Effects of charring on the carbon isotopic composition of grass (Poaceae) epidermis

Charred modern grass epidermis preserves the carbon isotopic composition of the parent plant photosynthetic pathway. Fifty-nine modern grasses and sedges were collected in lowland western Uganda. All charred epidermal samples from C-4 grasses or sedges preserve a carbon isotopic value within the range typical for C-4 plants (-17 to -10parts per thousand), and charred epidermal fragments from C-3 plants have carbon isotopic values between -30 and -26 parts per thousand. The process of charring results in a slightly enriched carbon isotopic signature (-11.9parts per thousand mean charred value as compared to -12.8parts per thousand mean unaltered grass tissue value). delta(13)C measurements of replicate samples from the same plant vary within 1-2parts per thousand, yet all values for the same plant stay within the expected values for the photosynthetic pathway of the plant. delta(13)C measurements on > 180-mum charred grass epidermal fragments extracted from surface sediment samples from three lakes on the lowland western Ugandan landscape confirm the predominant lowland C-4 grass input (delta(13)C = -16 to -19parts per thousand). These results demonstrate the utility of using carbon isotopic analysis of charred grass epidermis to reconstruct C-3 VS. C-4 grassland assemblages on the landscape, Furthermore, such downcore delta(13)C profiles can be used to highlight key zones Of C-3 VS. C-4 grass change for which taxonomic analysis of fossil grass epidermis could provide more detailed information regarding grassland community composition. (C) 2002 Elsevier Science B.V. All rights reserved.