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.