Growth, nitrogen fixation and ammonium assimilation in common bean (Phaseolus vulgaris):: effect of phosphorus

The impact of phosphorous nutrition on plant growth, symbiotic N-2 fixation, ammonium assimilation, carbohydrate and amino-acid accumulation, as well as on nitrogen, phosphorus and ATP content in tissues in common bean (Phaseolus vulgaris) plants was investigated. Plants inoculated with Rhizobium tropici CIAT899 were grown in Leonard jars under controlled conditions, with P-deficient (0 and 0.1 mM), P-medium (0.5, 1 and 1.5 mM) and P-high (2 mM) conditions in a N-free nutrient solution. The P application, increased leaf area, whole plant DW (67%), nodule biomass (4-fold), and shoot and root P content (4- and 6-fold, respectively) in plant harvested at the onset of flowering (28-days-old). However, P treatments decreased the total soluble sugar and amino acid content in vegetative organs (leaf, root and nodules). The root growth proved less sensitive to P deficiency than did shoot growth, and the leaf area was significantly reduced at low P-application. The absence of a relationship between shoot N content, and P levels in the growth medium could indicate that nitrogen fixation requires more P than does plant growth. The optimal amount for the P. vulgaris-R. tropici CIAT899 symbiosis was 1.5 mM P, this treatment augmented nodule-ARA 20-fold, and ARA per plant 70-fold compared with plants without P application.