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Title: Crop δ15N value expression in bone collagen of ancient fauna and humans : a new approach to palaeodietary and agricultural reconstruction
Author: Styring, Amy Keita
ISNI:       0000 0004 2720 2518
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2012
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Stable nitrogen (N) isotope analysis of human bone collagen has been used for almost three decades for reconstructing the diets of ancient humans. A major limitation in this 'standard model', using the 15N-enrichment of human bone collagen δ15N values over associated herbivore bone collagen δ15N values to Fsredict the relative contribution of animal protein to human diet, is the assumption that the δ15Nvalues of plants consumed by humans and herbivores are identical. The work described in this thesis was carried out with the aim of determining the δ15N values of amino acids in crop species likely to be consumed by humans and herbivores and assessing how these contribute to bulk collagen δ15N values. This serves to refine interpretations of ancient human diet, allowing more accurate estimation of the relative contribution of plant and animal protein to human diet in the past. This is particularly pertinent at Neolithic sites, where relatively high human bone collagen 01SN values have been interpreted as due to consumption of high proportions of animal protein. These relatively high δ15N values could in fact be due to consumption of manured crops, with higher 01SN values _ than the plants consumed by associated herbivores. This study began by determining a method for the accurate and precise determination of plant and animal protein amino acid 01SN values by GC-C-IRMS. It was concluded that hydrolysis of lipid-extracted plant material, followed by purification of amino acids using ion-exchange chromatography and derivatisation to their N-acetyl-i-propyl esters, gives accurate and precise amino acid 01SN values. This method accounts for 75% of the N in human bone collagen, over 68% of the N in wheat and barley grain and over 58% of the N in pulses. A preliminary investigation of bone collagen amino acid 01SN values from humans and fauna at archaeological sites in South Africa illustrated the potential of amino acid 01SN values in elucidating the factors contributing to the bulk collagen δ15N value. The next step was to elucidate plant amino acid N cycling in agriculturally relevant crop species and in parts of the plant tending to be preserved in the archaeological record. Amino acid 01SN values of experimentally grown barley and bread wheat grains and rachis and broad beans and peas were found to broadly relate to metabolic pathways involved in their biosynthesis and catabolism. Manuring resulted in a consistent 15N-enrichment of cereal grain and rachis amino acid 01SN values but no 15N-enrichment of pulse amino acid δ15N values. Investigation of the chemical composition of modem charred grains and grains from archaeological sites was then carried out, to determine whether modern grains charred under experimental conditions can provide suitable analogues for their archaeological counterparts. Since 'charring of modem charred grains results in the conversion of starch and protein into melanoidins with alkyl and aromatic C moieties, whereas archaeological grains contain only aromatic C, it was concluded that heating of modem grains to 230°C does not account for all of the changes in chemical composition associated with diagenesis. Finally, N isotope analysis of amino acids from human and herbivore bone collagen isolates from three Neolithic sites, together with N isotope analysis of preserved cereal remains, was used to estimate amino acid δ15N values of the plants consumed by humans and herbivores and thus to elucidate dietary influences on bulk bone collagen δ15N values. This demonstrated the potential of bone collagen amino acid δ15N values in the elucidation of differential contributions of plant and animal protein to the human diet, drawing attention to the significant effect of plant N isotope signatures on palaeodietary interpretation using bone collagen δ15N values.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available