Crescimento e acumulação de nitrogênio de plantas de feijoeiro originadas de sementes com alto teor de molibdênio

Abstract

RESUMO

Seeds enriched with phosphorus and molybdenum improve the contribution of biological nitrogen fixation to common bean as estimated by 15n isotope dilution

“…The effects of Mo-enriched seeds on shoot growth were of small magnitude (Figure 1a). These results contrast with those of Kubota et al (2008), which reported improved shoot growth of bean plants raised from seeds with high Mo concentration.…”

“…The effects of Mo-enriched seeds were less consistent than those reported by Vieira et al (2005) and Kubota et al (2008). Hence, the advantage of the simultaneous seed enrichment with P and Mo remains inconclusive.…”

“…For control plants, low-P high-Mo seeds reduced nodule mass as compared to high-P high-Mo seeds at low soil P level, and as compared to high-P low-Mo seeds at high soil P level (Figure 1b). Kubota et al (2008) also observed that bean plants originating from seeds with high Mo concentration showed reduced nodulation, although nitrogenase activity of root systems was not affected by seed Mo concentration. Since Mo supply is usually associated with increased nitrate reductase activity in bean plants (Pessoa et al, 2001), it is hypothesized that the additional Mo provided by enriched seeds would stimulate the assimilation of the N taken up from the soil, hence impairing nodule growth by a possible feedback mechanism induced by high concentration of reduced N compounds in roots (Leidi & Rodríguez-Navarro, 2000;Hogh-Jensen et al, 2002).…”

“…Since the limited P supply retards the development of nodulation in the common bean (Araújo & Teixeira, 2000), P-enriched seeds can provide P during initial stages of nodule formation and growth (Thomson et al, 1991). Bean plants originating from seeds with high Mo concentration had higher accumulation of biomass and N in shoots and higher root nitrogenase activity (Brodrick & Giller, 1991;Kubota et al, 2008) and also produced more grains in soil with low N content particularly when plants did not receive additional foliar Mo (Vieira et al, 2005). In spite of such encouraging results, studies evaluating the simultaneous seed enrichment with P and Mo are not available.…”

Application of molybdenum and a desiccant herbicide to the common bean under direct seeding

“…The increase in LNL can be explained by the Mo being directly related to N metabolism through its action on the enzymes nitrogenase and nitrate reductase. With an adequate supply of Mo, there is an improvement in the activity of these enzymes, enabling a better use of N by the bean plant (ARAÚJO et al, 2009;KUBOTA et al, 2008). On the other hand, part of the N accumulated in the leaves may also come from the decomposition of straw in previous years.…”