Resistance and change in a High Arctic ecosystem, NW Greenland: Differential sensitivity of ecosystem metrics to 15 years of experimental warming and wetting

Dramatic increases in air temperature and precipitation are occurring in the High Arctic (>70 degrees N), 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. In summer 2018, we assessed several metrics of ecosystem structure and function, including plant cover, greenness, ecosystem CO2 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 (delta C-13 and delta N-15). Wetting induced the most pronounced changes in ecosystem structure, accelerating the expansion of Salix arctica cover by 370% and increasing aboveground C, N, and biomass pools by 94%-101% and root C, N, and biomass pools by 60%-122%, increases which coincided with enhanced net ecosystem CO2 uptake. Further, wetting combined with warming enhanced plot-level greenness, whereas in isolation neither wetting nor warming had an effect. At the plant level, the effects of warming and wetting differed among species and included warming-linked decreases in leaf N and delta N-15 in S. arctica, whereas leaf N and delta N-15 in Dryas integrifolia did not respond to the climate treatments. Finally, neither plant- nor plot-level C and N allocation patterns nor soil C, N, delta C-13, or delta N-15 concentrations changed in response to our manipulations, indicating that these ecosystem metrics may resist climate change, even in the longer term. In sum, our results highlight the importance of summer precipitation in regulating ecosystem structure and function in arid parts of the High Arctic, but they do not completely refute previous findings of resistance in some High Arctic ecosystem properties to climate change.

Automated summary

Wetting induced significant changes in ecosystem structure, accelerating the expansion of Salix arctica cover and increasing carbon and nitrogen pools in both aboveground and root biomass. The combined effects of wetting and warming enhanced plot-level greenness, while at the plant level, responses to warming and wetting varied among species. Overall, while certain aspects of the High Arctic ecosystem responded to the experimental manipulations, others such as carbon and nitrogen allocation patterns and soil properties remained resilient in the face of climate change.