Maize,beans and the floral isotopic diversity of highland Oaxaca,Mexico

Oaxaca, Mexico has been inhabited by humans for over 10,000 years. From the time of earliest habitation, this environment provided a wide floral subsistence to its human inhabitants, notably documented at the cave site of Guila Naquitz. Light stable isotopes, primarily carbon and nitrogen, have been used in dietary and environmental reconstructions throughout Mexico and Central America. We report a large isotopic study of wild and market plants from Oaxaca that demonstrates 1) overlapping δ¹³C values of C4 plants, including maize, and plants that utilize the Crassulacean Acid Metabolism (CAM) pathway for biosynthesis, 2) the existence of a significant C4 grass biomass, 3) the lack of isotopic separation in the δ¹⁵N of legumes and non-leguminous plants and 4) the increase in the nitrogen isotopic composition of crop plants relative to wild plant averages. These four observations are potential complicating factors in interpretations involving the origins and spread of maize agriculture, the relative amount of maize in the diet and assessments of trophic level or meat contributions to the human diet.