Micro-nanoscale bone char alters Cd accumulation and rhizosphere functional genes to enhance rice yield and quality

Abstract This work investigates the impact of micro-nanoscale bone char (MNBC) soil amendment on Cd-stressed rice over a full life cycle, aiming to develop a sustainable remediation strategy integrating yield improvement and soil health. MNBC was sourced from widely available pork bones in the waste stream, and was generated by pyrolysis at 400 °C and 600 °C, followed by ball-milling to reduce the particle size to micro-nanoscale. A 140-day full-life-cycle experiments was conducted under greenhouse conditions, and soil samples across all the treatments were collected at different growth periods for metagenomic analysis. At harvest, rice grains were sampled for metabolomic analysis. Results showed that treatment with 600 °C MNBC significantly increased grain yield by 49.72%, while 400 °C MNBC increased the effective tiller number by 23.08%, compared to Cd treatment. Both types of MNBCs reduced Cd accumulation in rice tissues, with reductions of 65.0–68.7% in polished rice relative to the Cd treatment. Metabolomic analysis highlights MNBC modulated the nutritional value of the grains, effectively slowing down the biochemical processes of carbohydrates and branched-chain amino acids into simple sugars or polyols in rice grains. In the aerobic phase of soil, the acid-soluble Cd with MNBC treatments decreased by 31.56–35.51% as compared to the Cd treatment. Metagenomic analyses show that MNBC had a significant impact on the microbial communities involved in soil carbon, nitrogen, and phosphorus cycling, such as Actinomycetota, Cyanobacteria, and Gemmatimonadota, as well as on related genes; particularly enhancing the complexity of the phosphorus gene network. Overall, these findings demonstrate the significant potential of MNBC-enabled agriculture practices as a sustainable crop strategy. Graphical Abstract