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Rationale Carbon‐13 (13C)‐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 δ13C‐CO2 value of 400‰. A Los Gatos Research laser absorption spectrometer controlled the ambient δ13C‐CO2 value in the chamber through steering of the mass flow controllers with 13C‐enriched and natural abundance CO2 gas. Results Laser absorption spectroscopy steering kept the δ13C value of chamber air between 368 and 426‰. The resulting 1 kg dry matter of 13C‐labelled shoots showed an average δ13C 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 δ13C value of the stabile material did not differ significantly from that of bulk material. Conclusions Laser spectroscopy controlled 13C 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.

RC C R * collaborationWe present preliminary results for the determination of the leading strange and charm quarkconnected contributions to the hadronic vacuum polarization contribution to the muon's 𝑔 − 2. Measurements are performed on the RC ★ collaboration's QCD ensembles, with 3 + 1 flavors of 𝑂 (𝑎) improved Wilson fermions and C ★ boundary conditions. The HVP is computed on a single value of the lattice spacing and two lattice volumes at unphysical pion mass. In addition, we compare the signal-to-noise ratio for different lattice discretizations of the vector current.