Laser spectroscopy steered 13 C‐labelling of plant material in a walk‐in growth chamber

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 m(3) walk-in growth chamber with a continuous air delta(13) C-CO2 value of 400 per thousand. A Los Gatos Research laser absorption spectrometer controlled the ambient delta(13) 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 delta(13) C value of chamber air between 368 and 426 per thousand. The resulting 1 kg dry matter of (13) C-labelled shoots showed an average delta(13) C value of 384 per thousand and accuracy of 8 per thousand (half width of the 95% confidence interval). Only the oldest leaves showed larger heterogeneity. The growth chamber eliminated variability between plants. The delta(13) 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.