Contrasting wetland CH₄ emission responses to simulated glacial atmospheric CO₂ in temperate bogs and fens

Boardman, Carl P.; Gauci, Vincent; Watson, Jonathan S.; Blake, Stephen and Beerling, David J. (2011). Contrasting wetland CH₄ emission responses to simulated glacial atmospheric CO₂ in temperate bogs and fens. New Phytologist, 192(4) pp. 898–911.

DOI: https://doi.org/10.1111/j.1469-8137.2011.03849.x

Abstract

Wetlands were the largest source of atmospheric methane (CH₄) during the Last Glacial Maximum (LGM), but the sensitivity of this source to exceptionally low atmospheric CO₂ concentration ([CO₂]) at the time has not been examined experimentally. We tested the hypothesis that LGM atmospheric [CO₂] reduced CH4 emissions as a consequence of decreased photosynthate allocation to the rhizosphere. We exposed minerotrophic fen and ombrotrophic bog peatland mesocosms to simulated LGM (c. 200 ppm) or ambient (c. 400 ppm) [CO₂] over 21 months (n = 8 per treatment) and measured gaseous CH₄ flux, pore water dissolved CH₄ and volatile fatty acid (VFA; an indicator of plant carbon supply to the rhizosphere) concentrations. Cumulative CH₄ flux from fen mesocosms was suppressed by 29% (P < 0.05) and rhizosphere pore water [CH₄] by c. 50% (P < 0.01) in the LGM [CO₂], variables that remained unaffected in bog mesocosms. VFA analysis indicated that changes in plant root exudates were not the driving mechanism behind these results. Our data suggest that the LGM [CO₂] suppression of wetland CH₄ emissions is contingent on trophic status. The heterogeneous response may be attributable to differences in species assemblage that influence the dominant CH₄ production pathway, rhizosphere supplemented photosynthesis and CH₄ oxidation.

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