Nano biochar (N-BC) attracts increasing interest due to its unique environmental behavior. However, understanding of its formation, physicochemical characteristics, and stability of N-BC is limited. We therefore examined N-BC formation from bulk biochars (B-BCs) produced from peanut shell, cotton straw, Chinese medicine residues, and furfural residues at 300-600 °C. Carbon stability and colloidal processes of nano peanut shell biochars (N-PBCs) were further investigated. N-BCs formed from pore collapse and skeleton fracture during biomass charring, breakup due to grinding, and sonication. Amorphous fraction in B-BCs was more readily degraded into N-BCs than graphitic component. The sonication-formed N-PBCs contained 19.2-31.8% higher oxygen and fewer aromatic structures than the bulk ones, leading to lower carbon stability, but better dispersibility in water. Heteroaggregation of N-PBCs with goethite/hematite destabilized initially and then restabilized with increasing concentrations of N-PBCs. Compared with stacked complexes of N-PBCs-hematite, the association of goethite with N-PBCs could form interlaced heterostructures, thus shielding positive charges on goethite and causing greater heteroaggregation. These findings are useful for better understanding the formation of N-BCs and their environmental fate and behavior in soil and water.

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Many studies demonstrated that CeO2 nanoparticles (NPs) could protect plant from stress and improve plant growth, with a great application potential in agriculture. However, our knowledge of their fate particularly in asexual plants and their effect on the rhizosphere microbiome is limited. In this study, the transport and transformation of CeO2 NPs in an asexual plantstrawberry (Fragaria × ananassa Duch.)were investigated. The effects of root-exuded/newly formed Ce species on rhizosphere bacterial community were also examined. Strawberries were exposed to CeO2 NPs at 0–2000 mg/L for 45 days via a split-root system in the field. CeO2 NPs were taken up by the exposed mother ramet roots and then translocated to all the mother and daughter ramet tissues. As indicated by the analysis from high-resolution transmission electron microscopy and X-ray absorption near-edge structures, in addition to CeO2 NPs, CePO4, Ce­(III) acetate, and Ce­(III)-cysteine were found in the roots, and CePO4 was present in the rhizosphere soil. The Ce species in the rhizosphere soil decreased the rhizosphere microbial diversity, but stimulated the relative abundance of specific plant growth promoting rhizobacteria. These results provide new insights for understanding the benefits and sustainable applications of NPs.