Screening Of Silicate Mineral-solubilizing Bacteria And Their Effect On Silicon Dissolution In Soil

Silicon is the element which is useful to the healthy growth of plants. There is plenty of total silicon in soil, but most of them were unavailable to plant. Silicate mineral-solubilizing bacteria can dissolve silicate minerals (such as feldspars and micas) and release the elements of potassium and silicon. Studies on releasing potassium and phosphate by silicate bacteria are more, but the study on the soil silicon-dissolving capacity of the bacteria is not reported. The bacteria were isolated based on their plant growth-promoting characteristics and potential of feldspar-dissolution. The colonizing dynamics of the tested strains in paddy soil and their silicon-dissolving capacity in soil were studied. The study was also involved in the effects of the tested bacteria on the plant growth, available silicon in soil, and soil bacterial community in pot experiment. The study will provide important basis for the improvement of silicon nutrition in soil by the silicate mineral-solubilizing bacteria and the practical application of this bacteria.Strain N1-1 was screened from silicate bacteria of the laboratory. The strain is of high efficacy in silicate mineral-dissolution and production of IAA and siderophores. The strain was identified as Rhizobium sp.based on the physiological and biochemical characteristics and 16S rDNA gene sequence analysis. The gram-negative strain N1-1 can also fix nitrogen, dissolve phosphate minerals and produce arginine decarboxylase. Its optimum growth temperature is 28℃, and it can also survive in the absence of oxygen or pH 4 to11. By shake culture in the culture medium which contained K-feldspar for 7 days, the pH of culture solution decreased from 6.89 to 3.98.The concentration of Si and Fe were increased by 114.8% and 133.4% respectively compared with the control.Rhizobium sp.N1-1 and Bacillus edaphicus NBT were labeled by rifampicin. Rhizobium sp.7G2-gfp with gfp gene was gained by tri-parental conjugation. The colonizing dynamics of three labeled strains in paddy soil was studied. The results showed that strains N1-1R and NBT-R successfully colonized in paddy soil and the population of the strains reached to 103-104 cfu·g-1 soil after 48 days. The colonizing level of the strains in sterilized soil was higher than that of unsterilized soil. Strain NBT-R had the strongest colonizing ability in the tested stains. The inoculation with strain NBT-R increased the number of bacteria and actinomyces, and the amount of fungi was reduced after 14 days.The efficacy of dissolving silicon of different forms in paddy soil by the tested strains was studied. The results showed that the content of water-soluble silicon in soil was decreased apparently due to the inoculation of strains in 7-23 days. In 23rd day, the content of water-soluble silicon in soil was decreased by 15.2%-33.4%; the difference of all inoculants was significant compared with the control. The content of active silicon in soil which inoculated of strain NBT-R was increased in 48days, and by 14.9% in 7th day. The content of indefinite silicon was increased by 19.1%-43.1% in 23rd day. Inoculants did not change the balance of silicon conversion. The content of available silicon was increased by 3.0%-8.2% after 48 days and the content of available silicon in soil which inoculated of strain NBT-R was significantly increased compared with the control.The effects of the tested strains on the plant growth, available silicon in soil, and soil microorganism community in pot experiment were studied. The results showed that strains 7G2-gfp and NBT-R increased the content of silicon in rice and promoted rice growth apparently. The dry weights of shoots and roots of rice were increased by 43.0%-61.2% and 48.4%-70.6%.The content of silicon in shoots and roots of rice was increased by 12.9%-36.0% and 9.2%-23.2% compared to the uninoculated control, respectively. The content of available silicon in soil which inoculated of strain 7G2-gfb was significantly increased by 17.3%. The inoculants increased the number of soil bacterial and produced an effect on soil bacteria community.