Solar radiation drives methane emissions from the shoots of Scots pine.

Plants are recognized as sources of aerobically produced methane (CH 4 ), but the seasonality, environmental drivers and significance of CH 4 emissions from the canopies of evergreen boreal trees remain poorly understood. We measured the CH 4 fluxes from the shoots of Pinus sylvestris (Scots pine) and Picea abies (Norway spruce) saplings in a static, non-steady-state chamber setup to investigate if the shoots of boreal conifers are a source of CH 4 during spring. We found that the shoots of Scots pine emitted CH 4 and these emissions correlated with the photosynthetically active radiation. For Norway spruce, the evidence for CH 4 emissions from the shoots was inconclusive. Our study shows that the canopies of evergreen boreal trees are a potential source of CH 4 in the spring and that these emissions are driven by a temperature-by-light interaction effect of solar radiation either directly or indirectly through its effects on tree physiological processes.