KINETICS OF SUBSTRATE-INDUCED RESPIRATION (SIR) AND DENITRIFICATION -APPLICATIONS TO A SOIL AMENDED WITH SILVER

Silver is widely dispersed in the environment as a result of its indus trial and medical use. Although silver is toxic to microorganisms, its effects in soil are poorly investigated. In the present work, basal r espiration, substrate-induced respiration, and potential denitrificati on activity were used to evaluate effects of silver (Ag2SO4) on the so il microbial population. A new kinetic approach involving growth-assoc iated product formation was used to differentiate between growth of mi croorganisms and their activities. Moreover, the aerobic respirers wer e divided into growing and nongrowing types. The response by the respi ring microbial community varied depending on the contact time between silver and the soil. The activity of the nongrowing microbial populati on was affected when incubated with silver for 10 days, but the activi ty of the growing population was affected only when silver was added a t the time for induction of the substrate-induced respiration. The spe cific growth rate of the denitrifying bacteria was a very sensitive pa rameter and also indicated that part of the denitrifying population wa s resistant to silver. The results indicate that silver, in concentrat ions known to occur in sewage sludge amended soils, may seriously affe ct the microbial biomass. The results show that the presented kinetic approach is promising as a tool to estimate effects of soil pollution on the microbial biomass.