期刊
AGRICULTURAL AND FOREST METEOROLOGY
卷 158, 期 -, 页码 90-100出版社
ELSEVIER
DOI: 10.1016/j.agrformet.2012.02.009
关键词
Arctic; Branch bags; Light response curve; Phenology; Photosynthesis; Respiration; State of acclimation
资金
- NERC (UK) through the ABACUS consortium)
- MONTES [CSD 2008-00040]
- MICINN (Spain)
- British Ecological Society
- Natural Environment Research Council [NE/D005922/1] Funding Source: researchfish
- NERC [NE/D005922/1] Funding Source: UKRI
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, tau = 7 days) for maximum photosynthesis (beta(br)) than for quantum efficiency (alpha(br)) (tau = 5 days). High temperature-independent values of the respiration parameter (gamma(br)) during leaf and shoot expansion were consistent with associated higher growth respiration rates. The ratio gamma(br)/beta(br) 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. 640 g CO2 m(-2). (C) 2012 Elsevier B.V. All rights reserved.
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