Variation in soil microbial population and enzyme activities under faba bean as affected by pentachlorophenol

Pentachlorophenol (PCP) is a widely detectable toxic chemical with a detrimental effect on the functioning of ecosystems. A field trial was undertaken to study its effects on the activities, metabolic and genetic diversifies, as well as soil bacterial and fungal community composition. The seeds of faba bean (Vicia faba L.) were either treated (PCP) or left untreated (Control) with pentachlorophenol before sowing. During the vegetative period, soil samples were taken three times from the rhizosphere in order to assess the influence of PCP on soil enzymatic activity, metabolic diversity (Biolog EcoPlate), community of ammonia-oxidizing archaea (DGGE and t-RFLP) and the fungal and bacterial microbiome (NGS). PCP treatment led to a considerable reduction in the activities of enzymes connected with the N cycle (protease and urease) and showed a significant negative correlation with them (r = -0.934 and - 0.716, respectively). Dehydrogenase and respiration activities were also reduced by PCP. In contrast to other enzymes analysed, PCP significantly increased acid phosphomonoesterase activity compared to the Control (r = 0.850). PCP also decreased the carbon utilization efficiency of indigenous microbes and caused the lower utilization of amines, amides and carboxylic acids. The amount of isolated DNA was lower in PCP-treated soil than in the Control. The technique of t-RFLP fingerprinting revealed the changes caused by contamination and new specific fragments were observed in PCP-contaminated soil. Additionally, pentachlorophenol changed more fungal than bacterial structures in the faba bean rhizosphere. For most of the analysis parameters, the effect of PCP was notable during the entire analysis period of faba bean growth (from 5-6 leaves to pod formation). The results demonstrated the harmful effect of PCP on soil activity and changes in soil microorganism genetic diversity, which could result in the deterioration of the environment for soil function and processes as well as for plant growth.