Evaluation of beneficial and inhibitory effects of nitrate on nodulation and nitrogen fixation in common bean (Phaseolus vulgaris)

Abstract

The effects of applied nitrate on symbiotic nitrogen fixation in legumes are complex. Both inhibition and promotion of nodulation by nitrate have been observed in a dose‐dependent manner. The objectives of this study were to determine the effects of nitrate at different concentrations on root nodulation in different genotypes in common bean (Phaseolus vulgaris). Six genotypes were inoculated with the same rhizobial strain and grown hydroponically in growth pouches in a growth chamber and exposed to six nitrate concentrations, including 0, 2.5, 5, 10, 15, and 20 mM for 4 weeks. The tested genotypes included three recombinant inbred lines (RILs, 25, 46, and 70) that differed in their responses to nitrogen (based on observations of one field growing season), their parents (Mist and Sanilac—registered varieties), which are different in N‐fixing abilities, and one nonnodulating mutant (R99). Our results showed that small amounts of nitrate (2.5 and 5 mM) promoted nodule formation and increased nodule biomass, compared with plants in the 0 nitrate control treatment. In contrast, nitrate concentrations over 10 mM inhibited nodulation, resulting in reductions in nodule number and nodule biomass. Nodulation was completely inhibited by 15‐mM nitrate in all the genotypes. Regression analyses indicated that 5‐mM nitrate is the optimum concentration for promoting nodulation as measured by the total number of nodules formed, the number of effective nodules formed, and the nodule biomass formed. In contrast, nitrogen fixation was inhibited by all levels of nitrate. No genotypic differences were observed in nodulation among the three RILs and their parental cultivars, but all were significantly different than R99, a nonnodulating mutant.

Effects of Nitrogen Application on Nitrogen Fixation in Common Bean Production

“…Genotype-specific sensitivity of nitrogen fixation to mineral nitrogen was identified in common bean (Hardarson, 1993;Farid et al, 2016). Nitrogen concentrations of 2.5 and 5 mM had positive effects on SNF in beans (Jiang et al, 2020). Similarly, in controlled greenhouse and growth chamber experiments, Gan et al (2004) demonstrated that low concentrations (1 and 3.75 mM, kept constant) of inorganic nitrogen increase SNF in soybean.…”

Inhibition of N2 Fixation by N Fertilization of Common Bean (Phaseolus vulgaris L.) Plants Grown on Fields of Farmers in the Eastern Cape of South Africa, Measured Using 15N Natural Abundance and Tissue Ureide Analysis

“…Several studies have assessed N nutrition in common bean (Farid and Navabi, 2015;Farid et al, 2016;Jiang et al, 2020), and symbiotic N 2 fixation has generally been found to be lower in common bean when compared to other legumes (Farid et al, 2016). However, applying Rhizobium strain HB-429 to common bean crop increased plant growth, percent N derived from fixation (%Ndfa), the amount of N-fixed, and grain yield by 19, 17, 54, and 48%, respectively, over the uninoculated control in Ethiopia (Samago et al, 2018).…”

The Effect of Exogenous Nitrate on LCO Signalling, Cytokinin Accumulation, and Nodule Initiation in Medicago truncatula

“…Taken together, this suggests that nitrate interferes with nodulation on at least two different levels: high nitrate concentration (≥4 mM NO 3 − ) leads to a strong reduction in nodule numbers by interfering with cytokinin-induced pericycle and cortical cell divisions, whereas medial nitrate levels (1–2 mM NO 3 − ) reduce the symbiotic effectiveness of developing nodules. A recent study on the common bean ( Phaseolus vulgaris ) painted a similar picture [ 48 ]; with a nodulation experiment over a nitrate concentration range, the authors demonstrated that although medial levels of exogenous nitrate lead to increased numbers of nodules, the rate of N 2 fixation already drops at 2.5 mM NO 3 − . This dual effect of nitrate is consistent with an earlier report that also described a higher sensitivity to nitrate with regard to nitrogen-fixation rates compared to nodule formation [ 19 ].…”