There are growing evidences that trees emit methane through their stem, but this was often related to the transfer of CH₄ produced in anoxic soil layers. Microbial communities in the heartwood of trees when anaerobic conditions prevail can be another important but overlooked source of CH₄ in forests. Our objective was to characterize the variability of stem CH₄ emissions across individuals and species, and within individuals of five major species at the Ashiu experimental forest.
On four broadleaved species, we found significant CH₄ emission, especially on large trees at a height of more than 1.5 m while lower emission was often recorded at lower position along the trunk, which suggests that CH₄ is produced in the stem, not transported from the soil.
To test the hypothesis that stems of these species are home to a microbial community comprising methanogenic archaea, we are now extracting DNA from heartwood samples and amplifying the gene coding the methyl-coenzyme M reductase subunit alpha (mcrA), characteristics of methanogenic archaea.
The fact that not only soil methane dynamics but also internal production in tree stems must be accounted for in methane budget of forests is a paradigm shift in forest and environmental sciences.