Coastal wetland converted to uplands reduce the diversity of soil nitrogen-related functional communities

Land-use conversion exerts substantial effects on ecosystem functioning in coastal wetlands; however, its impacts on nitrogen (N)-related functional communities and associated biogeochemical processes remain unclear. In this study, we investigated the abundance and diversity of N-cycling functional communities and their environmental drivers following the conversion of coastal wetlands (CW) to tidal flats (TF), agricultural land (AL), and fallow land (FL) using a metagenomic approach. The results showed that the abundance of key functional genes involved in assimilatory nitrate reduction, denitrification, and nitrification declined significantly following the conversion of CW to AL or FL. Shannon diversity index of N-cycling related taxonomic groups also declined markedly in response to land-use conversion. Across all the land-use types, denitrification process was the predominant N transformation pathway, accounting for 50.9% to 52.7% of total N-cycling potential. Structural equation modeling further revealed that soil electrical conductivity was the primary environmental driver influencing the abundance and diversity of N-related functional genes, explaining 79.1% and 66.6% of the variation in functional genes and taxonomic groups, respectively. Collectively, these findings demonstrate that land-use conversion substantially alters the composition and diversity of N-cycling functional communities in wetland ecosystems, with important implications for wetland management and ecological restoration for sustaining soil multifunctionality.