Promising indicators for assessment of agroecosystems alteration among natural, reforested and agricultural land use in southern Brazil

Microbiological soil-quality indicators, especially related to C and N cycles, and microbial diversity may be useful tools to determine whether a particular environment responds to an imposed management or reclamation strategy. External influences such as forest clearance and soil management affect biological indicators making them useful to point out whether the land use strategy is sustainable. Accordingly, the aim of this work was to assess the utility of some soil chemical and microbiological properties and 16S rDNA diversity in bacteria domain and their significance as soil-quality indicators in different land use systems in southern Brazil, Paraná State. Nine sites with soil originated from basalt (Rhodic Ferralsol), previously covered with the Atlantic native forest were evaluated: a native forest tract as reference; three sites artificially reforested with native species, but with understory differently managed; secondary forest naturally regenerated from abandoned pasture; artificially reforested with eucalyptus; two wheat-cropped sites at differing vegetative stages; one site in fallow. Twenty-four chemical and microbiological properties and their derivatives were assessed, in addition to molecular diversity of bacteria domain based on denaturating gradient gel electrophoresis (DGGE) analysis. Amongst all variables, the most dissimilar along the sites were total organic C, microbial biomass C and N, and ammonification rate. Total organic C was highest in the native forest, followed by secondary forest, eucalyptus and the artificially reforested sites; the wheat-cropped and fallow sites produced the lowest values. This trend was also observed for ammonification rate, which was closely correlated to organic C. Microbial biomass C and N were also higher in the reforested sites, whereas for microbial N biomass, the eucalyptus site resembled to the wheat-cropped and fallow sites. The DGGE analysis revealed that the fallow, eucalyptus and wheat-cropped sites had less bacterial diversity. All the sites reforested with native species grouped with the native forest, while the eucalyptus, fallow and wheat-cropped sites formed separate clusters. A similar clustering pattern was observed when all chemical and microbiological properties were considered in a grouping analysis. The results for reforestation employing native species tended to be similar to those of the stable native forest, while the use of an exotic species (eucalyptus) tended to be similar to