Determining Photosynthetic Parameters from Leaf CO2 Exchange and Chlorophyll Fluorescence (Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Specificity Factor, Dark Respiration in the Light, Excitation Distribution between Photosystems, Alternative Electron Transport Rate, and Mesophyll Diffusion Resistance

Abstract

(A.L.); and lstituto di Biochimica ed Ecofisiologia Vegetali, 0001 6 Monterotondo Scalo, Rome, ltaly (F.L.)Using simultaneous measurements of leaf gas exchange and chlorophyll fluorescence, we determined the excitation partitioning to photosystem I1 (PSII), the CO,/O, specificity of ribulose-l,5-bisphosphate carboxylase/oxygenase, the dark respiration in the light, and the alternative electron transport rate to acceptors other than bisphosphoglycerate, and the transport resistance for CO, in the mesophyll cells for individual leaves of herbaceous and tree species. The specificity of ribulose-1,5-bisphosphate carboxylase/ oxygenase for CO, was determined from the slope of the O , dependente of the CO, compensation point between 1.5 and 21 ?& O,. Its value, on the basis of dissolved CO, and O , concentrations at 25.5"C, varied between 86 and 89. Dark respiration i n the light, estimated from the difference between the CO, compensation point and the CO, photocompensation point, was about 20 to 50% of the respiration rate in the dark. The excitation distribution to PSll was estimated from the extrapolation of the dependence of the PSll quantum yield on F/F, to F = O, where F is steady-state and F,,, is pulse-saturated fluorescence, and varied between 0.45 and 0.6. The alternative electron transport rate was found as the difference between the electron transport rates calculated from fluorescence and from gas exchange, and at low CO, concentrations and 10 to 21 % O*, it was 25 to 30% of the maximum electron transport. l h e calculated mesophyll diffusion resistance accounted for about 20 to 30% of the total mesophyll resistance, which also includes carboxylation resistance. Whole-leaf photosynthesis is limited by gas phase, mesophyll diffusion, and carboxylation resistances in nearly the same proportion in both herbaceous species and trees.

Pouteria torta: a native species of the Brazilian Cerrado as a bioindicator of glyphosate action

“…Using these parameters, the effective quantum yield of PSII (∆F/Fm') was calculated (Genty et al, 1989). ∆F/Fm' was used to estimate the apparent electron transport rate (ETR) (Bilger et al, 1995;Laisk and Loreto, 1996), and non-photochemical quenching (NPQ) was calculated according to Bilger and Bjorkman (1990).…”

Stomatal and non-stomatal limitations on leaf carbon assimilation in beech (Fagus sylvatica L.) seedlings under natural conditions

“…A value of 0.85 for total leaf absorptance was assumed (Evans and Loreto, 2000), and a factor of 0.5 for the partitioning of light between the two photosystems (Laisk and Loreto, 1996).…”

Eficiência fotossintética e consumo de água de Ipomoea triloba após aplicação de herbicidas

“…Embora 0,84 seja um valor médio para muitas espécies de plantas, trabalhos têm mostrado que o coeficiente de absorção da folha pode variar com a qualidade da luz, espécie, conteúdo de clorofila e refletância da folha. Para a fração de luz que é absorvida pelo complexo antena do PSII os trabalhos mostram que ocorre variação de acordo com a espécie, que se estende de 0,42 a 0,60 (Laisk & Loreto, 1996).…”