Influence of increasing combustion temperature on the AMS (14)C dating of modern crop phytoliths

Several attempts have been made to directly date phytoliths, but most (14)C results are not consistent with other independent chronologies. Due to the limited dataset, there is not a clear explanation for these discrepancies. Herein, we report the (14)C ages of phytolith-occluded carbon (PhytOC) from contemporary rice and millet crops that were combusted at different temperatures to investigate the relationship between the combustion temperature and resulting (14)C age. Our results show that the (14)C age of PhytOC increases directly with combustion temperature (up to 1100°C) and results in age overestimations of hundreds of years. Considerably older ages are observed at higher temperatures, suggesting that it may be possible to distinguish between two fractions of organic carbon in phytoliths: labile and recalcitrant carbon. These findings challenge the assumption that PhytOC is homogeneous, an assumption made by those who have previously attempted to directly date phytoliths using (14)C.