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

• The observation that plants produce methane (CH₄) 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 CH₄ 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 CH₄. 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 CH₄ formation under UV irradiation and heating. • A strong deuterium signal in the emitted CH₄ was observed from these labelled polysaccharides. • Results clearly demonstrate that ester methyl groups of pectin can serve as a precursor of CH₄, supporting the idea of a novel chemical route of CH₄ formation in plants under oxic environmental conditions.