Micro-nanoscale bone char modulates rhizosphere As-cycling genes and enhances soil fertility in arsenic-contaminated paddy soil

Abstract The contamination of arsenic (As) poses a serious challenge to both rice growth and human health. The present study utilized the micro- and nano-scale bone char (MNBC) derived from pork bones as a remediation agent for arsenic-affected paddy soil. MNBCs at 25 g/kg were applied to soil contaminated with As at 75 mg/kg. Compared to the As-alone treatment, the MNBC additions significantly enhanced soil biochemical functions through increased urease activity (93.80%–166.47%), catalase activity (35.2%–519.42%), and organic carbon content (9.15%–29.89%). Concurrently, MNBC reinforced microbial detoxification capacity via reducing abundance of As(V) reduction genes ( arsC and arsR abundances declined by 5.93%–52.29%) and elevating abundance of As methylation genes ( arsM abundance increased by 11.06%–19.66%). Notably, As speciation shifted with available-As increasing by 17.11%–48.65%, acid-soluble As increased by 210.5%–355.23%, while residual As decreased by 12.97%–46.42%, compared to the As-alone. Although the MNBC amendment did not alter As accumulation in rice tissues, it collectively improved soil health by enhancing microbial resilience and nutrient cycling functions. Overall, our finding demonstrated the potential of MNBCs to improve soil quality, mitigate soil arsenic stress in paddy soil, and further holistically restore As-contaminated paddy ecosystems. Graphical Abstract