Global methane emission estimates from ultraviolet irradiation of terrestrial plant foliage

Abstract

Summary• Several studies have reported in situ methane (CH 4 ) 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 CH 4 emissions from foliar pectin as a global CH 4 source.• We combine a relationship for spectrally weighted CH 4 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 CH 4 emissions from vegetation foliage.• Our results suggest that global foliar CH 4 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 CH 4 sources.• Our estimate is one to two orders of magnitude lower than previous estimates of global foliar CH 4 emissions. Recent studies have reported that pectin is not the only molecular source of UV-driven CH 4 emissions and that other environmental stresses may also generate CH 4 . Consequently, further evaluation of such mechanisms of CH 4 generation is needed to confirm the contribution of foliage to the global CH 4 budget.

A novel pathway of direct methane production and emission by eukaryotes including plants, animals and fungi: An overview

“…We noted above that it is highly likely that Keppler et al (2006) overestimated the amount of plant CH 4 (with the maximum reported value of 236 Tg CH 4 yr À1 ) and Bloom et al (2010) underestimated it (with the minimum reported value of 0.2 Tg CH 4 yr À1 ). Thus, we adopted here the estimates excluding these two studies of global plant-derived CH 4 and obtained a range of 15e176 Tg CH 4 yr À1 for global plant-derived CH 4 production, suggesting that the CH 4 that terrestrial plants release directly into the atmosphere represents 3%e24% of the global total (Fig.…”

“…By assuming UV radiation-induced CH 4 emissions from pectin as representing foliar CH 4 emissions, Bloom et al (2010) suggested a global contribution of 0.2e1.0 Tg plantderived CH 4 yr À1 . However, clear evidence shows that pectin is not the only precursor (Carmichael et al, 2014;Lenhart et al, 2014;Vigano et al, 2009), and several environmental stresses in addition to UV radiation have been observed to induce CH 4 production.…”

“…However, clear evidence shows that pectin is not the only precursor (Carmichael et al, 2014;Lenhart et al, 2014;Vigano et al, 2009), and several environmental stresses in addition to UV radiation have been observed to induce CH 4 production. Thus, whether Bloom et al (2010) underestimated the magnitude of this plant source of CH 4 has been a subject of debate (Bruhn et al, 2012;Fraser et al, 2015).…”

Is methane released from the forest canopy?

“…A global upscaling model for estimating aerobic CH4 emissions, based on lab results and considering only pectin content as a driver has been conducted recently by Bloom et al (2010). Their estimate is one to two orders of magnitude lower than previous estimates of global foliar CH4 emissions by Keppler et al (2006).…”

Use of a process-based model for assessing the methane budgets of global terrestrial ecosystems and evaluation of uncertainty

“…In addition, we considered the case of no plant emission (i.e., a third set of estimates), because a general consensus has not yet been reached over the significance of this process (e.g., Bloom et al, 2010).…”