ABSTRACT

Stable carbon-isotope ratios (¹³C/¹²C) and the abundance of carbon, nitrogen and sulfur were measured in flora and soil organic matter from the Sifton Bog and Point Pelee Marsh, which are located in the temperate climatic zone of southwestern, Ontario, Canada. Characteristic bog vegetation contains less N and S than marsh flora; however, invasive species (e.g., Typha) at the Sifton Bog have N and S contents that are similar to vegetation from the Point Pelee Marsh. Flora from both wetlands have δ¹³C values that are similar and characteristic of vegetation possessing the C₃ photosynthetic pathway. The only exception is Utricularia vulgaris L. at the Point Pelee Marsh, which is ¹³C-enriched (average δ¹³C =-18.4‰; range -18.8 to -17.6‰) probably because of CO₂ limitation during growth. Organic matter from peat soils at each wetland exhibits a similar depth distribution of C:N ratios and δ¹³C values. The C:N ratio of soil organic matter decreases with depth, consistent with consumption of labile carbohydrates and fixation of nitrogen by soil microorganisms. Both C:N ratios and δ¹³C values stabilize at a shallow depth in soils at the Point Pelee Marsh, consistent with greater decay efficiency and less recalcitrant vegetation in marsh than in bog environments. Paleovegetational changes associated with a fen to bog succession also may have contributed to the more gradual and larger change in δ¹³C values and C:N ratios observed for soil organic matter at the Sifton Bog.