Leaf respiration of snow gum in the light and dark. Interactions between temperature and irradiance.
We investigated the effect of temperature and irradiance on leaf respiration (R, non-photorespiratory mitochondrial CO(2) release) of snow gum (Eucalyptus pauciflora Sieb. ex Spreng). Seedlings were hydroponically grown under constant 20 degrees C, controlled-environment conditions. Measurements of R (using the Laisk method) and photosynthesis (at 37 Pa CO(2)) were made at several irradiances (0-2,000 micromol photons m(-2) s(-1)) and temperatures (6 degrees C-30 degrees C). At 15 degrees C to 30 degrees C, substantial inhibition of R occurred at 12 micromol photons m(-2) s(-1), with maximum inhibition occurring at 100 to 200 micromol 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 degrees C to 10 degrees C was lower than that at 15 degrees C to 30 degrees C. Moreover, although R was inhibited by low irradiance at 6 degrees C to 10 degrees C, it recovered with progressive increases in irradiance. The temperature sensitivity of R was greater in darkness than under bright light. At 30 degrees C and high irradiance, light-inhibited rates of R represented 2% of gross CO(2) uptake (v(c)), whereas photorespiratory CO(2) release was approximately 20% of v(c). If light had not inhibited leaf respiration at 30 degrees C and high irradiance, R would have represented 11% of v(c). 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.
Atkin
O K
OK
Environmental Biology, Research School of Biological Sciences, The Australian National University, Canberra, 0200 Australian Capital Territory, Australia. oka1@york.ac.uk
Evans
J R
JR
Ball
M C
MC
Lambers
H
H
Pons
T L
TL
D002245:Carbon Dioxide / Q000378:metabolism; D003624:Darkness; D005052:Eucalyptus / Q000378:metabolism* / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D010946:Plants, Medicinal; D013696:Temperature
D002245:Carbon Dioxide