Productivity of legume-rhizobial complex under the influence of growth-stimulating microorganisms

Abstract

The lack of a general transition to environmentally oriented (environmentally friendly) agriculture is primarily due to the fact that use of biologicals shows unstable effects. An impact of the introduced microorganisms on the native soil microbiota, in particular, on natural microbial-plant relations, remains little studied. The purpose of this work was to study the effect of growth-stimulating strains of Paenibacillus ehimensis IB 739, Pseudomonas koreensis IB-4 and Ps. chlororaphis IB-51 on the legume plant—an aboriginal microbial community ecosystem. Seeds of pea (Pisum sativum L.) variety Chishminsky 95, white lupine (Lupinus albus L.) variety Dega, chickpea (Cicer arietinum L.) variety Zavolzhsky, alfalfa changeable (Medicago ½ varia Martyn) variety Galia, white melilot (Melilotus albus Medik.) variety Chermasan were treated with liquid cultures of rhizosphere bacteria strains. Sterile tap water was the control, and well-known microbiological fertilizer Azotovit® based on Azotobacter chroococcum B-9029 strain was the standard. Seed germination percentage, plant size, the number of root nodules, root rot lesions, nitrogen accumulation in the soil and nitrogen assimilation by plants, and abundance of inoculants in the soil served as estimates of the effect of seed inoculation during 45-day pot experiment carried out under room temperature and natural lighting. Plants, along with the soil samples for counting inoculants, were collected on day 18 and day 45, the samples for assessing nitrogen accumulation were collected on day 45. The obtained data indicate the stimulating effect of strains P. ehimensis IB 739, Ps. koreensis IB-4, and Ps. chlororaphis IB-51 on the formation and function of various legume-rhizobial communities. Treatment with plant growth-promoting (PGP) microorganisms improved seed germination, plant growth and development. In seed treating with Ps. chlororaphis IB-51, the root length predominantly increased, whereas Ps. koreensis IB-4 strain stimulated the development of the aerial parts. The Ps. chlororaphis IB-51 and Ps. koreensis IB-4 were most effective on pea, lupine and chickpea plants with no growth stimulation on alfalfa and melilot plants The inoculation of seeds with tested bacterial strains was found to suppress of the development of microscopic fungi in the rhizosphere, as a result, the root rot on peas decreased from 66.7 % to 25.3-43.8 %, on lupine from 35.9 % to 20.3-25.0 %. The inoculants showed no inhibitory effect on rhizobia, on the contrary, nodulation became more abundant. After seed bacterization of fodder crops with P. ehimensis IB 739, the number of nodules on the roots increased 1.9-2.6 times. P. ehimensis IB 739 proved to be the most active in providing accumulation of nitrogen in plants and in the soil. The nitrogen concentration in the treated pea plants was 8.5 % vs. 3.9 % in the control, in lupine — 8.6 % vs. 5.0 % in the control. To summarize, the growth-promoting properties of a strain do not guarantee its favorable effect on the productivity of leguminous plants. Strains having similar characteristics can significantly differ in their effectiveness on the same legume crops.