POTENTIAL ACTIVITY AND DIVERSITY OF METHANOTROPHIC BACTERIA IN FOREST SOIL, PEAT, AND SEDIMENTS FROM A HYDROELECTRIC RESERVOIR (ROBERT-BOURASSA) AND LAKES IN THE CANADIAN TAIGA.

The potential activity and diversity of methanotrophic bacteria in samples from forest soil, peat, and sediment from a hydroelectric reservoir (Robert-Bourassa) and lakes located in the sub-arctic taiga were studied. Incubation experiments with soil slurries, methanotrophic bacterial counts, and direct PCR amplification of genes specific to methanotrophic bacteria were carried out on soil and sediment samples from three locations (nonflooded, periodically flooded, and flooded) from the reservoir. Sediments from three lakes located near the reservoir were also sampled to compare with nearby unperturbed aquatic systems. Only the uppermost part (5-10 cm) of soils and sediments was analyzed. Regardless of the incubation temperature, potential methane (CH4) oxidation rates were lower (0.028-0.066 [mu] mol CH4 g^-1 soil d^-1) in nonflooded forest soil compared to lacustrine sediments that exhibited potential oxidation rates generally close to those observed in periodically flooded or flooded forest soil (0.04-0.14 [mu]mol CH4 g^-1 soil d^-1), but far below the range of values (0.20-0.58 [mu]mol CH4 g^-1 soil d^-1) recorded in peat systems. Samples from flooded forest soil and peat had higher CH4 uptake activity, but this could not be related to a greater number of methanotrophic bacteria (pmoA probe-positive colonies). Analysis of genes specific to methanotrophic bacteria revealed a low diversity in the methanotrophic community, with the genus Methylocystis being dominant. Overall, samples of flooded soil and peat with higher CH4 production rates also had higher rates of CH4 oxidation by methanotrophic bacteria. Flooding also seems to modify the resilience of the methanotrophic community to temperature fluctuations, an important consideration for future studies.