Root exudates as molecular architects redefining carbon footprint of nitrogen-cycling in constructed wetlands: From ecological responses to application perspectives

Root exudates act as a universal currency in the rhizosphere, mediating microbial signaling, participating in nitrogen cycling, and potentially mitigating the carbon footprint of constructed wetlands (CWs). This review highlights the roles of root exudates in the molecular regulation of plant-microbial interactions and their potential use in eco-regulation strategies aimed at carbon-neutral nitrogen removal in CWs. Specifically, the characteristics of root exudates released by CWs macrophytes, and their dynamics features under environmental fluctuations were synthesized, followed by a detailed summary of the colonization mechanisms of N-cycling microorganisms mediated by the dual roles of root-derived signaling molecules. Furthermore, molecular-level insights into the niche differentiation, metabolic patterns and ecological functions of microbial communities involved in nitrogen conversion responding to macrophyte-regulated exudates were comprehensively elucidated. The promising application scenarios of exudate-enhanced nitrogen removal and greenhouse gas mitigation were delineated, together with the challenges associated with practical implementation. Though translating microscale regulatory mechanisms into large-scale applications remains challenging, a forward-looking research roadmap is proposed to deepen the multidimensional mechanistic understandings of the interplays between root exudates and N-cycling microbes, advance technical innovations in root exudates engineering and promote eco-regulation toward climate-friendly CWs. This review aims to provide nature-based guidance for designing and operating optimized CWs for water remediation, with particular emphasis on the management of nitrogenous pollutants through low carbon approaches.