13C and 15N incorporation into litter compounds of Norway spruce after short-term labelling assessed by compound specific isotope analysis
2 Department of Geography, University of Zurich
3 Department of Soil Science of Temperate and Boreal Ecosystems, University of Göttingen
4 Soil Biogeochemistry, Martin-Luther University Halle-Wittenberg
O 3.3 in Research Yields: Ideas Pursued to the End
10.10.2013, 16:00-16:15, H6, GEO
Short-term pulse labelling of plant litter combined with compound specific isotope analysis (CSIA) is an excellent tool to determine plant C and N allocation after photosynthetic fixation and nitrogen assimilation. Compound specific isotope analysis of distinct substance classes gives us a detailed understanding of the metabolic pathways driven by plants.
15N labelling was performed by stem injection. The tracer solution, containing 1g of 15NH415NO3 (98 at% 15N) dissolved in distilled water, was administered to each tree over a period of seven days.
After one week trees were exposed to an 13C enriched carbon dioxide atmosphere under gas-tight foil shapes. In general, each tree was labelled with 33g of Na213CO3-tracer (99 at% 13C). After 6 h the cover was removed, trees were felled, cutted in coarse peaces and the needles were immediately harvested and dried.
This labelling achieved a high enrichment in the needles of Norway spruce (155,0 ‰ 13C ± 12,7 and 957,4 ‰ 15N ± 74,4): 63,5% of the applied 13C and about 54% of the 15N were incorporated. To investigate the hypotheses that short-term pulse labelling can’t achieve a uniformly labelling of all litter compounds we investigated four individual substance classes by CSIA and the water soluble fraction (w.s.fr.) of the needles. The amino acids, fatty acids as well as the water soluble carbohydrates represented a labile litter pool which was generated very fast: the proportion of 13C in the amino acid pool was 0.24%, in the fatty acid pool 0.28% and in the carbohydrates of the w.s.fr. 0.29%. In contrast the hemicellulose sugars and n–alkanes are more stable compounds with a lower turnover: only 0.05% and 0.02% of the incorporated 13C was found in these pools, respectively. In total, 54.8% of the incorporated 13C were found in the substances of the analyzed compound classes. The remaining 45.2% of 13C can be assumed to be incorporated in structural compounds like cellulose and lignin. Based on our results we can conclude that the in–situ tree labelling approach is very efficient in determining C allocation pathways in plants. During 6 h C was allocated in a broad spectra of plant metabolites but not homogenously. Thus, an investigation of the C incorporation into the individual plant metabolite pools is needed, for a further interpretation of the results of degradation studies performed with labelled litter of pulse-labelling experiments.
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