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Gewählte Doctoral Thesis:

Sonja Leitner (2017): Impact of Extreme Weather Events on Soil Nitrogen Cycling and Greenhouse Gas Emissions.
Doctoral Thesis - Institut für Bodenforschung (IBF), BOKU-Universität für Bodenkultur, pp 111. UB BOKU obvsg FullText

Abstract:

Climate change research anticipates a shift in global precipitation patterns and an increase in the frequency and intensity of extreme weather events like severe droughts and heavy rainstorms in Central Europe. To examine the impact of repeated droughts and rainstorms on soil respiration (Rs) and N cycling, a precipitation manipulation experiment was conducted in an Austrian beech forest. Responses of soil processes were monitored using high-resolution GHG flux measurements and soil microdialysis. Repeated severe drying-rewetting cycles reduced Rs and shifted its climate sensitivity from temperature-dependence to moisture-dependence. Furthermore, drought led to an accumulation of N in the soil, which, upon rewetting, was mobilized in the form of nitrate and amino acids. This rewetting N flush was larger if the preceding drought had been longer, indicating that N can be lost via leaching if a severe drought is followed by heavy rain. A second rewetting experiment was conducted in a semi-arid grassland in California at the end of the dry season, and soil N diffusion and emissions of NO and N2O were monitored during the first 30h post-wetting. Immediately upon rewetting, nitrate was mobilized and NO and N2O flux increased. This soil rewetting N flush was short-lived and disappeared after 2h, indicating high microbial immobilization rates. 27h after rewetting, ammonium diffusion increased, coinciding with elevated N-gas emissions, indicating that at this time point microbial nitrification was the primary NO and N2O production pathway. These results corroborate our theory that N accumulates in dry soil, and, upon rewetting, can be mobilized and fuel GHG emissions from soil. This PhD thesis showed that although natural ecosystems are buffered against weather fluctuations, extreme weather events can trigger disproportionate responses that are short in duration but contribute substantially to ecosystem C and N cycling.

Betreuer: Zechmeister-Boltenstern Sophie

1. Berater: Zimmermann Michael

2. Berater: Hochbichler Eduard