The application of Bacillus Megaterium alters soil microbial community composition, bioavailability of soil phosphorus and potassium, and cucumber growth in the plastic shed system of North China

The long-term continuous mono-cropping and application of large amount of chemical fertilizers have led to a dramatic degradation of soil quality in the intensive vegetable production system. It is important to develop more sustainable, environmentally friendly and high-efficiency agroecosystems for vegetable production in plastic shed systems. Field experiments were performed to explore the impacts of Bacillus megaterium application on cucumber yields, the bioavailability of soil phosphorus (P) and potassium (K), properties of soil microbial communities in a plastic shed production system with cucumber mono-cropped for more than 15 years. The field trails were set up with four treatments of conventional fertilization as control (CON), conventional fertilization with Bacillus megaterium (CON + BM), conventional fertilization reduced by 10 % P and 10 % (or 5 %) K from chemical fertilizer with Bacillus megaterium (CON + BM - PK1), conventional fertilization reduced by 20 % P and 20 % (or 10 %) K from chemical fertilizer with Bacillus megaterium (CON + BM - PK2). Results illustrated that CON + BM treatment significantly increased the cucumber yields by 11.8 %–15.2 % and P and K accumulation in cucumber fruits and roots by 27.5 %–46.1 % and 17.8 %–45.1 %, respectively. The treatments of CON + BM - PK1 and CON + BM - PK2 did not decrease the yields and quality of cucumber, and the bioavailability of soil P and K compared with CON + BM. Moreover, the strain of Bacillus megaterium can efficiently colonize the soil at the early stage of inoculation and improved the richness of soil bacterial and fungal communities significantly. High-throughput sequencing identified that the application of Bacillus megaterium did not change the compositions of the predominant bacterial phyla Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, and predominant fungal phylum Ascomycota in soil, but increased the relative abundances of the beneficial bacterial genera and fungal orders and suppressed the development of pathogenic bacterial genus significantly. Principal coordinate analysis revealed that the structures of soil bacterial and fungal communities in the CON + BM treatment were dramatically separated from CON at the early stage of inoculation. Moreover, soil pH, available K (AK), total P (TP), and total K (TK) were dramatically related to the changes of soil bacterial community structure, while soil AK and TK were dramatically linked to the variations of soil fungal community structure. The findings indicated that the application of Bacillus megaterium might contribute to the development of a more sustainable production system of vegetables in plastic shed via improving the properties of soil microbial community and the bioavailability of soil P and K.