Responses of aerobic microbial communities and soil respiration to water-level drawdown in a northern boreal fen.

On a global basis, peatlands are a major reserve of carbon (C). Hydrological changes can affect the decomposition processes in peatlands and in turn can alter their C balance. Since 1959, a groundwater extraction plant has generated a water-level gradient at our study site that has gradually changed part of the wet fen into a dry peatland forest. The average water-level drawdown of the gradient (from a pristine 9 cm to 26 cm in the dry end) is close to an estimate predicted by an increase in mean global temperature of 3 degrees C. We studied the total microbial community of the aerobic surface peat in four locations along the gradient through phospholipid fatty acid and PCR-DGGE methods. Additionally, field measurements of soil respiration showed a threefold increase in the C-emission rate at the driest location compared with the wettest one, indicating enhanced decomposition. Also, both fungal and bacterial biomass increased in the drier locations. At the species level, the fungal community changed due to water-level drawdown whereas actinobacteria were less sensitive to drying. The majority of fungal sequences were similar to ectomycorrhizal (ECM) fungi, which dominated throughout the gradient. Our results indicate that ECM fungi might act as important facultative decomposers in organic-rich environments such as peatlands.

Methanotrophic bacteria in boreal forest soil after fire.

Methane-oxidizing bacteria are the only terrestrial sink for atmospheric methane. Little is known, however, about the methane-oxidizing bacteria that are responsible for the consumption of atmospheric methane, or about the factors that influence their activity and diversity in soil. Effects of fire and its end-product, wood ash, on the activity and community of methane oxidizing bacteria were studied in boreal forest 3 months and 12 years after the treatments. Fire significantly increased the atmospheric CH(4) oxidation rate. Both fire and wood ash treatments resulted in increased soil pH, but there was no correlation with methane oxidation rates. Changes in the methane-oxidizing bacterial community due to treatments were not detected by cultivation-independent recovery and comparative sequence analysis of pmoA gene products from soil. Phylogenetic analysis showed that a majority of the pmoA sequences obtained belonged to the "upland soil cluster alpha", which has previously been detected in diverse forest environments.