Fen_SoilCore_CN

In 2019 a new soil core initiative focusing on carbon and nitrogen pools was implemented in the GeoBasis Zackenberg program.
Two plots of 10 by 10 meters were allocated for the sampling of 20cm soil cores + aboveground biomass, one on the heath and one in the fen. From each plot five soil cores were taken and labelled according to the system: location (Fen/Heath) + number of core (1-10, were 1-5 were sampled in the Fen and 6-10 on the heath). The aboveground biomass samples, where 10 by 10cm. In the fen the diameter of the soil cores was 5.2cm and on the heath 2.7cm. The diameter of the cores were a compromise between what was practically possible and a wish for minimum impact, as these arctic ecosystems have a relatively slow recovery. The cores were kept intact and immediately frozen. The cores were brought to the lab at Department of Geosciences and Natural Management, where they were defrosted and separated into 8 different pools: Leaf, Litter, Stem, Moss, Roots from 0-5cm (0 being the surface), Soil from 0-5cm, Roots from 5-20cm and Soil from 5-20cm. The pools were dried for 48 hours at 70°C, where after subsamples were crushed using Retsch mixer mill MM200. The representativeness of the subsamples was assessed visually. From each sub sample, three replicates were analyzed for fraction of C%, N%, Delta-D-13‰ and Delta-N-15‰ isotope values. The total carbon and nitrogen contents are measured in solid samples on an elemental analyser (Flash 2000, Thermo Scientific, Bremen, Germany). For analysis of organic material, a 2mg sample of homogenized and dried soil is weighed out into tin combustion cups. For soils either 10 or 20mg was weighed, depending on organic content. Acetanilide (Merck, Darmstadt, Germany) and soil standards (Elemental Microanalysis, Okehampton, UK) are used for elemental analyser mass calibration.
Leaf area index (LAI) was determined in ImageJ from photos of the green aboveground biomass taken in the lab, following the procedure in Schneider, C. A., Rasband, W. S., & Eliceiri, K. W. (2012). NIH Image to ImageJ: 25 years of Image Analysis. Nature Methods, 9(7), 671–675. Soil core sampling in the fen and on the heath is planned to be repeated every fifth year, next sampling year being 2024.