Influence of nutrient, toxic metal and herbicide contents on the soil bacterial communities in tropical vegetable growing areas.

The relationship between bacterial diversity and the bioavailability of nutrients, toxic metals and the herbicide oxyfluorfen in a tropical vegetable growing area was evaluated. The study was conducted in a vegetable growing area located in the mountainous region of Rio de Janeiro (Brazil), and samples were collected in areas of vegetable cultivation and areas of environmental reserve. Fertility analyses and determination of the pseudototal levels of toxic metals in the soil samples were performed. The profile of the soil bacterial community was determined by amplification of the 16S rRNA gene and separation by DGGE. The results showed that the levels of toxic metals and elements associated with soil fertility were higher in vegetable production areas. These differences in the physical and chemical characteristics of the soil favored the presence of a greater number of OTUs in the cultivation areas (17.3-27 OTUs) than in the areas of environmental reserve (13-22 OTUs). Therefore, this study demonstrates that the presence of toxic metals and the herbicide oxyfluorfen and the increase in fertility in soils in areas with intensive vegetable cultivation resulting from the intensive management adopted in these areas promotes a differentiation of the bacterial profiles in soils in tropical vegetable growing areas.