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，一项聚焦于碳氮库的新型土壤岩芯（soil core）采样计划在GeoBasis Zackenberg计划（GeoBasis Zackenberg Program）中正式启动。本次研究选取两块10米×10米的样地，用于采集20厘米土壤岩芯与地上生物量样品，其中一块位于欧石楠荒原，另一块位于沼泽湿地。每块样地各采集5个土壤岩芯，并按照以下规则标记：采样地点（沼泽/欧石楠荒原）+岩芯编号（1-10，其中沼泽湿地采集1-5号岩芯，欧石楠荒原采集6-10号岩芯）。地上生物量采样采用10厘米×10厘米的样方。沼泽湿地区域的土壤岩芯直径为5.2厘米，欧石楠荒原区域为2.7厘米。该直径尺寸在实际操作可行性与生态影响最小化之间取得了平衡——此类北极生态系统的自然恢复速度相对缓慢，因此需要尽可能降低采样对其的扰动。采集得到的岩芯保持完整结构，并立即进行冷冻保存。随后所有岩芯被运送至地球科学与自然管理系（Department of Geosciences and Natural Management）实验室，经解冻后被划分为8个组分：叶片（Leaf）、枯落物（Litter）、茎秆（Stem）、苔藓（Moss）、0-5厘米根系（0代表地表）、0-5厘米土壤、5-20厘米根系以及5-20厘米土壤。所有组分在70℃下烘干48小时，之后使用Retsch混合球磨仪MM200（Retsch mixer mill MM200）对其子样品进行粉碎处理。子样品的代表性通过目视评估的方式进行校验。从每个子样品中选取3个重复样本，分析其碳百分含量（C%）、氮百分含量（N%）、δ¹³C和δ¹⁵N同位素值。总碳、氮含量通过元素分析仪（Flash 2000，赛默飞世尔科技，德国不来梅）对固体样品进行测定。对于有机物料分析，称取2mg均质干燥后的土壤样品至锡制燃烧杯中；对于土壤样品，称取量为10mg或20mg，具体取值取决于样品的有机碳含量。本次实验使用乙酰苯胺（默克，德国达姆施塔特）与土壤标准物质（Elemental Microanalysis，英国奥克汉普顿）完成元素分析仪的质量校准。叶面积指数（Leaf Area Index, LAI）通过ImageJ软件（ImageJ）对实验室拍摄的绿色地上生物量照片进行分析，分析流程遵循Schneider等（2012）发表的方法：《NIH Image到ImageJ：25年图像分析》，《自然-方法》，9(7)，671–675。本研究计划每五年重复开展一次沼泽湿地与欧石楠荒原的土壤岩芯采样，下一次采样年份为2024年。