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Impact of droughts and heavy rain on greenhouse gas emissions and soil microbial activities in a beech forest

Sophie Zechmeister-Boltenstern1, Sonja Leitner1, Michael Zimmermann1
1 Institute of Soil Research, University of Natural Resources and Life Sciences Vienna

P 3.26 in Fluxes between the atmosphere and ecosystems

Poster Session 2 on Tuesday, 16:30-18:00

Both the frequency and the intensity of weather extremes such as long drought periods and heavy rainfall events are likely to increase in mid Europe over the next decades. Soil moisture is one of the major factors controlling microbial processes, and feedback effects between altered precipitation and changed soil fluxes of the greenhouse gases CO2, CH4 and N2O could intensify climate change. 

We address the following research questions:

  • Will total soil emissions of greenhouse gases be reduced by extended drought periods or will potential pulses during rewetting periods compensate or even outweigh this reduction, thereby leading to increased overall fluxes?
  • How do soil microbial activities respond to increased frequency and intensity of drying-rewetting cycles in a beech forest?

We use roofs to exclude rainfall from reaching beech forest floor and simulate drought periods, and a sprinkler system to simulate heavy rainfall events. We applied repeated dry-wet cycles in two intensities: 1 resp. 2 months drought followed by 75 resp. 150mm irrigation. We took soil samples 1 day before, 1 day after and 1 week after rewetting events and analyzed them for soil nutrients and extracellular enzyme activities. Soil fluxes of CO2, N2O and CH4 were constantly monitored with an automated flux chamber system. Soil microbial community composition is measured via PLFAs to investigate microbial stress resistance and resilience. 

Emissions of CO2 were increased in the first 24 to 48h after rewetting, and then slowly decreased again. Furthermore, we observed a pulsed release of inorganic nitrogen which resulted in high concentrations of NH4 and NO3 in the first 24h after soil rewetting, especially in summer when soil temperatures were high. Results of the first year also show that experimental rainfall manipulation has influenced soil extracellular enzymes. Potential phenoloxidase activity was significantly reduced in stressed treatments compared to control plots. All measured hydrolytic enzymes (cellulase, chitinase, phosphatase and protease) and phenoloxidase responded strongly to rewetting events with significantly increased activities. Overall, our results indicate that repeated dry-wet cycles strongly influence microbial soil processes, even in the first year of experimental rainfall manipulation.

Letzte Änderung 19.06.2014