Multi-year data-model evaluation reveals the importance of nutrient availability over climate in arctic ecosystem C dynamics

Efrén López-Blanco, Marcin Jackowicz-Korczynski, Mikhail Mastepanov, Kirstine Skov, Andreas Westergaard-Nielsen, Mathew Williams, Torben R. Christensen

Research output: Contribution to journalArticlepeer-review

Abstract

Arctic tundra is a globally important store for carbon (C). However, there is a lack of reference sites characterising C exchange dynamics across annual cycles. Based on the Greenland Ecosystem Monitoring (GEM) programme, here we present 9-11 years of flux and ecosystem data across the period 2008-2018 from two wetland sites in Greenland: Zackenberg (74°N) and Kobbefjord (64°N). The Zackenberg fen was a strong C sink despite its higher latitude and shorter growing seasons compared to the Kobbefjord fen. On average the ecosystem in Zackenberg took up ∼-50 g C m-2 yr-1 (range of +21 to-90 g C m-2 yr-1), more than twice that of Kobbefjord (mean ∼-18 g C m-2 yr-1, and range of +41 to-41 g C m-2 yr-1). The larger net carbon sequestration in Zackenberg fen was associated with higher leaf nitrogen (71%), leaf area index (140%), and plant quality (i.e. C:N ratio; 36%). Additional evidence from in-situ measurements includes 3 times higher levels of dissolved organic carbon in soils and 5 times more available plant nutrients, including dissolved organic nitrogen (N) and nitrates, in Zackenberg. Simulations using the soil-plant-atmosphere ecosystem model showed that Zackenberg's stronger CO2 sink could be related to measured differences in plant nutrients, and their effects on photosynthesis and respiration. The model explained 69% of the variability of net ecosystem exchange of CO2, 80% for photosynthesis and 71% for respiration over 11 years at Zackenberg, similar to previous results at Kobbefjord (73%, 73%, and 50%, respectively, over 8 years). We conclude that growing season limitations of plant phenology on net C uptake have been more than counterbalanced by the increased leaf nutrient content at the Zackenberg site.

Original languageEnglish
Article number094007
JournalEnvironmental Research Letters
Volume15
Issue number9
DOIs
Publication statusPublished - 2020 Sept 1

Subject classification (UKÄ)

  • Physical Geography
  • Climate Research

Free keywords

  • Arctic tundra
  • Ecosystem respiration
  • Greenland
  • Net ecosystem exchange
  • Nutrient availability
  • Photosynthesis

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