CARBON ISOTOPE ANALYSIS OF PLANTS AND TOOTH ENAMEL OF HERBIVORES FROM THE TIBETAN PLATEAU

The carbon isotope analysis to the modern grasses from the Gyirong Basin in the Tibetan Plateau shows that C₃ plants are absolutely dominant in the region at the very high altitude, but relatively rare C₄ plants still exist. The Gyirong Basin is situated in the southwestern Tibet, China and near the Nepal border, with the altitude of about 4000 m. This vegetation analysis include 53 species of grasses, among them there are 51 species of C₃ plants and 2 species of C₄ plants. The δ¹³C value of C₃ grasses from Gyirong is from -21.8 per mil to -29.1 per mil, with a mean of -25.3 per mil. The δ¹³C value of C₄ grasses from Gyirong is -11.5 per mil and -11.2 per mil respectively, with a mean of -11.3 per mil. The average δ¹³C value of grasses from Gyirong is -24.8 per mil. The C₄ plants discovered in the Gyirong Basin are Salsola nepalensis of Chenopodiaceae and Pennisetum flaccidum of Gramineae, which imply that the C₄ plants influenced by the low atmospheric water are also distributed in regions with very high altitude and correct the viewpoint of no C₄ plants above 3500 m high. The carbon isotope analysis to tooth enamel of the modern herbivores in the Gyirong Basin indicates that the carbon isotopic composition of the structure carbonate in mammalian apatite still has a stable enriched relationship to that of the vegetation diet in the region with the very high altitude. The enamel analysis includes 26 specimens from domestic horses (Equus caballus), yaks (Bos mutus) and goats (Capra hircus). The δ¹³C value of tooth enamel of domestic horses in Gyirong is from -12.8 per mil to -13.8 per mil, with a mean of -13.2 per mil; the δ¹³C value of yaks is from -10.7 per mil to -14.2 per mil, with a mean of -12.6 per mil; and the δ¹³C value of goats is from -8.8 per mil to -12.1 per mil, with a mean of -10.5 per mil. The average δ¹³C value of the whole enamel specimens is -12.1 per mil, and it is enriched in ¹³C by 12.7 per mil relative to the vegetation diet of these herbivores. As a result, the carbon isotope of tooth enamel is an accurate indicator to reflect the vegetation types and environmental conditions.