Seasonal controls on net branch CO 2 assimilation in sub-Arctic Mountain Birch (Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti)

Rafael Poyatos*, Jemma Gornall, Maurizio Mencuccini, Brian Huntley, Robert Baxter

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

3 Citations (Scopus)


Forests at northern high latitudes are experiencing climate-induced changes in growth and productivity, but our knowledge on the underlying mechanisms driving seasonal CO 2 fluxes in northern boreal trees comes almost exclusively from ecosystem-level studies on evergreen conifers. In this study, we measured growing season whole-branch CO 2 exchange in a deciduous tree species of the tundra-taiga ecotone, Mountain Birch (Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti), at two locations in northern Fennoscandia: Abisko (Sweden) and Kevo (Finland). We identified strong seasonal and environmental controls on both photosynthesis and respiration by analysing the parameters of light response curves. Branch-level photosynthetic parameters showed a delayed response to temperature, and, at Kevo, they were well described by sigmoid functions of the state of acclimation (S). Temperature acclimation was slower (time constant, τ=7days) for maximum photosynthesis (β br) than for quantum efficiency (α br) (τ=5days). High temperature-independent values of the respiration parameter (γ br) during leaf and shoot expansion were consistent with associated higher growth respiration rates. The ratio γ brbr was positively related to temperature, a result consistent with substrate-induced variations in leaf respiration rates at the branch level. Differences in stand structure and within-site variation in the active period of C uptake determined the spatiotemporal patterns in net assimilation amongst branches. Growing season CO 2 uptake of individual branches on a leaf area basis did not show a significant relationship with total incident photosynthetically active radiation, and did not differ across sites, averaging ca. 640gCO 2m -2.

Original languageAmerican English
Pages (from-to)90-100
Number of pages11
JournalAgricultural and Forest Meteorology
Publication statusPublished - 15 Jun 2012


  • Arctic
  • Branch bags
  • Light response curve
  • Phenology
  • Photosynthesis
  • Respiration
  • State of acclimation


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