Isotopic composition of cellulose from aquatic organisms

Abstract

The stable isotopic ratios of oxygen, carbon and the non-exchangeable carbon-bound hydrogen of cellulose from marine plants (algae and higher vascular forms) and animals (tunicates) collected in their natural habitats and from freshwater vascular plants grown in the laboratory under controlled conditions were determined. The δ^(18)O values of cellulose from all the plants and animals were 27 ±3% more positive than the δ^(18)O values of the waters in which the organisms grew. Temperature had little or no influence on this relationship for three species of freshwater vascular plants that were analyzed. The relationship between the δ^(18)O values of cellulose and the water used in its synthesis is probably established by the isotopic fractionation that occurs during the hydration of carbonyl groups of the intermediates involved in cellulose synthesis. The δD values of the non-exchangeable hydrogen of cellulose (determined by analyzing cellulose nitrate) from different organisms that grew in the same environment differed by large amounts. This difference ranged up to 200‰ for different species of algae collected at a single site: the corresponding difference for different species of tunicates and vascular plants was 60 and 20‰ respectively. The δD values of cellulose nitrate from different species of freshwater vascular plants grown in water of constant temperature and isotopic composition differed by as much as 60‰ The relationship between the δD values of the carbon-bound hydrogen of cellulose and the water used in its synthesis displayed a significant temperature dependence for four species of freshwater vascular plants that were analyzed. The δD values of cellulose nitrate prepared from different parts of one of the plants grown under constant conditions differed by 40‰ Hydrogen isotopic fractionation during cellulose synthesis appears to be more variable among different species and displays a larger temperature dependence than was suggested by previous studies.

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