The Arctic is undergoing rapid warming and increases in precipitation (wetting) which may lead to significant active layer thawing and decreases in permafrost distribution and carbon (C) storage in soils. Loss of permafrost C has the potential to result in a significant positive feedback to climate change by amplifying rising atmospheric CO2 levels. At the same time, climate change may increase C fixation of tundra plants and increase rates of C inputs to soils. However, we currently have a limited understanding of belowground C allocation and the role organo-mineral interactions play for long-term C sequestration in Arctic soils.
Here, we investigated the rate and mechanism of soil C sequestration in High Arctic tundra after 15 years (2004-2018) of climate manipulation in NW Greenland. Soil samples (n=4/treatment) were collected to 30 cm depth (0-2 cm (O/A horizon), 2-10 cm (A/rhizosphere horizon), 20-30 cm (C horizon)) from four treatments: (+4◦C summer warming (T2), +50% summer precipitation (W), and +4◦C warming × +50% summer precipitation (T2W)), and an ambient climate control (C). Each warming/wetting treatment had a surface coverage consisting of native vascular plants (V; Dryas integrifolia M. Vahl., Salix arctica Pall., Carex rupestris All.) and bare ground/cryptogamic crust (B; overlying vegetation removed). Samples were analyzed for bulk C and N content and stable isotope composition, pH, and exchangeable Fe, Al, and Ca. We also determined 14C content of C in the bulk soil and low and high density fractions in surface soils from vegetated plots.
Results/Conclusions
Preliminary results show that plant cover significantly affected C and N cycling within the surface horizons (0-10 cm). Vegetated plots had greater C and N contents and C/N ratios and were depleted in δ13C and δ15N. Both wetting treatments increased C and N in vegetated surface soils. We found no impact of warming alone on soil properties. These results further support previous analyses of land-atmosphere C fluxes indicating that changes in precipitation promote C storage in High Arctic tundra systems. Mineral and 14C analyses will reveal if wetting treatments result in changes to the capacity of these soils to sequester C and offer a unique opportunity to test whether the fraction of organic C retained by reactive minerals in semi-arid soils is vulnerable to climate change.