Global methane emission estimates from ultraviolet irradiation of terrestrial plant foliage

Several studies have reported in situ methane (CH4) emissions from vegetation foliage, but there remains considerable debate about its significance as a global source. Here, we report a study that evaluates the role of ultraviolet (UV) radiation-driven CH4 emissions from foliar pectin as a global CH4 source. We combine a relationship for spectrally weighted CH4 production from pectin with a global UV irradiation climatology model, satellite-derived leaf area index (LAI) and air temperature data to estimate the potential global CH4 emissions from vegetation foliage. Our results suggest that global foliar CH4 emissions from UV-irradiated pectin could account for 0.2-1.0 Tg yr-1, of which 60% is from tropical latitudes, corresponding to < 0.2% of total CH4 sources. Our estimate is one to two orders of magnitude lower than previous estimates of global foliar CH4 emissions. Recent studies have reported that pectin is not the only molecular source of UV-driven CH4 emissions and that other environmental stresses may also generate CH4. Consequently, further evaluation of such mechanisms of CH4 generation is needed to confirm the contribution of foliage to the global CH4 budget.