Soil organic carbon, isotopic ratios and nitrogen analysis from different samples of the Mt. Kilimanjaro

Fieldwork took place in February and March in 2011 and 2012. Sampling was conducted on 50-50m plots established at each of the 60 Kili studied sites (12 ecosystems x 5 transects). Surface litter and mineral topsoil (0–5 cm) were sampled at five locations at each plot. Additionally, fresh mature leaves of the five most abundant plant species covering 80% of total plant biomass per site were collected. All sampled materials (leaves, litter, and soil) were air-dried until constant weight, and leaf material was subsequently ovendried at 70 °C for 60 h prior to grinding. Soil was sieved to 2mm with visible root fragments being further removed prior to grinding with a mixer mill (MM200, Retsch, Haan Germany). Soil pH was determined with a pH meter (MultiCal SenTix61,WTW,Weilheim, Germany) in a 0.01MCaCl2 solution, with a CaCl2-to-soil ratio of 2 V 1. Particle size distribution was determined gravimetrically using the pipette method (van Reeuwijk, 2002). All soil, litter, and leaf samples were analysed with a dry combustion elemental analyser (Costech International S.p.A., Milano, Italy) fitted with a zero-blank autosampler coupled to a ThermoFinnigan DeltaPlus XL using continuous-flow isotope ratio mass spectrometry (CF-IRMS) for the determination of the abundance of elemental C and N and their stable isotopic composition (d13C, d15N). Precisions (standard deviations) on internal standards for elemental C and N concentrations and stable isotopic compositions were better than 0.08% and 0.2 ‰, respectively.

野外调查工作于2011年及2012年的2至3月间开展。采样工作在60个Kili研究样地中进行，每类样地对应12个生态系统，每个生态系统布设5条样带，样方规格为50m×50m。在每个样方的5个采样点位采集地表凋落物与矿质表层土壤（0~5cm）。此外，针对每个研究样地，采集占该样地总植物生物量80%的5种优势植物的成熟新鲜叶片。

所有采集得到的样品（叶片、凋落物与土壤）均经风干至恒重；其中叶片样品后续置于70℃烘箱中烘干60小时，再进行研磨处理。土壤样品先过2mm孔径筛，剔除可见根系碎片后，使用混合研磨仪（MM200，德国莱驰Retsch公司，哈恩市）进行研磨。

土壤pH值采用MultiCal SenTix61型pH计（德国WTW公司，魏因海姆市）测定，浸提液为0.01mol/L氯化钙溶液，液土比为2:1。土壤颗粒粒径分布采用吸移管重量法（van Reeuwijk, 2002）进行测定。

所有土壤、凋落物及叶片样品均使用配备零空白自动进样器的干式燃烧元素分析仪（dry combustion elemental analyser，Costech International S.p.A.，意大利米兰市），结合连续流同位素比值质谱法（continuous-flow isotope ratio mass spectrometry, CF-IRMS，ThermoFinnigan DeltaPlus XL）进行分析，以测定元素碳、氮的含量及其稳定同位素组成（δ¹³C、δ¹⁵N）。内部标准的元素碳、氮浓度及稳定同位素组成的精密度（标准偏差）分别优于0.08%和0.2‰。