Seasonal and Spatial Variations in Functional Genes and Microbial Community of Feammox and Its Associated Processes in Urban Green Heart Soil

Abstract

Research on Fe3+ reduction coupled to anaerobic ammonium oxidation (Feammox) and its associated processes in the moderately low-dissolved oxygen (DO) urban natural environment is lacking. To clarify seasonal and spatial variations in Feammox, iron-reducing, and anaerobic ammonium oxidation (anammox) in urban green spaces, we examined the physicochemical indices and functional genes acd, acm, Geo, and hszA in topsoils and wetland soils across four seasons. Further, we performed 16S rRNA high-throughput sequencing. The Feammox-related gene acm was detected in all topsoil samples. Season and habitat affected soil physicochemical indices influencing gene distributions. Moisture content (45.3%) and Fe3+ (13.3%) mediated genetic changes. Competition between Feammox and iron-reducing bacteria (IRB) lowered the distributions of acd and acm in summer and increased these in winter. The acd and acm distributions were higher in wetland soil than in forestland soil. The dominant phyla, Nitrospirota, Actinobacteriota, and Desulfobacterota, correlated positively. Network analysis revealed that the relative abundances of acd, Geo, and hszA correlated positively with Flavobacterium and Thermomonas, Subgroup_2, and Candidatus_Solibacter, respectively. Feammox, iron-reducing, and anammox microorganisms correlated positively but competition existed between certain taxa. Candidatus, Sphingomonas, and Geobacter are linked to Feammox, iron reduction, and anammox. Here, we demonstrated the theoretical feasibility of developing Feammox-based nitrogen removal technology under moderately low-DO conditions, providing a reference for elucidating the ecological contribution of Feammox in an urban green heart.