• KiLi Sub Project 3:
  Linking nutrient cycles, land use and biodiversity along an altitudinal gradient at
  Mt. Kilimanjaro

From 03/2010 to 07/2016

Project leader:  Yakov Kuzyakov, Ralf Kiese
PhD Student:  Holger Pabst, Friederike Gerschlauer, James Mnyonga, Adrian Guetlein, Joscha Becker, Emanuel Ndossi

To understand impacts of climate and land use changes on biodiversity and accompanying ecosystem stability and services at the Mt. Kilimanjaro, detailed understanding and characterization of the current biotic and abiotic controls on ecosystem C, N and nutrient cycling are needed. The 1st phase showed that nutrients and C were up to 3 times depleted in ecosystems with high management intensity. Higher N2O and inorganic N losses in managed, but faster N turnover in natural ecosystems indicate much tighter N cycling and nutrient reutilization in natural ecosystems and may explain together with results of other nutrients’ availabilities differences in productivity and biodiversity. In phase 2 we will extend and complete our detailed studies with established methods on the characterization of C, N and nutrient cycling in ecosystems at higher altitudes (> Ocotea), Savanna, and additional transects. Specific focus will be given to “hot moments” of nutrient turnover, losses vs. availability such as transition from dry to wet and/ or wet seasons. For a more comprehensive system understanding the started nutrient input-output studies are proposed to be complemented by investigating nutrient input via atmospheric deposition and for N also via biological N2 fixation (BNF). We hypothesize that, in particular, BNF is playing a key role for N acquisition and for compensating observed substantial ecosystem N losses e.g. by leaching in the Ocotea forest. Furthermore, gross N turnover studies will be extended by investigation of Feammox and associated formation of N2O, but also NO and N2. In particular the latter being of importance within the ecosystem N budget of tropical ecosystems. Process studies on nutrient turnover together with results of nutrient inputs and losses (greenhouse gases and leaching) will allow estimating full ecosystem specific nutrient balances and availabilities. This information will be used to quantify differences in limitations for ecosystem productivity and biodiversity across climatic and land use gradients. Studies on aggregate stability as well as thermal and microbial stability of soil C will reflect vulnerability of intensively managed soils to erosion and degradation. Finally, data obtained by field and laboratory studies of SP3, but also from other SPs, will be used for testing and application of a plot scale biogeochemical model linked to a dynamic vegetation model (SP5) for calculation of key C and N ecosystem processes including full greenhouse gas balances. The biogeochemical model will be used for upscaling the results in space (from subset of plots to the total of 60 plots) and in time (complete yearly time series). The simulation results on biogeochemical site characteristics will be available for plant traits (SP5) in order to connect nutrient cycling/availability with ecosystem productivity and biodiversity.