崇明东滩湿地土壤硝酸盐异化还原成铵过程及其影响因素

In this study, nitrogen isotope tracer combined with slurries incubation experiment was used to investigate spatial distribution and associated biogeochemical controls of dissimilatory nitrate reduction to ammonium in the soils ranging from the low to high intertidal sites in Chongming East wetland. The results indicated that the potential rates of dissimilatory nitrate reduction to ammonium (DNRA) were in the range of 0.17~0.71 nmol•g^-1•h^-1. DNRA rates highly varied across the sampling sites, and were generally higher in low intertidal sites, and lower in high intertidal sites. DNRA rates were significantly related to E_h, DOC, NO₃ ^-, and sulfate, indicating that they crucial factors controlling DNRA activity. In addition, the nrfA abundance showed a strong influence on DNRA rates. Stepwise regression analysis further suggested that DOC and TOC were main factors regulating DNRA rate and nrfA abundance, contributing 78.8% and 50.3% to the total variations, respectively. The amount of nitrate reduction to ammonium performed by DNRA was approximately 2.5~10.4 t •km^-2•a^-1, accounting for roughly 0.68%~2.85% of total annual inorganic nitrogen flux transported into the Yangtze Estuary, suggesting that DNRA plays a crucial role in controlling the nitrogen fate in estuarine wetland. Overall, these results indicate that the variations in environmental conditions and organic matter and nitrate availability induced by the tidal fluctuation affect DNRA process, which further plays an important role regulating the nitrogen dynamics in estuarine ecosystems.