title: Thermodynamic balance of photosynthesis and transpiration at increasing CO2 concentrations and rapid light fluctuations.
abstract: Experimental and theoretical flux models have been developed to reveal the influence of sun flecks and increasing CO2 concentrations on the energy and entropy balances of the leaf. The rapid and wide range of fluctuations in light intensity under field conditions were simulated in a climatic gas exchange chamber and we determined the energy and entropy balance of the leaf based on radiation and gas exchange measurements. It was estimated that the energy of photosynthetic active radiation (PAR) accounts for half of transpiration, which is the main factor responsible for the exportation of the entropy generated in photosynthesis (Sg) out of the leaf in order to maintain functional the photosynthetic machinery. Although the response of net photosynthetic production to increasing concentrations of CO2 under fluctuating light is similar to that under continuous light, rates of transpiration respond slowly to changes of light intensity and are barely affected by the concentration of CO2 in the range of 260-495 ppm, in which net photosynthesis increases by more than 100%. The analysis of the results confirms that future increases of CO2 will improve the efficiency of the conversion of radiant energy into biomass, but will not reduce the contribution of plant transpiration to the leaf thermal balance.
authors.affiliation: Department of Physical Chemistry, University of Alcalá, Alcalá de Henares, 28871 Madrid, Spain.
authors.forename: Dolores
authors.initials: D
authors.lastname: Marín
authors.affiliation: Department of Plant Biology, University of Alcalá, Alcalá de Henares, 28871 Madrid, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Martín
authors.affiliation: Department of Plant Biology, University of Alcalá, Alcalá de Henares, 28871 Madrid, Spain.
authors.forename: Patricia H
authors.initials: PH
authors.lastname: Serrot
authors.affiliation: Department of Plant Biology, University of Alcalá, Alcalá de Henares, 28871 Madrid, Spain. Electronic address: bartolome.sabater@uah.es.
authors.forename: Bartolomé
authors.initials: B
authors.lastname: Sabater
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis*; D008027:Light; D008962:Models, Theoretical; D010788:Photosynthesis; D018526:Plant Transpiration; D013816:Thermodynamics
chemical_list: D002245:Carbon Dioxide
keywords: Entropy production; Fluctuating light; High CO(2); PAR; Photosynthetic efficiency; Structural entropy; Transpiration; photosynthetic active radiation