Carbon Dioxide and Water Exchange between Spruce Forest and Atmosphere in Spring—Summer under Different Weather Conditions

Abstract

Results of eddy covariance measurements of carbon dioxide and water fluxes above a spruce forest in the middle taiga subzone from April to August 2013 and 2016 are presented. The ecosystem of the spruce forest turned from source to sink CO2 at mean daily air temperatures below zero in late March and early April; in 2016, it was 2 weeks earlier than in 2013. The maximum net ecosystem exchange of CO2 (NEE) was recorded at the end of June and beginning of July. In 2016, the mean daily NEE of spruce forest decreased at a high air temperature and a low amount of precipitation in the beginning of the growing season; turning from the sink CO2 to the source was observed in early August. The net exchange of CO2 between spruce and the atmosphere from April to August 2013 reached 327 g C/m2 and, in 2016, 174 g C/m2. The seasonal evapotranspiration of the spruce forest in these years was 239–247 mm/m2 and the mean value of water-use efficiency for photosynthesis (WUE) in the season was 2.3–3.3 g C/kg H2O. WUE was relatively constant during the growing season, resulting from a close relationship between the exchange of CO2 and water, the main processes that ensure the production of organic matter in the spruce-forest ecosystem.