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

Abstract

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 m M ), P‐medium (0.5, 1 and 1.5 m M ) and P‐high (2 m M ) 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 m M P, this treatment augmented nodule‐ARA 20‐fold, and ARA per plant 70‐fold compared with plants without P application.