Effect of phosphorus deficiency on the growth, symbiotic N2 fixation and proton release by two bean (Phaseolus vulgaris) genotypes

This study compared the growth, nodulation, N-2 fixation and proton release by two bean genotypes (Phaseolus vulgaris L., BAT477 and DOR364) in response to P deficiency in nutrient solution. For plants grown at 5 muM P for 42 days, shoot and root biomass were 55-62% and 82-88%, respectively, of that of plants grown at 25 muM P. Phosphorus deficiency decreased nodule biomass and size, with the decrease being smaller in BAT477 than in DOR364. Total nitrogenase activity of plants grown at 5 muM P was 50% of that of plants grown at 25 muM P, and reached the maximum earlier in BAT477 than in DOR364. However, nitrogenase activity per unit nodule mass was similar in both genotypes and was unaffected by P supply. Proton release was generally similar in both genotypes. There were high correlations between proton release and uptake of excess cations, with a slope of 1.44 for BAT477 and 0.85 for DOR364. It is suggested that the two genotypes differ in root exudation.