THE INFLUENCE OF VARIOUS RHIZOBIUM-MELILO TI STRAINS ON LUCERNE MASS AND NITROGEN ACCUMULATION ON THE MINERAL NITROGEN BACKGROUND

Comparative assessment of genetically modified Rhizobium meliloti stra ins SKhM1-48, SKhM1-105, SKhM1-214, and SKhM1-226, as well as the orig inal strain SKhM1 was carried out in an experiment with lucerne vegeta tion on wet forest soil with mineral nitrogen introduced at 8 mg N-15 per 100 g soil. A significant increase in the lucerne green mass (tota lled for three hay harvests) was demonstrated for strains SKhM1-105, S KhM1-214, and SKhM1-226, as compared to the original strain, as a resu lt of increased mass of the second and third hay harvests on the miner al nitrogen background over those without it. At the same time, accumu lation of the total and air nitrogen in the plant biomass was not incr eased. The lucerne inoculation with strains SKhM1-105, SKhM1-214, and SKhM1-226 increased the mass of the second hay harvest through increas ed consumption of the labeled mineral nitrogen and, in the case of SKh M1-105, increased consumption of the air nitrogen, The increased mass of the plants inoculated with these strains at the third haymaking was not accompanied by increased nitrogen accumulation. In the absence of mineral nitrogen, both the mutant and the original R. meliloti strain s exerted similar effects on the plant growth, All these strains were highly competitive with the soil nodule bacteria. A microfield experim ent with the modified SKhM1-105 strain on the mineral nitrogen backgro und also demonstrated significant increase in mass and nitrogen consum ption al the second haymaking, as well as in the total lucerne biomass in the absence of increased accumulation of nitrogen. We propose that the increased mass of the plants inoculated with the mutant strains S KhM1-105, SKhM1-214, and SKhM1-226 without increased accumulation of n itrogen is due to synthesis of physiologically active substances in th ese strains and enhanced consumption of nutrients from the sail.