Lead Influence on the Main Properties of Bradyrhizobium Japonicum

R. DONKOVA
"N.Poushkarov" Institute of Soil Science, BG - 1080 Sofia, Bulgaria

Abstract

DONKOVA, R., 2006. Lead influence on the main properties of Bradyrhizobium japonicum.Bulg. J. Agric. Sci., 12: 683-687

The possibility to increase soil nitrogen as a result of biological nitrogen fixation, to obtain a profitable and ecologically clean production determines the increased interest to the factors that limit the trend of the process. This especially applies to the symbiotic system “Rhizobium - legumes” that has priority in the process of nitrogen fixation. The effect of lead in concentration two times Permissible Level Content on the basic properties of Br. japonicum was studied in pot experiment with two soils (Leached Smolnitsa and Alluvial-Meadow soil) and soybean variety "Daniela". The virulence of the nodule bacteria (nodule number, nodule dry weight, nodule volume), fixed nitrogen amount and grain yield were determined. For each soil the variant without seed inoculation and unpolluted soil was included as a control. The obtained results showed, that lead in amount two times the Permissible Level Content decreased the virulence, symbiotically fixed nitrogen and the efficiency of the Bradyrhizobium japonicum strain 646. In polluted soils, the studied properties of Bradyrhizobium japonicum are decreased depending on the soil properties. The negative influence was more clearly pronounced in the Alluvial - Meadow soil. The different degree of the lead influence can be explained with the higher cation exchange capacity of the Haplic Vertisol. As a result the bigger part of the lead is bound in the soil absorption complex, and thus has lower toxicity.

Key words: heavy metals, nitrogen fixation, B. japonicum, virulence