Soil carbon storage, respiration potential, and organic matter quality across an age and climate gradient in southwestern Greenland

Abstract

Geological factors influence biological cycling of organic carbon in soils but are not well represented in our understanding of Arctic carbon dynamics. Landscape age, for instance, directly affects quantity and quality of soil carbon, which are two strong controls of the temperature sensitivity of soil organic matter. We investigated soil carbon storage, respiration potential, and organic matter quality for microbial decomposition across a climate and landscape age gradient in southwest Greenland that deglaciated during the Holocene. We measured soil respiration during a 370-day laboratory incubations of active layer soils collected from four study areas across this gradient (ages 1.8 9 10 2 , 6.8 9 10 3 , and 1.0 9 10 4 , coinciding with a climate gradient from drier inland to wetter coastal terrain) and used a soil respiration model comparison approach to assess the substrate quality of stored organic matter for microbial decomposers. Soils store more than three times greater organic carbon at the 10,000-year-old, maritime climate study areas than the 180-year-old, continental climate study areas. Respiration rates were highest in the surface soils of the coastal areas. Model comparisons reveal important heterogeneity in the quality of organic matter for microbial decomposition between areas: coastal soils were best modeled by both one-and two-pooled models, and inland soils were best represented by one-pooled respiration models. Together, the measures of carbon quality (C:N, CO 2 production, and model parameters estimating initial CO 2 production rates from different organic matter pools) show that shallow soils at the southern coastal area, Kobbefjord, had the highest respiration rates from the recalcitrant carbon pool. This study reveals differences in carbon storage and turnover associated with landscape age and climate factors in western Greenland. When applied to thermodynamic theory, which predicts that temperature sensitivity increases with carbon recalcitrance, our findings suggest that carbon stored in coastal soils may be more sensitive to climate warming than inland soils.

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

“…We expected that differences in vegetation height were correlated with differences in abiotic characteristics, but the environmental variables we measured were remarkably similar between study areas. Both sampling areas were deglaciated approximately 7000 ka (Levy et al 2012), and landscape age has been shown to have a significant effect on soil characteristics, such as C storage (Bradley-Cook and Virginia 2015). Adiabatic winds from the GrIS, which we did not measure, could be one cause for the observed differences in plant height if the winds increase evapotranspiration in an already arid environment or cause damage to plant tissues (Larcher 2003).…”

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

“…After the incubation period, we collected a 10-mL gas sample from the jar headspace, on which we measured CO 2 concentration by injecting the gas into a LiCor-8100 infrared gas analyzer via a trace gas extension valve (LiCor products, Lincoln, NE). We measured the headspace volume for each sample using a dilution function [78] as described in Bradley-Cook and Virginia [79] in order to calculate CO 2 production from headspace concentration.…”

Regional and local scale variations in soil organic carbon stocks in West Greenland

“…Since the last deglaciation, predominantly periglacial processes reshaped the glacial landscape ( Stäblein , ; Ozols and Broll , ; Willemse et al., ; Henriksen , ; Müller et al., ). The maximal possible time for soil formation since the last deglaciation is around 10,000 years in SISI and 6,800 years in RUSS ( cf Bradley‐Cook and Virginia , ). Dominant soils are acid haplic Cambisols and Cryosols in both study areas ( Stäblein , ; Jones et al., ; Henkner et al., ; Kühn and Henkner , ).…”

“…However, the estimation of soil organic carbon stocks (SOCS) of permafrost‐affected soils is highly uncertain as, for one reason, there is an unbalanced distribution of studies across the Arctic focusing on Alaska, Siberia and Canada, while Greenland is underrepresented ( Tarnocai et al., ; Hugelius et al., ; Köchy et al., ; Ping et al., ). For West Greenland predominantly Umbrisols and Cambisols are reported ( cf Jensen et al., ; Bradley‐Cook and Virginia , ; Petrenko et al., ; Kühn and Henkner , ), which could store a significantly higher amount of SOC than thin and less developed soils in East and North Greenland ( Elberling et al., , ; Palmtag et al., , ).…”

“…Vegetal activity ( CAVM Team , ) and permafrost thickness ( Van Tatenhove and Olesen , ) increase towards the ice margin. Another interpretation of lower amounts of SOCS with increasing distance from the coast to the ice margin in West Greenland is related to the Holocene deglaciation history of the Greenland Ice Sheet, with decreasing age of exposed surfaces from the coast to the ice margin ( Levy et al., ; Bradley‐Cook and Virginia , ). However, these findings are in contrast with large scale estimates of SOCS in West Greenland showing no differences between the coast and the ice margin ( Jones et al., ; Hugelius et al., ; Köchy et al., ).…”