title: A novel mechanistic interpretation of instantaneous temperature responses of leaf net photosynthesis.
abstract: Steady-state rates of leaf CO2 assimilation (A) in response to incubation temperature (T) are often symmetrical around an optimum temperature. A/T curves of C3 plants can thus be fitted to a modified Arrhenius equation, where the activation energy of A close to a low reference temperature is strongly correlated with the dynamic change of activation energy to increasing incubation temperature. We tested how [CO2] < current atmospheric levels and saturating light, or [CO2] at 800 µmol mol(-1) and variable light affect parameters that describe A/T curves, and how these parameters are related to known properties of temperature-dependent thylakoid electron transport. Variation of light intensity and substomatal [CO2] had no influence on the symmetry of A/T curves, but significantly affected their breadth. Thermodynamic and kinetic (physiological) factors responsible for (i) the curvature in Arrhenius plots and (ii) the correlation between parameters of a modified Arrhenius equation are discussed. We argue that the shape of A/T curves cannot satisfactorily be explained via classical concepts assuming temperature-dependent shifts between rate-limiting processes. Instead the present results indicate that any given A/T curve appears to reflect a distinct flux mode, set by the balance between linear and cyclic electron transport, and emerging from the anabolic demand for ATP relative to that for NADPH.
authors.affiliation: Chair of Tree Physiology, Institute of Forest Sciences, Georges-Köhler-Allee 53/54, 79110, Freiburg, Germany. joerg.kruse@ctp.uni-freiburg.de.
authors.forename: Jörg
authors.initials: J
authors.lastname: Kruse
authors.affiliation: College of Sciences, King Saud University, P.O. Box 2455, Riyadh, 11451, Saudi Arabia.
authors.forename: Saleh
authors.initials: S
authors.lastname: Alfarraj
authors.affiliation: Chair of Tree Physiology, Institute of Forest Sciences, Georges-Köhler-Allee 53/54, 79110, Freiburg, Germany.|College of Sciences, King Saud University, P.O. Box 2455, Riyadh, 11451, Saudi Arabia.
authors.forename: Heinz
authors.initials: H
authors.lastname: Rennenberg
authors.affiliation: Faculty of Agriculture and Environment, The University of Sydney, Sydney, NSW, 2006, Australia.
authors.forename: Mark
authors.initials: M
authors.lastname: Adams
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D004579:Electron Transport; D007700:Kinetics; D008027:Light; D051336:Mitochondrial Membranes / Q000378:metabolism / Q000528:radiation effects; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism; D065749:Phoeniceae / Q000502:physiology* / Q000528:radiation effects; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D018526:Plant Transpiration / Q000502:physiology* / Q000528:radiation effects; D013696:Temperature; D020524:Thylakoids / Q000378:metabolism / Q000528:radiation effects
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: Cyclic electron flow; Non-linear Arrhenius plot; Photorespiration; Temperature response