Aerobic methane production in Scots pine shoots is independent of drought or photosynthesis

Shoot-level emissions of aerobically produced methane (CH₄) may be an overlooked source of tree-derived CH₄, but insufficient understanding of the interactions between their environmental and physiological drivers still prevents the reliable upscaling of canopy CH₄ fluxes. We utilised a novel automated chamber system to continuously measure CH₄ fluxes from the shoots of Pinus sylvestris (Scots pine) saplings under drought to investigate how canopy CH₄ fluxes respond to the drought-induced alterations in their physiological processes and to isolate the shoot-level production of CH₄ from soil-derived transport and photosynthesis. We found that aerobic CH₄ emissions are not affected by the drought-induced stress, changes in physiological processes, or decrease in photosynthesis. Instead, these emissions vary on short temporal scales with environmental drivers such as temperature, suggesting that they result from abiotic degradation of plant compounds. Our study shows that aerobic CH₄ emissions from foliage are distinct from photosynthesis-related processes. Thus, instead of photosynthesis rates, it is more reliable to construct regional and global estimates for the aerobic CH₄ emission based on regional differences in foliage biomass and climate, also accounting for short-term variations of weather variables such as air temperature and solar radiation.