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Elevated atmospheric CO 2 does not affect per se the preference for symbiotic nitrogen as opposed to mineral nitrogen of Trifolium repens L.
Author(s) -
Zanetti S.,
Hartwig U.A.,
Nösberger J.
Publication year - 1998
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.1998.00307.x
Subject(s) - trifolium repens , nitrogen fixation , repens , nitrogen , nutrient , chemistry , zoology , horticulture , botany , biology , organic chemistry
The objective of this investigation was to examine the effect of an elevated atmospheric CO 2 partial pressure ( p CO 2 ) on the N‐sink strength and performance of symbiotic N 2 fixation in Trifolium repens L. cv. Milkanova. After initial growth under ambient p CO 2 in a nitrogen‐free nutrient solution, T. repens in the exponential growth stage was exposed to ambient and elevated p CO 2 (35 and 60 Pa) and two levels of mineral N (N‐free and 7·5 mol m –3 N) for 36 d in single pots filled with silica sand in growth chambers. Elevated p CO 2 evoked a significant increase in biomass production from day 12 after the start of CO 2 enrichment. For plants supplied with 7·5 mol m –3 N, the relative contribution of symbiotically fixed N (%N sym ) as opposed to N assimilated from mineral sources ( 15 N‐isotope‐dilution method), dropped to 40%. However, in the presence of this high level of mineral N, %N sym was unaffected by atmospheric p CO 2 over the entire experimental period. In plants fully dependent on N 2 fixation, the increase in N yield reflects a stimulation of symbiotic N 2 fixation that was the result of the formation of more nodules rather than of higher specific N 2 fixation. These results are discussed with regard to physiological processes governing symbiotic N 2 fixation and to the response of symbiotic N 2 fixation to elevated p CO 2 in field‐grown T. repens .