Land use and seasonal effects on a Mediterranean soil bacterial community.

To evaluate the effects of management practices and seasons on a soil bacterial community and the composition of ammonia-oxidizing bacteria (AOB), molecular screenings were compared among Mediterranean (Sardinia) soils with different plant covers and different agricultural practices, namely cork oak forest, tilled/non-tilled vineyard, hay crop and pasture. We compared the fingerprints from both independent replicates and pooled samples to ascertain the best approach for studying the environmental effects on bacterial composition. The soil microbial biomass, which was estimated from the amounts of extracted soil dsDNA, was 2 to 3 folds higher in the spring than in the autumn; in the spring, it was negatively correlated with the intensity of land use. A 16S rDNA DGGE experiment confirmed that both the land use and season markedly affect the composition of the soil bacterial community. Tilled vineyard soil exhibited the lowest similarities in community structures, suggesting that tillage induced the most marked disturbance among the tested land management methods. Distinct AOB populations were found for each type of land use; among these types, the cork oak forest proved to be a protective habitat for AOB against environmental changes. Our results suggest that the comparative community level and group-specific fingerprinting enabled an accurate evaluation of multiple factors in soil bacterial structures when performed with both independent and pooled replicates.