It has been proposed that plants are capable of producing methane by a novel and unidentified biochemical pathway. Emission of methane with an apparently biological origin was recorded from both whole plants and detached leaves. This was the first report of methanogenesis in an aerobic setting, and was estimated to account for 10–45 per cent of the global methane source. Here, we show that plants do not contain a known biochemical pathway to synthesize methane. However, under high UV stress conditions, there may be spontaneous breakdown of plant material, which releases methane. In addition, plants take up and transpire water containing dissolved methane, leading to the observation that methane is released. Together with a new analysis of global methane levels from satellite retrievals, we conclude that plants are not a major source of the global methane production.

References

Adl S.M, et al. 2005 The new higher level classification of eukaryotes with emphasis on the taxonomy of protists. J. Eukaryot. Microbiol. 52, 399–451.doi:10.1111/j.1550-7408.2005.00053.x. . Crossref, PubMed, ISI, Google Scholar
Bergamaschi P, et al. 2007 Satellite chartography of atmospheric methane from SCIAMACHY on board ENVISAT: 2. Evaluation based on inverse model simulations. J. Geophys. Res. 112, D02304 doi:10.1029/2006JD007268. . Crossref, ISI, Google Scholar
Billings S.A, Richter D.D& Yarie J . 2000 Sensitivity of soil methane fluxes to reduced precipitation in boreal forest soils. Soil Biol. Biochem. 32, 1431–1441.doi:10.1016/S0038-0717(00)00061-4. . Crossref, ISI, Google Scholar
Braga do Carmo J, Keller M, Dezincourt Dias J, Barbosa de Camargo P& Crill P . 2006 A source of methane from upland forests in the Brazilian Amazon. Geophys. Res. Lett. 33, L04809 doi:10.1029/2005GL025436. . Crossref, ISI, Google Scholar
Bruhn D, Mikkelsen T.N& Ambus P . 2007 Aerobic emission of methane by terrestrial plant material in response to stress. Am. Geophys. Union. 88, Fall Meet. Suppl., Abstract, p. B53A-0940. Google Scholar
Colmer T.D . 2003 Long-distance transport of gases in plants: a perspective on internal aeration and radial oxygen loss from roots. Plant Cell Environ. 26, 17–36.doi:10.1046/j.1365-3040.2003.00846.x. . Crossref, ISI, Google Scholar
Croft M.T, Lawrence A.D, Raux-Deery E, Warren M.J& Smith A.G . 2005 Algae acquire vitamin B12 through a symbiotic relationship with bacteria. Nature. 438, 90–93.doi:10.1038/nature04056. . Crossref, PubMed, ISI, Google Scholar
Dueck T.A, et al. 2007 No evidence for substantial aerobic methane emission by terrestrial plants: a δ¹³C-labelling approach. New Phytol. 175, 29–35.doi:10.1111/j.1469-8137.2007.02103.x. . Crossref, PubMed, ISI, Google Scholar
Dyhrman S.T, Chappel P.D, Haley S.T, Moffett J.W, Orchard E.D, Waterbury J.B& Webb E.A . 2006 Phosphonate utilization by the globally important marine diazotroph Tricodesmium. Nature. 396, 68–71.doi:10.1038/nature04203. . Crossref, ISI, Google Scholar
Ellis L.B.M, Roe D& Wackett L.P . 2006 The University of Minnesota biocatalysis/biodegradation database: the first decade. Nucleic Acids Res. 34, D517–D521.doi:10.1093/nar/gkj076. . Crossref, PubMed, ISI, Google Scholar
Ferretti D.F, Miller J.B, White J.C.W, Lassey K.R, Lowe D.C& Etheridge D.M . 2006 Stable isotopes provide revised global limits of aerobic methane emissions from plants. Atmos. Chem. Phys. Discuss. 6, 5867–5875. Crossref, Google Scholar
Fiedler S, Holl B.S& Jungkunst H.F . 2005 Methane budget of a Black Forest spruce ecosystem considering soil pattern. Biogeochemistry. 76, 1–20.doi:10.1007/s10533-005-5551-y. . Crossref, ISI, Google Scholar
Frankenberg C, Meirink J.F, van Weele M, Platt U& Wagner T . 2005 Assessing methane emissions from global space-borne observations. Science. 308, 1010–1014.doi:10.1126/science.1106644. . Crossref, PubMed, ISI, Google Scholar
Frankenberg C, et al. 2006 Satellite chartography of atmospheric methane from SCIAMACHY on board ENVISAT: analysis of the years 2003 and 2004. J. Geophys. Res. 111, D07303 doi:10.1029/2005JD006235. . Crossref, ISI, Google Scholar
Gogoi N, Baruah K.K, Gogoi B& Gupta P.K . 2005 Methane emission characteristics and its relations with plant and soil parameters under irrigated rice ecosystem of northeast India. Chemosphere. 55, 1677–1684.doi:10.1016/j.chemosphere.2004.11.047. . Crossref, ISI, Google Scholar
Hideg E& Vass I . 1996 UV-B induced free radical production in plant leaves and isolated thylakoid membranes. Plant Sci. 115, 251–260.doi:10.1016/0168-9452(96)04364-6. . Crossref, ISI, Google Scholar
Houweling S, Rockmann T, Aben I, Keppler F, Krol M, Meirink J.F, Dlugokencky E.J& Frankenberg C . 2006 Atmospheric constraints on global emissions of methane from plants. Geophys. Res. Lett. 33, L15821 doi:10.1029/2006GL026162. . Crossref, ISI, Google Scholar
Huang J, Su Z& Xu Y . 2005 The evolution of microbial phosphonate degradative pathways. J. Mol. Evol. 61, 682–690.doi:10.1007/s00239-004-0349-4. . Crossref, PubMed, ISI, Google Scholar
Karl D.M, Beversdorf L, Bjorkman K.M, Church M.J, Martinez A& DeLong E.F . 2008 Aerobic production of methane in the sea. Nat. Geosci. 1, 473–478.doi:10.1038/ngeo234. . Crossref, ISI, Google Scholar
Keppler F, Hamilton J.T.G, Brass M& Rockmann T . 2006 Methane emissions from terrestrial plants under aerobic conditions. Nature. 439, 187–191.doi:10.1038/nature04420. . Crossref, PubMed, ISI, Google Scholar
Keppler F, Hamilton J.T.G, McRoberts W.C, Vigano I, Brass M& Rockmann T . 2008 Methoxyl groups of plant pectin as a precursor of atmospheric methane: evidence from deuterium labelling studies. New Phytol. 179, 808–814.doi:10.1111/j.1469-8137.2008.02411.x. . Crossref, PubMed, ISI, Google Scholar
Kittridge J.S& Roberts E . 1969 A carbon-phosphorous bond in nature. Science. 164, 37–42.doi:10.1126/science.164.3875.37. . Crossref, PubMed, ISI, Google Scholar
Kovacs E& Keresztes A . 2002 Effect of gamma and UV-B/C radiation on plant cells. Micron. 33, 199–210.doi:10.1016/S0968-4328(01)00012-9. . Crossref, PubMed, ISI, Google Scholar
Miller J.B, Gatti L.V, D'Amelio M.T.S, Crotwell A.M, Dlugokencky E.J, Bakwin P, Artaxo P& Tans P.P . 2007 Airborne measurements indicate large methane emissions from the eastern Amazon basin. Geophys. Res. Lett. 34, L10809 doi:10.1029/2006GL029213. . Crossref, ISI, Google Scholar
Moreira M.Z, Sternberg L.D.S.L, Martinelli L.A, Victoria R.L, Barbosa E.M, Bonates L.C.M& Nepstad D.C . 1997 Contribution of transpiration to forest ambient vapour based on isotopic measurements. Glob. Change Biol. 3, 439–450.doi:10.1046/j.1365-2486.1997.00082.x. . Crossref, ISI, Google Scholar
Nouchi I, Mariko S& Aoki K . 1990 Mechanism of methane transport from the rhizosphere to the atmosphere through rice plants. Plant Physiol. 94, 59–66.doi:10.1104/pp.94.1.59. . Crossref, PubMed, ISI, Google Scholar
R Development Core Team. 2007 R: a language and environment for statistical computing. 2.5.0. Vienna, Austria: R Foundation for Statistical Computing. Google Scholar
Raven J.A . 1996 Into the voids: the distribution, function, development and maintenance of gas spaces in plants. Ann. Bot. 78, 137–142.doi:10.1006/anbo.1996.0105. . Crossref, ISI, Google Scholar
Rockmann T, Vigano I, Holzinger R, van Weelden H& Keppler F . 2007 News about methane emissions from plant matter. Am. Geophys. Union. 88, Fall Meet. Suppl., Abstract, pp. B51F-05. Google Scholar
Rusch H& Rennenberg H . 1998 Black alder (Alnus glutinosa (L.) Gaertn.) trees mediate methane and nitrous oxide emissions from the soil to the atmosphere. Plant Soil. 1998, 1–7.doi:10.1023/A:1004331521059. . Crossref, ISI, Google Scholar
Shimazaki K.I, Doi M, Assmann S.M& Kinoshita T . 2007 Light regulation of stomatal movement. Annu. Rev. Plant Biol. 58, 219–247.doi:10.1146/annurev.arplant.57.032905.105434. . Crossref, PubMed, ISI, Google Scholar
Staddon P.L . 2004 Carbon isotopes in functional soil ecology. Trends Ecol. Evol. 19, 148–154.doi:10.1016/j.tree.2003.12.003. . Crossref, PubMed, ISI, Google Scholar
Sterling C& Kalb A.J . 1959 Pectin changes in peach during ripening. Bot. Gaz. 121, 111–113.doi:10.1086/336052. . Crossref, Google Scholar
Teh Y.A, Silver W.L& Conrad M.E . 2005 Oxygen effects on methane production and oxidation in humid tropical forest soils. Glob. Change Biol. 11, 1283–1297.doi:10.1111/j.1365-2486.2005.00983.x. . Crossref, ISI, Google Scholar
Vigano I, Holzinger R& Rockmann T . 2007 The isotope signature of methane emitted from plant matter upon irridiation with UV light. Am. Geophy. Union. 88, Fall Meet. Suppl., Abstract, p. B53A-0938. Google Scholar
Wang Z.P, Han X.G, Wang G.G, Song Y& Gulledge J . 2008 Aerobic methane emission from plants in the inner Mongolia steppe. Environ. Sci. Technol. 42, 62–68.doi:10.1021/es071224l. . Crossref, PubMed, ISI, Google Scholar
Whiticar M.J& Ednie A.C . 2007 Aerobic methane generation from plants (AMP)? Yes, mostly!. Am. Geophys. Union. 88, Fall Meet. Suppl., Abstract, p. B53A-0939. Google Scholar
Willis K.J& McElwain J.C The evolution of plants. 2002 Oxford, UK:Oxford University Press. Google Scholar
Yavitt J.B& Knapp A.K . 1995 Methane emission to the atmosphere through emergent cattail (Typha latifolia L.) plants. Tellus B. 47, 521–534.doi:10.1034/j.1600-0889.47.issue5.1.x. . Crossref, Google Scholar
Zeikus J.G . 1977 The biology of methanogenic bacteria. Bacteriol. Rev. 41, 514–541. Crossref, PubMed, Google Scholar
Zeikus J.G& Ward J.C . 1974 Methane formation in living trees: a microbial origin. Science. 184, 1181–1183.doi:10.1126/science.184.4142.1181. . Crossref, PubMed, ISI, Google Scholar
Zhaxybayeva O, Gogarten J.P, Charlebois R.L, Doolittle W.F& Papke R.T . 2006 Phylogenetic analyses of cyanobacterial genomes: quantification of horizontal gene transfer events. Genome Res. 16, 1099–1108.doi:10.1101/gr.5322306. . Crossref, PubMed, ISI, Google Scholar