© 2001 Heron Publishing—Victoria, Canada
Temperature response of leaf photosynthetic capacity in seedlings from seven temperate tree species
Erwin Dreyer (1), Xavier Le Roux (2), Pierre Montpied (1), François Alain Daudet (2) and Frederic Masson (1)
1. Ecophysiologie Forestière, INRA Nancy, 54280 Champenoux, France / 2. UA Physiologie Intégrée de l'Arbre (PIAF, INRA-Université Blaise Pascal), Domaine de Crouelle, 234 avenue du Brezet, 63039
Clermont Ferrand, France / Received April 11, 2000
Summary
Seedlings of seven temperate tree species (Acer pseudoplatanus L., Betula pendula Roth, Fagus sylvatica L., Fraxinus excelsior L., Juglans regia L., Quercus petraea Matt. Liebl. and Quercus robur L.) were grown in a nursery under neutral filters transmitting 45% of incident global irradiance. During the second or third
year of growth, leaf photosynthetic capacity (i.e., maximal carboxylation rate, Vcmax, maximal photosynthetic electron transport rate, Jmax, and dark respiration, Rd) was estimated for five leaves from each species at five or six leaf temperatures (10, 18, 25, 32, 36 and 40 °C). Values
of Vcmax and Jmax were obtained by fitting the equations of the Farquhar model on response curves of net CO2 assimilation (A) to sub-stomatal CO2 mole fraction (ci), at high irradiance. Primary parameters describing the kinetic properties of Rubisco (specificity factor, affinity for CO2 and for O2, and their temperature responses) were taken from published data obtained with spinach and tobacco, and were used for all
species. The temperature responses of Vcmax and Jmax, which were fitted to a thermodynamic model, differed. Mean values of Vcmax and Jmax at a reference temperature of 25 °C were 77.3 and 139 μmol m–2 s–1, respectively. The activation energy was higher for Vcmax than for Jmax (mean values of 73.1 versus 57.9 kJ mol–1) resulting in a decrease in Jmax/Vcmax ratio with increasing temperature. The mean optimal temperature was higher for Vcmax than for Jmax (38.9 versus 35.9 °C). In addition, differences in these temperature responses were observed among species. Temperature optima
ranged between 35.9 and above 45 °C for Vcmax and between 31.7 and 43.3 °C for Jmax, but because of data scatter and the limited range of temperatures tested (10 to 40 °C), there were few statistically significant
differences among species. The optimal temperature for Jmax was highest in Q. robur, Q. petraea and J. regia, and lowest in A. pseudoplatanus and F. excelsior. Measurements of chlorophyll a fluorescence revealed that the critical temperature at which basal fluorescence begins toincrease
was close to 47 °C, with no difference among species. These results should improve the parameterization of photosynthesis
models, and be of particular interest when adapted to heterogeneous forests comprising mixtures of species with diverse ecological
requirements.
Keywords:
broad-leaved trees, maximal carboxylation rate, maximal electron transport rate, non-photorespiratory respiration, optimal
temperature, photosynthesis model.
