Microbial Communities in Standing Dead Trees in Ghost Forests are Largely Aerobic, Saprophytic, and Methanotrophic

Standing dead trees (snags) are recognized for their influence on methane (CH₄) cycling in coastal wetlands, yet the biogeochemical processes that control the magnitude and direction of fluxes across the snag-atmosphere interface are not fully elucidated. Herein, we analyzed microbial communities and fluxes at one height from ten snags in a ghost forest wetland. Snag-atmosphere CH₄ fluxes were highly variable (- 0.11-0.51 mg CH₄ m^-2 h^-1). CH₄ production was measured in three out of ten snags; whereas, CH₄ consumption was measured in two out of ten snags. Potential CH₄ production and oxidation in one core from each snag was assayed in vitro. A single core produced CH₄ under anoxic and oxic conditions, at measured rates of 0.7 and 0.6 ng CH₄ g^-1 h^-1, respectively. Four cores oxidized CH₄ under oxic conditions, with an average rate of - 1.13 ± 0.31 ng CH₄ g^-1 h^-1. Illumina sequencing of the V3/V4 region of the 16S rRNA gene sequence revealed diverse microbial communities and indicated oxidative decomposition of deadwood. Methanogens were present in 20% of the snags, with a mean relative abundance of < 0.0001%. Methanotrophs were identified in all snags, with a mean relative abundance of 2% and represented the sole CH₄-cycling communities in 80% of the snags. These data indicate potential for microbial attenuation of CH₄ emissions across the snag-atmosphere interface in ghost forests. A better understanding of the environmental drivers of snag-associated microbial communities is necessary to forecast the response of CH₄ cycling in coastal ghost forest wetlands to a shifting coastal landscape.