, Volume 74, Issue 2, pp 236–246 | Cite as

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

  • T. H. E. Heaton
Original Papers


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 δ 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 δ 15N and aridity, but this is less marked than the correlation between the δ 15N values of animal bones and aridity. At coastal or saline sites, however, the mean δ 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.

Key words

Plants 15N/14N ratios Climate Coastal Saline 


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  1. Acocks JPH (1975) Veld types of South Africa. Mem Bot Survey S Afr 40 (Dept of Agriculture, Pretoria)Google Scholar
  2. Allen ON, Allen EK (1981) The leguminosae. MacMillan, LondonGoogle Scholar
  3. Ambrose SH, De Niro MJ (1986a) Reconstruction of African human diet using bone collagen carbon and nitrogen isotope ratios. Nature 319:321–324Google Scholar
  4. Ambrose SH, De Niro MJ (1986b) The isotopic ecology of East African mammals. Oecologia (Berlin) 69:395–406Google Scholar
  5. Ashton PJ, Schoeman FR (1983) Limnological studies on the Pretoria Salt Pan; a hypersaline maar lake. Hydrobiologia 99:61–73Google Scholar
  6. Delwiche CC, Steyn PL (1970) Nitrogen isotope fractionation in soils and microbial reactions. Env Sci Tech 4:929–935Google Scholar
  7. Delwiche CC, Zinke PJ, Johnson CM, Virginia RA (1979) Nitrogen isotope distribution as a presumptive indicator of nitrogen fixation. Bot Gaz 140 (Suppl):S65-S69Google Scholar
  8. De Niro MJ, Hastorf CA (1985) Alteration of 15N/14N and 13C/12C ratios of plant matter during the initial stages of diagenesis: Studies utilizing archaeological specimens from Peru. Geochim et Cosmochim Acta 49:97–115Google Scholar
  9. Farnsworth P, Brady JE, De Niro MJ, MacNeish R (1985) A re-evaluation of the isotopic and archaeological reconstructions of diet in the Tehuacan Valley. Am Antiquity 50:102–116Google Scholar
  10. Focht DD (1973) Isotope fractionation of 15N and 14N in micro-biological nitrogen transformations: a theoretical model. J Environ Quality 2:247–252Google Scholar
  11. Grobbelaar N, Clarke B (1972) A qualitative study of the nodulating ability of legume species: List 2. J S Afr Bot 38:241–247Google Scholar
  12. Grobbelaar N, Clarke B (1975) A qualitative study of the nodulating ability of legume species: List 3. J S Afr Bot 41:29–36Google Scholar
  13. Heaton THE (1986) Isotopic studies of nitrogen pollution in the hydrosphere and atmosphere: a review. Chem Geol (Isotope Geoscience) 59:87–102Google Scholar
  14. Heaton THE (1987) 15N/14N ratios of nitrate and ammonium in rain at Pretoria, South Africa. Atmos Environ 21:843–852Google Scholar
  15. Heaton THE, Collett GM (1985) The analysis of 15N/14N ratios in natural samples, with emphasis on nitrate and ammonium in precipitation. CSIR Res Rep 624, Counc Sci Ind Res, PretoriaGoogle Scholar
  16. Heaton THE, Vogel JC, Von la Chevallerie G, Collett G (1986) Climatic influence on the isotopic composition of bone nitrogen. Nature 322:822–823Google Scholar
  17. Hoering TC, Ford HT (1960) Isotope effect in the fixation of nitrogen by Azotobacter. J Am Chem Soc 82:376–378Google Scholar
  18. Karamanos RE, Rennie DA (1980) Changes in natural 15N abundance associated with pedogenic processes in soil. 1. Changes associated with saline seeps. Can J Soil Sci 60:337–344Google Scholar
  19. Karamanos RE, Voroney RP, Rennie DA (1981) Variation in natural N-15 abundance of central Saskatchewan soils. Soil Sci Soc Amer J 45:826–828Google Scholar
  20. Mariotti A, Pierre D, Vedy JC, Bruckert S, Guillemot J (1980) The abundance of natural nitrogen 15 in the organic matter of soils along an altitudinal gradient (Chablais, haute-Savoie, France). Catena 7:293–300Google Scholar
  21. Mariotti A, Mariotti F, Champigny M, Amarger N, Moyse A (1982) Nitrogen isotope fractionation associated with nitrate reductase and uptake of NO3- by Pearl Miller. Plant Physiol 69:880–884Google Scholar
  22. Minagawa M, Wada E (1984) Stepwise enrichment of 15N along food chains: Further evidence and the relation between δ15N and animal age. Geochim et Cosmochim Acta 48:1135–1140Google Scholar
  23. Rennie DA, Paul EA, Simmons LE (1976) Natural nitrogen-15 abundance of soil and plant samples. Can J Soil Sci 56:43–50Google Scholar
  24. Riga A, Van Praag HJ, Brigode N (1971) Rapport isotopique naturel de l'azote dans quelques sols forestiers et agricoles de Belgique soumis à divers traitements culturaux. Geoderma 6:213–222Google Scholar
  25. Schoeninger MJ, De Niro MJ (1984) Nitrogen and carbon isotopic composition of bone collagen from marine and terrestrial animals. Geochim et Cosmochim Acta 48:625–639Google Scholar
  26. Schoeniger MJ, De Niro MJ, Tauber H (1983) Stable nitrogen isotope ratios of bone collagen reflect marine and terrestrial components of prehistoric human diet. Science 220:1381–1383Google Scholar
  27. Shearer G, Kohl DH, Chien S-H (1978) The nitrogen-15 abundance in a wide variety of soils. Soil Sci Soc Am J 42:899–902Google Scholar
  28. Stock WD, Lewis OAM (1986) Atmospheric input of nitrogen to a coastal fynbos ecosystem of the south-western Cape Province, South Africa. S Afr J Bot 52:273–276Google Scholar
  29. Virginia RA, Delwiche CC (1982) Natural 15N abundance of presumed N2-fixing and non N2-fixing plants from selected ecosystems. Oecologia (Berlin) 54:317–325Google Scholar
  30. Vogel JC, Seely MK (1977) Occurrence of C-4 plants in the central Namib Desert. Madoqua (Windhoek) 10:75–78Google Scholar
  31. Vogel JC, Fuls A, Ellis RP (1978) The geographical distribution of Kranz grasses in South Africa S Afr J Sci 74:209–215Google Scholar
  32. Wada E, Imaizumi R, Takai Y (1984) Natural abundance of 15N in soil organic matter with special reference to paddy soils in Japan: biogeochemical implications on the nitrogen cycle. Geochemical J (Geochemical Soc Japan) 18:109–123Google Scholar
  33. Weather Bureau (1965) Average monthly rainfall up to the end of 1960. Climate of South Africa, WB29 Dept of Transport, PertoriaGoogle Scholar
  34. Weather Bureau (1986) Climate statistics up to 1984. Climate of South Africa, WB40 Dept of Environment Affairs. PretoriaGoogle Scholar

Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • T. H. E. Heaton
    • 1
  1. 1.Natural Isotopes Division, National Physical Research LaboratoryCSIRPretoriaSouth Africa

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