Effects of potato intercropped with maize on soil bacterial diversity

One of the reasons for the replanting problem in continuous potato cropping is the change in the soil microbial community structure. Many studies have shown that reasonable intercropping can alleviate replant disease, and the relationships of crop-soil-microorganisms are a hot topic in current agricultural ecosystem research. Therefore, the objective of this study was to examine the difference in the soil bacterial community composition after continuous potato and maize monoculture and intercropping. The IonS5^TMXL high-throughput sequencing platform was used to analyze the soil bacterial community composition and diversity under maize monoculture (M), potato monoculture (P), and potato intercropped with maize (PM). The results revealed that soil organic matter significantly increased in the treatment of potato intercropped with maize (P < 0.05), when compared with the monocultures. However, there were no significant changes in the soil total nitrogen, available nitrogen, total phosphorus, available potassium, and pH among different treatments. Moreover, the total 56 787 Operational Taxonomic Units (OTUs) of bacteria were classified as 46 phyla, 55 classes, 114 orders, 208 families, and 455 genera. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant phyla and accounted for 57.68%-65.11% of the total relative abundance of bacteria. The diversity index (Shannon-Wiener and Simpson) and the richness index (ACE and Chao1) of soil bacterial communities did not change; however, the relative abundance of the soil bacterial communities changed at the phylum and genus levels. Compared to the potato monoculture, the relative abundance of Proteobacteria decreased significantly after potato was intercropped with maize (P=0.023), while the relative abundance of Planctomycetes increased (P=0.043). Furthermore, Gemmatimonas and Candidatus Solibacter, with lower relative abundance, were found to be more easily influenced by the planting patterns. Moreover, intercropping increased the relative abundance of Arthrobacter, Blastococcus, and Bacillus. With the change in the bacterial community, the soil bacterial functions were separately classified into 7 and 35 functional categories at hierarchy level 1 and 2, respectively, using the KEGG function prediction, which implied abundant soil bacteria functions. From this, we garnered that soil bacteria were active in metabolic processes, genetic information processing, and cellular processes. Furthermore, the metabolic functional groups in the 7 primary functional layers had significant differences between potato intercropped with maize and potato monoculture (P=0.046). Additionally, forward selection of the soil environmental factors was used, and the result of the Monte Carlo test showed that there was no significant correlation between soil physicochemical and biological properties and the soil bacterial community composition and diversity after the five-year experiment. In conclusion, the relationship between the interspecific mutualism and competition in potato intercropped with maize was the driving factor of the change in the soil bacterial community.