The carbon stable isotope composition of pollen

The delta(13)C value of plant tissue is increasingly used to infer environmental and ecological conditions in modern and ancient enviromnents. Isolation techniques and morphological descriptions have been established that characterize plant pollen for the greater part of the Phanerozoic eon. If the delta(13)C value of fossil pollen could be used as an indicator of the carbon isotope composition of ancient pollinating communities, it could provide insight into ancient paleoenviromnents. Previous studies have revealed a correlation between the delta(13)C value of pollen and the delta(13)C value of bulk plant tissue in a few isolated species; this study sought to quantify the isotopic relationship between modern pollen and stem and leaf tissues across all the major phylogenetic clades of the tracheophytes. One-hundred and seventy-five different species of tracheophytes were collected from 11 arboreta and botanical gardens across the United States and analyzed for delta(13)C value of pollen, leaf, and stem tissue. The carbon isotope difference between pollen and leaf tissue values in the same species was = +/-3.00parts per thousand for >90% of data pairs, and the same relationship was true for comparisons between pollen and stem tissue. When the data was examined by phylogenetic clade, it was found that some groups, such as the Cornales and Ericales, exhibited a much closer and more consistent correlation between pollen and stem and leaf tissue. It was also noted that green-stemmed clades tended to show delta(13)C(stem)<delta(13)C(pollen) while woody-stemmed clades showed the opposite (delta(13)C(pollen)<delta(13)C(stem)), a difference attributable to the different chemical composition of the two types of stem tissue. The chemical preparation method involving Schulze's solution that is commonly employed to isolate pollen from pre-Quaternary sediments was shown not to affect the carbon isotope composition of pollen by more than 0.23parts per thousand. The manual isolation of sufficient pollen from the fossil record for delta(13)C analysis of a single species would be prohibitively laborious; however, these results showed that when understood in terms of paleobotanical taxonomy, delta(13)C analyses of bulk fossil pollen can be used to infer the delta(13)C value of the ancient plant community to within 1.5parts per thousand. (C) 2004 Elsevier B.V. All rights reserved.