Soil microbial biomass, activities and diversity in Southern Italy areas chronically exposed to trace element input from industrial and agricultural activities

Abstract

High concentrations of trace elements in the soil can have toxic effects on the microbial community which plays a key role in fundamental ecosystem processes like the organic matter decomposition and nutrient cycles. The aim of this study was to evaluate if trace element concentrations in soils chronically exposed to industrial and agricultural activities did affect the soil microbial community, in terms of biomass, activity and diversity. Soil samples differing in trace elements (As, Cd, Co, Cr, Cu, Ni, Pb, V, Zn) concentrations were analysed for the total microbial biomass (Cmic), fungal mycelium, microbial activity, indexes of microbial community structure (fungal percentage of total Cmic) and microbial metabolism (metabolic quotient or qCO2; carbon mineralization rate or CMR), and genetic bacterial diversity (richness, Shannon index and evenness of bacterial groups). Relationships of the microbial variables with individual trace element concentrations, relative Overall Contamination Index (OCI), and ordinary soil properties (pH, water content, organic C content, electrical conductivity) were assessed by simple and multivariate statistical analysis. Neither OCI nor single element concentrations determined a significant reduction in soil microbial biomass, activity and diversity, these variables being mainly driven by soil organic C and water content. Only soil Cr concentration affected indexes of the microbial metabolism and structure, without causing stressful conditions. Even Cmic and bacterial diversity showed higher values in soils richer of Cr. The results suggest that the concentrations of considered trace elements measured in our soils, or probably their bioavailable fractions, did not cause toxic effects on the microbial community. However, the chronic exposure to different patterns of trace element contamination probably elicited site-specific adaptive responses in microbial populations.