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キーワード:
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要旨:
Lakes are a significant source of atmospheric CH4 and play an important role in the
global carbon cycle. Little information on methane production in high-altitude lakes is
available. We determined the methanogenic archaeal community composition, the
methanogenic pathways, and carbon isotope fractionation in lake sediments and wetland
soils on the Tibetan Plateau at about 4000m above sea level (asl). We measured CH4
production rates and the d13C of CO2, CH4, and acetate in the presence and absence of
methyl fluoride, an inhibitor of acetotrophic methanogenesis, in sediments of five lakes
(Awong Co, Bangong Co, Gongzhu Co, Daze Co, and Ranwu) and wetland soils adjacent
to Bangong Co and Ranwu. Methane in Bangong Co sediment and in the wetland soil near
Ranwu was mainly produced by acetotrophic methanogenesis, whereas methane in the
sediments of the two saline lakes Awong Co and Gongzhu Co was mainly generated by
hydrogenotrophic methanogensis; chemolithotrophic acetogenesis and methanoldependent
methanogenesis may also have played a role. The stable carbon isotope
fractionation during CH4 production from CO2 was relatively large (average e =78%).
The methanogenic communities were similar to those found in lowland lake sediments, but
those of saline and nonsaline Tibetan lakes differed. Hydrogenotrophic methanogens were
dominant in lake sediments, while acetotrophic methanogens were dominant in wetland
soils. Our results revealed diversity in the methanogenic communities and their
methanogenic pathways and indicated that they are affected by sediment characteristics,
such as salinity. However, the CH4 production rates ranging from 6 to 122 nmol day1 g
dry weight1 showed no relationship to environmental characteristics and were not limited by microbial abundance.
