Effect Of Tylosin On Soil Microbial Activity And Community Diversity

Plate count, soil microbial biomass, Polymerase chain reaction- denaturing gradient gel electrophoresis(PCR-DGGE) and microcalorimetry were employed to investigate microbial diversity and activity in red soils influenced by the concentrations and incubation time of tylosin. The main results were shown as following:1. The residues of tylosin in the soil were determined. At 1st day, the residue concentrations of tylosin decreased to less than 50% compared to the initial addition concentrations. No tylosin residues were determined in the treatments (500 mg kg-1and 1000 mg kg-1) at the 14th day and 21st day, respectively. At 56th day, the concentrations of tylosin in the treatment of 2000 mg kg-1 couldn’t been determined.2. Tylosin residues in the soil inhibited the numbers of bacteria distinctly. At 7th day, the numbers of bacteria in the treatments of low, medium and high concentrations of tylosin decreased markedly by 67.4%,55.1% and 75.8%, the activity of actinomyces were depressed slightly, and that of fungi were stimulated. At the middle incubation time(42 th day), tylosin remarkly promoted the growth of bacteria, the numbers of bacteria in the medium concentrations(1000 mg kg-1) and the high concentrations(2000 mg kg-1) of treatments were remarkably higher than ck. At the late incubation time, the numbers of bacteria, actinomyces and fungi resumed to the level of initial time.3. The residues of tylosin in the soil had slightly influence on microbial biomass carbon and nitrogen. Microbial biomass C/N were stimulated distinctly by 41.7% and 51.2%, respectively, in the treatments of 1000mg kg-1 and 2000 mg kg-1 Medium and high concentrations of tylosin remarkably affected microbial biomass C/N in the soil.4. All treatments of addition of tylosin all had strong negative effect on the activity of urease, being decreased by 17.4%,30.0% and 24.6%, repectively, in the treatments of low, medium and high concentrations of addition of tylosin in the early incubation time(lst day-14th day). Only high concentrations of tylosin depressed markedly the activity of acidic phosphoric acid enzyme by 23.0% in these period (1st day-14th day). At the middle incubation time, high concentration of tylosin stimulated the two enzymes remarkably. To the late incubation time, tylosin had no effect on the two enzymes.5. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis demonstrated that tylosin had gradual effect on the diversity of microbial populations. The values of shannon index and eveness index in the treatments of addition of tylosin all decreased, suggesting that tylosin reduced the diversity of microbial populations evidently.6. The results of microcalorimetric determination showed that mcrobial metabolic activities were depressed in the initial incubation time. The total heat evolution(Q) was positively correlated with the number of microorganisms, soil microbial biomass and soil enzymes, whereas the peak time (tmax) was negatively connected with number of microorganisms and soil microbial biomass.