PS 68-145 - The effects of pH on carbon mineralization to CO2 and CH4 in peatlands across an ombrotrophic-minerotrophic gradient

Thursday, August 11, 2011
Exhibit Hall 3, Austin Convention Center
Nathanael M. Eisenhut, Center for Ecology and Evolutionary Biology, University of Oregon, Eugene, OR, Rongzhong Ye, Land, Air, and Water Resources, University of California, Davis, Davis, CA, Brendan J. M. Bohannan, Center for Ecology & Evolutionary Biology, University of Oregon, Eugene, OR, Qusheng Jin, Department of Geological Sciences, University of Oregon, Eugene, OR and Scott D. Bridgham, Institute of Ecology and Evolution, University of Oregon, Eugene, OR

Methane (CH4)  is a major greenhouse gas, and wetlands are the largest natural source of CH4.  Production and emissions of CH4 vary greatly among different wetland types, and it is essential to understand fundamental controls over CH4 production to be able to predict how future climate change will impact these fluxes.  Peatlands exist along an ombrotrophic (rain-fed only) to minerotrophic (with groundwater inputs) gradient within the landscape that reflect their hydrogeomorphic position in the landscape, and soil pH is one of several factors that co-vary along this gradient.  The efficiency of CH4 production under anaerobic conditions varies greatly along this peatland gradient, but the underlying mechanisms that explain this variation are poorly known.  The objectives of this experiment were to determine to what extent that differences in soil pH among different types of peatlands along this hydrogeomorphic gradient control (i) total CH4 and CO2 production rates and (ii) the efficiency of CH4 production vs. CO2 production.  We adjusted the pH of peat slurries from an ombrotrophic bog, an intermediate fen, and a rich fen to 4 levels (3.5, 4.5, 5.5, and 6.5), followed by anaerobic incubation for 7 days. 


Increasing pH significantly enhanced CO2 production.  In the bog, CO2 production increased 216%, 300%, and 544% when the pH was raised from 3.5 to 4.5, to 5.5, and to 6.5 respectively; the increase in the rich fen was 127%, 154%, and 209%, correspondingly.  Adjustment of pH significantly influenced CH4 production, but the effects depended on time and peat types.  On the 2nd day of incubation, the rates in the bog were not different among pH levels, but rates in the intermediate and rich fens were lower at pH 3.5 than those at higher pH.  On the 7th day of incubation, CH4 production rates in the bog at pH 3.5 were significantly lower those at  higher pH.  Likewise, the rates in the intermediate fen at pH 3.5 were significantly lower than those at higher pH.  pH effects on percentages of CH4 production to total mineralized carbon (CH4 + CO2) were only significant in the rich fen.  At pH 3.5, CH4 accounted for only 4.2% of total productions, which was significantly lower than those at pH 4.5 (11.7%), pH 5.5 (18.4%), and pH 6.5 (12.2%).  pH is an important environmental factor controlling carbon mineralization to CO2 and CH4 productions in peatlands. 

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