Leaf gas exchange measurements
Gas exchange measurements were performed immediately on the day that
plants were moved back to their original growth bay (i.e. 63 and 83 DAP
for warm and cool grown plants, respectively), as well as on the second
and seventh day of recovery following the heatwave treatment. Within
each treatment combination, five plants with similar height and leaf
number were chosen for leaf gas exchange measurements, which were
conducted between 0930 and 1400 h on one recent, fully expanded leaf per
plant with a portable open path gas exchange analyser (LI-6400XT,
Li-Cor, Lincoln, NE, USA) equipped with a red-blue diode light source
(6400-02B) and an external CO2 injector (6400-01). Light
saturated CO2 assimilation rates (Asat,
µmol m-2 s-1), and stomatal
conductance (gs, mol m-2s-1) were measured at 1200 µmol m-2s-1 photosynthetic photon flux density (PPFD). Leaf
dark respiration (Rn, µmol m-2s-1) was measured 2 hours after sunset on the same day
with the same leaf used for photosynthesis measurements at zero PPFD.
During the gas exchange measurements, CO2 and air
temperature in the cuvette were configured to match that of the ambient
growth environment, and flow rate was set to 500 mL
min-1. The range for RH and VPD in the cuvette was
50~70% and 1.0~2.0 kPa during the gas
exchange measurements, respectively.