Methane Oxidation Potential and Niche Differentiation of Aerobic Methanotrophs in Coastal Mangrove Forest Soils along a 370 Km Long Coastline in Taiwan

Mangrove forests are key blue carbon ecosystems, but their net sink potential depends on methane oxidation in soils. In this study, DNA-based stable isotope probing was employed to decipher the changes of potentially active methanotrophic communities across five different mangrove forests along a 370 km coastline of Taiwan, with <i>Kandelia obovata</i> dominating the northern sites (Hsinchu and Miaoli) and <i>Avicennia marina</i> dominating the central and southern sites (Changhua, Tainan, and Pingtung). The results showed that the CH₄ oxidation potentials ranged from 10 to 60 nmol CH₄ g^-1 hr¹ in the mangrove forest soils. The <i>pmoA</i> sequencing of fresh soils revealed that unclassified <i>Methylomonadaceae</i>-affiliated methanotrophs, <i>Methylomicrobium-jap-rel</i>, <i>Methylobacter</i>, and <i>Methylomonas</i> were predominant in <i>K. obovata</i> forests. In contrast, unclassified <i>Methylomonadaceae</i>-affiliated methanotrophs and <i>Methylomonas</i> dominated in <i>A. marina</i> forests. Furthermore, <i>Methylomonadaceae</i>-affiliated methanotrophs were positively correlated to soil TOC and TN. DNA-SIP analysis further identified unclassified <i>Methylomonadaceae</i>-affiliated methanotrophs, <i>Methylomonas</i>, and <i>Methylobacter</i> as potentially active methanotrophs in <i>K. obovata</i> forests. In contrast, other unclassified <i>Methylomonadaceae</i>-affiliated methanotrophs and methanotrophs belonging to the deep-sea-1 and deep-sea-3 clusters were potentially active in <i>A. marina</i> forests. Overall, this study revealed distinct biogeographic patterns of methanotrophs in Taiwan's coastal mangrove ecosystems and highlighted the ecological role of <i>Methylomonadaceae</i> in mangrove CH₄ cycling.