Lability classification of soil organic matter in the northern permafrost region

• Published in: Biogeosciences
• Main Authors: Kuhry, Peter, Barta, Jiri, Blok, Daan, Elberling, Bo, Faucherre, Samuel, Hugelius, Gustaf, Jørgensen, Christian J., Richter, Andreas, Šantrůčková, Hana, Weiss, Niels
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus GmbH 2020
• Subjects: Soil Science; Geochemistry; permafrost
• Online Access: https://lup.lub.lu.se/record/1c1a3b52-a918-499c-bc15-12038fbeff07; https://doi.org/10.5194/bg-17-361-2020

The large stocks of soil organic carbon (SOC) in soils and deposits of the northern permafrost region are sensitive to global warming and permafrost thawing. The potential release of this carbon (C) as greenhouse gases to the atmosphere does not only depend on the total quantity of soil organic matter (SOM) affected by warming and thawing, but it also depends on its lability (i.e., the rate at which it will decay). In this study we develop a simple and robust classification scheme of SOM lability for the main types of soils and deposits in the northern permafrost region. The classification is based on widely available soil geochemical parameters and landscape unit classes, which makes it useful for upscaling to the entire northern permafrost region. We have analyzed the relationship between C content and C- CO2 production rates of soil samples in two different types of laboratory incubation experiments. In one experiment, ca. 240 soil samples from four study areas were incubated using the same protocol (at 5 ĝ C, aerobically) over a period of 1 year. Here we present C release rates measured on day 343 of incubation. These long-term results are compared to those obtained from short-term incubations of ca. 1000 samples (at 12 ĝ C, aerobically) from an additional three study areas. In these experiments, C- CO2 production rates were measured over the first 4 d of incubation. We have focused our analyses on the relationship between C- CO2 production per gram dry weight per day ( μ gC- CO2 gdw -1 d -1 ) and C content (%C of dry weight) in the samples, but we show that relationships are consistent when using C ĝ• N ratios or different production units such as μ gC per gram soil C per day ( μ gC- CO2 gC -1 d -1 ) or per cm 3 of soil per day ( μ gC- CO2 cm -3 d -1 ). C content of the samples is positively correlated to C- CO2 production rates but explains less than 50 % of the observed variability when the full datasets are considered. A partitioning of the data into landscape units greatly reduces variance and provides ...