Landscape variation in soil carbon stocks and respiration in an Arctic tundra ecosystem, west Greenland

ABSTRACT

The magnitude and acceleration of carbon dioxide emissions from warming Arctic tundra soil is an important part of the Region’s influence on the Earth’s climate system. We investigated the links between soil carbon stocks, soil organic matter decomposition, vegetation heterogeneity, temperature, and environmental sensitivities in dwarf shrub tundra near Kangerlussuaq, Greenland. We quantified carbon stocks of forty-two soil profiles using bulk density estimates based on previous studies in the region. The soil profiles were located within six vegetation types at nine study sites, distributed across an environmental gradient. We also monitored air and soil temperature and measured in situ soil respiration to quantify variation in carbon flux between vegetation types. For spatial extrapolation, we created a high-resolution land cover classification map of the study area. Aside from a single soil profile taken from a fen soil (54.55 kg C m⁻²; 2.13 kg N m⁻²), the highest carbon stocks were found in wet grassland soils (mean, 95% CI: 34.87 kg C m⁻², [27.30, 44.55]). These same grassland soils also had the highest mid-growing-season soil respiration rates. Our estimation of soil carbon stocks and mid-growing-season soil respiration measurements indicate that grassland soils are a “hot spot” for soil carbon storage and soil carbon dioxide efflux. Even though shrub, steppe, and mixed vegetation had lower average soil carbon stocks (14.66 – 20.17 kg C m⁻²), these vegetation types played an important role in carbon cycling at the landscape scale because they cover approximately 50 percent of the terrestrial landscape and store approximately 68 percent of the landscape soil organic carbon. The heterogeneous soil carbon stocks in this landscape may be sensitive to key environmental changes, such as shrub expansion and climate change. These environmental drivers could possibly result in a trend toward decreased soil carbon storage and increased release of greenhouse gases into the atmosphere.

KEYWORDS:

• Soil organic carbon
• landscape heterogeneity
• tundra
• soil respiration
• soil temperature

Acknowledgments

We are deeply grateful to Courtney Hammond Wagner and Ruth Heindel for superb field assistance, to Leehi Yona for helping with sample processing and analysis, and to Paul Zietz for laboratory support. Furthermore, we thank Amy Burzynski and Jonathan Chipman for contributions to the mapping and spatial analysis, Thomas Kraft for guidance on the ordination analysis, Ruth Heindel for providing comments on the manuscript, and all Virginia Lab members for moral support. We are thankful to CH2M Hill Polar Services for unfaltering logistical support in Kangerlussuaq that enabled productive fieldwork. This research was funded by an NSF grant (Award #: 0801490) to Ross Virginia, with additional support from the Institute of Arctic Studies, in the Dickey Center for International Understanding at Dartmouth.