The utilization of reclaimed water is one of the most important ways of alleviating the shortage of water resources for agricultural irrigation. As an effective disposal method for biomass waste, biochar has been widely used in the improvement and remediation of agricultural environments. However, few studies have been performed on the effects of biochar application on microbial community structures and pathogen abundances in rhizosphere soils irrigated with reclaimed water. Based on a pot experiment, high throughput sequencing technology and quantitative polymerase chain reaction (PCR) methods were used to investigate the effects of different biochars on the microbial community structure and diversity and pathogen abundance of rhizosphere soils irrigated with reclaimed water. The results showed that four different types of biochars had different effects on the soil nutrient status. Rice hull-derived biochar and rice straw-derived biochar resulted in significantly increased soil pH with reclaimed water irrigation, while peanut shell-derived biochar, rice straw-derived biochar, and wheat straw-derived biochar significantly increased EC values (P<0.05). The Sobs index, Shannon index, and Chao1 index of bacterial community in the rhizosphere soil significantly increased with rice straw-derived biochar treatment, while the Simpson index significantly decreased by adding peanut shell-derived biochar, rice hull-derived biochar, and wheat straw-derived biochar (P<0.05). There were differences in the relative abundances of bacterial communities in rhizosphere soils under different treatments. The dominant taxonomic groups at the phylum level were Proteobacteria, Actinobacteria, Chloroflexi, Bacteroidetes, and Acidobacteria. The dominant genera included Pseudomonas, Rheinheimera, Arthrobacter, Sphingomonas, and Aeromonas (relative abundance>5%). Redundancy (RDA) and heatmap analyses showed that the diversities and compositions of bacterial communities in rhizosphere soils in different treatments were closely related to soil EC values, organic matter, total nitrogen, and cadmium contents. Biochar application had no significant effect on the abundances of Aeromonas hydrophila and Bacillus cereus. Rice straw-derived biochar and peanut shell-derived biochar could significantly reduce the γ-Proteobacteria, while rice hull-derived biochar and wheat straw-derived biochar could significantly reduce the relative abundance of AOA (P<0.05). In conclusion, there were no obvious negative effects observed from reclaimed water irrigation on soil quality. Biochar application not only significantly improved the physicochemical properties of the soil, but also impacted the bacterial community structure and the abundance of the functional bacteria in the rhizosphere soil, which was closely related to the soil properties.
Keywords: bacterial community; biochar; pathogens; reclaimed water irrigation.