Seeds with high molybdenum concentration improved growth and nitrogen acquisition of rhizobium-inoculated and nitrogen-fertilized common bean plants

Fernanda Fátima Delgado Almeida,Bruno José Rodrigues Alves,Adelson Paulo Araújo

doi:10.1590/s0100-06832013000200008

Abstract

Seeds of common bean (Phaseolus vulgaris) with high molybdenum (Mo) concentration can supply Mo plant demands, but to date no studies have concomitantly evaluated the effects of Mo-enriched seeds on plants inoculated with rhizobia or treated with N fertilizer. This work evaluated the effects of seed Mo on growth and N acquisition of bean plants fertilized either by symbiotic N or mineral N, by measuring the activities of nitrogenase and nitrate reductase and the contribution of biological N2 fixation at different growth stages. Seeds enriched or not with Mo were sown with two N sources (inoculated with rhizobia or fertilized with N), in pots with 10 kg of soil. In experiment 1, an additional treatment consisted of Mo-enriched seeds with Mo applied to the soil. In experiment 2, the contribution of N2 fixation was estimated by 15N isotope dilution. Common bean plants grown from seeds with high Mo concentration flowered one day earlier. Seeds with high Mo concentration increased the leaf area, shoot mass and N accumulation, with both N sources. The absence of effects of Mo application to the soil indicated that Mo contents of Mo-enriched seeds were sufficient for plant growth. Seeds enriched with Mo increased nitrogenase activity at the vegetative stage of inoculated plants, and nitrate reductase activity at late growth stages with both N sources. The contribution of N2 fixation was 17 and 61 % in plants originating from low- or high-Mo seeds, respectively. The results demonstrate the benefits of sowing Mo-enriched seeds on growth and N nutrition of bean plants inoculated with rhizobia or fertilized with mineral N fertilizer.

Highlights

Besides being a component of the nitrogenase enzyme of diazotrophic microorganisms, the transition element molybdenum occurs in four enzymes catalyzing diverse redox reactions in plants (Mendel & Hänsch, 2002)
Experiment 1 Averaged across all replications, common bean plants flowered 36.5 and 35.5 days after emergence (DAE) for plants grown from seeds with low or high Mo concentration, respectively, with no effect of N sources on days to flowering
The results clearly demonstrated the benefits of sowing Mo-enriched seeds to improve growth and N nutrition of common bean plants both when inoculated with rhizobia or receiving N fertilization

Summary

Introduction

Besides being a component of the nitrogenase enzyme of diazotrophic microorganisms, the transition element molybdenum occurs in four enzymes catalyzing diverse redox reactions in plants (Mendel & Hänsch, 2002). Root nodules of common bean act as a strong sink for Mo derived from seed or external sources in order to maintain adequate rates of N2 fixation (Brodrick & Giller, 1991). Since crops require low amounts of Mo, this nutrient can be provided by seed pellets, while on the other hand, seed pelleting with molybdate can impair seed respiration, reduce the survival of the rhizobia inoculated on seeds, and reduce plant nodulation and the efficiency of N2 fixation (Campo et al, 2009). Bean yields are not affected by high Mo rates applied to foliage, and Mo fertilizer in the amount required to increase seed content is relatively inexpensive (Vieira et al, 2005; Campo et al, 2009)

Objectives

Methods

Results

Discussion

Conclusion