| Summary: | Dramatic increases in air temperature and precipitation are occurring in the High Arctic (70 °North), yet few studies have characterized the long-term responses of High Arctic ecosystems to the interactive effects of experimental warming and increased rain. Beginning in 2003, we applied a factorial summer warming and wetting experiment to a polar semidesert in northwest Greenland. Twenty-four 0.8 × 1 meter (m) experimental plots were established in three homogenous 70 m × 60 m areas. Plots were assigned to one of four different climate treatments: low-level warming (T1), high-level warming (T2), wetting (W), combined warming and wetting (T2W), and unmanipulated control (CTL). In summer 2018, we assessed several metrics of ecosystem structure and function, including plant cover, ecosystem carbon dioxide exchange, aboveground (leaf, stem) and belowground (litter, root, soil) carbon (C) and nitrogen (N) concentrations (%) and pools, as well as leaf and soil stable isotopes (δ13C and δ15N). Plant cover was assessed via the point-frame technique in 2003 and a digital "point-frame" in 2018. Ecosystem carbon dioxide exchange was assessed at 15-minute intervals with the chamber technique. To assess ecosystem structure we removed 20x20 centimeter turfs, dried them in the lab, and sorted and analyzed all components (i.e. stems, leaves, roots, soils) for C and N content. Leaf ecophysiology was assessed by clipping fully developed green leaves and analyzing their C, N, δ13C, and δ15N content.
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