Stable Isotope Composition (C and N) of Vegetation in Subtropical Andes: Piedmont ‘Anomaly’ and its Implications for Paleo (Ecology) and Human Diet Reconstruction

Isotope baselines are fundamental to infer diets, and to evaluate trophic relationships between humans, animals, and plants. In this study, we aim to detect spatial patterns of δ13C and δ15N of different plant types (C3, C4 and CAM) along environmental gradients in the eastern slopes of the southern Andes, in order to use them as a baseline to reconstruct animal diet, mobility, and trophic relations in the area. The stable isotope composition of dominant plants was analyzed along an environmental gradient from the mountains to the plains in southern Mendoza. The expected isotope gradients of increasing δ13C and δ15N with decreasing altitude and increasing aridity was not found in our region. The spatial distribution of the C3/C4 ratio showed a non-linear pattern, with higher C4 abundances at intermediate altitudes, probably given by atmospheric circulation patterns, which generate aridity and C4 dominance at intermediate altitudes. These climate, geologic, and vegetation patterns may affect ecosystem and animal δ13C, which also showed non-linear trends in previously published material. These non-linear trends open the opportunity to explain previous δ13C results obtained from collagen of human and animal bones, which follow the C3/C4 ratio found in this study.