Photosynthetic light and temperature responses of Eucalyptus cloeziana and Eucalyptus argophloia

Acclimation of gas exchange to temperature and light was determined in 18-month-old plants of humid coastal (Gympie) and dry inland (Hungry Hills) provenances of Eucalyptus cloeziana F.Muell., and in those of a dry inland provenance of Eucalyptus argophloia Blakely. Plants were acclimated at day/night temperatures of 18/13, 23/18, 28/23 and 33/28°C in controlled-temperature glasshouses for 4 months. Light and temperature response curves were measured at the beginning and end of the acclimation period. There were no significant differences in the shape and quantum-yield parameters among provenances at 23, 28 and 33°C day temperatures. Quantum yield [μmol CO₂ μmol^–1 photosynthetic photon flux density (PPFD)] ranged from 0.04 to 0.06 and the light response shape parameter ranged from 0.53 to 0.78. Similarly, no consistent trends in the rate of dark respiration for plants of each provenance were identified at the four growth temperatures. Average values of dark respiration for the plants of the three provenances ranged from 0.61 to 1.86 μmol m^–2 s^–1. The optimum temperatures for net photosynthesis increased from 23 to 32°C for the humid- and from 25 to 33°C for the dry-provenance E. cloeziana and from 21 to 33°C for E. argophloia as daytime temperature of the growth environment increased from 18 to 33°C. These results have implications in predicting survival and productivity of E. cloeziana and E. argophloia in areas outside their natural distribution.