EFFECTS OF NITROGEN-FIXING AND PHOSPHATE-SOLUBILIZING MICROORGANISMS FROM THE FAR EAST AGRICULTURAL SOILS ON THE CEREAL SEED GERMINATION
Mineral fertilizers which can significantly increase crop productivity have an adverse effect on the soil and the environment as a whole when used for a long time. Microorganisms, as an alternative to mineral fertilizers, stimulate plant growth and development due to their ability to fix nitrogen, produce siderophores, phytohormones and enzymes, dissolve inaccessible elements of mineral nutrition, suppress plant pathogens, and increase consumption of water and nutrients. However, the effectiveness of such preparations highly depends on factors of a new environment. We believe that bacteria from soils that have long been exposed to various agricultural practices may be good plant stimulants. In the presented study, for the first time, we have isolated local active strains of nitrogen-fixing and phosphate-mobilizing bacteria from soils subjected to 74-year stationary intensive farming in the conditions of the Russian Far East and revealed isolates and their combinations which stimulate wheat and barley seed germination and seedling growth. The aim of the work was to study the plant-stimulating properties of nitrogen-fixing and phosphate-mobilizing bacteria from soils that have been actively exposed to mineral fertilizers for a long time. Bacteria were isolated from soils sampled in October 2015 (the experimental field 8, Federal Research Center for Agrobiotechnology FEB RAS, Ussuriysk, Primorsky Territory, Russia). The seeds of wheat Triticum aestivum L. cultivar Primorskaya 50, and barley Hordeum vurlage L. cultivar Tikhookeanskii (collection of the Federal Research Center for Agrobiotechnology FEB RAS) were treated. Of 68 bacterial isolates with different cultural and morphological properties, three isolates, the Acinetobacter spp. N1, Azotobacter spp. N2, and Clostridium spp. N3 were nitrogen fixers, and four isolates, the Serratia spp. P6, Bacillus spp. P7), Arthrobacter spp. P8, and Pantoea spp. P19 were phosphate-mobilizing bacteria. Tests with the monocultures of nitrogen-fixing and phosphate-mobilizing isolates and their different binary compositions showed a 13-51 % increase (p ≤ 0.05) in wheat seed germination energy and 15-54 % increase (p ≤ 0.05) in barley seed germination energy compared to the untreated control. Laboratory germination of wheat seeds increased by 2-32 %, barley seeds by 7-30 % compared to untreated control. The barley seedlings were 1.8 times longer, and the roots were 2.7 times longer. Th binary combination N2P19, P6P19, and P8P19 caused the highest height of seedlings (120-140 mm, p ≤ 0.05), and with P6P7, N2P19, and P6P19 the roots were the longest (120-130 mm, p ≤ 0.05). These results allow us to conclude that short-term soaking seeds in the suspensions of the tested nitrogen-fixing and phosphate-mobilizing isolates improves seed germination energy and laboratory germination, and increases shoot and root length. Binary bacterial compositions have a greater effect on seed germination than monocultures. The strains N1 ( Acinetobacter spp.), N2 ( Azotobacter spp.), and P19 ( Pantoea spp.) are the best stimulants. Species-specific differences in plant response to the treatment is probably due to lack of genetic, biochemical and physiological complementarities between specific plant species and the bacteria.