LB 15-138 - CANCELLED - Wood microbiomes contribute to tree stem methane emissions from temperate forests

Forests are active sites of methane (CH4) uptake and emission through various biotic and abiotic pathways. While CH4 uptake by soils in upland temperate forest systems is considered a significant sink for atmospheric CH4, tree stems have recently been identified as important sites of CH4 efflux across diverse ecosystem types, leading to concerns that tree emissions may offset or diminish net CH4 uptake in upland systems. Recent investigations across ecosystems have found the presence of CH4 release from plant surfaces to be widespread, and this growing recognition of widespread CH4 efflux from plant surfaces suggests that even small fluxes per unit area could be relevant for the purposes of global greenhouse gas accounting in many ecosystems. Despite this, tree methane emissions from the upland forests of the northeast United States have been relatively understudied. Further, there remain important unresolved questions about the origins (soil vs. plant tissue) of plant-emitted CH4 and the variability between species and across environmental gradients. Here, we measured stem CH4 emissions from 160 individual tree stems across 17 species spanning an upland- to-wetland gradient in the Yale-Myers Forest (Union, Connecticut). We cored these trees and quantified the abundance of endophytic methanogens and methanotrophs using digital droplet PCR, compared microbial abundances with measured fluxes, and used amplicon sequencing to explore the cross-domain microbial communities harboring these methanogens and methanotrophs. We found that methane emissions were pervasive among tree species, with all species having positive mean CH4 fluxes to the atmosphere. We found the widespread presence of methanogens in the living wood of these trees, and found positive correlations between methanogen abundances and methane emission rates within certain species. We further found diverse and distinct bacterial, archaeal, and fungal communities inhabiting these trees, with relationships between microbial taxa and diversity and methanogen abundances. Overall, our results indicate that CH4 release through trees comprise a significant gross flux that can be partially explained by a within-stem CH4 produced by endophytic methanogens, and find that these methanogens are part of a rich and as yet largely unexplored tree microbiome.