Fig. 1.

Measured carbon isotope discrimination during photosynthetic induction of sorghum (Tx430) using a tunable diode laser absorption spectroscope (TDL) coupled to a gas‐exchange system (LI‐6400XT). (a) Sample [CO₂]; (b) the observed leaf photosynthetic discrimination (Δ¹³C_obs); (c) ξ, an estimate of the uncertainty in Δ¹³C_obs and ϕ calculations; (d) error of Δ¹³C_obs going from dark to high light (1800 μmol m⁻² s⁻¹). Time 0 s refers to when the light was switched on. Open dots represent the data points where the error of Δ¹³C_obs was > 50%. The TDL was calibrated after every 600 s of measurement. The gas from leaf chamber was not measured during the calibration and the measurement of reference gas (140 s), which occurred from c. 490 to 640 s and c. 1215 to 1365 s. Leaf gas‐exchange and carbon discrimination of the youngest fully expanded leaf was measured on 40‐d‐old sorghum (Tx430) plant. The leaf was dark‐adapted for 30 min before the measurement. Each data point is the mean (±SE) of eight plants (n = 8).