Effects of PGPR and γ-PGA on maize growth and rhizosphere microbial community in saline soil

The application of plant growth-promoting rhizosphere (PGPR) and Gamma-polyglutamic acid (γ-PGA) has a potential role in improving plant tolerance under abiotic stress, while their combined effects remain largely unexplored. This study aimed to evaluate the effects of the joint effects of PGPR and γ-PGA on maize growth and rhizosphere microbial communities under salt stress. A pot experiment consisting of two strain treatments (CK, M10), two γ-PGA treatments (γ0, γ1) and two salt treatments (S1, S2) was performed for this purpose. The results showed that under S1 treatment, the combined application of M10 and γ-PGA could increase plant height, leaf area and dry weight by 11.27%, 36.45% and 8.39% respectively (P<0.05). Under S2 treatment, the combined application of M10 and γ-PGA could increase corn plant height, leaf area and dry weight by 34.46%, 142.80% and 55.81% respectively (P<0.05). In addition, the combined application of M10 and γ-PGA reduced the Na+ content in leaves by 59.43% (P<0.05). The combined application of M10 and γ-PGA significantly increased the proportion of bacterial Firmicutes (mainly including Bacillus_firmus_g_Bacillus and Bacillus_selenatarsenatis) in maize rhizosphere soil. Leaf-Na+ (P<0.001), root-K+ (P<0.01), leaf-total phosphorus (P<0.05), root-total phosphorus (P<0.01) and electron transfer rate (P<0.01) had a significant effect on the changes in the structure of maize rhizosphere bacterial community. The interaction network results showed that the combined application of M10 and γ-PGA could significantly improve the strain numbers that were directly related to plant growth factors. This study not only demonstrated the benefits of the combined application of M10 and γ-PGA in improving plant salt tolerance but also provided insights into the mechanism of plant growth from the perspective of rhizosphere microbial community changes.