clean water control (CK1), salt stress (S), and saline-alkali stress (A). The subplot factor was microbial inoculant treatment, including: with microbial inoculant (M) and without microbial inoculant (W). The whole-growth-period field experiment was conducted continuously for two seasons in 2024 and 2025 in the same field. It adopted a two-factor design, with the main plot being microbial inoculant treatment (with microbial inoculant M, without CK2) and the subplot being maize cultivar. The seedling experiment measured plant and root phenotypes, leaf photosynthetic traits, and antioxidant physiological indices. The field experiment measured topsoil chemical properties, bacterial and fungal community diversity, biomass, and yield.

Results (1) Pot experiment Under S and A stress, M treatment significantly improved maize root morphology, reduced oxidative damage, and increased leaf chlorophyll content and net photosynthetic rate by 9.90%–158.47% and 8.01%–47.70%, respectively, compared with W treatment, thereby enhancing maize tolerance to salt and saline-alkali stress. (2) Field experiment Compared with CK2, M treatment significantly reduced rhizosphere soil pH and electrical conductivity at the silking stage, promoted aboveground biomass accumulation, increased soil ammonium and nitrate nitrogen contents, and raised maize yield. In M treatment, the relative abundances of Acidobacteria and Bacillota (formerly Firmicutes, including Bacillus) in rhizosphere soil bacteria showed an increasing trend at the phylum level; phyla such as Acidobacteria and Planctomycetota (formerly Planctomycetes), and genera such as Bacillus and Nitrospira, were significantly correlated with rhizosphere soil chemical properties and yield. In M treatment, the relative abundances of Basidiomycota and Mortierellomycota in rhizosphere soil fungi also showed an increasing trend.

Conclusions Application of a Bacillus subtilis-based microbial inoculant to saline-alkali soil reduced maize rhizosphere pH and elevated ammonium nitrogen levels, thereby decreasing the relative abundance of Pseudomonadota and increasing that of Acidobacteria. The Acidobacteria taxa secrete cellulase and chitinase to mobilize soil nutrients, improving N and P availability. This promotes shoot and root development, boosts leaf antioxidant and photosynthetic functions, and increases grain yield in maize grown under saline-alkali conditions.