Exogenous nitrogen addition inhibits sulfate-mediated anaerobic oxidation of methane in estuarine coastal sediments

Abstract

Anaerobic oxidation of methane (AOM) plays an important role in regulating methane (CH4) emissions from coastal wetland ecosystems. In recent decades, coastal estuarine wetlands have been subjected to great environmental pressure associated with terrestrial nitrogen (N) input. Here, we used 13CH4 to quantify AOM rates in coastal wetland sediments with and without vegetation in the Yangtze River Estuary in East China. Impact of addition of inorganic N forms (NO3−, NO2− and NH4+) on AOM process was assessed by 13CH4 anaerobic oxidation into 13C-CO2 and 13C-SOC, as well as by community structure and quantitative characteristics of anaerobic methanotrophic (ANME) archaea. The results showed that AOM process occurred in the bare wetland (BW) and reed wetland (RW). Inorganic N addition, regardless of N forms, notably decreased AOM rates by 14–58% in the BW sediments and by 26–65% in the RW sediments. Rates of 13CH4 assimilation into SOC, which were similar to but faster than rates of AOM into CO2, were reduced by 12%–66% under inorganic N addition. After 120-day anaerobic incubation, the net changes in the relative abundance of ANME-2 and ANME-3 were significantly correlated with AOM rates in the RW and BW, respectively, thereby indicating their contribution to the variation in AOM under N addition. Our findings provide insight into the potential consequences of terrestrial N input; these may weaken CH4 consumption by anaerobic oxidation in the Yangtze River Estuary, and decrease carbon stabilization and storage in coastal wetland sediments.