Nitrate Effect on Nodulation of Soybean by Bradyrhizobium japonicum¹

Abstract

It is not known whether NO−3 inhibition of nodulation is primarily due to effects on the host plant or on the bacterials train. This study was conducted to evaluate the effect of NO−3 on nodule appearance and development of nitrogenase (acetylene reduction) activity of various Glycine max (L.) Merr. cultivar ✕ Bradyrhizobiumja ponicum (Kirchner) Buchanan strain combinations. Plants were grown hydroponically in controlled environment cabinets. NO−3 was either resupplied daily (“maintained”) during the growth period or allowed to deplete with plant growth (“rundown”). Nodule development was delayed all NO−3 treatment conditions (both maintained and rundown), the delay being more severe at higher NO−3 concentrations. The external concentration of NO−3 rather than the rate of NO−3 uptake appeared to have a major effect on the initial stages of nodulation. Treatment conditions providing similar rates of NO−3 up take from different solution NO−3 concentrations( 4.0 mM rundown vs. 0.5. mM maintained) resulted in a more marked inhibition of nodule appearance at the higher level of solution NO−3. Maintaining the solution concentration of NO−3 at 1.0 mM following the appearance of nodules greatly retarded, or prevented, the development of nitrogenase activity (C2H2 reduction). Minor differences in the tolerance of nodulation to NO−3 were observed among eight B. j. uponicum strains (preselected from 46 strains). More variation existed among 12 soybean cultivars (preselected from 23 cultivars) with respect to their ability to nodulate in the presence of NO−3. The cvs. Elf and Avoyelles were notable in having good nodulation tolerance to NO−3 when infected by USDA110. This indicated that, with selection and breeding, enhanced NO−3 tolerance of nodulation between soybean and B. japonicum should be possible.

Effect of Localized Nitrate Application on Isoflavonoid Concentration and Nodulation in Split-Root Systems of Wild-Type and Nodulation-Mutant Soybean Plants

“…It has also been reported that symbiotic efficiency of soybean plants grown on NO3-is slightly affected by B. japonicum strain (18), but it appears that the host plant is in primary control of nodulation in the presence of NO3 (3,8). Once nodulation has occurred, subsequent nodulation on new roots of normal plants is suppressed by a plant process called autoregulation (14,21).…”

“…Nitrate inhibition of nodulation is a common regulatory feature of legume root nodule symbiosis which is primarily controlled by the host plant (3,8). Split-root studies have demonstrated a localized NO3-effect on nodulation in soybean (1 3) and clover (2).…”

Inoculant formulation and fertilizer nitrogen effects on field pea: Nodulation, N2 fixation and nitrogen partitioning

“…Waterer and Vessey (1993) reported that inhibition of nodulation is dependent on the concentration of N in the soil solution and that a depletion of inhibitory concentrations (as might occur in the root zone due to active plant N uptake) could provide a window during which nodulation could occur. Gibson and Harper (1985) similarly reported that evidence of nodulation on plants was observed when the growing plant depleted nitrate levels. Although spring soil tests indicated relatively high levels of nitrate N at Fort Vermillion in 1996, it is likely that rhizosphere levels of nitrate-N were depleted relative to the bulk soil due to active plant uptake and thus were not inhibitory to nodulation.…”

Selection and Initial Characterization of Partially Nitrate Tolerant Nodulation Mutants of Soybean

“…Although sensitivity of nodulation to NO3-has been the subject of numerous studies, no definitive reports have been published which elucidate the mechanisms of inhibition. For soybean it appears that the host plant, rather than the bacterial strain, is in primary control of the level of N2 fixation (5). With Since the nts mutants selected by Gresshofls group were derived from the cultivar Bragg which is a Maturity Group VII line and cannot be grown to maturity under Midwest growing conditions, the current study was initiated to select nodulation mutants from a background which can be field tested in the major Midwest soybean production area.…”