Abstract:

Coastal wetlands are key transitional ecosystems located at the terrestrial-aquatic interface, and influenced by multiple environmental factors such as tidal regimes, salinity gradients, and distribution of halophyte vegetation, thereby forming unique nitrogen (N) cycling patterns. Coastal wetlands play a critical role in alleviating nearshore eutrophication and maintaining ecosystem functions. Although the drivers of soil N removal processes in coastal wetlands have been widely studied, existing research has largely focused on environmental factors or microbial processes separately, whereas the regulating mechanisms of halophytes on microbial denitrification still lacks a systematic review. Halophyte root functional traits are also increasingly considered a key functional attribute in regulating the coupling relationship between vegetation characteristics and soil nitrogen cycling processes. This study systematically reviews current knowledge on the effects of hydrological and salinity gradients, as well as halophytes, on N removal in coastal wetlands, with a particular focus on root traits. We integrate how root chemical, physiological, and morphological traits influence microbial N removal through carbon (C) inputs, radial oxygen loss, and rhizosphere microenvironment regulation. The study further reveals the regulatory mechanisms of root-mediated microbial community restructuring, enrichment of key denitrifying taxa, and the regulation of N removal via coupled elemental cycles, including C–N and iron–N interactions. The aim of this review is to fill the systematic knowledge gap between halophyte root traits to microbial N removal in coastal wetlands, and provide a theoretical basis for advancing future research.

Key words: coastal wetland, nitrogen removal processes, root traits, root-microbial interactions, rhizosphere processes