The influence of long-term copper contamination on the diversity of bacterial communities was investigated in an ex-vineyard soil. Two sites of the same area but exhibiting different 3-fold exchangeable copper (Ex-Cu) concentrations were analysed. Culturable bacterial community structure was assessed using a variety of approaches: determination of culturable bacteria number, analyses of 132 isolates, and denaturing gradient gel lectrophoresis (DGGE) patterns of bacterial biomass grown on agar plates and of soil DNA. There was no significant difference in the number of total heterotrophs at the two sites, whereas the percentage of fast-growing bacteria growing in 1 day, was lower at the site with the higher Ex-Cu content. A high percentage of Cu-tolerant bacteria was found in both sites (63-70%) and it was relatively independent of the Cu content. Shifts in species composition of the culturable bacterial community were detected by analysing isolates from the two soils, Gram-positive bacteria prevailed in the less-polluted soil while Gram-negative bacteria in the more-polluted soil. Each sample site had a community with a different metal resistance pattern. Our study seems to indicate that in this soil ecosystem, copper influenced the culturable bacterial communities, affecting the structural diversity and altering some of the metal resistance of the microorganisms. The Sorensen similarity index calculated on DGGE profiles of 16S rDNA of total and culturable bacterial communities indicated a different species composition at the two sites, although both sites had the same biodiversity degree and different dominance.
The effects of the addition of compost, prepared from vegetable market refuse and stomach contents of slaughtered cattle, were studied in a sandy soil contained in pots and kept in a greenhouse environment. Comparison was made between: i) a treatment involving pots containing compost mixed with 5% soil, ii) four treatments in which increasing quantities of compost homogeneously taken from the same lot (0, 10000, 20000, 30000 kg ha -l) were integrated with NPK mineral fertilizer to equalize available nutrients; iii) an untreated control. At 3, 4, and 5 years from the date of treatment, after various other crops, sunflower was planted. The yield obtained, though it fell off from year to year, was approximately double in the case of 95% compost. The other four treatments also resulted in production increases compared with the untreated control. Production was found to rise progressively with increasing quantities of compost. The improvement in soil chemistry and microbiology, as shown by analyses performed 5 years after treatment with compost, suggests that the rise in crop production may be attributed to an overall improvement in all components involved in the fertility of the soil used, in our experimental conditions.
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