The response of high arctic ecosystems' carbon dioxide exchange to changing climate is uncertain and may be important from a climate-change perspective. In this study, the net ecosystem carbon dioxide exchange during four growing seasons is examined by combining measurements and modeling from a high arctic fen in northeastern Greenland. The summer-season net ecosystem exchange shows large interannual variations, fluctuating from an uptake of −50 g C m−2 to −123 g C m−2. Through ecosystem

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... g, we can observe that leaf area index development and the maximum Rubisco capacity are more important controls on the interannual variability of net ecosystem carbon dioxide exchange than meteorological conditions. Furthermore, we present a hypothesis linking the interannual variability in maximum Rubisco capacity with leaf nitrogen content and leaf area index development. This hypothesis may provide a method to model seasonal net ecosystem carbon dioxide exchange in detail without having to resort to elaborate fitting procedures using measured carbon dioxide flux data.