Photosynthetic response to temperature
The responses of net photosynthesis (Asat) to
temperature were measured about two weeks after commencing the water
deficit treatment (i.e. 51 and 58 DAP for warm and cool grown plants,
respectively). Five plants within each temperature × water treatment
combination were randomly selected and were transferred to a vacant bay
to manipulate the measurement temperature. Measurements were carried out
between 0930 and 1400 h to ensure irradiance was not limiting.
Temperature in the glasshouse bay was initially cooled down to
15oC, and then warmed up to 45oC at
5oC intervals. Once the desired temperature was
achieved, plants were maintained at each targeted temperature for at
least 30 min before measurements were taken to maximize the equilibrium
between leaf and air temperature. Asat was then recorded
at saturated PPFD (1200 µmol m-2s-1) and growth CO2 concentration (420
ppm) , with the temperature in the cuvette tracking the ambient air
temperature. Photosynthesis temperature (AT) response curves were
generated by plotting Asat against its corresponding
leaf temperature.