Assessing turnover rates of soil organic matter by means of compound-specific stable carbon isotope ratios (d13C)

DFG GL 327/4-3,4

Assessing turnover rates of soil organic matter by means of compound-specific stable carbon isotope ratios (δ13C)

The aim of this project is the assessment of turnover rates of soil organic matterconstituents by means of compound-specific stable carbon isotope ratio determination (δ13C) using Gas Chromatography - Combustion - Isotope Ratio Mass Spectrometry (GC-C-IRMS). In a former project-phase, well established analytical methods for biomarker determination such as lignin, amino acids, benzenepolycarboxylic acids) were optimized for GC-C-IRMS analysis and method-induced isotope fractionation identified and eliminated. In the current project period, special emphasis is made to microbial biomarkers such as phospholipid fatty acids, amino sugars and neutral sugars. A main focus lies on further method optimization, especially the reduction of the foreign-carbon addition during derivatization. The optimized GC-C-IRMS methods will be applied to a set of different experiments working with artificial and natural isotope labeling such as agricultural soils incubated with labeled glucose under controlled conditions, C3 grassland soils incubated with maize slurry in the field. Furthermore, the effects of elevated atmospheric CO₂ concentrations on soil organic matter turnover will be evaluated using the Zurich Free Air Carbon dioxide Enrichment facility.