Das Projekt "The role of plant-soil-microbe interactions in the cycling of nitrogen in floodplains" wird vom Umweltbundesamt gefördert und von Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft durchgeführt. This project is part of the large multidisciplinary CCES project RECORD (Assessment and Modeling of Coupled Ecological and Hydrological Dynamics in the Restored Corridor of the River Thur). It deals with the role of microbial transformations and plant uptake in the cycling of nitrogen in different functional processing zones of a restored section of river Thur. The results will help to gain a better understanding of the filter function of restored river corridors and of their potential to emit greenhouse gases. Main hypothesis: Nitrogen fluxes and transformations in floodplains strongly depend on the specific response of microorganisms and dominant plants in different functional processing zones to the hydrologic conditions that vary with season and flooding events. Objectives: At the example of a restored section of river Thur, we want to gain a better insight into the role of riparian systems as sink or source of nitrogen species and the potential risks for drinking water sources and atmosphere. Specific objectives: - quantify the rates of microbial nitrogen transformations within the model floodplain: comparison between different functional processing zones, temporal variations due to seasonal climatic and biological effects and flooding events, dependence on governing soil parameters (temperature, moisture, redox potential). - quantify the rates of nitrogen species uptake by model plants (Phalaris arundinacea, Salix alba): potential uptake depending on nutrient availability and nutrient balance; effects of plant age and and temporary flooding. - measure and model nitrogen species concentrations in the soil solution and nitrous oxide emissions: comparison between different functional processing zones, temporal variations due to seasonal climatic and biological effects and flooding events. Methods: - Sampling and monitoring plots with a diameter of 8m have been set-up in different functional processing zones: (i) pasture in a neighboring non-restored section, (ii) river-forest transect including weakly colonized gravel, gravel covered by fine over-bank material densely overgrown with reed grass (Phalaris arundinacea) and other herbaceous species, zone planted with willow (Salix alba) during the restoration, mixed deciduous forest dominated by ash, (iii) old riparian willow forest. - Microbial nitrogen transformation rates are determined from soil samples taken from within the plots at specific times. Mineralisation immobilisation turnover (MIT) is determined by isotopic dilution, potential denitrification by acetylen-inhibition incubation. - Specific nitrate and ammonium uptake rates by model plants are determined in hydroponic treatments in the climate chamber. - Soil respiration and trace gas efflux/influx is measured by in-situ gas sampling from within large rings permanently installed on the plots followed by GC analysis. Etc.