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Nitrogen Assimilation in an Improved Alfalfa Population 1
Author(s) -
Phillips Donald A.,
Cunningham Scott D.,
Bedmar Eulogio J.,
Sweeney T. Colleen,
Teuber Larry R.
Publication year - 1985
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/cropsci1985.0011183x002500060027x
Subject(s) - rhizobium , biology , nitrogen fixation , population , nitrate , nitrogenase , rhizobiaceae , symbiosis , sinorhizobium meliloti , medicago sativa , nitrogen , botany , strain (injury) , nitrogen assimilation , horticulture , agronomy , bacteria , inoculation , chemistry , ecology , demography , anatomy , sociology , organic chemistry , genetics
Alfalfa ( Medicago sativa L.), which is capable of fixing N 2 in symbiosis with Rhizobium meliloti , normally is grown in soils with varying amounts of available N. We have demonstrated previously that population selected from ‘African’ and ‘Hairy Peruvian’ for increased dry matter and N assimilation under both N 2 ‐ and NH 4 NO 3 ‐dependent conditions outperformed the original parental materials when grown with the extremes of N nutrition, i.e., totally dependent on N 2 or completely sustained by mineral N. The objective of this study was to compare i) growth and N assimilation of the original Hairy Peruvian (HP) and the improved Hairy Peruvian 32 (HP32) with various strains of R. meliloti and no nitrate and ii) one strain of R. meliloti and different levels of nitrate. Tests showed that, although only one strain of Rhizobium had been present during selection, HP32 grown in the absence of combined N increased N 2 fixation in three other strains of R. meliloti by 22 to 53% relative to the same strains in HP. When HP and HP32 were tested with 0, 1, 2, or 8 m M nitrate in symbiosis with the Rhizobium strain used during the selection process, HP32 assimilated an average of 32% more total N than HP under all N regimes. Estimates of N 2 fixation using the 15 N‐dilution method under those conditions showed that HP32 fixed an average of 38% more N 2 than HP under all nitrate treatments. The inhibition of N 2 fixation by nitrate, however, was proportionately similar in HP and HP32. The fact that HP32 increased N 2 fixation by all strains of R. meliloti tested suggests that HP32 has some general physiological trait which might be used to improve the symbiotic performance of the mediocre indigenous Rhizobium strains that nodulate alfalfa in many soils.