title: Variation in carbon isotope discrimination within and among Sphagnum species in a temperate wetland.
abstract: Field samples of bryophytes are highly variable in carbon isotope discrimination values (Δ, a measure of13CO2uptake relative to12CO2), but it is unknown what affects Δ under field conditions, or how variation in Δ relates to bryophyte performance. This study employed field and greenhouse common garden studies to evaluate the influence of microsite, seasonal, and genetic variation on Δ in peatmosses. Three species of Sphagnum that occupy hollow (S. recurvum), carpet (S. palustre), and hummock (S. tenerum) habitats were sampled for relative growth rates (RGR), C:N ratio, and Δ throughout a growing season. Values of Δ ranged from 19.0 to 27.1‰. This variation was unrelated to species (P=0.61). However, Δ varied seasonally (P<0.001), with lower discrimination in the spring (mean 22.5‰), followed by summer (23.8‰) and winter (24.7‰). There was also significant microsite variation (P=0.015) which disappeared when plants were grown in a common garden. In both spring and summer, microsite variation in Δ was inversely related to RGR (P<0.001), but unrelated to C:N ratios (P>0.08). These results suggest that environmental, not genetic, variation at microsites affects Δ in non-vascular plants. However, environmental control of Δ is unlike that in vascular plants where water limitation lowers chloroplastic demand and increases resistance to carbon uptake. In non-vascular plants, water limitation lowers chloroplastic demand and decreases resistance to carbon uptake. These processes have additive effects and generate high spatial and seasonal variability in Δ.
authors.affiliation: Department of Biological Sciences, Union College, Schenectady, NY 12308, USA, e-mail: rices@union.edu Tel.: +1-518-3886243, Fax: +1-518-3886429, , , , , , US.
authors.forename: S K
authors.initials: SK
authors.lastname: Rice
keywords: 13C/12C; Carbon:nitrogen ratio; Key words Carbon isotope discrimination; Physiological ecology; Sphagnum