Effects of chicken and pig manures application on heavy metal in different soil types and on bacterial in the rhizosphere soil of Chinese cabbage

In China, due to the rapid growth of the livestock and poultry farming industries, large amounts of manure are produced every year, which contains large amounts of heavy metals, and field application of this manure as fertilizer leads to the accumulation of heavy metals (HMs) in soils. In this study, a pot experiment and 16S rRNA gene sequencing were used to study the soil chemical properties and bacterial community characteristics of the Chinese cabbage rhizosphere in purple soil, red soil and yellow soil under fertilizer (CF), chicken manure (CM) and pig manure (PM) application. Compared with the CK and CF, chicken manure (CM3 and CM6) and pig manure (PM3 and PM6) application significantly increased the soil pH, soil organic matter (SOM), Cu and Zn contents, with greater increases at higher application rates. There were no significant changes in the total and available Cd and Pb contents in purple soil, but the contents of these heavy metals significantly decreased in red soil and yellow soils. The application of fertilizer increased the Cu, Zn, Cd, and Pb contents in the shoots of Chinese cabbage, while the trends of heavy metals contents differed by soil type and manure type under other treatments. PERMANOVA revealed that the application of chicken manure and pig manure significantly affected the bacterial community structure of the cabbage rhizosphere soil regardless of soil type (P = 0.001). Network analysis revealed that application of chemical fertilizers enhanced network complexity, whereas the opposite was true for application of chicken and pig manure, and the relative abundance of Proteobacteria increased by 1.69% ~ 6.21%, 2.41% ~ 5.41% and 5.65% ~ 12.12%, respectively. Redundancy analysis (RDA) revealed that pH, SOM and Zn were the main factors affecting the bacterial communities in the rhizosphere soil. The response of rhizosphere bacteria to different soil types differed. A correlation heatmap revealed that Lysobacter and Sphingomonas were heavy metal-resistant strains. The effects of Cu and Zn on bacteria in different rhizosphere soils were quite different. This study provides a reference for the safe application of livestock manure to agricultural fields, and the results suggest that heavy metal-resistant strains can be used to assist in the remediation of HM-polluted environments.