Abstract
<p>Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is a crucial link between carbon and nitrogen cycles in estuarine and coastal ecosystems. However, the factors that affect the heterogeneous variability in n-DAMO microbial abundance and activity across estuarine and intertidal wetlands remain unclear. This study examined the spatiotemporal variations in n-DAMO microbial abundance and associated activity in different estuarine and intertidal habitats via quantitative PCR and <sup>13</sup>C stable isotope experiments. The results showed that <em>Candidatus '</em>Methylomirabilis oxyfera<em>' </em>(<em>M. oxyfera</em>)-like DAMO bacteria and <em>Candidatus '</em>Methanoperedens nitroreducens<em>' </em>(<em>M. nitroreducens</em>)-like DAMO archaea cooccurred in estuarine and intertidal wetlands, with a relatively higher abundance of the <em>M. oxyfera</em>-like bacterial <em>pmoA</em> gene (4.0×10<sup>6</sup>-7.6×10<sup>7</sup> copies g<sup>-1</sup> dry sediment) than the <em>M. nitroreducens</em>-like archaeal <em>mcrA</em> gene (4.5×10<sup>5</sup>-9.4×10<sup>7 </sup>copies g<sup>-1</sup> dry sediment). The abundance of the <em>M. oxyfera</em>-like bacterial <em>pmoA</em> gene was closely associated with sediment pH and ammonium (<em>P</em><0.05), while no significant relationship was detected between <em>M. nitroreducens</em>-like archaeal<em> mcrA</em> gene abundance and the measured environmental parameters (<em>P</em>>0.05). High n-DAMO microbial activity was observed, which varied between 0.2 and 84.3 nmol <sup>13</sup>CO<sub>2</sub> g<sup>-1</sup> dry sediment day<sup>-1 </sup>for nitrite-DAMO bacteria and between 0.4 and 32.6 nmol <sup>13</sup>CO<sub>2</sub> g<sup>-1</sup> dry sediment day<sup>-1 </sup>for nitrate-DAMO archaea. The total n-DAMO potential tended to be higher in the warm season and in the upstream freshwater and low-salinity estuarine habitats and was significantly related to sediment pH, total organic carbon, Fe(II), and Fe(III) contents (<em>P</em><0.05). In addition to acting as an important methane (CH<sub>4</sub>) sink, n-DAMO microbes had the potential to consume a substantial amount of reactive N in estuarine and intertidal environments, with estimated nitrogen elimination rates of 0.5-224.7 nmol N g<sup>-1</sup> dry sediment day<sup>-1</sup>. Overall, our investigation reveals the distribution pattern and controlling factors of n-DAMO bioprocesses in estuarine and intertidal marshes and gains a better understanding of the coupling mechanisms between carbon and nitrogen cycles.</p>
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