Summary
Nitrogen (N2) fixation was estimated along an aridity gradient in Namibia from the natural abundance of 15N (δ15N value) in 11 woody species of the Mimosacease which were compared with the δ15N values in 11 woody non-Mimosaceae. Averaging all species and habitats the calculated contribution of N2 fixation (N f ) to leaf nitrogen (N) concentration of Mimosaceae averaged about 30%, with large variation between and within species. While in Acacia albida N f was only 2%, it was 49% in Acacia hereroensis and Dichrostachys cinerea, and reached 71% in Acacia melifera. In the majority of species N f was 10–30%. There was a marked variation in background δ15N values along the aridity gradient, with the highest δ15N values in the lowland savanna. The difference between δ15N values of Mimosaceae and non-Mimosaceae, which is assumed to result mainly from N2 fixation, was also largest in the lowland savanna. Variations in δ15N of Mimosaceae did not affect N concentrations, but higher δ15N-values of Mimosaeae are associated with lower carbon isotope ratios (δ13C value). N2 fixation was associated with reduced intrinsic water use efficiency. The opposite trends were found in non-Mimosaceae, in which N-concentration increased with δ15N, but δ13C was unaffected. The large variation among species and sites is discussed.
This is a preview of subscription content, log in via an institution to check access.
References
Besler H (1972) Klimaverhältnisse und klimageomorphologische Zonierung der zentralen Namib (Südwestafrika). Stuttg Geogr Stud 83:1–209
Farquhar DG, Hubick KT, Condon AG, Richards RA (1989) Carbon isotope fractionation and plant water-use efficiency. Ecol Stud 68:21–40
Gebauer G (1991) Natural nitrogen isotope ratios in different compartments of Norway spruce from a healthy and a declining stand. Proceedings of the International Symposium on the use of stable isotopes in plant nutrition, soil fertility and environmental studies, IAEA Vienna 1990, in press
Gebauer G, Schulze E-D (1991) Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge, NE Bavaria. Oecologia 87:198–207
Giess W (1971) A prelininary vegetation map of South West Africa. Dinteria 4:1–114
Högberg P (1986a) Soil nutrient availability, root symbiosis and tree species composition in tropical Africa: a review. J Trop Ecol 2:359–372
Högberg P (1986b) Nitrogen-fixation and nutrient relations in Savanna woodland trees (Tanzania). J Appl Ecol 23:675–688
Högberg P (1990) 15N natural abundance as a possible marker of the ectomycorrhizal habit of trees in mixed African woodlands. New Phytol 115:483–486
Merxmüller H (1972) Prodromus einer Flora von Südwestafrika. J Cramer, Lehre
Osmond CB, Ziegler H, Stichler W, Trimborn P (1975) Carbon isotope discrimination in alpine succulent plants supposed to be capable of Crassulacean Acid Metabolism (CAM). Oecologia 28:323–328
Palgrave KC (1983) Trees of South Africa. C. Struck Publishers, Cape Town
Rundel PW, Ehleringer JR, Nagy KA (1988) Stable isotopes in ecological research. (Ecological Studies, vol 68) Springer, Berlin Heidelberg New York
Schulze E-D, Hall AE (1982) Stomatal responses, water loss and CO2 assimilation rates of plants in contrasting environments. Encyclopedia Plant Physiol 12B:181–230
Schulze E-D, Schulze I (1976) Distribution and control of photosynthetic pathways in plants growing in the Namib desert, with special regard to Welwitschia mirabilis Hook. fil. Madoqua 9:5–13
Schulze E-D, Ziegler H, Stichler W (1976) Environmental control of crassulacean acid metabolism in Welwitschia mirabilis Hook. Fil. in its range of natural distribution in the Namib desert. Oecologia 24:323–334
Shearer G, Kohl DH (1989) Estimates of N2 fixation in ecosystems: The need for and basis of the 15N abundance method. Ecol Stud 68:342–374
Shearer G, Kohl DH, Virginia RA, Bryan BA, Skeeters JL, Nilsen ET, Sharifi MR, Rundel RW (1983) Estimates of N2-Fixation from the natural abundance of 15N in Sonoran Desert Ecosystems. Oecologia 56:365–373
Virginia RA, Jarrell WM, Rundel PW, Shearer G, Kohl DH (1989) The use of variation in the natural abundance of 15N to assess symbiotic nitrogen fixation by woody plants. Ecol Stud 68:375–394
Walter H (1964) Die Vegetation der Erde in ökophysiologischer Betrachtung. Bd. I. Gustav Fischer Verlag, Stuttgart
Author information
Authors and Affiliations
Additional information
This paper is prepared in memory of J. Visser, who took part in the collection of species, but died in 1990
Rights and permissions
About this article
Cite this article
Schulze, ED., Gebauer, G., Ziegler, H. et al. Estimates of nitrogen fixation by trees on an aridity gradient in Namibia. Oecologia 88, 451–455 (1991). https://doi.org/10.1007/BF00317592
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00317592