Protocol for repeated A/Ci measurements
Repeated A /Ci responses were determined to test the acclimation of the major A /Cicurve parameters to TPU-limiting conditions. TheA /Ci measurements were performed by a visual basic script controlling a set of flow controllers attached to the inlet of a LI-COR 6800. Oxygen was held constant at 210 kPa (21%), CO2 was varied to achieve ranges of CO2mole fractions from 50 to 1500 ppm, and humidified nitrogen made up the balance. (It is generally preferred to express gas levels as partial pressure but since we mixed gases by volume we use mole fractions generally µmol mol-1, ppm.) Plants were acclimated to ambient CO2 (about 400 ppm) for an hour after dawn before the first curve. During the first 15 min of this acclimation period, light levels were gradually raised until 1000 µmol m-2 s-1. After that point,A /Ci curves were measured every 2.5 h until an hour before dusk, and the plants were given 8 h of darkness, then an hour of acclimation to the light the next day before resuming curves every 2.5 h. From the end of the first curve until the end of the experiment, plants were subjected to an experimental level of CO2, either 150 ppm (low), 400 ppm (ambient), or 1500 ppm CO2 (elevated). Curves were analyzed according to Gregory et al. (2021).