Screening Of Low Temperature Adapted Plant Growth-promoting Rhizobacteria And Investigation Of Their Promoting Effects

Excellent microbial strains are the basis of microbial fertilizer,and Low temperature adaptive strains are of great significance for the development of biofertilizer used in agricultural production of cold area.This study focused on the screening of low temperature adaptive plant growth promoting rhizobacteria.The rapid growth strains were isolated from plates spread with diluted solution of soil samples,and the obtained isolated were further tested for their growth at low temperature and plant growth promoting characters.Finally,two Bacillus spp.strains,D4 and R1 were isolated and optimized for liquid fermentation,the microbial fertilizers based on these strains were developed and their plant-growth promoting effects in pot and field experiments were investigated.The main results were as follows:1.All the 36 strains isolated from the first round screening were confirmed to grow fast at low temperature,and 8 strains could produce NH3 and IAA,and strain D4 had the highest level of IAA production,reaching 162mg L-1.2.The 8 strains were evaluated in pot experiment for their growth promoting effect of corn and tomato,after thirty days,the plant height and biomass were significantly higher than control.In the pot experiment of corn,5 strains showed varied growth effects;In tomato pot assay,2 strains showed varied growth effects.Through 16S rDNA sequencing and phylogenetic analysis,these eight isolates were identified as Bacillus genera(Bacillus spp.);Strains D4 is Bacillus megatherium while strains R1 is Bacillus pumilus.3.Liquid fermentation media of these two Bacillus spp.strains were optimized using single factor and orthogonal tests.The optimal liquid fermentation medium for D4 and R1 was as following:3%molasses,0.75%chemical nitrogen source,0.25%magnesium sulfate,0.2%potassium dihydrogen phosphate,0.2%calcium chloride,0.05%ferrous sulfate?4.According to the growth curves of two Bacillus spp.strains.10%(v/w)fermentation cultures at 72h was mixed with manure compost to make the microbial fertilizers,the growth promoting effects of the developed microbial fertilizers were evaluated in pot and field experiments in different season,the soil enzyme activities are also determined.The D4 biofertilizer contains the spore number of about 4.6×109 CFU g-1 dry weight and R1 biofertilizers of about 6.0×109CFU g-1 dry weight.The results of tomato pot experiment showed that the application of microbial fertilizer alone and combined application of microbial fertilizer with chemical fertilizer increased plant height and biomass of tomato.The results of green vegetables in pot and field experiments showed that the combined application of microbial fertilizer with chemical fertilizer increased plant height,root length,biomass and yield of green vegetables.Soil enzyme activities showed that the combined application of microbial fertilizer with chemical fertilizer increased soil invertase,catalase and alkaline phosphatase activities significantly.