Soil carbon storage and temperature sensitivity associated with shrub and graminoid vegetation in Kangerlussuaq, Greenland

Abstract:

The Arctic tundra is experiencing rapid change, including warming temperatures, shrub expansion and shifts in precipitation patterns. Environmental conditions and vegetation cover are strong controls on soil carbon storage, respiration, and temperature sensitivity of decomposition. Temperature control of soil organic matter processing is particularly important in permafrost soils, which contain more than two times the carbon in the atmosphere and exist at the freeze-thaw threshold. To investigate sensitivity of decomposition to abiotic controls in a heterogeneous landscape, we conducted a laboratory incubation experiment on mineral soils collected in shrub and graminoid vegetation types near Kangerlussuaq, Greenland. We crossed temperature and moisture treatments and measured soil respiration rates over a seven-week incubation period. We measured soil carbon and nitrogen concentrations through elemental analysis and conducted sequential chemical extractions to measure carbon fractions and quantify soil carbon quality. Results show soils overlain by graminoids have higher carbon concentrations at shallow depth and respiration rates than soils overlain by shrub (mean ± 1 s.e. organic carbon concentration, 0-10 cm: graminoid = 68.7 ± 8.1 mg C * g soil^-1, shrub = 48.8 ± 2.9 mg C * g soil^-1). Temperature sensitivity was higher in graminoid soils, with no effect from soil moisture level. Carbon fractions and quality varied by vegetation type and profile depth. This study informs our understanding of the relationship between carbon quality and the temperature and moisture sensitivity of decomposition in western Greenland and demonstrates the importance of landscape heterogeneity in understanding soil carbon response to environmental drivers.