New ecophysiological information from intramolecular isotope variation: methods, analysis and implications for biogeochemistry
Abstract
Conventional isotope applications in ecology and biogeosciences measure isotope ratios (e.g. δ13C) of whole molecules. However, for primary metabolites large intramolecular isotope variation - isotopomer variation - has long been known. This variation reflects enzyme fractionations and encodes metabolic information. We will for two example studies present approaches to measure such intramolecular variation, concepts for data analysis, and models to derive physiological interpretations. First, intramolecular 13C distributions of an annually-resolved Pinus nigra chronology. We show that the intramolecular 13C distribution of tree-ring cellulose shows large variation, with differences between isotopomers exceeding 10‰Ṫhus, individual 13C isotopomers of cellulose constitute distinct 13C inputs into major global C pools. When glucose units with the observed intramolecular 13C pattern are broken down, CO2 with strongly differing δ13C will be released; affecting isotope signals of atmosphere-biosphere C exchange fluxes. Furthermore, cluster analysis shows that tree-ring glucose exhibits several independent intramolecular 13C signals, which constitute distinct ecophysiological information channels. 13C fractionation by stomata/Rubisco explains only part of isotopomer variation, suggesting that whole-molecule 13C analysis likely misses a large part of the isotope information stored in tree rings. Second, results from a study of deuterium isotopomers in tree rings. We compare data from growth chamber experiments, FACE studies and tree-ring series covering the anthropogenic CO2 since industrialization. The increase in CO2 should have led to increased photosynthesis, but this CO2 fertilization effect is poorly constrained on long time scales. A substantial part or the expected increase of photosynthesis is due to expected CO2-driven suppression of photorespiration. Data will also be compared to herbaceous C3 species, with the goal to quantify the CO2-driven suppression of photorespiration during recent decades.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2019
- Bibcode:
- 2019EGUGA..2117592S