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G. Lepoint, P. Dauby, M. Fontaine, J.-M. Bouquegneau, S. Gobert

Carbon and Nitrogen Isotopic Ratios of the Seagrass Posidonia oceanica: Depth-related Variations

Nitrogen (?¹⁵N) and carbon (?¹³C) isotopic compositions of Posidonia oceanica were determined during three seasons along a bathymetric gradient (4–38m depth).The ?¹⁵N values are low (2.2±0.9 ? ) and variable. They do not show any relation to depth or sampling dates. There is a significant difference between the ?¹⁵N values of the youngest and the oldest leaves, probably as a result of N resorption and senescing during leaf ageing. The ?¹³C values of young Posidonia leaves vary with depth, showing the relationship between ?¹³C values and primary productivity rate, and the use of a bicarbonate/CO₂ mixture as an inorganic carbon source. The ?¹³C values of the oldest P. oceanica leaves are depleted in ¹³C compared to those of young leaves. This modification of the ¹³C signatures in relation to leaf age is particularly important between 20 and 29 m depth. This modification could be related to photosynthetic rate change during ageing, but also to change in carbohydrate composition and content.

Botanica Marina, Walter de Gruyter

Print ISSN: 0006-8055
Volume: 46, 11/2003
Pages: 555 - 561

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