Impact of repeated dry-wet cycles on soil CO2 efflux and extracellular enzyme activities in a beech forest

Wien

2014

Artikel aus einer ZeitschriftUnselbständiges Werk

17215

200189769

Climate change research predicts that both frequency and intensity of weather extremes such as severe droughts and heavy rainfall events will increase in mid Europe over the next decades. Because soil moisture is one of the major factors controlling microbially-driven soil processes, this might have a major impact on soil organic matter decomposition and nutrient cycling. This in turn can lead to feedback effects between altered precipitation and changed soil CO2 fluxes which can intensify climate change. Decomposition of plant litter and soil organic matter is driven by microbial extracellular enzymes and thus highly susceptible to water stress. Furthermore, drought enhances soil hydrophobicity and formation of cracks that represent preferential flow paths for soil water, which in combination with rapid soil wetting during heavy rainfalls can lead to substantial nutrient loss via leaching. To investigate the impact of repeated dry-wet cycles on soil nutrient cycling and CO2 efflux we are conducting a precipitation manipulation experiment in a temperate Austrian beech forest. Roofs exclude rainfall and simulate drought periods, and heavy rainfall events are simulated with a sprinkler system. We apply repeated dry-wet cycles in two intensities: one treatment receives 6 cycles of 1 month drought followed by 75 mm irrigation, and a parallel treatment receives 3 cycles of 2 months drought followed by 150 mm irrigation. Soil samples are taken before and after rewetting events and analyzed for soil nutrients and extracellular enzyme activities. Soil CO2 efflux is constantly monitored with an automated flux chamber system, and environmental parameters recorded via dataloggers. The results of the first year 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. 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. Emissions of CO2 were increased in the first 24 to 48h after rewetting, and then slowly decreased. Overall, our results indicate that repeated dry-wet cycles strongly influence microbial soil processes, even in the first year of experimental rainfall manipulation. The next 2 years will show whether these changes are permanent, or if the system adapts to the new precipitation regime.