Effects of microbial inoculants on phosphorus and potassium availability, bacterial community composition, and chili pepper growth in a calcareous soil: a greenhouse study

Purpose Phosphorus (P) and potassium (K) are two important essential nutrient elements for plant growth and development but their availability is often limited in calcareous soils. The objective of this study was to determine the effects of applying microbial inoculants (MI, containing effective strains of Bacillus megaterium and Bacillus mucilaginous) on the availability of P and K, plant growth, and the bacterial community in calcareous soil. Materials and methods A greenhouse experiment was conducted to explore the effects of the addition of MI (control: without MI addition; treatment: with MI addition at the rate of 60 L ha(-1)) on the concentrations of P and K in soil and plant, soil bacterial community diversity and composition, and chili pepper (Capsicum annuum L.) growth. Results and discussion The results showed that MI inoculation significantly increased the fruit yields by 28.5% (p < 0.01), available P and K in the rhizosphere soil by 32.1% and 28.1% (p < 0.05), and P and K accumulation in the whole plants by 40.9% and 40.2%, respectively (p < 0.05). Moreover, high-throughput sequencing revealed that Proteobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, and Gemmatimonadetes were the dominant phyla of soil bacteria. MI application did not significantly impact the diversity and composition of soil bacterial communities, but increased relative abundances of bacterial genera Flavobacterium responsible for promoting root development across growing stages (p < 0.05), and changed the soil bacterial community structure associated closely with soil properties of available P, K, and pH in soil. Conclusions The application of MI improved the bioavailability of P and K and plant growth due to its impact on the soil bacterial community structure.