Premium
Partitioning of Symbiotically Fixed Nitrogen in Soybeans and Alfalfa 1
Author(s) -
Henson R. A.,
Heichel G. H.
Publication year - 1984
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/cropsci1984.0011183x002400050039x
Subject(s) - biology , perennial plant , forage , growing season , nitrogen fixation , nitrogen , loam , agronomy , botany , soil water , chemistry , ecology , genetics , organic chemistry , bacteria
A growing body of evidence suggests a differential partitioning of soil N and symbolically fixed N 2 among organs during ontogeny of some legumes. This partitioning is poorly understood for soybeans [ Glycine max (L.) Merr.] and only meager evidence of this phenomenon is available for perennial forage legumes such as alfalfa ( Medicago saliva L.). Therefore, we compared the partitioning of fixed N, among organs of soybean and alfalfa grown on a silt loam (Typic Hapludoll) by periodically sampling throughout one growing season. Dinitrogen fixation and partitioning of fixed N 2 were measured with the 15 N isotope dilution technique. Evidence of differential N partitioning was obtained for both species. The roots of alfalfa contained a higher proportion of fixed N 2 throughout the growing season compared with the stems, leaves, and the whole plant. The roots, stems, and young seeds of soybeans contained a lower proportion of fixed N2 throughout the season compared with the whole plant. In comparison with the N composition of the whole plant, the N in pod walls contained a higher proportion of fixed N 2 and that in green leaflets was unchanged. Senesced leaflets and petioles exhibited a reduced proportion of fixed N 2 coincident with an increased proportion of fixed N 2 in the whole plant. This suggests a preferential mobilization of fixed N 2 compared with soil N. The results suggest a differential allocation of symbiotic N 2 in alfalfa and soybean that is related to the availability of soil N and the composition of the mobile N reserves at specific developmental stages. The accumulation of symbiotic N 2 in pod walls of soybean might reflect a limitation of N transport to young seeds, and deserves further investigation.