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Comparisons of δ 13C Values in Leaves of Aquatic Macrophytes from Different Habitats in Britain and Finland; Some Implications for Photosynthetic Processes in Aquatic Plants

C. B. Osmond, N. Valaane, S. M. Haslam, P. Uotila and Z. Roksandic
Oecologia
Vol. 50, No. 1 (1981), pp. 117-124
Published by: Springer in cooperation with International Association for Ecology
Stable URL: http://www.jstor.org/stable/4216431
Page Count: 8
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Comparisons of δ 13C Values in Leaves of Aquatic Macrophytes from Different Habitats in Britain and Finland; Some Implications for Photosynthetic Processes in Aquatic Plants
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Abstract

The δ 13C values of submerged aquatic plants from contrasting but relatively defined habitats, and the δ 13C values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the δ 13C values of dissolved inorganic carbon in the water were also measured. Plant δ 13C values in the vicinity of -40 to -50‰ were found in rapidly flowing spring waters with carbonate δ 13C values of -16 to -21‰, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO₂ via $\text{RuP}_{2}$ carboxylase. Plant δ 13C values in the vicinity of -10 to -15‰ in sluggish water with carbonate δ 13C values of about -5‰ were observed, consistent with the notion that boundary layer diffusion and/or HCO₃⁻ uptake may determine the δ 13C value of submerged aquatic plants in these circumstances. Comparisons of δ 13C values of the same or related species growing in waters of similar carbonate δ 13C value but different flow rates confirmed this view; more negative δ 13C values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the δ 13C values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The δ 13C value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO₂, as opposed to atmospheric carbon. The contributions of these variations in δ 13C of the carbon source, and of isotope fractionation in diffusion, to the δ 13C value of submerged parts of dimorphic plants is discussed.

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