Early nitrogen supplementation stimulates the nodulation and growth of common bean plants inoculated with rhizobium

Bárbara Cavalheiro Zoffoli,Rosângela Straliotto,Adelson Paulo De Araújo,Luciana Fernandes Brito

doi:10.4025/actasciagron.v43i1.55105

Abstract

The initial development of common bean plants (Phaseolus vulgaris L.) relying on symbiotic nitrogen (N) can be limited by delayed active N2 fixation, requiring supplemental N which in turn may inhibit the symbiosis. Five experiments were carried out in hydroponics to identify the initiation of nodulation and nitrogenase activity in common bean cultivars, and the effects of additions of mineral N on plant nodulation and growth. Three experiments evaluated the initial growth of five inoculated bean cultivars in the absence or presence of mineral N, and two experiments evaluated the effect of the moment of mineral N addition until the beginning of reproductive stage. The first root nodules appeared 10 days after plant transplant (DAT) and nitrogenase activity initiated 11 DAT. Cultivars of large seeds had lower initial nodulation and nitrogenase activity than those of small seeds. Inoculated plants showed limited shoot growth that lasted until 21-25 DAT as compared to inoculated plants receiving mineral N. Addition of mineral N reduced nodule mass more intensively than nodule number and more strongly nitrogenase activity. Nitrogen applied until 15 DAT enhanced nodulation and nitrogenase activity without limiting shoot growth, as compared to plants receiving N throughout their growth. Otherwise, plants that received N after 15 DAT had lower nodule mass and nitrogenase activity than plants only inoculated. The results indicate that symbiotic N did not suffice to an adequate growth of common beans and some supplemental N is necessary. This N should be added in the beginning of growth cycle to stimulate plant growth without inhibiting further nodulation and N fixation.

Highlights

Common bean (Phaseolus vulgaris L.) plants can associate symbiotically with several types of bacteria from the rhizobia group, forming nodules in the roots where the conversion of atmospheric N2 to ammonium occurs
Common bean plants of different cultivars were inoculated with the rhizobium and grown in trays with nutrient solution to identify the initiation of nodulation and nitrogenase activity
The nitrate that was applied for 14 days reduced the nodule mass, which blocked both the early and late steps of nodule development (Imsande, 1986). These results indicate that some initial N supply is necessary to guarantee adequate common bean plant growth that were inoculated with rhizobium, but the continuous addition of the mineral N could be detrimental to the symbiosis

Summary

Introduction

Common bean (Phaseolus vulgaris L.) plants can associate symbiotically with several types of bacteria from the rhizobia group, forming nodules in the roots where the conversion of atmospheric N2 to ammonium occurs. The establishment of the symbiosis between the rhizobia and legumes requires the successful infection of legume roots, which is a multifaceted developmental process that is driven by bacteria, but it is under the control of the host (Murray, 2011). Plants may primarily regulate nodulation via a systemic mechanism called the autoregulation of nodulation in response to existing infection events (Reid, Ferguson, Hayashi, Lin, & Gresshoff, 2011). Legumes regulate nodulation in response to environmental N availability as a means of preferentially obtaining N from sources that are energetically favorable relative to the energy costs of both nodulation and nitrogenase activity (Streeter & Wong, 1988; Reid et al, 2011). Nitrate can inhibit N2 fixation by many factors, such as through a decreased nodule number and mass, restricted N fixation activity as well as the acceleration of nodule senescence or disintegration (Nanjareddy et al, 2014; Saito et al, 2014)

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