*2.5. Leaf Gas Exchange: CO<sup>2</sup> Response Curves*

The 5th leaves from TE plants were placed in the chamber of a Li-COR 6400, which was fitted with a 2 cm × 3 cm red/blue LED Li-COR standard light source (88%R/12%B). The leaf temperature was set to 24 ◦C, with a relative humidity of 55–65% and a light level of 300 µmol m−<sup>2</sup> s −1 . CO<sup>2</sup> response curves were specifically preformed at a light level of 300 µmol m−<sup>2</sup> s −1 to assess the leaf photosynthetic capacity at, or near, an average growth condition. Thus, the maximum rate of Rubisco carboxylation (Vcmax) and the maximum rate of electron transport (Jmax) are associated with a non-saturated light level. Three leaves from separate plants under each treatment were used at 20, 54, and 134 DIT, corresponding with 5 December 2018, 8 January 2019, and 29 March 2019, respectively. Measurements were performed on cloudy days. CO<sup>2</sup> response curves began at the ambient CO<sup>2</sup> concentration (800 µL L−<sup>1</sup> ) and reduced gradually to 50 µL L−<sup>1</sup> . After the 50 µL L−<sup>1</sup> measurement, the CO<sup>2</sup> concentration was set to 800 µL L−<sup>1</sup> and was held steady until plant photosynthetic parameters returned to levels established during the beginning of the experiment. The CO<sup>2</sup> level was then increased incrementally to 2000 µL L−<sup>1</sup> , at which point the CO<sup>2</sup> response curve was terminated. At each CO<sup>2</sup> concentration, the photosynthetic rate was allowed to reach a steady state; then, a measurement was taken to produce values for that CO<sup>2</sup> concentration. Photosynthetic rates were plotted against internal CO<sup>2</sup> concentration (C<sup>i</sup> ) and fitted to the FvCB model [30] and temperature-corrected [31,32] to determine the maximum rate of photosynthesis under Rubisco-limited and RuBP-limited conditions.
