ABSTRACT
RATIONALE: Carbon-13 (13 C)-labelled plant material forms the basis for experiments elucidating soil organic carbon dynamics and greenhouse gas emissions. Quantitative field-scale tracing is only possible if plants are labelled homogeneously in large quantities. By using a laser spectrometer to automatically steer the isotopic ratio in the chamber, it is possible to obtain large amounts of homogeneously labelled plant material. METHODS: Ninety-six maize plants were labelled for 25 days until tassel formation in a 15 m3 walk-in growth chamber with a continuous air δ13 C-CO2 value of 400. A Los Gatos Research laser absorption spectrometer controlled the ambient δ13 C-CO2 value in the chamber through steering of the mass flow controllers with 13 C-enriched and natural abundance CO2 gas. RESULTS: Laser absorption spectroscopy steering kept the δ13 C value of chamber air between 368 and 426. The resulting 1 kg dry matter of 13 C-labelled shoots showed an average δ13 C value of 384 and accuracy of 8 (half width of the 95% confidence interval). Only the oldest leaves showed larger heterogeneity. The growth chamber eliminated variability between plants. The δ13 C value of the stabile material did not differ significantly from that of bulk material. CONCLUSIONS: Laser spectroscopy controlled 13 C labelling of plants in a walk-in growth chamber successfully kept the isotopic ratio of the CO2 in the chamber air constant. Therefore, large quantities of material were labelled homogeneously at the inter- and intra-plant level, thus establishing a method to provide high-quality input for quantitative isotopic tracer studies.
