N trace gas emissions from tropical savanna ecosystems and responses to global changes

• Applicant: Dr. Christian Werner
• Subject Area: Atmospheric Science
• Term: from 2008 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 83657822

The tropical savanna biome covers approximately 11.5% of the global land surface. Savanna soils of these ecosystems are thought to contribute substantially to the global atmospheric concentration of nitrous oxide (N2O) and other important atmospheric trace gases (NO, CH4, CO2). Savannas are characterised by a strong seasonality of dry and wet seasons, with rewetting events mostly accompanied by significant pulse emissions of N and C trace gases. Frequent fire events induce further variability in the soil-atmosphere exchange due to effects on N and C inputs via litter fall, storage, loss and, thus, availability of nutrients in the soil. In contrast to the importance of savanna systems for the global atmospheric N trace gas budgets only relatively few in-situ measurements of the soil-atmosphere trace gas exchange have been performed and estimates about the sink/ source strength are still highly uncertain. We will use state-of-the-art experimental and modelling approaches to improve the understanding of N and C transformation processes in savannas under current environmental conditions and predicted future land-uses and climate. Detailed high time resolution field measurements (covering at least an entire year) on N and C trace gas exchange and underlying environmental process controls will be conducted in Australian savannas and will be combined with supplementary data from ongoing projects of Australian partner institutions. Australian savannas cover approximately 20% of the continent and occur along a steep rainfall and temperature gradient, thus, covering a wide range of climatic and environmental conditions, which are representative for other savanna regions worldwide. Therefore, this project will generate data and models which are applicable not only for Australian but also for savanna systems of other continents. Our close collaboration with Australian researchers will enhance the quality of research outcomes from the proposed project as well as the Australian partner project (Australian Research Council Linkage project LP0774812 - Integrated assessment of disturbance and land-use change on total greenhouse gas balance and nutrient cycling in savanna ecosystems ). Data from both projects will be used to develop and refine the biogeochemical model ForestDNDC-tropica / MOBILE. Model development will be based on advanced Bayesian calibration techniques and will, for the first time, provide a detailed uncertainty assessment of model parameters and model outputs. Furthermore, by implementing an established fire module in our model framework we will be able to simulate the combined effects of fire management, land-use and climate change on nutrient turnover in tropical savanna ecosystems. The improved model will be used to investigate nutrient cycling and the soilatmosphere exchange of N and C trace gases for a range of tropical savanna ecosystems of Northern Australia, specifically including the effect of fire. Further, the ForestDNDC-tropica / MOBILE model will be coupled to a GIS database for calculating inventories of N trace gas exchange for the savanna systems of tropical Australia. Specific model simulations will be conducted covering projected climatic effects (e.g., changes in drought and fire intensity and frequency) and land-use change scenarios for this region in order to assess their impact on ecosystem N nutrient cycling and associated trace gas exchange.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Klaus Butterbach-Bahl