Beschreibung:
<jats:sec><jats:title>Rationale</jats:title><jats:p>Carbon‐13 (<jats:sup>13</jats:sup>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.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Ninety‐six maize plants were labelled for 25 days until tassel formation in a 15 m<jats:sup>3</jats:sup> walk‐in growth chamber with a continuous air δ<jats:sup>13</jats:sup>C‐CO<jats:sub>2</jats:sub> value of 400‰. A Los Gatos Research laser absorption spectrometer controlled the ambient δ<jats:sup>13</jats:sup>C‐CO<jats:sub>2</jats:sub> value in the chamber through steering of the mass flow controllers with <jats:sup>13</jats:sup>C‐enriched and natural abundance CO<jats:sub>2</jats:sub> gas.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Laser absorption spectroscopy steering kept the δ<jats:sup>13</jats:sup>C value of chamber air between 368 and 426‰. The resulting 1 kg dry matter of <jats:sup>13</jats:sup>C‐labelled shoots showed an average δ<jats:sup>13</jats:sup>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 δ<jats:sup>13</jats:sup>C value of the stabile material did not differ significantly from that of bulk material.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>Laser spectroscopy controlled <jats:sup>13</jats:sup>C labelling of plants in a walk‐in growth chamber successfully kept the isotopic ratio of the CO<jats:sub>2</jats:sub> 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.</jats:p></jats:sec>