Does growth temperature affect the temperature responses of photosynthesis and internal conductance to CO2? A test with Eucalyptus regnans

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Tree Physiology, 28:11–19

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Does growth temperature affect the temperature responses of photosynthesis and internal conductance to CO₂? A test with Eucalyptus regnans

C. R. Warren

School of Biological Sciences, The University of Sydney, NSW 2006, Australia () / Received April 26, 2007; accepted May 30, 2007; published online October 15, 2007

Summary

Internal conductance to CO₂ transfer from intercellular spaces to chloroplasts (g _i) poses a major limitation to photosynthesis, but only three studies have investigated the temperature dependance of g _i. The aim of this study was to determine whether acclimation to 15 versus 30 °C affects the temperature response of photosynthesis and g _i in seedlings of the evergreen tree species Eucalyptus regnans F. Muell. Six-month-old seedlings were acclimated to 15 or 30 °C for 6 weeks before g _i was estimated by simultaneous measurements of gas exchange and chlorophyll fluorescence (variable J method). There was little evidence for acclimation of photosynthesis to growth temperature. In seedlings acclimated to either 15 or 30 °C, the maximum rate of net photosynthesis peaked at around 30 or 35 °C. Such lack of temperature acclimation may be related to the constant day and night temperature acclimation regime, which differed from most other studies in which night temperatures were lower than day temperatures. Internal conductance averaged 0.25 mol m^–2 s^–1 at 25 °C and increased threefold from 10 to 35 °C. There was some evidence that g _i was greater in seedlings acclimated to 15 than to 30 °C, which resulted in seedlings acclimated to 15 °C having, if anything, a smaller relative limitation due to g _i than seedlings acclimated to 30 °C. Stomatal limitations were also smaller in seedlings acclimated to 15 °C than in seedlings acclimated to 30 °C. Based on chloroplast CO₂ concentration, neither maximum rates of carboxylation nor RuBP-limited rate of electron transport peaked between 10 and 35 °C. Both were described well by an Arrhenius function and had similar activation energies (57–70 kJ mol^–1). These findings confirm previous studies showing g _i to be positively related to measurement temperature.

Keywords: carbon dioxide, diffusion, internal resistance, mesophyll resistance, photosynthesis, transfer conductance, transfer resistance.

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