Methane emissions from terrestrial plants under aerobic conditions

Abstract

Methane is an important greenhouse gas and its atmospheric concentration has almost tripled since pre-industrial times. It plays a central role in atmospheric oxidation chemistry and affects stratospheric ozone and water vapour levels. Most of the methane from natural sources in Earth's atmosphere is thought to originate from biological processes in anoxic environments. Here we demonstrate using stable carbon isotopes that methane is readily formed in situ in terrestrial plants under oxic conditions by a hitherto unrecognized process. Significant methane emissions from both intact plants and detached leaves were observed during incubation experiments in the laboratory and in the field. If our measurements are typical for short-lived biomass and scaled on a global basis, we estimate a methane source strength of 62-236 Tg yr(-1) for living plants and 1-7 Tg yr(-1) for plant litter (1 Tg = 10(12) g). We suggest that this newly identified source may have important implications for the global methane budget and may call for a reconsideration of the role of natural methane sources in past climate change.

Evidence for methane production by saprotrophic fungi

“…1a) the CH 4 mixing ratio increased without a concomitant increase in CO 2 . Thus, CH 4 released from the dead plant material resulted from the process shown by Keppler et al 7 and Vigano et al 21 Experiments in which labelled 13 C-glucose was supplied as a carbon source to the fungi not only unambiguously demonstrated that the CH 4 originated from the labelled substrate but also excluded any possibility of ingress from the laboratory atmosphere to the samples as the source of CH 4 . In addition, the laboratory atmosphere, which was measured alternately with every sample, never exceeded 2,000 p.p.b.v.…”

“…The collective evidence from fungi, plants 7 and animal cells 9 indicates that aerobic CH 4 formation may not be an exotic process, but could be widespread in nature. Further research is needed to elucidate the mechanism of CH 4 formation in fungi and its possible relevance for ecology and the global CH 4 budget.…”

“…Traditionally, biogenic CH 4 was thought to be formed only by prokaryotic microorganisms (methanogens; archaea) under strictly anoxic conditions in wetland soils and rice paddies, the intestines of termites and ruminants, and human and agricultural waste 6 . However, recently CH 4 formation was also reported to occur under oxic conditions in terrestrial vegetation 7,8 and in animals 9 .…”

“…The finding that dead and living plants can emit CH 4 under oxic conditions and without the intervention of microorganisms 7,8,10 justifies a search for other biotic but non-prokaryotic CH 4 sources in fungi and animals 11 . Less well known are the findings of Ghyczy et al 9,12 who demonstrated that endothelial cells from rat liver produced CH 4 when exposed to site-specific inhibitors of the electron transport chain (ETC).…”

Emission of nitrous oxide and carbon dioxide from semi-arid tropical soils in Chiapas México

“…Although the impact of land use and land cover on the global average surface albedo (biogeophysical effect) and on the atmospheric concentration of carbon dioxide (CO 2 ), nitrous oxide (N 2 O) and methane (CH 4 ) has been included in international climate change assessments (IPCC, 2001), less attention has been paid to the role of land use change and differences in regional temperatures, precipitation, vegetation and other climate variables, particularly in arid and semi-arid regions (Pielke, 2005;Keppler et al, 2006).…”