Fingerprinting soil organic matter in the arctic to help predict CO 2 flux

Abstract

In the past 30 years, the arctic climate has warmed appreciably and there is evidence for a significant polar amplification of global warming in the future. A warming and drying of northern soils could result in an increase in organic matter decomposition and positive feedback to future climate warming. Northern ecosystems have accumulated 25–33% of the world's soil carbon, much of which is preserved as poorly decomposed plant remains. The soil organic matter (SOM) decomposition rate, however, depends on many variables such as temperature, nutrient availability, pH, oxidation/reduction potential, and chemical composition of the SOM. This paper addresses the effect of SOM composition on CO 2 respiration in arctic soil. In order to isolate the effect of SOM composition on respiration rate, 19 soils from the circumpolar arctic were incubated in a 25 °C, nutrient-rich, pH neutral, constantly mixed environment. The SOM composition was studied using pyrolysis-gas chromatography/mass spectrometry (py-GC/MS), an analytical technique that produces a “fingerprint” of SOM. Correlations were made between SOM composition and CO 2 respiration rate for the 19 soils. From these data, a model was built to predict respiration rates in soil subjected to similar incubation conditions using py-GC/MS fingerprints. Results go on to compare model predictions of measured respiration in laboratory incubations of 15 soils from four different locations in the Northern and Western Alaska Transects. Predictions for cumulative respiration over a 70-day laboratory respiration test were within 20% of measured values.