Fig. 1

Profile of bacterial communities in Cr-contaminated soils. A The biomass of bacteria in Cr-contaminated soil. The petal lengths of the rose represent the value of log (copies/g soil) quantified by fluorogenic quantitative PCR reactions with 16S rRNA gene, which generally decreased with the increase of Cr contamination in both sites. B Redundant analysis (RDA) of bacteria in different soil samples. The results showed nitrate, ammonium, total nitrogen, organic matter and total phosphorus had the closest correlation with the composition of bacteria. The bacterial communities of each sample clustered most closely with samples under similar geochemical conditions. Specifically, L1, L2 and Z1 with low available Cr concentration were more similar, and L3 and Z2 with slightly higher pollution levels were clustered together. Z3 and Z4 were dramatically different from those in other sites