Dr Amy Styring

© 2019 Elsevier Ltd In this study the stable nitrogen (δ15N) and carbon (δ13C) isotopic compositions of carbonized cereal grains from 18 archaeological sites in Poland, dating from the Early Neolithic to the turn of the Bronze Age and the Iron Age, were determined. There were two main aims of this study. The first aim was to test the archaeologically accepted model of a change from intensive ‘horticulture’ in the Early Neolithic in Lesser Poland to more extensive cultivation in the Middle Neolithic, which is expected to be evidenced by decreasing levels of manuring and labour input, reflected especially in a shift to lower cereal grain δ15N values. The second aim was to assess how cereal grain δ13C values reflect crop watering conditions and landscape openness regionally and through time. Despite the limited plant material, the study showed that all cereal plots potentially received some inputs of manure (including household waste), but there seems to be a clear regional difference in the intensity of manuring practice in the Early Neolithic, with greater manure application on plots in southern Poland than in northern Poland. Moreover, cereal plots in southern Poland in the Early Neolithic seem to have been located on soils with higher water retention and/or within denser vegetation than plots in northern Poland. In the Middle Neolithic, however, plots in southern Poland seemed to have expanded into areas with lower water availability or that were more open, supporting the evidence from former archaeological interpretations that agriculture spread into different, usually elevated areas at this time.

Amino acid δ15N values of foliage of various plant taxa, grown at the experimental farm stations of North Wyke, UK and Bad Lauchstädt, Germany were determined by GC-C-IRMS. The difference between δ15N values of glutamate (Glx) and phenylalanine (Phe) were found to differ significantly between woody and herbaceous plants, with mean Δ15NGlx-Phe (i.e. δ15NPhe - δ15NGlx) values of -9.3 ± 1.6‰ and -5.8 ± 2.1‰, respectively. These differences in values are hypothesised to be due to the involvement of Phe in the phenylpropanoid pathway, by which lignin and other phenolic secondary metabolites are produced, leading to isotopic fractionation and enrichment of the remaining Phe pool available for protein biosynthesis. This results in the more negative Δ15NGlx-Phe values observed in woody plants relative to herbaceous plants, as the former are assumed to produce more lignin. To test this assumption, plant leaf tissue lignin concentrations were estimated by solid state 13C cross-polarisation, magic-angle-spinning (CPMAS) NMR spectroscopy for a subset of plants, which showed that tree foliage has a higher concentration of lignin (12.6 wt%) than herbaceous foliage (6.3 wt%). The correlation of lignin concentration with Δ15NGlx-Phe values demonstrates that the difference in these values with plant type is indeed due to differential production of lignin. The ability to estimate the lignin content of plants from amino acid δ15N values will, to give one example, allow refinement of estimates of herbivore diet in present and past ecosystems, enabling more accurate environmental niche modelling.