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).