Species-level controls of foliar methane and nitrous oxide fluxes: roles of traits and microbes in temperate trees

SUMMARY The contribution of tree foliage to atmospheric methane (CH 4 ) and nitrous oxide (N 2 O) fluxes remains a major uncertainty in global GHG budgets. We made repeated in situ measurements of foliar CH 4 and N 2 O fluxes across 25 temperate tree species interplanted at a forest restoration site using high-resolution laser spectroscopy. Tree foliage was consistently a net CH 4 sink and a net N 2 O source in all species. Foliar CH 4 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 4 -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 4 uptake overwhelmingly dominates the net climate forcing effect. Our results suggest that the large and predictable differences in foliar CH 4 uptake among tree species and associated differences in foliar microbial communities are of importance in understanding and potentially enhancing the global terrestrial CH 4 sink.