title: Component carbon fluxes and their contribution to ecosystem carbon exchange in a pine forest: an assessment based on eddy covariance measurements and an integrated model.
abstract: We used a combination of eddy flux, canopy, soil and environmental measurements with an integrated biophysical model to analyze the seasonality of component carbon (C) fluxes and their contribution to ecosystem C exchange in a 50-year-old Scots pine forest (Pinus sylvestris L.) in eastern Finland (62 degrees 47' N, 30 degrees 58' E) over three climatically contrasting years (2000-2002). Eddy flux measurements showed that the growing Scots pine forest was a sink for CO2, with annual net C uptakes of 131, 210 and 258 g C m-2> year-1 in 2000, 2001 and 2002, respectively. The integrated process model reproduced the annual course of daily C flux above the forest canopy as measured by the eddy covariance method once the site-specific component parameters were estimated. The model explained 72, 66 and 68% of the variation in daily net C flux in 2000, 2001 and 2002, respectively. Modeled annual C loss by respiration was 565, 629 and 640 g C m-2 year-1, accounting for 77, 77 and 65% of annual gross C uptake, respectively. Carbon fluxes from the forest floor were the dominant contributors to forest ecosystem respiration, with the fractions of annual respiration from the forest floor, foliage and wood being 46-62, 27-44 and 9-10%, respectively. The wide range in daily net C uptake during the growing season was largely attributable to day-to-day fluctuations in incident quantum irradiance. During just a few days in early spring and late autumn, ecosystem net C exchange varied between source and sink as a result of large daily changes in temperature. The forest showed a greater reduction in gross C uptake by photosynthesis than in C loss by respiration during the dry summer of 2000, indicating that interannual variability in ecosystem net C uptake at this site was modified mostly by summer rainfall and vapor pressure deficit.
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, P.O. Box 416, 610041 Chengdu, P.R. China. kaiyun@joesuu.fi
authors.forename: K-Y
authors.initials: KY
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Kellomäki
authors.forename: T S
authors.initials: TS
authors.lastname: Zha
authors.forename: H
authors.initials: H
authors.lastname: Peltola
mesh_terms: D002244:Carbon / Q000378:metabolism; D017753:Ecosystem; D008962:Models, Theoretical; D028223:Pinus / Q000502:physiology*; D012987:Soil; D014197:Trees / Q000502:physiology*; D014887:Weather
chemical_list: D012987:Soil; D002244:Carbon