Leaf Respiration of Snow Gum in the Light and Dark. Interactions between Temperature and Irradiance1


American Society of Plant Physiologists


We investigated the effect of temperature and irradiance on leaf respiration (R, non-photorespiratory mitochondrial CO2 release) of snow gum (Eucalyptus pauciflora Sieb. ex Spreng). Seedlings were hydroponically grown under constant 20°C, controlled-environment conditions. Measurements of R (using the Laisk method) and photosynthesis (at 37 Pa CO2) were made at several irradiances (0–2,000 μmol photons m−2 s−1) and temperatures (6°C–30°C). At 15°C to 30°C, substantial inhibition of R occurred at 12 μmol photons m−2 s−1, with maximum inhibition occurring at 100 to 200 μmol photons m−2 s−1. Higher irradiance had little additional effect on R at these moderate temperatures. The irradiance necessary to maximally inhibit R at 6°C to 10°C was lower than that at 15°C to 30°C. Moreover, although R was inhibited by low irradiance at 6°C to 10°C, it recovered with progressive increases in irradiance. The temperature sensitivity of R was greater in darkness than under bright light. At 30°C and high irradiance, light-inhibited rates of R represented 2% of gross CO2 uptake (vc), whereas photorespiratory CO2 release was approximately 20% of vc. If light had not inhibited leaf respiration at 30°C and high irradiance, R would have represented 11% of vc. Variations in light inhibition of R can therefore have a substantial impact on the proportion of photosynthesis that is respired. We conclude that the rate of R in the light is highly variable, being dependent on irradiance and temperature.

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