Abstract: By the method of triparent conjugation, the marker gene luxAB was successfully transferred intoBacillus K2116 strain, the cotton growth promotion rhizobacteria, and marked strain K2116L was obtained. The plasmid with luxAB did not lose after 15 transfers, and the strain was genetically stable. The rowth character and K-releasing ability of the marked strain were not affected by the plasmid. Strain K2116L could successfully survive in both sterilized and non-sterilized yellow cinnamon soil (YC), yellow fluovo-aquic soil (YF), and red soil (RS). The individuals of bacteria in these three sterilized soils were higher than those in non-sterilized soils, and decreased in the order of YC>YF>RS. Strain K2116L was capable of competition with native bacteria for space and nutrients in the test soils. Rhizoboxes were used to trace the colonization dynamics of the strain around cotton root. In rhizosphere soil, the colonization density reached to 1.0×10⁶ cfu·g^-1 and 4.5×10⁵ cfu·g^-1, respectively, at the depths of 0-2 cm and 2-4 cm after cotton grew for 12 days, and reached the highest at the depth>4 cm on day 18. On the surface of all root segments and also on day 18, the colonization density reached the highest level, with 1.76×10⁶ cfu·g^-1 on the surface of 0-2 cm segment and 1.6×10⁵ cfu·g^-1 on that of >8 cm segments. The supplement of nutrients could obviously increase the colonization density in rhizosphere soil and on root surface, and the marked strain could proliferate continually with the growth of cotton roots.

Key words: Arable soil, Dissolved organic matter, Hydrophilic, Biodegradable, Vertical fractionation