Das Projekt "Effect of drought on C cycling in the plant-soil system - which roles play lignin and lipids?" wird vom Umweltbundesamt gefördert und von Universität Zürich, Geographisches Institut durchgeführt. Drought events are predicted to occur more frequently and for a longer duration due to climate change. Especially, severe droughts most likely increase in Central Europe during the summer season, when commonly plants actively grow. Due to this drought C uptake by plants and its translocation towards soil can be expected to decrease. Thus, this has a strong influence on the plant driven sequestration of C in soil and also drought might promote C loss in the soil. Furthermore, it remains questionable, if the plant-soil system can adapt to drought to further resist to severe droughts. Strong effects of drought were described for the regulation of lipid formation in plants including fatty acids as part of cell membranes and alkanes as part of the wax layer, whereas so far no information is available, if lipid incorporation into soils and lipid turnover therein is also influenced by drought. For another part of plant tissues like lignin a response on drought cannot be expected as lignin formation is not directly connected to the regulation of the stomata and the wax formation. However, as influences of drought on lignin and lipid cycling in the plant-soil system remain largely unknown, but they are part of intermediate stable C pool in soil, it should be known, whether drought might improve their mineralisation or storage in soils. In this proposal, we will determine CO2 uptake by plants, translocation of C from plants to soil and soil C fluxes of two different plant communities (grass and heath) that are exposed to a severe drought of 14 weeks under field conditions. Additionally, plots are differentiated that were previously exposed to annual drought or control conditions. C cycling is investigated under field conditions by help of a triple 13CO2 pulse labeling experiment and subsequent analyses of the isotope label in plant and soil samples. The whole experiment was performed under rainout shelters installed on the Bayreuth EVENT I experiment in summer 2011. Further, a laboratory experiment will be conducted, where under controlled conditions only soil moisture is regulated to drought and control conditions, respectively and via a continuous 13CO2 labeling C cycling in the plant-soil system is determined. All samples from the EVENT I experiment and the laboratory experiment will be analysed for their d13C isotopic values to trace the bulk C fluxes. In addition to the bulk C, lipids including fatty acids, alkanes and alcohols and lignin monomers will be monitored for the whole sample set to determine the regulation of lipid and lignin formation in plants under drought and especially to investigate the incorporation and mineralisation of bulk C and at a molecular level for lipids and lignin during the drought. This research will serve the following central goals: 1. Determine effect of increasing drought on C uptake by plants and bulk C, lipid and lignin translocation towards soil. usw.
Das Projekt "Nitrogen effect on molecular dynamics in forest soils (end of thesis)" wird vom Umweltbundesamt gefördert und von Universität Zürich, Geographisches Institut durchgeführt. Atmospheric nitrogen deposition affects many forests and their ecosystem functions, including organic matter cycling in soils of temperate forests. But it is not clear how, and what the underlying mechanisms are. Here we asked the question: Do compounds with high intrinsic nitrogen content (typical for microbially-derived biomass) respond differently to atmospheric nitrogen deposition than compounds with low nitrogen content (such as plant-derived biomass)? Two facts delayed the progress of the project in the first year. From May 2010 to June 2011 the PhD student Marco Griepentrog successfully completed make-up classes for the recognition of his Fachhochschule degree by the University of Zurich. His workload (30 credit points or 900 working hours) was 50Prozent of the annual workload of a full time student, and delayed the progress of the project. Furthermore the PI Dr. Alexander Heim has left research in November 2010 and started a new position in industry and the co-PI Prof. Michael Schmidt stepped in as PI. Despite the delay the project eventually progressed well thanks to the hard-working PhD student Marco Griepentrog, who worked in the lab and simultaneously compiled a detailed methodological literature review on preparative soil fractionation procedures. His review revealed striking discrepancies in the application of this frequently used method, and was submitted to a peer-reviewed journal and is still under revision. With a competitive travel grant from the European Science Foundation, Marco Griepentrog worked at the University of Ghent (Belgium) and could measure compound-specific isotope ratios of amino sugars reliable in soil density fractions for the first time, using a novel analytical technique. This was the first time that amino sugars were measured in density fractions, and we could show that especially bacterial amino sugars were associated with soil minerals. Furthermore, when combined with stable isotope labeling, it became evident that amino sugar turn over much slower when associated with soil minerals. Another unexpected result was that fungal residues turn over at the same rate as total organic carbon, while bacterial amino sugars turn over slower. The fact that fungal amino sugars turn over faster than bacterial amino sugars contradicts with previous assumptions, and our measurements are the first to show that. Results have been presented at several international conferences, and now a manuscript circulates between co-authors to be submitted to a high impact scientific journal later this year. For the final year, we plan to focus on another compound class and propose a change of the initially planned target compound lignin. Own results showed that the isotopic label might not be detectable in lignin but in fatty acids, since they have been shown to turnover faster. usw.
