Stimulation of symbiotic N{sub 2} fixation in trifolium repens L. under elevated atmospheric pCO{sub 2} in a grassland ecosystem
- Swiss Federal Institute of Technology, Zurich (Switzerland); and others
Symbiotic N{sub 2} 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 CO{sub 2} partial pressure (pCO{sub 2}). The effect of elevated pCO{sub 2} (60 Pa) on symbiotic N{sub 2} fixation ({sup 15}N-isotope dilution method) was investigated using Free-Air-CO{sub 2}-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 N{sub 2} fixation increased significantly in T. repens under elevated pCO{sub 2}. All additionally assimilated N was derived from symbiotic N{sub 2} fixation, not from the soil. In the mixtures exposed to elevated pCO{sub 2}, an increased amount of symbiotically fixed N (+7.8, 8.2, and 6.2 g m{sup {minus}2} a {sup {minus}1} in 1993, 1994, and 1995, respectively) was introduced into the system. Increased N{sub 2} fixation is a competitive advantage for T. repens in mixed swards with paster grasses and may be a crucial factor in maintaining the C:N ratio in the ecosystem as a whole. 57 refs., 1 fig., 3 tabs.
- OSTI ID:
- 508483
- Journal Information:
- Plant Physiology (Bethesda), Vol. 112, Issue 2; Other Information: PBD: Oct 1996
- Country of Publication:
- United States
- Language:
- English
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