Silicon, oxygen and carbon isotope composition of wheat (Triticum aestivum L.) phytoliths : implications for palaeoecology and archaeology

Six mature wheat (Triticum aestivum L.) plants from one crop were collected one week before harvest, and organs were separated as follows: culm, rachis, leaf sheaths, leaf blades and inflorescence bracts. Percentage silica (% SiO2), % C, % N and 13C were determined in these samples. Phytoliths isolated from the individual organs were subsequently analysed for 29Si, 30Si, and 18O, as well as % C, % N and 13C from occluded organic material within the phytoliths. Percentage silica was highest in the leaf sheaths and leaf blades and lower in the inflorescence bracts, culm and rachis. 30Si and 29Si were highly correlated, and both increased in the upper parts of the plant. It appears there are two routes for Si transport within the plant, and that heavier isotopes increase towards the end of both routes. The 18O results indicate that the culm and the leaf blades were the sites of highest 18O, with lower values in the rachis, leaf sheath and inflorescence. There was no correlation between the accumulation of either heavy silicon isotope (29Si and 30Si) and heavy oxygen accumulation (18O). 13C values were typical of C3 species, and whole plant and isolated phytolith values were similar. Low % N concentrations were detected in phytoliths