Abstract
Tree stems are an important and unconstrained source of methane, yet it is uncertain if there are internal microbial controls (i.e. methanotrophy) within tree bark, that may reduce methane emissions. Using multiple lines of evidence, we demonstrate here that unique microbial communities dominated by methane oxidising bacteria (MOB) dwell within bark of Melaleuca quinquenervia, a common, invasive and globally distributed lowland species. Laboratory incubations of methane inoculated M. quinquenervia bark reveal methane consumption (up to 96.3 µmol m-2 bark d-1) and distinct isotopic δ13C-CH4 enrichment characteristic of MOB. Molecular analysis indicates unique microbial communities reside within the bark, with methane-oxidising bacteria primarily from the genus Methylomonas comprising up to 25 % of the total microbial community. Methanotroph abundance was linearly correlated to methane uptake rates (R2 = 0.76, p = 0.006). Finally, field-based methane oxidation inhibition experiments demonstrate that bark-dwelling MOB reduce methane emissions by 36 ± 5 %. These multiple, complementary lines of evidence indicate that bark-dwelling MOB represent a novel and potentially significant methane sink, and an important frontier for further research.