Perspectives on the effects of biochar amendment on GHG emission-related microbial activities of constructed wetlands

Constructed wetlands (CWs) have been recognized as a high-efficiency performance, cost-effective, and environmentally friendly ecotechnology for contaminated water remediation. However, the CWs may also produce substantial amounts of greenhouse gases (GHGs), along with carbon and nitrogen (N) transformations. As a critical component of CWs, the substrate plays a key role in determining both the wastewater treatment efficiency and the ecological impact of CW systems. Recently, biochar has been introduced as an innovative substrate in CWs specifically for the purpose of mitigating GHGs emissions. This review comprehensively summarizes and evaluates the performance of biochar amendments in CWs, particularly focusing on their effectiveness in the removal of nitrogen and organic contaminants, as well as their role in reducing GHGs emissions. Furthermore, the mechanisms involved in these performances, which biochar affects on the related microbial activities, that were designated by various indicators (e.g., microbial abundance, enzyme activities, and functional gene expression), are systematically analyzed, especially emphasis on the microbial processes involved in CH4 and N2O dynamics. Future research should focus on optimizing biochar modification techniques to enhance redox and microbial regulatory functions, integrating multi-omics technology to elucidate microbial pathways, and developing nutrient biogeochemical cycling models to predict long-term performance. Additionally, constructing global-scale GHG emission models for CWs and assessing the durability and economic feasibility of biochar in field applications are critical steps toward sustainable deployment. This review highlights the significant potential of biochar-amended CWs and provides a forward-looking perspective to guide future innovations in low-carbon wastewater treatment systems.