Summary
Nitrogen fixation in the natural, Agropyron-Koeleria grassland ecosystem was studied using the C2H2-C2H4 and N15 assays. Small soil samples and also undisturbed soil cores were used for analyses. Both techniques indicated that grassland and associated cultivated soils had low fixation rates (0.6–1.8 kg/ha per 28 days in the laboratory and, 1 kg/ha per season under actual field conditions). Algal colonies (Nostoc spp.) on the soil surface were active fixers when the surface of the grassland was moist. However, their small biomass limits the extent of fixation in most areas.
In native grassland, 16 legumes bore nodules. The three most common speciesVicia americana, Thermopsis rhombifolia andOxytropis sericea, all of which had active nodules, contributed 10 per cent of the total nitrogenase activity.
The non-legumesElaeagnus commutata andShepherdia argentea were profusely nodulated with active nodules, but were confined to specific habitats. No nodules were found onArtemisia orOpuntia spp.
The major, heterotrophic, asymbiotic bacteria in the soil were clostridia. These utilize substrates produced by aerobic cellulose and hemicellulose degrading organisms to fix N in anaerobic microsites. The C2H2:N2 reduction ratio was 3 to 1 in large, aerobic core samples, but was greater under water-logged conditions where high fixation rates occurred.
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References
Babiuk, L.A. and Paul, E. A., Can. J. Microbiol. 16, 57–62 (1970).
Bremner, J. M. In Methods of Soil Analysis. Part 2. Chemical and microbiological properties. pp. 1149–1178. Am. Soc. Agron., Madison, Wisc. (1965).
Farnsworth, R. B. and Hammond, R. W., Agr. Abs. pp. 93 (1968).
Hardy, R. W. F. et al., Plant Physiol. 43, 1185–1207 (1968).
Mayland, H. F. and McIntosh, T. H., Nature (Lond.) 209, 421–422 (1966).
Mayland, H. F. et al., Soil Sci. Soc. Am. Proc. 30, 56–60 (1966).
Moore, A. W., Can. J. Botany 42, 952–955 (1964).
Porter, L. K. and Grable, A. R., Agron. J. 61, 521–523 (1969).
Rice, W. A. et al., Can. J. Microbiol. 13, 829–836 (1967).
Rice, W. A. and Paul, E. A. Can. J. Microbiol. 17, 1049–1056 (1971).
Rice, W. A. and Paul, E. A. (In preparation).
Shtina, E. A. et al., Ninth Int. Congr. Soil Sci. Trans. 2, 151–158 (1968).
Stewart, W. D. P., Science 158, 1426–1432 (1967).
Stewart, W. D. P. et al., Proc. Natl. Acad. Sci. USA 58, 2071–2078 (1967).
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Paul, E.A., Myers, R.J.K. & Rice, W.A. Nitrogen fixation in grassland and associated cultivated ecosystems. Plant Soil 35, 495–507 (1971). https://doi.org/10.1007/BF02661874
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DOI: https://doi.org/10.1007/BF02661874