The synergistic effect of extracellular polysaccharide-producing salt-tolerant bacteria and biochar promotes grape growth under saline-alkaline stress

Grapes (Vitis vinifera) are a vital economic crop worldwide but are severely threatened by soil salinization and alkalization. While extracellular polysaccharides are known to improve soil conditions, it remains unclear how rhizosphere microorganisms that can produce extracellular polysaccharides enhance the tolerance of plants to salt-alkali conditions. This study selected Bacillus subtilis B4 and Pseudomonas resinovorans B9 based on their high levels of production of extracellular polysaccharides and subjected them to pot and field experiments. Our results demonstrated that both strains significantly promoted the growth of grape shoots, reduced the salinity of soil, and increased the levels of phosphorus and potassium in both the plants and soil. Compared to traditional B. subtilis, B9 performed better, and this was further enhanced when the strain was co-applied with biochar. 16S rRNA high-throughput sequencing was used to show that the combination of bacteria and biochar reshaped the native rhizosphere microbial community, altered its functional abundances, and improved the properties of soil, thus, ultimately promoting plant growth and enhancing salt-alkali tolerance. This study expands the microbial species available to improve the tolerance of grape to salt and ameliorate the saline-alkaline soils, thus, providing a theoretical basis for the combined application of microbial inoculants and biochar.