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.