Comparison of carbon and nitrogen storage in mineral soils of graminoid and shrub tundra sites, western Greenland

Abstract

Shrub species are expanding across the Arctic in response to climate change and biotic interactions. Changes in belowground carbon (C) and nitrogen (N) storage are of global importance because Arctic soils store approximately half of global soil C. We collected 10 (60 cm) soil cores each from graminoid- and shrub-dominated soils in western Greenland and determined soil texture, pH, C and N pools, and C:N ratios by depth for the mineral soil. To investigate the relative chemical stability of soil C between vegetation types, we employed a novel sequential extraction method for measuring organo-mineral C pools of increasing bond strength. We found that (i) mineral soil C and N storage was significantly greater under graminoids than shrubs (29.0 ± 1.8 versus 22.5 ± 3.0 kg·C·m−2 and 1.9 ± .12 versus 1.4 ± 1.9 kg·N·m−2), (ii) chemical mechanisms of C storage in the organo-mineral soil fraction did not differ between graminoid and shrub soils, and (iii) weak adsorption to mineral surfaces accounted for 40%–60% of C storage in organo-mineral fractions — a pool that is relatively sensitive to environmental disturbance. Differences in these C pools suggest that rates of C accumulation and retention differ by vegetation type, which could have implications for predicting future soil C pool storage.

Temperature sensitivity of mineral soil carbon decomposition in shrub and graminoid tundra, west Greenland

“…= 7). These results correspond with a soil carbon concentration analysis conducted by Petrenko et al [35], which shows significantly larger carbon pools in graminoid soils (Table 2).…”

“…The shallow graminoid soils we studied have significantly lower C:N ratios than shallow shrub soils [35], so our finding that they are more temperature sensitive than shallow shrub soils does not support thermodynamic predictions that temperature sensitivity decreases with carbon quality. It is possible that the relationship between quality and temperature sensitivity is constrained by other soil factors and limitations, such as nitrogen availability.…”

“…Other soil organic matter properties, such as the abundance of polysaccharides and proteins, are strongly [40]. Our results show that not only is the carbon pool larger in graminoid soils than in shrub soils [35], but CO 2 mineralization potential is higher as well. This suggests that graminoid soils, which occupy a smaller fraction of our study area than shrubs, are nonetheless a "hot spot" for carbon storage and atmospheric exchange relative to shrub soils.…”

“…We measured respiration from mineral soils at two depth increments within the active layer (0-20 cm and 20-40 cm below the organic layer) collected from graminoid-dominated (Poa pratensis) and shrub-dominated (Betula nana and Salix glauca) vegetation, in a fully crossed laboratory experiment with multiple temperature and moisture treatment levels. Because graminoid soils have larger organic carbon pools and lower C:N ratios than shrub soils [35], we hypothesized that: (1) graminoid soils would have higher rates of decomposition and lower temperature sensitivity than shrubs as a result of a larger soil carbon pool and higher soil carbon quality, as measured by C:N; (2) deep soils would have lower decomposition rates and higher temperature sensitivity compared to near-surface soils due to a smaller and lower quality soil carbon pool;…”

Changing Lake Dynamics Indicate a Drier Arctic in Western Greenland

“…Graminoid species mostly belong to the grass and sedge families ( Poacea and Cyperaceae) , and there are numerous low‐lying forb and herbaceous species interspersed across the landscape. Soils are generally humus‐poor brown gelisols, and contain approximately 22.5–29.0 kg C/m 2 , depending on landscape position and vegetation type (Petrenko et al, ).…”