INFLUENCE OF N2-FIXING BACTERIA ON PEA PLANTS AND HUMUS FRACTIONS IN SOIL EXPERIMENTALLY POLLUTED WITH CADMIUM

Heavy metals accumulation has negative effects on plant growth and yields, especially in leguminous sensible species, as well as on soil processes, such as nutrients cycling, humification or degradation of various pollutants. Under the impact of heavy metals, inoculation with effective N2-fixing bacterial strains could positively influence plant development and soil processes. A greenhouse experiment has been carried out in order to assess changes in growth and nodulation of pea plants, cultivar CORINA inoculated with Rhizobium leguminosarum bv. leguminosarum strain Mz 805,under the influence of growing concentrations of cadmium in soil (1ppm, 3ppm and 30ppm), as compared with non-inoculated plants and non-polluted control. The paper presents the results concerning the effect of cadmium on plant growth, nodulation parameters and yields at main developing stages. These parameters significantly decreased when cadmium increased. The values of regression coefficients calculated were higher in non-inoculated variants than in inoculated ones. Chromatography revealed that in rhizosphere of pea plants inoculated with strain Mz 804, composition of humus fractions THAC, TFAC and FAC I was modified by the different nature of root exudates.