Roles of biochar-derived dissolved organic matter in soil amendment and environmental remediation: A critical review

Biochar is an emerging, cost-effective, and renewable carbonaceous material with abundant functional groups and tuneable mesoporous structure, showing a promising performance in fertility improvement, nutrient retention, microbial activity enhancement, and contaminant immobilization, etc. Dissolved organic matter (DOM) from biochar, which can be readily mobilized during soil application, is a key component for the soil matrix, microbial community, and the fate of contaminants. Comprehensive assessments of both positive and negative effects of biochar-derived DOM present critical environmental implications. This paper is the first of its kind to critically review the compositions and structures of biochar-derived DOM as well as its multiple roles in soil application. The effects of biochar-derived DOM on stabilization or migration/mobilization of contaminants/nutrients, as well as stimulation or inhibition of microbial activity and plant growth, depend on the nature of biochar-derived DOM, pollutant properties, soil characteristics, and environmental conditions including weather and hydrological conditions. The long-term stability of biochar-derived DOM is vital during soil application and involves various interactions such as physical disintegration, infiltration, sorption, and biotic/abiotic oxidation. Further studies of biochar-derived DOM are necessary for us to understand the fate of DOM and minimize the ecological and environmental risks (e.g., toxicity, competitive sorption, blockage effect, and solubilization) of biochar application.