Karim, M. R.; Thomas, S.

The contribution of tree foliage to atmospheric methane (CH) and nitrous oxide (N2O) fluxes remains a major uncertainty in global GHG budgets. We made repeated in situ measurements of foliar CH and N2O fluxes across 25 temperate tree species interplanted at a forest restoration site using high-resolution laser spectroscopy. Tree foliage was consistently a net CH sink and a net N2O source in all species. Foliar CH oxidation increased by ~33% in fall relative to spring and was ~3-fold higher in shade-tolerant than shade-intolerant angiosperm species. Species differences accounted for most of the variability in fluxes, while correlations with soil emissions were comparatively weak. Microbial DNA sequencing revealed that the highest CH-oxidizing angiosperm species (Tilia americana) harbored abundant Type I methanotrophs, whereas the lowest-oxidizing species (Prunus virginiana) had nearly 100-fold lower methanotroph abundance, with a foliar microbial community dominated by facultative methylotrophs. Global warming potential (GWP) scaling indicates that foliar CH uptake overwhelmingly dominates the net climate forcing effect. Our results suggest that the large and predictable differences in foliar CH uptake among tree species and associated differences in foliar microbial communities are of importance in understanding and potentially enhancing the global terrestrial CH sink.