Growing season variability of net ecosystem CO2 exchange and evapotranspiration of a sphagnum mire in the broad-leaved forest zone of European Russia

The spatial and temporal variability of net ecosystem exchange (NEE) of CO2 and evapotranspiration (ET) of a karst-hole sphagnum peat mire situated at the boundary between broad-leaved and forest-steppe zones in the central part of European Russia in the Tula region was described using results from field measurements. NEE and ET were measured using a portable measuring system consisting of a transparent ventilated chamber combined with an infrared CO2/H2O analyzer, LI-840A (Li-Cor, USA) along a transect from the southern peripheral part of the mire to its center under sunny clear-sky weather conditions in the period from May to September of 2012 and in May 2013. The results of the field measurements showed significant spatial and temporal variability of NEE and ET that was mainly influenced by incoming solar radiation and ground water level. The seasonal patterns of NEE and ET within the mire were quite different. During the entire growing season the central part of the mire was a sink of CO2 for the atmosphere. NEE reached maximal values in June-July (-6.8 +/- 4.2 mu mol m(-2) s(-1)). The southern peripheral part of the mire, due to strong shading by the surrounding forest, was a sink of CO2 for the atmosphere in June-July only. ET reached maximal values in the well-lighted central parts of the mire in May (0.34 +/- 0.20 mm h(-1)) mainly because of high air and surface temperatures and the very wet upper peat horizon and sphagnum moss. Herbaceous species made the maximum contribution to the total gross primary production (GPP) in both the central and the peripheral parts of the mire. The contribution of sphagnum to the total GPP of these plant communities was relatively small and ranged on sunny days of July-August from -1.1 +/- 1.1 mgC g(-1) of dry weight (DW) per hour in the peripheral zone of the mire to -0.6 +/- 0.2 mgC g(-1) DW h(-1) at the mire center. The sphagnum layer made the maximum contribution to total ET at the mire center (0.25 +/- 0.10 mm h(-1)) and the herbaceous species on the peripheral part of the mire (0.0 3 +/- 0.03 mm h(-1)).