This work aimed to explore the effects of three combined bacterial inoculants of Bacillus spp. on the growth of Quercus mongolica seedlings, and clarify the growth-promoting effects of different bacterial inoculants, so as to provide a theoretical basis for the application of Bacillus in the cultivation of Q. mongolica seedlings.

The container seedlings of the one-year-old Q. mongolica seedlings were inoculated with Bacillus subtilis inoculants (B1), B. subtilis and Bacillus licheniformis mixed inoculants (B2) as well as B. subtilis, B. licheniformis and Bacillus amyloliquefaciens mixed inoculants (B3). Each bacterial inoculant had two concentrations of the stock solution (C0) and 20-fold diluent (C2), and water was used as the control (CK). Subsequently, the effects of different types and concentrations of bacterial inoculants on the growth indexes, photosynthetic parameters and non-structural carbohydrates (NSC) of Q. mongolica seedlings were analyzed.

Bacillus increased the seedling height, ground diameter, leaf number and biomass accumulation of Q. mongolica seedlings, enhanced the photosynthesis of seedlings, and also changed the morphology and NSC distribution pattern of roots. Bacterial inoculants B1, B2 and B3 increased the biomass ratio of leaves, stems and roots, reduced the NSC content of seedlings, elevated the ratio of soluble sugar to starch in leaves, and promoted the distribution of NSC to roots. B1 was better than B2 in promoting seedling biomass and photosynthesis. However, the B2 inoculant showed greater effects on the aboveground part, root morphology and NSC of seedlings than the B1 inoculant.

Bacillus inoculants can regulate the growth of Q. mongolica seedlings and improve their growth potential. Among the three kinds of bacterial inoculants, the mixed inoculant of B. subtilis, B. licheniformis and B. amyloliticus has the best effect. This study can provide theoretical support for the application of Bacillus in the cultivation of high-quality seedlings of Q. mongolica.