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 2024.2019年，一项聚焦碳氮库的新型土壤岩心采样计划在GeoBasis Zackenberg计划中正式启动。 该计划划定两块10米×10米的样地，用于采集20cm深土壤岩心及地上生物量样品：一块设于石楠生境（heath），另一块设于沼泽生境（fen）。每块样地采集5个土壤岩心，命名规则为：生境类型（沼泽/石楠）+岩心编号（1~10，其中沼泽生境采样编号1~5，石楠生境采样编号6~10）。地上生物量样品的采样区域为10cm×10cm。 沼泽生境的土壤岩心直径为5.2cm，石楠生境则为2.7cm。岩心直径的选择兼顾了实操可行性与最小环境扰动的需求——由于此类北极生态系统的恢复速度相对缓慢，尽可能降低采样对其的影响尤为重要。岩心采集后保持完整结构并立即冷冻保存。随后将岩心转运至地球科学与自然资源管理系实验室，在实验室中对岩心进行解冻，并将其分为8个组分：叶片（Leaf）、枯落物（Litter）、茎秆（Stem）、苔藓（Moss）、0~5cm根系（0为地表层）、0~5cm土壤、5~20cm根系以及5~20cm土壤。 将各组分置于70℃条件下烘干48小时，随后使用Retsch mixer mill MM200对分装子样品进行粉碎处理。通过目视评估子样品的代表性。从每个子样品中选取三份平行样，分析其碳百分比（C%）、氮百分比（N%）以及δ¹³C和δ¹⁵N同位素比值。固体样品的总碳、氮含量使用元素分析仪（Flash 2000，赛默飞世尔科技，德国不来梅）进行测定。针对有机物质分析时，称取2mg经均质化处理的干燥土壤样品，置于锡制燃烧杯中；针对土壤样品，则根据其有机碳含量称取10mg或20mg样品。元素分析仪的质量校准采用乙酰苯胺（Merck，德国达姆施塔特）与土壤标准物质（Elemental Microanalysis，英国奥克汉普顿）。 叶面积指数（Leaf Area Index, LAI）通过ImageJ软件对实验室中拍摄的绿色地上生物量照片进行分析计算得出，分析流程遵循Schneider等（2012）发表于《Nature Methods》的方法：*NIH Image to ImageJ: 25 years of Image Analysis*，9(7): 671–675。 该计划规划每五年重复开展一次沼泽与石楠生境的土壤岩心采样工作，下一次采样年份为2024年。