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.

δ15N measurements are conducted to get an indication of how open or tight N cyling of different ecosystems/ landuse systems are. The higher the δ15N value the more 15N enriched the samples are. In addition 13C data and SOC were measured.