Effects of application rates of poly-γ-glutamic acid on vegetable growth and soil bacterial community structure

In this study, we investigated the effect of high-molecular-weight gamma-PGA (over 4000 kDa) produced by Bacillus sp. A-5 on Chinese cabbage (Brassica rapa L. ssp. chinensis L.) productivity, apparent fertilizer utilization efficiencies, and soil bacterial community structure. Compared to CF treatment, gamma-PGA application at low rates (PO and P1) decreased vegetable yield by 14.29% and 17.30%, respectively; however, P2, P3, and F2 (moderate and high doses of gamma-PGA application) offset the chemical fertilizer reduction and thereby increased the apparent utilization efficiencies by 27.82-52.27% for N, 17.05-64.59% for P, and 32.73-41.43% for K. With reduced fertilizer application, the P2, P3, and F2 treatments increased soil bacterial community diversity, richness, and evenness; in contrast, the PO and P1 treatments decreased these variables. In conclusion, gamma-PGA can enhance the apparent fertilizer utilization efficiencies and increase the relative abundances of potential plant-growth-promoting bacteria in soil in a concentration-dependent manner, thereby improving Chinese cabbage yield.