Abstract
Symbiotic N2 fixation is one of the main processes that introduces N into terrestrial ecosystems. As such, it may be crucial for the sequestration of the extra C available in a world of continuously increasing atmospheric CO2 partial pressure (pCO2). The effect of elevated pCO2 (60 Pa) on symbiotic N2 fixation (15N-isotope dilution method) was investigated using Free-Air-CO2-Enrichment technology over a period of 3 years. Trifolium repens was cultivated either alone or together with Lolium perenne (a nonfixing reference crop) in mixed swards. Two different N fertilization levels and defoliation frequencies were applied. The total N yield increased consistently and the percentage of plant N derived from symbiotic N2 fixation increased significantly in T. repens under elevated pCO2. All additionally assimilated N was derived from symbiotic N2 fixation, not from the soil. In the mixtures exposed to elevated pCO2, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m-2 a-1 in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N2 fixation is a competitive advantage for T. repens in mixed swards with pasture grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole.
Full Text
The Full Text of this article is available as a PDF (902.6 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Denison R. F., Hunt S., Layzell D. B. Nitrogenase activity, nodule respiration, and o(2) permeability following detopping of alfalfa and birdsfoot trefoil. Plant Physiol. 1992 Mar;98(3):894–900. doi: 10.1104/pp.98.3.894. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Finn G. A., Brun W. A. Effect of Atmospheric CO(2) Enrichment on Growth, Nonstructural Carbohydrate Content, and Root Nodule Activity in Soybean. Plant Physiol. 1982 Feb;69(2):327–331. doi: 10.1104/pp.69.2.327. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Heim I., Hartwig U. A., Nosberger J. Current Nitrogen Fixation Is Involved in the Regulation of Nitrogenase Activity in White Clover (Trifolium repens L.). Plant Physiol. 1993 Nov;103(3):1009–1014. doi: 10.1104/pp.103.3.1009. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Weisbach C., Hartwig U. A., Heim I., Nosberger J. Whole-Nodule Carbon Metabolites Are Not Involved in the Regulation of the Oxygen Permeability and Nitrogenase Activity in White Clover Nodules. Plant Physiol. 1996 Feb;110(2):539–545. doi: 10.1104/pp.110.2.539. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Williams L. E., Dejong T. M., Phillips D. A. Effect of changes in shoot carbon-exchange rate on soybean root nodule activity. Plant Physiol. 1982 Feb;69(2):432–436. doi: 10.1104/pp.69.2.432. [DOI] [PMC free article] [PubMed] [Google Scholar]