Greater Abundance of Betula nana and Early Onset of the Growing Season Increase Ecosystem CO₂ Uptake in West Greenland

Expansion of deciduous shrubs is a common observation throughout the Arctic, with implications for carbon (C) cycling. Shrubs may increase net ecosystem C uptake through greater leaf area and gross ecosystem photosynthesis (GEP), and/or through cooler summer soils and reduced ecosystem respiration (...

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Bibliographic Details
Published in:Ecosystems (New York) 2016-11, Vol.19 (7), p.1149-1163
Main Authors: Cahoon, Sean M. P., Sullivan, Patrick F., Post, Eric
Format: Article
Language:English
Subjects:
Biomedical and Life Sciences
Carbon dioxide
Community composition
Dispersal
Drought
Ecology
Ecosystems
Environmental Management
Geoecology/Natural Processes
Growing season
Hydrology/Water Resources
Life Sciences
Original Articles
Phenology
Photosynthesis
Plant communities
Plant ecology
Plant populations
Plant Sciences
Shrubs
Summer
Terrestrial ecosystems
Tundra
Zoology
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Summary:Expansion of deciduous shrubs is a common observation throughout the Arctic, with implications for carbon (C) cycling. Shrubs may increase net ecosystem C uptake through greater leaf area and gross ecosystem photosynthesis (GEP), and/or through cooler summer soils and reduced ecosystem respiration (ER). We used a space-for-time substitution combined with experimental warming at a Low Arctic site in West Greenland to examine the biophysical effects of increased temperature and Betula nana abundance on ecosystem CO₂ exchange. Communities dominated by Betula were much stronger C sinks than graminoid communities due to greater GEP and lower ER. The warming treatment had little effect on GEP, ER, or net ecosystem CO₂ exchange (NEE). The start of the growing season has been advancing at our study site, as indicated by long-term observations of plant phenology. In a retrospective analysis, we estimate that earlier onset of the growing season has increased the strength of the ecosystem C sink at rates of 1.3 and 2.1 g C m⁻² y⁻¹ in Betula and graminoid tundra, respectively, since 2002. However, earlier, and presumably longer, growing seasons may be associated with greater potential for drought stress. Our data suggest that mid-summer drought-induced GEP declines may partially offset C gains associated with an earlier start to the growing season. Our results suggest greater deciduous shrub abundance and longer growing seasons will likely lead to greater net C uptake in our study area, while highlighting important complexities associated with drought and plant community composition.
ISSN:1432-9840
1435-0629
DOI:10.1007/s10021-016-9997-7