title: Intraspecific variation in photosynthetic responses of trebouxioid lichens with reference to the activity of a carbon-concentrating mechanism.
abstract: The photosynthetic responses of a range of trebouxioid lichens were investigated to determine whether variations in net assimilation rates shown by populations of the same species collected from different habitats could be correlated with adjustments in carbon-concentrating mechanism (CCM) activity. The activity of a CCM was inferred from the high affinity for CO2[i.e. low CO2compensation point (Γ); low external CO2concentration at which half-maximal assimilation rates are reached (K0.5 CO2)], the release of a pool of accumulated dissolved inorganic carbon (Ci) during light/dark transient measurements of CO2exchange and values for carbon isotope discrimination intermediate between those characteristic of C3and C4terrestrial plants. Higher net and gross assimilation rates were expressed by lichens collected from shaded woodland habitats. The higher rates were not accounted for by variations in chlorophyll content. Lichens with high assimilation rates also showed an increased affinity for CO2as demonstrated by low CO2compensation points and K0.5values and the magnitude of the Cipool accumulated upon illumination and released after darkening of the thalli. However, there was no correlation between assimilation rates and organic matter or instantaneous carbon isotope discrimination measurements, with the latter remaining roughly consistent whatever the provenance or species of the lichen material. The data are discussed with reference to significant environmental factors which are likely to control photosynthesis in the habitats studied.
authors.affiliation: Department of Agricultural and Environmental Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, UK Fax: 0191 2225229; e-mail: e.c.smith@ncl.ac.uk, , , , , , GB.
authors.forename: Elizabeth C
authors.initials: EC
authors.lastname: Smith
authors.affiliation: Department of Agricultural and Environmental Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, UK Fax: 0191 2225229; e-mail: e.c.smith@ncl.ac.uk, , , , , , GB.
authors.forename: H
authors.initials: H
authors.lastname: Griffiths
keywords: Carbon isotope discrimination; Carbon-concentrating mechanism; Key words Lichen; Photosynthesis; Phycobiont