N trace gas emissions from tropical savanna ecosystems and responses to global changes
Zusammenfassung der Projektergebnisse
In this project, the soil atmosphere exchange of tropical savanna soils of Northern Australia was investigated. Based on a) semi-continuous, automated in situ measurements of the soilatmosphere exchange of N2O, NOx, CH4, CO2, b) an intensive incubation experiment on intact soil cores determining the soil-atmosphere exchange of N2O, NO, and N2 under controlled soil moisture and soil temperature conditions, and c) a partner project at a nearby savanna site the gaseous losses of the C and N cycle of this region were characterized in detail. The results indicate that, despite of large areal coverage, tropical savanna regions in Northern Australia contribute little to the greenhouse gas balance of the continent as the nutrient poor soils and the tight nitrogen cycle lead to low N2O emissions. The conducted studies confirm our hypothesis that the annual budget of NO emissions is dominated by strong break-of-season pulse emissions of NO, but these strong pulses were not found for N2O emissions (although a clear seasonal pattern driven by moisture availability in the dry and wet seasons was observed). Surprisingly, soil denitrification N2 emission was dominating the gaseous loss of N in our laboratory incubation experiment. The prescribed burn of the litter layer at our measurement site and the results of a comparable fire experiment by the partnering ARCLP research project could not back the hypothesis that seasonal burning of savanna results in lowered soil emissions of N2O and NO due to N depletion. However, our model simulations indicate that repetitive fires indeed lead to lower nitrogen states of the system and thus also decrease N gas emissions. The findings of the conducted field and laboratory measurements were used to improve and validate the biogeochemical model LandscapeDNDC. Within this project, the model was extended by a) developing a new simple vegetation stand dynamic and succession model, b) incorporating the fire module SPITFIRE and c) introducing plant functional type descriptions of tropical savanna. A new database holding all required model drivers was developed and the pre- and postprocessing tools created in this project will also benefit follow-up projects that make use of LandscapeDNDC. The improved model was driven with this new database to simulate the biogeochemical dynamics in the Northern Australian savanna region and to calculate the soil-atmosphere exchange of GHG and NO in high spatial and temporal resolution. The model results indicate that the region is a weak source for N2O and a stronger source for NO emissions. Projections for future climate conditions indicate a weak increase of N2O and NO emissions. Future work should be directed at a) improving the biogeochemical process description in LandscapeDNDC to incorporate the high observed N2 emissions, b) to assess the impact of increasing atmospheric CO2 concentrations on vegetation dynamics and thus c) also on the C and N cycle. This is needed since N gas emissions were found to be strongly dependent on decomposition of produced vegetation litter and N competition between plants and microbes. However, for the latter it will also be necessary to better capture the spatial effect of biological nitrogen fixation.
Projektbezogene Publikationen (Auswahl)
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(2011), Seasonal variation and fire effects on CH4, N2O and CO2 exchange in savanna soils of northern Australia, Agr Forest Meteorol, 151(11), 1440–1452
Livesley, S. J., S. P. P. Grover, L. B. Hutley, H. Jamali, K. Butterbach-Bahl, B. Fest, J. Beringer, and S. K. Arndt
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(2012), Land use change and the impact on greenhouse gas exchange in north Australian savanna soils, Biogeosciences, 9(1), 423–437
Grover, S. P. P., S. J. Livesley, L. B. Hutley, H. Jamali, B. Fest, J. Beringer, K. Butterbach-Bahl, and S. K. Arndt
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(2013), LandscapeDNDC: a process model for simulation of biosphere–atmosphere–hydrosphere exchange processes at site and regional scale, Landscape Ecol, 28, 615–636
Haas, E., S. Klatt, A. Fröhlich, P. Kraft, C. Werner, R. Kiese, R. Grote, L. Breuer, and K. Butterbach-Bahl
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(2014), Full uncertainty quantification of a regional N2O and NO3 inventory using the biogeochemical model LandscapeDNDC, AGU Fall Meeting, San Francisco, Dec. 2014
Haas, E., S. Klatt, D. Kraus, C. Werner, I. Santabarbara, R. Kiese, and K. Butterbach-Bahl
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(2014), Gaseous Nitrogen Losses from Tropical Savanna Soils of Northern Australia: Dynamics, Controls and Magnitude of N2O, NO, and N2 emissions, AGU Fall Meeting, San Francisco, Dec. 2014
Werner, C., T. Hickler, L. Hutley, and K. Butterbach-Bahl
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(2014), N2O, NO, N2 and CO2 emissions from tropical savanna and grassland of northern Australia: an incubation experiment with intact soil cores, Biogeosciences, 11(21), 6047–6065
Werner, C., K. Reiser, M. Dannenmann, L. B. Hutley, J. Jacobeit, and K. Butterbach-Bahl
