Nitrogen Metabolism of Normal and High‐Seed‐Protein Soybean

Abstract

Nitrogen metabolism differences, including N2 fixation, between high‐and normal‐seed‐protein soybean [Glycine max (L.) Merr.] lines of equivalent plant maturity and seed yielding ability have not been determined in field tests. A replicated field experiment was conducted in 1985 and 1986 to determine such differences on a Mattapex silt loam (fine, silty, mixed, mesic Aqualfic Hapludult) with low soil N. The study used the nodulating‐nonnodulating N difference method to estimate N2 fixation of two soybean lines with contrasting seed protein levels. Eight sequential harvests were conducted from R5 (beginning seed) to combine harvest for the dry weights and N contents of vegetative and reproductive portions of the plants. There was no significant difference between the 2‐yr mean seed yields of the high‐ and normal‐protein lines, but the high‐protein line was 2 d later in maturity. The high‐protein line accumulated more N, fixed more N2, and remobilized more N to the seed than did the normal‐protein line (231 vs. 194, 114 vs. 77, and 87 vs. 76 kg ha−1, respectively). The greater N accumulation by the high‐protein line resulted from N2 fixation being sustained until the late R6 (full seed) stage. Nodule occupancy by strains of Bradyrhizobium japonicum was similar for the high‐ and normal‐seed‐protein lines. Thus, the ability to sustain N2 fixation until later stages of reproduction is a host plant attribute that may contribute to the greater N metabolism of a high‐seed‐protein soybean.

Nitrogen accumulation and redistribution in soybean genotypes with variation in seed protein concentration

“…We also found genotypic variation in these traits related to N redistribution, but none of the variation was related to seed N concentration or total seed N at maturity in the six genotypes in our experiment. Consistent with our findings, Leffel et al (1992) found no increase in remobilization efficiency [(maximum vegetative N -vegetative N at R8)/maximum vegetative N] in a single high seed protein genotype. There was no relationship between the contribution of redistributed N and yield in commercial cultivars from maturity groups II to V (Zeiher et al 1982), II (Vasilas et al 1995) or 00 and 0 (Kumudini et al 2002).…”

“…Leffel et al (1992) found that N fixation of a single high-protein genotype was higher than the normal protein control during seed filling. Vasilas et al (1995) and Kumudini et al (2002) found the high yield was associated with greater N acquisition during seed filling, instead of a larger supply from redistribution.…”

Genotype x Bradyrhizobium japonicum strain interactions in dinitrogen fixation and agronomic traits of soybean (Glycine max L. Merr.)

“…In soybean, the occurrence of cultivar x Bradyrhizobium strain interactions was established for the percent N derived from the atmosphere (Rennie & Dubetz, 1984) or for the amount of fixed N2 (Ravuri & Hume, 1993) in field trials. However, such effects were not detected by other authors (Leffel et al, 1992), sometimes even in spite of refined experimental designs (Buttery & Dirks, 1987). The importance ofcultivar x strain interactions remains unpredictable as they depend on the combinations studied.…”

“…The extra cost of N2 fixation could be assumed by most field-grown legume crops without any major loss of productivity since factors other than energy supply for N2 fixation were generally involved in legume growth limitation (Herridge & Bergersen, 1988). Improving N2 fixation then should not penalize productivity and could even facilitate the elaboration of high seed protein contents in soybean (Leffel et al, 1992). Indeed, rapid N2 fixation during pod filling was shown to contribute to increased seed yield and seed protein content (Imsande, 1992).…”

Beneficial microorganisms for soybean (Glycine max (L.) Merr), with a focus on low root-zone temperatures

“…Genetic variation among soybean cultivars exists in all aspects of the signaling pathway; some genotypes are better able to select strains with greater symbiotic efficiency or maintain nitrogen fixation later in the growing season (Leffel et al 1992;de O. Chueire and Hungria 1997;Rengel 2002;Salvagiotti et al 2008;Messmer et al 2011). Mycorrhizal fungi are less host-specific than rhizobia, but the extent and benefit of colonization nonetheless depend on host genotype (Rengel 2002;Messmer et al 2011).…”