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 (CH) 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 CH fluxes were highly variable (- 0.11-0.51 mg CH m h). CH production was measured in three out of ten snags; whereas, CH consumption was measured in two out of ten snags. Potential CH production and oxidation in one core from each snag was assayed in vitro. A single core produced CH under anoxic and oxic conditions, at measured rates of 0.7 and 0.6 ng CH g h, respectively. Four cores oxidized CH under oxic conditions, with an average rate of - 1.13 ± 0.31 ng CH g h. 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 CH-cycling communities in 80% of the snags. These data indicate potential for microbial attenuation of CH 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 CH cycling in coastal ghost forest wetlands to a shifting coastal landscape.