ALICE · Advanced laser techniques to investigate C isotope discrimination during decomposition
FP6 — Marie Curie Actions (Human Resources and Mobility)
- Duration
- 2005-04-04 → 2009-04-03
- EU contribution
- €211,000
- Participants
- 1
- Scheme
- TOK
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Results in brief
Final Activity Report Summary - ALICE (Advanced laser techniques to investigate C isotope discrimination during decomposition)
Most of the current research on the carbon cycle, which makes use of isotopic approaches, is based on the assumption that no discrimination occurs during respiration and decomposition processes. The verification of this assumption is needed to improve our understanding of soil carbon dynamics. The objectives of this project were twofold: 1. to develop, implement and test state of the art ultra sensitive spectroscopic methods for laboratory and field measurements of isotope ratio in carbon dioxide (CO2) at ambient concentrations 2. to apply this new spectroscopic device to determine fractionation during respiration processes. Optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS), which is one of the most advanced laser-based spectroscopic methods, was implemented and optimised for measuring the ratio of 13C to 12C in CO2 at ambient concentrations. The technique was based on measuring the transmission of a tuneable diode laser beam at 2 µm through a V-shaped high-finesse optical cavity with an effective path length of 30 km, in a volume of only 1 litre. The optical feedback effect was employed to narrow and lock the frequency of the laser beam for efficient coupling into the cavity. Owing to the long optical path, our prototype instrument was able to operate at CO2 concentrations as low as 200 ppm, yielding an accuracy of ±0.4 in delta-13C for a 100 seconds integration time and a 6 minute calibration interval. The instrument was compact, portable, cryogen-free and able to determine the isotopic ratio from a continuous flow in real time, without sample preparation. Thanks to the high temporal resolution and the non-invasive nature of the analysis, the diode laser spectrometer enabled us to investigate isotopic fractionation effects in soil respiration processes. In particular, we measured 13C-CO2 derived from the microbial oxidation of simple organic compounds, mixed with silicon dioxide powder and subsequently subjected to laboratory incubations, with known values of the 13C/12C ratio. These investigations confirmed the validity of the hypothesis of no discrimination during respiration processes, at least at the accuracy level of the laser spectrometer. Simultaneously, leaf litter incubation experiments were performed in order to determine whether temporal changes in different carbon sources or direct microbial discrimination could be responsible for the observed changes in isotopic composition in 13C (delta13C) of litter respired CO2. The measurements showed a significant discrimination during litter decomposition. The temporal variations of this discrimination were mostly caused by the variations of the delta13C of respired CO2 than by those of the remaining bulk material. Litter respired CO2 was 13C-enriched respective to the bulk litter material. This discrimination, however, seemed to be 'apparent'. In fact, our results argued in favour of a time-varying contribution of at least three different pools to the temporal variation of both respired CO2 and its delta13C. Further chemical and isotopic analyses using nuclear magnetic resonance (NMR) would allow for better constraining of our models. Moreover, these results strongly suggested taking into account the apparent discrimination occurring during organic matter decomposition in studies employing natural abundance isotope techniques.
Data: CORDIS, © European Union
Project objective
The ALICE project is aimed at acquiring two post-doctoral fellows with a research experience of less than 10 years to develop and apply an advanced laser spectroscopic methodology for laboratory and field investigations on isotopic fractionation effects associated to soil-atmosphere exchange processes. If C isotopic fractionation associated to photosynthesis and to dark respiration and photorespiration processes is quantified, our understanding of discrimination during decomposition is still poor.Current isotopic research on the C Cycle is based on the assumption that no discrimination occurs during respiration and decomposition processes. This hypothesis needs unambiguous testing. The research proposed is highly innovative not only for its scientific component but also for the methodological approach. In fact, the ALICE project is designed to convert the state-of-the-art spectroscopic technique into a deployable technology capable of providing accurate determinations of d13C-CO2 at atmospheric concentrations. Off-axis integrated cavity output spectroscopy will be implemented, using a room-temperature semiconductor diode laser at the unusual wavelength of 2.053 micron.In this spectral region, 12CO2 and 13CO2 molecules exhibit interesting absorption features, with optimum spectroscopic parameters for isotope ratio determinations. The use of a diode laser and a pair of small optical cavities enables to build a very compact device, suitable for field applications, satisfying, at the same time, the need of an extremely high detection sensitivity, as required to measure d13C in atmospheric CO2.Exploiting the high temporal resolution and the non-invasive nature of the analysis, the diode laser spectrometer will enable to design a number of laboratory and field experiments aimed at shining light on isotopic fractionation effects in soil respiration processes. As a result, we expect to produce a complete isotope discrimination model as well as to test the existing ones.
Original text from CORDIS.
Participants
- SECONDA UNIVERSITA DI NAPOLI · CASERTACoordinatorCity levelItaly
Links
Data: CORDIS, © European Union