title: Long-term responses of the green-algal lichen Parmelia caperata to natural CO2enrichment.
abstract: Acclimation to elevated CO2was investigated in Parmelia caperata originating from the vicinity of a natural CO2spring, where the average daytime CO2concentration was 729 ± 39 μmol mol-1dry air. Thalli showed no evidence of a down-regulation in photosynthetic capacity following long-term exposure to CO2enrichment in the field; carboxylation efficiency, total Ribulose bisphosphate carboxylase/oxygenase (Rubisco) content, apparent quantum yield of CO2assimilation, and the light-saturated rate of CO2assimilation (measured under ambient and saturating CO2concentrations) were similar in thalli from the naturally CO2enriched site and an adjacent control site where the average long-term CO2concentration was about 355 μmol mol-1. Thalli from both CO2environments exhibited low CO2compensation points and early saturation of CO2uptake kinetics in response to increasing external CO2concentrations, suggesting the presence of an active carbon-concentrating mechanism. Consistent with the lack of significant effects on photosynthetic metabolism, no changes were found in the nitrogen content of thalli following prolonged exposure to elevated CO2. Detailed intrathalline analysis revealed a decreased investment of nitrogen in Rubisco in the pyrenoid of algae located in the elongation zone of thalli originating from elevated CO2, an effect associated with a reduction in the percentage of the cell volume occupied by lipid bodies and starch grains. Although these differences did not affect the photosynthetic capacity of thalli, there was evidence of enhanced limitations to CO2assimilation in lichens originating from the CO2-enriched site. The light-saturated rate of CO2assimilation measured at the average growth CO2concentration was found to be significantly lower in thalli originating from a CO2-enriched atmosphere compared with that of thalli originating and measured at ambient CO2. At lower photosynthetic photon flux densities, the light compensation point of net CO2assimilation was significantly higher in thalli originating from elevated CO2, and this effect was associated with higher usnic acid content.
authors.affiliation: Departamento de Biología Vegetal I, Facultad de Biología, Universidad Complutense, Madrid, E-28040, Spain e-mail: balaguer@eucmax.sim.ucm.es, Tel.: +34-1-3945047, Fax: +34-1-3945034, , , , , , ES.
authors.forename: L
authors.initials: L
authors.lastname: Balaguer
authors.affiliation: Departamento de Biología Vegetal II, Facultad de Farmacia, Universidad Complutense, Madrid, E-28040, Spain, , , , , , ES.
authors.forename: E
authors.initials: E
authors.lastname: Manrique
authors.affiliation: Centro de Ciencias Medioambientales (CSIC), Serrano 115 dup., Madrid, E-28006, Spain, , , , , , ES.
authors.forename: A
authors.initials: A
authors.lastname: de Los Rios
authors.affiliation: Centro de Ciencias Medioambientales (CSIC), Serrano 115 dup., Madrid, E-28006, Spain, , , , , , ES.
authors.forename: C
authors.initials: C
authors.lastname: Ascaso
authors.affiliation: Department of Plant Ecology, Umeå University, S-90187 Umeå, Sweden, , , , , , SE.
authors.forename: K
authors.initials: K
authors.lastname: Palmqvist
authors.affiliation: Air Pollution Laboratory, Department of Agricultural and Environmental Science, Ridley Building, The University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, UK, , , , , , GB.
authors.forename: M
authors.initials: M
authors.lastname: Fordham
authors.affiliation: Air Pollution Laboratory, Department of Agricultural and Environmental Science, Ridley Building, The University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, UK, , , , , , GB.
authors.forename: J D
authors.initials: JD
authors.lastname: Barnes
keywords: Key words Elevated CO2; Lichenized green algae; Photobiont ultrastructure; Photosynthetic performance; Rubisco