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

• Published in: Environmental research letters Vol. 15; no. 9; pp. 94007 - 94020
• Main Authors: López-Blanco, Efrén, Jackowicz-Korczynski, Marcin, Mastepanov, Mikhail, Skov, Kirstine, Westergaard-Nielsen, Andreas, Williams, Mathew, Christensen, Torben R
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.09.2020
• Subjects: Annual cycles; arctic tundra; Carbon; Carbon dioxide; Carbon sequestration; Dissolved organic carbon; Dissolved organic nitrogen; Ecological monitoring; Ecosystem models; ecosystem respiration; Ecosystems; Fens; Greenland; Growing season; Herbivores; Leaf area; Leaf area index; Leaves; net ecosystem exchange; Nitrogen; Nutrient availability; Nutrient content; Nutrient dynamics; Nutrients; Organic nitrogen; Photosynthesis; Plants; Respiration; Tundra; Greenland
• ISSN: 1748-9326; 1748-9326
• DOI: 10.1088/1748-9326/ab865b

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.