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Fluxes and 13C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought
K.-H. Knorr1, B. Glaser2, and C. Blodau1
1Limnological Research Station and Department of Hydrology, University of Bayreuth, Universitätsstraß e 30, 95440 Bayreuth, Germany
2Department of Soil Physics, University of Bayreuth, Universitätsstraß e 30, 95440 Bayreuth, Germany
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Abstract. The impact of drought and rewetting on carbon cycling in peatland ecosystems
is currently debated. We studied the impact of experimental drought and
rewetting on intact monoliths from a temperate fen over a period of ~300 days, using a permanently wet treatment and two treatments undergoing
drought for 50 days. In one of the mesocosms vegetation had been removed. Net
production of CH4 was calculated from mass balances in the peat and
emission using static chamber measurements and results compared to 13C
isotope budgets of CO2 and CH4 and energy yields of acetoclastic
and hydrogenotrophic methanogenesis. Drought retarded methane production
after rewetting for days to weeks and promoted methanotrophic activity.
Based on isotope and flux budgets, aerobic soil respiration contributed 32–96% in the wet
and 86–99% in the other treatments. Drying and
rewetting did not shift methanogenic pathways according to δ 13C
ratios of CH4 and CO2. Although δ13C ratios indicated
a prevalence of hydrogenotrophic methanogenesis, free energies of this
process were small and often positive on the horizon scale, suggesting that
methane was produced very locally. Fresh plant-derived carbon input
apparently supported respiration in the rhizosphere and sustained
methanogenesis in the unsaturated zone according to a 13C-CO2 labelling experiment. The study documents that drying and rewetting in a
rich fen soil may have little effect on methanogenic pathways but result in
rapid shifts between methanogenesis and methanotrophy. Such shifts may be
promoted by roots and soil heterogeneity, as hydrogenotrophic methanogenesis
occurred locally even when conditions were not conducive for this process in
the bulk peat.
Discussion Paper (PDF, 2753 KB) Interactive Discussion (Final Response, 4 Comments)
Citation: Knorr, K.-H., Glaser, B., and Blodau, C.: Fluxes and 13C isotopic composition of dissolved carbon and pathways of methanogenesis in a fen soil exposed to experimental drought, Biogeosciences Discuss., 5, 1319-1360, 2008. Bibtex EndNote Reference Manager
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