Abstract: The luxAB gene were inserted into the chromosome of Rhizobium fredii by conjugation.R.fredii lux3 which could nodulate soybean and fix nitrogen efficiently was used in studying on molecular ecology of R. fredii. The survival and activity of R.fredii lux3 were studied following inoculation into soil microcosms at different matric potentials.Survival were significantly (P<0.05) greater in sterile soil at -30 and -750 kPa than that in nonsterile soil.Survival at -1500 kPa was not affected by autoclaving of soil.The activity of R. fredii lux3 in soil were influenced significantly by different matric potentials.Reactivation decreased greately with prolonged starvation.Population activity was measured by liquid scillination, dehydrogenase activity and respiration.Metabolic activity measured by luminescence decreased significantly with time (P<0.05).Luminescence following amendment with substrates ( potential luminescence,PLf) demonstrated the time required for activation of the starved inoculum.Therefore,luxABgene was a convenient and useful marker for R.fredii.

Key words: Rhizobium fredii, Matric potential, Survival, luxAB gene, Shenyang, storm water management model (SWMM), low impact development, sponge city