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Seasonal controls on net branch CO2 assimilation in sub-Arctic Mountain Birch (Betula pubescens ssp. czerepanovii (Orlova) Hamet-Ahti)
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2012 (English)In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 158-159, p. 90-100Article in journal (Refereed) Published
Abstract [en]

Forests at northern high latitudes are experiencing climate-induced changes in growth and productivity, but our knowledge on the underlying mechanisms driving seasonal CO2 fluxes in northern boreal trees comes almost exclusively from ecosystem-level studies on evergreen conifers. In this study, we measured growing season whole-branch CO2 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 (βbr) than for quantum efficiency (αbr) (τ=5days). High temperature-independent values of the respiration parameter (γbr) during leaf and shoot expansion were consistent with associated higher growth respiration rates. The ratio γbr/βbr 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 CO2 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. 640gCO2m−2.

Place, publisher, year, edition, pages
2012. Vol. 158-159, p. 90-100
Keywords [en]
Arctic, Branch bags, Light response curve, Phenology, Photosynthesis, Respiration, State of acclimation
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Natural Sciences
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URN: urn:nbn:se:polar:diva-8265OAI: oai:DiVA.org:polar-8265DiVA, id: diva2:1302574
Available from: 2019-04-05 Created: 2019-04-05 Last updated: 2019-04-05

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http://www.sciencedirect.com/science/article/pii/S0168192312000743
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