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Does growth irradiance affect temperature dependence and thermal acclimation of leaf respiration? Insights from a Mediterranean tree with long-lived leaves.Zaragoza-Castells J, Sánchez-Gómez D, Valladares F, Hurry V, Atkin OK Department of Biology, University of York, PO Box 373, York, YO10 5YW, UK. Understanding the response of leaf respiration (R) to changes in irradiance and temperature is a prerequisite for predicting the impacts of climate change on plant function and future atmospheric CO(2) concentrations. Little is known, however, about the interactive effects of irradiance and temperature on leaf R. We investigated whether growth irradiance affects the temperature response of leaf R in darkness (R(dark)) and in light (R(light)) in seedlings of a broad-leaved evergreen species, Quercus ilex. Two hypotheses concerning R(dark) were tested: (1) the Q(10) (i.e. the proportional increase in R per 10 degrees C rise in temperature) of leaf R(dark) is lower in shaded plants than in high-light-grown plants, and (2) shade-grown plants exhibit a lower degree of thermal acclimation of R(dark) than plants exposed to higher growth irradiance. We also assessed whether light inhibition of R(light) differs between leaves exposed to contrasting temperatures and growth irradiances, and whether the degree of thermal acclimation of R(light) is dependent on growth irradiance. We showed that while growth irradiance did impact on photosynthesis, it had no effect on the Q(10) of leaf R(dark). Growth irradiance had little impact on thermal acclimation when fully expanded, pre-existing leaves were exposed to contrasting temperatures for several weeks. When R(light) was measured at a common irradiance, R(light)/R(dark) ratios were higher in shaded plants due to homeostasis of R(light) between growth irradiance treatments and to the lower R(dark) in shaded leaves. We also showed that R(light) does not acclimate to the same degree as R(dark), and that R(light)/R(dark) decreases with increasing measuring and growth temperatures, irrespective of the growth irradiance. Collectively, we raised the possibility that predictive carbon cycle models can assume that growth irradiance and photosynthesis do not affect the temperature sensitivity of leaf R(dark) of long-lived evergreen leaves, thus simplifying incorporation of leaf R into such models. Published 5 June 2007 in Plant Cell Environ, 30(7): 820-33.
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