Growth and nodulation in faba bean-rhizobia symbiosis under different soil phosphorus levels: acid phosphatase and phosphorus deficiency tolerance

The symbiosis faba bean-rhizobia behaviors under different soil phosphorus levels were studied. The plants were grown under symbiotic nitrogen fixation without fertilizers application. At flowering and maturity stages, ten plants per site were harvested and analyzed for their growth and nodulation, phosphorus and nitrogen contents. The acid phosphatases activity was analyzed in nodules and rhizospheic soils. Results showed that the nodular and shoot dry biomass were associated to the richness of the soil in available phosphorus. The highest and significant dry biomass was noted in plants of site 2 having a highest level in soil available phosphorus (85 and 0.66 g .plant -1 for shoots and nodules respectively) while the lowest values were noted with the plants of site 3 (43.75 and 0.43 g .plant -1 for shoots and nodules) showing the smallest soil available phosphorus. The P contents were associated with the soil P availability. The highest values were noted in plants of site 2 (11.46 mg P. g DW -1 for shoots and 19.50 mg P. g DW -1 for nodules). The amounts of nitrogen accumulated ranged from 2.51 to 4.37 mg . g DW -1 in shoots and from 3.36 to 6.01 mg . g DW -1 in nodules. The soil phosphorus level influenced the potassium sorption. Low levels of soil available phosphorus accentuated the enzymatic activity of acid phosphatase in nodules and rhizospheric soil. The increase in acid phosphatases activity could be an adaptation mechanism developed by faba bean plants for tolerance to phosphorus deficiency stress.