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Dry Matter, Nitrogen Distribution, and Dinitrogen Fixation in Contrasting Alfalfa Symbioses 1
Author(s) -
Fishbeck K. A.,
Heichel G. H.,
Vance C. P.
Publication year - 1987
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1987.0011183x002700060023x
Subject(s) - biology , dry matter , nitrogen fixation , nitrogenase , germplasm , medicago sativa , fixation (population genetics) , symbiosis , agronomy , botany , bacteria , biochemistry , genetics , gene
Improving dinitrogen (N 2 ) fixation of alfalfa ( Medicago sativa L.) requires combining effective rhizobial strains and host genotypes capable of enhanced N 2 fixation. Glasshouse experiments on pot‐grown alfalfa determined how changes in the rhizobial and host genomes associated with N 2 fixation affect dry matter and N yields and distribution at vegetative, flower bud, and 30% flowering developmental stages. We compared dry matter and N yield and distribution in a host‐ and a rhizobial‐conditioned ineffective (Fix + ) and in a related effective (Fix + ) symbiotic combination, and investigated the effect of combined N on N 2 fixation and on the distribution of symbolically fixed N 2 in two unrelated Fix + alfalfa germplasms. Dry matter and N yield and response to added N (0, 40, 80 kg/ha) of the host‐conditioned and the rhizobial‐conditioned Fix − combinations were similar. Without combined N, both Fix − combinations distributed relatively less dry matter and N to aerial organs than did the Fix + combination. Neither the type of Fix − combination nor traits in the Fix + germplasms supportive of increased N 2 fixation altered the relative distribution of dry matter among plant organs; however, N concentration in individual organs varied with supplemental N in the Fix − but not the Fix + combinations. Dry matter and N yields of the two unrelated Fix + combinations differed only without combined N. Supplemental N was more inhibitory to N 2 fixation by Fix + germplasm selected for enhanced nitrogenase activity compared with unselected Fix + germplasm. Either source of ineffective nodulation in Fix − combinations would be appropriate for developing non‐fixing controls for physiological investigations of N 2 fixation and for use in programs to evaluate and enhance N 2 fixation in alfalfa.