Gas exchange measurements
All measurements were assessed with the LI-COR 6800 photosynthesis
system with light provided by the light emitting diodes (LEDs) in the
fluorescence head. CO2 concentration in the air
(C a) was set to 400 ppm, whereas the light
intensity was set to the ambient light intensity in the chamber, which
also corresponded to the light intensity treatment. Air temperature in
the leaf chamber was also set to the ambient air temperature in the
chamber. RH was set to 35 or 50% for the HT and control treatments
respectively. The vapor pressure deficit ranged from 1.5 to 1.9 kPa for
the control and 2.5 to 5 kPa for temperatures 35 °C to 45 °C.
TheA/C i measurements were performed using the auto
program settings in the LI-COR 6800 instrument with the following
sequence of CO2 concentration in the chamber: 400, 200,
50, 100, 150, 250, 300, 350, 500, 600, 800 and 1000 ppm.
CO2 levels were changed at 2 min intervals to prevent
complete deactivation of rubisco at certain low CO2concentration, especially under HT conditions. The 2 min was also
sufficient to reach the new CO2 setpoints and establish
steady photosynthetic rates. A/C i analyses were
performed according to Sharkey et al. (Sharkey, Bernacchi,
Farquhar, & Singsaas, 2007), using an improved version of the Excel
Sheet from (Sharkey, 2016). Representative individual curves were fitted
separately and the extracted parameters were averaged across replicates
for each treatment.