Utilization of the acetylene reduction assay to screen for tolerance of symbiotic N² fixation to limiting P nutrition in common bean

Abstract

The limitation of symbiotic nitrogen fixation due to P deficiency restricts the development of a sustainable agriculture, particularly in Mediterrancan and tropical soils. Common bean genotypes, APN18, BAT271, PVA846, POT51, G2633 and G12168, were grown in an aerated N‐free nutrient solution at low (72 μmol plant‐1 week‐1) and control P supplies (360 μmol plant‐1 week‐1). Nitrogenase activity was estimated by in situ measurements of acetylene reduction activity (ARA) in a flow‐through system. During the assays, maximum values of ARA (peak ARA) were reached between 20 and 30 min after exposure to C2H2, depending on P treatment and growth stage. Thereafter, a decline in C2H4 evolution was observed. This decline was most pronounced in low‐P plants and there was a significant genotypic effect. ARA per plant was decreased by P deficiency, mostly because nodulation was delayed and the number and mass of nodules were reduced. The ARA decrease during pod filling was also activated by P deficiency. ARA per g dry weight nodule was increased by P deficiency in G2633 and G12168, unchanged in APN18, BAT271 and POT51 and decreased in PVA846. Except for the climbing type IV G2633, total N at harvest for all P treatments was correlated with the cumulative value of peak ARA and with peak ARA at early pod‐filling which was the highest peak ARA throughout the growth cycle of type III bushy genotypes. We conclude that if phenology and growth habit are carefully considered, peak ARA is a reliable screen of genotypes for N2 fixation tolerance to P deficiency. Selection of lines with early nodulation under P deficiency is also advisable, and the effect of P deficiency on the nodule functioning needs to be considered.

Genotypic difference in the short-term response of nitrogenase activity (C2H2 reduction) to salinity and oxygen in the common bean

“…There was no apparent C 2 H 2 -induced decline for these measurements by contrast with the C 2 H 2 -induced decline described for P deficient common beans [33]. The NaCl (0.1 M) was injected in the flask with a syringe one hour after starting ARA measurements.…”

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

“…A técnica de redução de acetileno apresenta deficiências para a quantificação da fixação biológica de N, em particular em plantas disturbadas como no caso deste trabalho, mas pode ser útil na comparação de diferentes genótipos de feijoeiro sob distintos estados nutricionais (Vadez et al, 1997), permitindo a identificação do efeito estimulatório do Mo da semente na atividade da nitrogenase (Quadro 1). A maior atividade da nitrogenase em plantas oriundas de sementes com alto teor de Mo (Quadro 1; Brodrick & Giller, 1991), assim como a maior atividade da nitrogenase em plantas que receberam adubação foliar com Mo (Vieira et al, 1998a), demonstra a importância do Mo para a fixação biológica de N. Entretanto, deve-se considerar a hipótese de que a maior acumulação de N em plantas oriundas de sementes enriquecidas com Mo pode também ser conseqüência de maior atividade da nitrato redutase, que poderia incrementar a assimilação do N absorvido do solo (Vieira et al, 1998a).…”

Nitrogen and phosphorus availability limit N2 fixation in bean

“…Moreover, the P requirement of legumes is affected by the mode of N nutrition (Cassman et al, 1981). N # -fixing plants have a greater need for P than nitrate-supplied plants (Israel, 1987) and the P requirement seems particularly great in bean (Graham & Rosas, 1979) though cultivars with a lesser requirement are known (Vadez et al, 1997). Only limited research has been conducted into the effects on N # fixation of the interactions between N and P (Gates & Wilson, 1974 ;Graham, 1981).…”