Processes of litter and soil organic matter transformation during extreme drying/wetting as assessed by compound-specific isotope approaches

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Recently, intensive droughts followed by heavy rainfall can already be observed in Europe as proposed by climate models. Shifts in amount, intensity and frequency of precipitation could change soil structure and soil organic matter quality and thus turnover in temperate forest ecosystems. Contradicting results have been reported from drying and wetting experiments in field and laboratory studies or from observations of natural drying and wetting periods. To verify different interpretations, a combination of stable and radio-isotopes and biomarker .analyses seems a promising tool. This can be achieved by establishing tracer experiments in the drying and wetting fields (13C and 15NJ and in controlled laboratory studies (14C, 13C, and 15N) and by analysing the 13C, 14C and 15N signatures not only in the bulk SOM but also in biomarkers characterizing chemically defined SOM pools, e.g. microbially and plant-derived sugars, phospholipid fatty acids (PLFA) and benzenepolycarboxylic acids (BPCA). The combination of biomarker and isotope (δ13C, 14C and δ 15N) analysis allows not only deducing SOM turnover after drying / wetting but also to identify the involved microbial community and the fate of chemically defined compounds during SOM decomposition and turnover under the experimental manipulations.