ALBERT

Description: 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.

Description: Ten sites covering six different ecosystems were selected for detailed situ N2O and CH4 exchange measurements. The six different ecosystems represent main (semi) natural forest types along an elevational and thus climatic gradient (savanna, lower montane, Ocotea, and Podocarpus forest) as well as the main land-use gradient between 1,300–1,800 m a.s.l. (lower montane forest, homegarden, and coffee plantation). The initial sampling started in February 2011 on one transect (Machame) and included savanna, coffee plantation, homegarden, lower montane, Ocotea, and Podocarpus forest and lasted until July 2013. From September 2013 until end of 2015, we focused on additional forest sites and conducted more measurements at a lower montane, Ocotea and Podocarpus forest located at another transect (Mweka), Each site was equipped with at least 5 spatially replicated chambers (25.2 x 15.2 x 14.7 cm. Gas sampling was performed with 60 ml gas tight syringes equipped with a one-way LuerLock stop-cock (VWR International, Darmstadt, Germany). Each chamber was sampled five times during chamber closure(t0 = 0, t1 = 15, t2 = 30, t3 = 45, and t4 = 60 min). A total of 45 ml of headspace sample was taken and used to flush and finally over-pressurize(5 ml) 10 ml glass vials (SRI Instruments, Bad Honnef, Germany). The samples were shipped within 4 weeks to KIT, IMK-IFU (Garmisch- Partenkirchen, Germany) for further analysis using an auto sampler (HT200H; HTA s.r.l, Brescia, Italy) coupled to a gas chromatograph (8610 C; SRI Instruments, Torrence, USA) equipped with an electron capture detector (ECD N2O) and a flame ionization detector/methanizer (FID: CH4 and CO2). Samples were continuously calibrated with standard gas samples (N2O: 406 ppb; CH4: 2,110 ppb; CO2: 407.9 ppm, Air Liquide, Düsseldorf, Germany). Flux rates were calculated with R version 3.2.0 including HMR package 0.3.1 for calculating the GHG flux rates by linear increase or decrease in gas concentration over time (N = 5).

Description: Soil core sampling in Tanzania was conducted during the dry season, in February 2011 and 2012. Here, one undisturbed soil core (12.5 cm inner diameter, 25 cm length) was collected at each of the 60 research plots. Cores were covered at the bottom and top with Parafilm M_ (Bemis Company, Inc. Oshkosh, WI, USA) lids to allow air exchange. They were shipped within a month to laboratory facilities at KIT, IMK-IFU, Germany, where they were kept air-dried at room temperature until further processing.Before being measured for GHG emissions (CO2, CH4, N2O), the soil cores were pre-incubated (Lovibond incubator ET 651-8, Tintometer GmbH, Germany) for 2 weeks at the site-specific mean annual temperature (MAT). They were watered with 4 mm of standard rain mixture equivalents after the first week and then again hr before the start of the measurement period (Breuer, Kiese, & Butterbach-Bahl, 2002). Each soil core was measured for GHG exchange once per week over a 5 week period (N = 5). During this time, moisture levels and temperature (_0.5°C) were kept stable. Measurements of CO2, CH4, and N2O concentration changes were monitored with a dual quantum cascade laser (Aerodyne Research Inc., Billerica, MA, USA, precision) at 1 Hz time intervals.To do so, soil cores were closed gas-tight with a lid (forming a headspace volume of 2 L). 50 ml/min of headspace air was then directed to the spectrometer and recirculated into the headspace volume over a 15 min time period. Mean ecosystem-specific GHG exchange rates were finally calculated from five replicated soil core measurements. As for the in situ GHG experiment, flux rates were calculated via the linear regression of concentration increases/decreases over time.

Description: Gross rates of N turnover were investigated during wet season (May 2011), dry season (February 2012), and during the transition from dry to wet season (October 2011), thus accounting for the main seasons of tropical ecosystems in the Mt. Kilimanjaro region.Gross ammonification and nitrification rates were measured with the 15N soil pool dilution method (Davidson and others 1991; Dannenmann and others 2006). We used composite sieved-soil samples which were incubated on site after 15N labeling. At every site (100 m 9 100 m), samples from 3 replicated subplots were extracted at t1 = 0.5 h and t2 = 24 h after labeling and single rates were used to calculate mean turnover rates for a given site and sampling date.

Description: At ten different sites in the Kilimanjaro region we installed two identical suction cups (SK 20, UMS, Munich, Germany) at 10, 40, and 80 cm soil depths (6 in all) and set them to a vacuum of -400 hPa to allow continuous soil water sampling into brown Duran glass bottles (SF 1,000 ml, UMS, Munich, Germany) stored 50 cm belowground in a covered bucket. Soil water sampling and in situ GHG exchange measurements were conducted simultaneously. The water was decanted into 1L polyethylene bottles (VWR International GmbH, Darmstadt, Germany) and transported to the Nkweseko research station. There, two subsamples were filtered with 0.2 lm syringe filters (Minisart, Sartorius, Goettingen, Germany) and subsequently frozen and stored for a maximum of 6 months. After transportation to KIT IMK-IFU, Germany, total ammonium (NH4+) and nitrate (NO3-) concentrations were measured by colorimetry using an Epoch Microplate Spectrophotometer (BioTek, VT, USA) according to (Dannenmann et al., 2009). Subsamples were analyzed for total extractable nitrogen (DN) and total extractable organic carbon (DOC) using a multi-N/C 3100 combined chemo-luminescence infrared analyzer (Jena Analytik AG, Germany), as described by Bim€uller et al. (2014). Extractable organic nitrogen (DON) was calculated by subtracting mineral N (NH4+ and NO3-) from DN. Annual leaching rates were calculated from mean annual N concentrations multiplied by seepage water formation as calculated from mean annual precipitation - mean annual ETa (estimated from MODIS).