Spatial variation in plant community functions regulates carbon gas dynamics in a boreal fen ecosystem

The aim of this study was to asses how the variability in carbon gas exchange at the plant community scale affected the C gas exchange estimates at the ecosystem scale in a fen that was homogeneous in a micrometeorological sense, that is, had an even surface topography and plant cover. CO₂ and CH₄ exchange was measured at the plant community scale with chambers and at the ecosystem scale with the eddy covariance (EC) technique. Community-scale measurements were upscaled to the ecosystem scale by weighting the community-specific estimates by the area of the community. All communities were net CO₂ sinks and CH₄ sources during the growing season, but net ecosystem production (NEP) and CH₄ emissions ranged from 21 to 190 g CO₂-C m^-2 and from 4.3 to 13 g CH₄-C m^-2, respectively, between the communities. The seasonal estimates of NEP and CH₄, upscaled to the 200 m radius from the EC tower, were 82 and 7.9 g CH₄-C m^-2, which agreed well with the EC measurements. As the communities differed markedly in their C gas dynamics, their proportions controlled the ecosystem scale estimates. Successful upscaling required detailed knowledge on the proportions and leaf area of the communities.