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.