Microbial dynamics and activity of denitrifying anaerobic methane oxidizers in China's estuarine and coastal wetlands

Abstract

Estuarine and coastal wetlands, which act as large sources of methane (CH₄) and undergo substantial loading of anthropogenic nitrogen (N), provide ideal conditions for denitrifying anaerobic methane oxidation (DAMO) to occur. Yet the microbial mechanisms governing DAMO and the main driving factors in estuarine and coastal ecosystems remain unclear. This study investigated the spatiotemporal distribution and associated activity of DAMO microorganisms along a wide swath of China's coastline (latitudinal range: 22-41°N) using molecular assays and isotope tracing techniques. We uncovered significant spatial and seasonal variation in DAMO bacterial community structure, whereas DAMO archaeal community structure exhibited no seasonal differences. The abundance of DAMO bacterial pmoA gene (2.2 × 10⁵-1.0 × 10⁷ copies g^-1) was almost one order of magnitude higher than that of DAMO archaeal mcrA gene (8.7 × 10⁴ -1.8 × 10⁶ copies g^-1). A significant positive correlation between pmoA and mcrA gene abundances (p < 0.01) was observed, indicating that DAMO bacteria and archaea may cooperate closely and thus complete nitrate elimination. Potential DAMO rates, in the range of 0.09-23.4 nmol ¹³CO₂ g^-1 day^-1 for nitrite-DAMO and 0.03-43.7 nmol ¹³CO₂ g^-1 day^-1 for nitrate-DAMO, tended to be greater in the relatively warmer low-latitudes. Potential DAMO rates were weakly positively correlated with gene abundances, suggesting that DAMO microbial activity could not be predicted directly by gene abundance alone. The heterogeneous variability of DAMO was shaped by interactions among key environmental characteristics (sediment texture, N availability, TOC, Fe³⁺, salinity of water, and temperature). On a broader continental scale, potential N removal rates of 0.1-11.2 g N m^-2 yr^-1 were estimated via nitrite-DAMO activity in China's coastal wetlands. Overall, our results highlight the widespread distribution of DAMO microbes and their potential role in eliminating excess N inputs and reducing CH₄ emissions in estuarine and coastal ecosystems, which could help mitigate global warming.

Keywords: Denitrifying anaerobic methane oxidation; Estuarine and coastal wetlands; Nitrogen removal; mcrA gene; pmoA gene.