The 15N/14N ratios of plants in South Africa and Namibia: relationship to climate and coastal/saline environments

Summary Data are presented for the ¹⁵N/¹⁴N ratios of 140 indigenous terrestrial plants from a wide variety of natural habitats in South Africa and Namibia. Over much of the area, from high-rainfall mountains to arid deserts, the ¹⁵N values of plants lie typically in the range -1 to +6; with no evident differences between C₃ plants and C₄ grasses. There is a slight correlation between ¹⁵N and aridity, but this is less marked than the correlation between the ¹⁵N values of animal bones and aridity. At coastal or saline sites, however, the mean ¹⁵N values for plants are higher than those at nearby inland or non-saline sites-e.g.: arid Namib coast (10 higher than inland Namib); wet Natal beach (5 higher than inland Natal); saline soils 500 km from coast (4 higher than non-saline soils). High values were also found at one site where there were no marked coastal or saline influences. These environmental effects on the isotopic composition of plants will extend upwards to the animals and humans they support. They therefore have important consequences for the use of nitrogen isotope data in the study of the dietary habits and trophic structures of modern and prehistoric communities.