Stable carbon isotope variability in the seagrass Posidonia oceanica: evidence for light intensity effects

Publisher Website
Google Scholar
Abstract
Stable carbon isotope ratios were determined for leaves of the seagrass Posidonia oceanica (L.) Delile collected over a 38 m depth gradient at Bay of Calvi, Corsica. Although variability in .delta.13C values among individual leaves at specific depths was as high as 6.permill., there was an overall trend towards less discrimination against 13C at the shallowest water levels. The mean .delta.13C value of leaves of 5 m was -11.0.permill. and declined to a minimum mean of -16.4.permill. at 35 m. Isotopic variability in individual leaves divided into thirds was consistent with this trend, except in those leaf sections nearest to the meristem, whose .delta.13C values did not vary with depth. A variety of explanations for these observations were considered, including the effects of light intensity, temperature, pressure, relative water motion, seasonal varibility in biochemical fractionation, isotopic variability in the dissolved inorganic carbon pool, and differential use of bicarbonate and dissolved carbon dioxide on the carbon isotopic composition of P. oceanica. Differences in light intensity and consequently photosynthetic rate are most likely to influence discrimination against 13C and thus account for the observations reported here.