New Wrinkle in Carbon Cycling

BIOGEOCHEMISTRY

A bacterium living on and inside the cells of Sphagnum moss in peat bogs has been discovered to oxidize methane to carbon dioxide, which the moss then uses as a carbon source for photosynthesis. This symbiotic relationship helps to better explain the fate of CH₄ produced by decaying plants in wetland ecosystems, an important part of Earth's carbon cycle that affects the concentration of greenhouse gases in the atmosphere.

Jaap S. Sinninghe Damst? of the Royal Netherlands Institute for Sea Research, Alfons J. P. Smolders and Ashna A. Raghoebarsing of Radboud University, in the Netherlands, and colleagues identified the bacterium as a relative of a Methylocella species (Nature 2005, 436, 1153). In lab studies, the researchers incubated moss plants with ¹³C-labeled methane to show rapid in situ bacterial oxidation of ¹³CH₄ to ¹³CO₂.

Over several days, the moss fixed the ¹³CO₂ into carbohydrates, which was monitored by measuring the formation of a ¹³C-containing sitosterol. The team confirmed the findings by comparing the lab results with the natural abundance of the carbon isotope in moss plants in a peat bog.

Atmospheric CO₂ was originally believed to be the main carbon source for peat mosses. But earlier work by the Netherlands team indicated that atmospheric CO₂ alone is not sufficient to account for the growth of some peat mosses.

Overall, the moss uses the recycling mechanism to generate about 15% of its carbon intake. This efficient recycling is important, because it reduces the amount of methane--a potent greenhouse gas--that enters the atmosphere, Damst? notes. The team plans to study the phenomenon in other peat bogs. If the recycling is a general phenomenon, it should have an impact on the modeling of global climate change.