Biological Activity of Eutrophic Peaty Soils in the Central Floodplain of the Poros River (Tomsk Oblast)

The biological activity of eutrophic peat soils on the floodplain of the Poros River located in the paleovalley of the Tom River (Tomsk oblast, Western Siberia) was studied. Microbial biomass, respiration intensity, methanogenesis, nitrogen fixation, and denitrification were determined in soils of native and long-drained areas on the left-bank and right-bank floodplain. Microbial biomass stock in the 1-m layer of the studied soils ranged from 240 to 1068 g/m2, and basal respiration rate ranged from 87 to 351 μg CO2/(g per day). Nitrogen cycle activity indicators were characterized by low values: 3–12 ng C2H4/(g per day) for nitrogen fixation estimated by the acetylene reduction method and 0.1 to 8 μg N2O/(g per day) for denitrification. It was found that 27 years of the floodplain drainage by a network of open channels contributed to a 2–4.5-fold increase in the total microbial biomass (owing to the fungal component in the upper eutrophic peat horizon and the bacterial component in the underlying peat layer) and in the respiratory and nitrogenase activities. At the same time, the activities of methanogenesis and denitrification decreased. The negative effect of the long-term drainage—the loss of up to 45% of carbon and 50% of nitrogen stocks—manifested itself in the surface eutrophic peat TE horizon (0–25 cm).