Response of microbial biomass and carbon dynamics to changing hydrological conditions in old peat deposits
Peatlands play key roles in the global ecosystem carbon (C) balance, as important C-stores. Their efficiency as long-term C-stores or atmospheric C sink is affected by the rate of microbial mineralization. Most studies on the climate change effects on the microbial communities and C-cycling in peatlands have focused on the surface layers. This thesis compared microbial biomass, community composition and internal C cycling processes in drained vs. natural peat profiles with focus on deep old peat. Using the phospholipid fatty acid (PLFA) and rRNA gene analyses, the study particularly looked at the impact of long-term drainage and the short-term effects of temperature and water content on the microbial communities as well as measured how these affected peat decomposition process e.g. by the bulk peat δ13C analysis and CO2/CH4 gas release. The results showed that low microbial activity and biomass are the major factors responsible for the low C losses and activities from old peat. Although the MBC measured by chloroform fumigation extraction (CFE) did not show drainage effects, drainage increased the total microbial PLFA biomass (m-3) up to the deepest layers of the fen but decreased it in the bog site. In the combined site data, drainage also decreased the average (± SE) proportion of archaeal to prokaryotic DNA from 44.9 ± 2.4 % to 20.1 ± 2.6 %. The differences found in PLFAs over the peat column because of drying were likely due to concomitant changes in vegetation cover. Although the living MBC appears to be a small fraction of peat total C (TC; highest range from 0.8 % to 2.0 % in the fen peat site), the study indicated that the MBC might contribute substantially more (both as living MBC and necromass) to the C storage of peatlands at regional or global scales than originally thought. The study identified microbial biomass as a primary constraint in peat decomposition and C cycling. ...
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- Väitöskirjat