Effects of hydrochar application on the Cd bioavailability and microbial community in soil

In order to explore the remediation effect of hydrochar application on cadmium (Cd)-contaminated soil and corresponding mechanism, a pot experiment was conducted to analyze the effects of different corn stalk hydrochars at different application ratios (1% and 3%) on the Cd bioavailability in soil, plant uptake and microbial response. Results showed that compared with CK, hydrochar application significantly increased the soil organicmatter and organic carbon contents, and diethylenetriamine pentaacetic acid extracted Cd (DTPA-Cd) content in soil and Cd content in rape leaf were decreased by 5.01%~20.98% and 10.82%~4.16%, respectively. The increased hydrothermal temperature and hydrochar application ratio contributed to reducing the DTPA-Cd content in soil. Additionally, hydrochar application substantially enhanced the bacteria diversity and abundance in rhizosphere soils, and obviously changed the microbial community structure. Compared with CK hydrochar application significantly reduced the relative abundance of Actinobacteriota, and increased the relative abundances of Proteobacteria and Bacteroidota in rhizosphere soils. Redundancy analysis showed that soil dissolved organic carbon content was the key factor influencing the bacterial community structure in rhizosphere soil. Therefore, hydrochar has great potential for the remediation of metal-contaminated soils, but its long-term effect on soil heavy metals needs further research.