Nanobiochar as a multifunctional amendment for coupled water-soil-biota systems: applications in agricultural production, environmental remediation, and arid ecosystem restoration

Nanobiochar, engineered carbon nanoparticles derived from biomass, represents an emerging interface between nanotechnology and environmental engineering. Produced through mechanical, thermal, and hydrothermal processes, nanobiochar exhibits a markedly higher specific surface area, enhanced surface reactivity, and improved sorption capacity relative to conventional bulk biochar. This review synthesizes recent advances in nanobiochar production pathways, physicochemical characteristics, and the mechanistic controls governing its functional performance across environmental systems. In agricultural applications, nanobiochar has been shown to enhance plant growth by improving nutrient cycling, mitigating salinity stress through ionic immobilization, reducing nitrogen losses via slow-release fertilizer delivery, and fostering beneficial soil microbial communities. Beyond agroecosystems, nanobiochar-based materials demonstrate strong potential for heavy metal immobilization, organic contaminant adsorption, and wastewater treatment. The review further highlights an emerging and largely unexplored frontier in dryland restoration, where nanobiochar may interact with biological soil crusts (BSCs). Preliminary evidence suggests that, when used as a carrier for pioneer cyanobacteria, nanobiochar could contribute to substrate stabilization, potentially influence exopolysaccharide production, and affect soil moisture retention under arid conditions. Considering the global extent of drylands, nanobiochar–BSC systems may offer an exploratory pathway for restoration with possible implications for long-term carbon sequestration. Nevertheless, challenges related to energy-intensive production and large-scale deployment remain and require careful optimization. Overall, this review elucidates key design–function relationships underlying nanobiochar performance, emphasizes the need for responsible upscaling, and identifies critical research priorities for its application in sustainable agriculture, environmental remediation, and ecosystem restoration.