The effects of pH, temperature, and DOM on anaerobic carbon mineralization and methanogenic efficiencyin ombrotrophic and minerotrophic Alaskan peatlands

Methane (CH4) production varies greatly at ombrotrophic (OP) and minerotrophic peatlands (MP), which have different sources of nutrients. These two trophic endmembers usually are found within a short distance in Alaska. The trophic status of peatlands is associated with distinguished surface vegetation and contrasting pH, which also regulates methanogenesis. Projected global warming and melting of permafrost could dramatically change the hydrology of Alaskan peatlands, which may turn ombrotrophic peatlands into minerotrophic ones. Such trophic status change would result in changes in porewater (PW) pH and the quantity and quality of dissolved organic matter (DOM), which in together with projected temperature (T) increase will affect the anaerobic carbon mineralization and methanogenic efficiency in Alaskan peatlands. To better understand how pH, T, and DOM affect fermentation and methanogenesis in OP and MP, laboratory mesocosm manipulation experiments were conducted using peats and PW collected from the minerotrophic Frozen Pond (FP) and ombrotrophic Goldencreek Bog (GB) in Fairbanks, Alaska. The manipulation includes increasing T, changing pH to the value of the reciprocal site, exchanging porewater, covarying two of the above three factors, and changing all three factors in parallel experiments, respectively. Results suggest increasing T increased methanogenesis in both sites. Changing the pH didn't affect primary fermentation in either sites. Lowering pH in FP to GB value (3.9) did diminish the methanogenesis but increasing pH in GB to 6.5 didn't lead to higher CH₄production. Although the PW from GB has higher [DOM] and more humic material, it didn't affect the methanogenesis when incubated with the peats from FP. However, it did inhibit syntrophy at FP compared to the control. The PW from FP brought methanogens to GB but only slightly increased CH4 production. A combination of the two-factor manipulation didn't bring much change compared to single factor manipulation. But when all three factors changed in GB, it increased methanogenesis and carbon remineralization rates dramatically. It seems pH is the only factor affecting these processes when incubate peat from FP.