Methoxyl groups of plant pectin as a precursor of atmospheric methane: evidence from deuterium labelling studies

Abstract

Summary• The observation that plants produce methane (CH 4 ) under aerobic conditions has caused considerable controversy among the scientific community and the general public. It led to much discussion and debate not only about its contribution to the global CH 4 budget but also about the authenticity of the observation itself. Previous results suggested that methoxyl groups of the abundant plant structural component pectin might play a key role in the in situ formation process of CH 4 . Here, this effect is investigated using an isotope labelling study.• Polysaccharides, pectin and polygalacturonic acid, with varying degrees of trideuterium-labelled methyl groups in the methoxyl moieties, were investigated for CH 4 formation under UV irradiation and heating.• A strong deuterium signal in the emitted CH 4 was observed from these labelled polysaccharides.• Results clearly demonstrate that ester methyl groups of pectin can serve as a precursor of CH 4 , supporting the idea of a novel chemical route of CH 4 formation in plants under oxic environmental conditions.

Three years of greenhouse gas column-averaged dry air mole fractions retrieved from satellite – Part 2: Methane

“…However, the potential role of plants has become now further controversial after a recent study by Dueck et al (2007) questioning the measurements of Keppler et al (2006). Using an independent method based on 13 C labelling and laser-based measurements, Dueck et al (2007) did not find evidence for substantial CH 4 emissions of plants under aerobic conditions while Keppler et al (2008) confirm their earlier work by providing evidence that methoxyl groups of pectin can act as a source of atmospheric CH 4 under aerobic conditions. Nevertheless, the contribution of emissions from plants to the global methane budget remains uncertain.…”

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

“…soil or plant water) and whether plants have their own mechanism(s) to produce CH 4 have been debated (Bruhn et al, 2012;Keppler et al, 2009;Nisbet et al, 2009). Evidence is now accumulating to indicate that plants can produce CH 4 even in the presence of oxygen (Bruggemann et al, 2009;Bruhn et al, 2009Bruhn et al, , 2014Cao et al, 2008;Fraser et al, 2015;Keppler et al, 2008;Lenhart et al, 2014;McLeod et al, 2008;Messenger et al, 2009;Mikkelsen et al, 2011;Reid, 2009, 2011;Sanhueza and Donoso, 2006;Sinha et al, 2007;Vigano et al, 2009Vigano et al, , 2008Wang et al, 2009aWang et al, , 2009bWang et al, , 2011aWatanabe et al, 2012;Wishkerman et al, 2011).…”

“…pectin, lignin, cellulose and leaf surface wax) (Bruhn et al, 2014;Keppler et al, 2008;McLeod et al, 2008;Messenger et al, 2009;Vigano et al, 2009Vigano et al, , 2008 have been extensively tested. The majority of studies reported substantial CH 4 emissions, while Bowling et al (2009) reported no evidence for substantial CH 4 emissions by a conifer forest under high UV radiation, to which a soil CH 4 sink might contribute.…”

“…Based on d 13 C results, Keppler et al (2006) presumed that the observed CH 4 production stemmed from a C 1 metabolite pool. Pectin was first tested as a potential carbonaceous precursor because it has large amounts of various types of methyl groups (Bruhn et al, 2009;Keppler et al, 2006Keppler et al, , 2008 (Fig. 2).…”

Abiotic methanogenesis from organosulphur compounds under ambient conditions

“…It has been shown that CH 4 can be produced abiotically from plant material by exposing it to ultraviolet (UV) irradiation [15][16][17][18] . A reaction of reactive oxygen species (ROS) with methoxyl groups of pectic polysaccharides was suggested as a possible route to CH 4 formation under UV radiation 19 .…”