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 uncertain in global greenhouse gas (GHG) budgets. We investigated whether species identity, shade tolerance, and leaf‐associated microbes influence foliar CH 4 and N 2 O exchange. We conducted 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, complemented by colocated soil flux measurements, and targeted microbial DNA sequencing. Tree foliage consistently acted as a net CH 4 sink and net N 2 O source. Foliar CH 4 oxidation increased by c. 33% in fall and was approximately threefold higher in shade‐tolerant than shade‐intolerant angiosperms, whereas N 2 O emissions were highest in shade‐intolerant species with limited seasonality. Species identity explained most flux variability, with the highest‐CH 4 ‐oxidizing angiosperm ( Tilia americana ) showing an order‐of‐magnitude higher particulate methane monooxygenase ( pmoA ) copy numbers and much greater Type I methanotroph representation than the lowest‐CH 4 ‐oxidizing species ( Prunus virginiana ). Foliar CH 4 uptake dominated the net non‐CO 2 climate forcing effect despite consistent N 2 O emissions. These findings highlight tree species identity and shade tolerance as key axes of foliar CH 4 uptake and N 2 O emission, with abundance and species composition of leaf‐associated methanotrophs also tracking species‐level variation in foliar CH 4 uptake.