Methanotrophic symbionts provide carbon for photosynthesis in peat bogs

Abstract

Wetlands are the largest natural source of atmospheric methane1, the second most important greenhouse gas2. Methane flux to the atmosphere depends strongly on the climate3; however, by far the largest part of the methane formed in wetland ecosystems is recycled and does not reach the atmosphere4,5. The biogeochemical controls on the efficient oxidation of methane are still poorly understood. Here we show that submerged Sphagnum mosses, the dominant plants in some of these habitats, consume methane through symbiosis with partly endophytic methanotrophic bacteria, leading to highly effective in situ methane recycling. Molecular probes revealed the presence of the bacteria in the hyaline cells of the plant and on stem leaves. Incubation with 13C-methane showed rapid in situ oxidation by these bacteria to carbon dioxide, which was subsequently fixed by Sphagnum, as shown by incorporation of 13C-methane into plant sterols. In this way, methane acts as a significant (10–15%) carbon source for Sphagnum. The symbiosis explains both the efficient recycling of methane and the high organic carbon burial in these wetland ecosystems.

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Figure 1: Methane oxidation potential of different parts of submerged and non-submerged Sphagnum mosses as a measure of methanotrophs associated.
Figure 2: In situ detection of the new methanotroph in S. cuspidatum with fluorescently labelled rRNA-targeted oligonucleotide probes.
Figure 3: Incorporation of 13 C label in biological markers for Sphagnum (circles) and methanotrophic bacteria (squares).

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Acknowledgements

We thank K. T. van de Pas-Schoonen, A. Pol, H. P. M. Geurts, J. Eygensteyn, M. van Mullekom, J. Berk, H. Tomassen and M. M. A. van Herpen for technical support. Part of this study was supported by the Dutch Ministry of Agriculture, Nature Management and Food quality (Research Program ‘Overlevingsplan Bos en Natuur’).

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Correspondence to Alfons J. P. Smolders or Jaap S. Sinninghe Damsté.

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Competing interests

The 16S rRNA gene sequences were deposited at GenBank under accession number AY163571. Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

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Raghoebarsing, A., Smolders, A., Schmid, M. et al. Methanotrophic symbionts provide carbon for photosynthesis in peat bogs. Nature 436, 1153–1156 (2005) doi:10.1038/nature03802

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