Stable carbon isotope ratios of flooded and nonflooded sunflowers (Helianthus annuus)

Abstract

The current view regarding stable carbon isotope ratios (.delta.13C values) of C3 plants is that they can be related to the ratio of intercellular (leaf) to ambient partial pressures of CO2. Flooded H. annuus L. have reduced photosynthetic rates without significant increases in diffusive resistance. This should lead to higher ratios of intercellular over ambient partial pressures of CO2 and, consequently, more negative .delta.13C values. Although whole apices and leaves of flooded and nonflooded sunflowers show no differences in .delta.13C, the aqueous fractions of leaf extracts (partitioned against chloroform) do, particularly when expressed relative to the total tissue .delta.13C. This shift (-0.6.permill.) is in the direction expected and provides confirmation that the lower photosynthetic rates of flooded sunflowers are not due simply to stomatal closure. Chloroform-soluble fractions were depleted in 13C by about 4.4.permill. relative to the aqueous fractions.