Effects of long-term heavy metals contamination on soil microbial characteristics in calcareous agricultural lands (Saiss plain, North Morocco)

Soil is a natural resource and support for all economic activities. Its role is particularly crucial in agriculture. However, agro systems are vulnerable to all natural or anthropogenic disturbances such as erosion, organic or inorganic pollution. In this study, conducted in the region of Fez (Morocco), effects of irrigation with contaminated watercourses were investigated on soil heavy metal contents and microbiological characteristics, in comparison with a control soil. The total heavy metal concentrations of contaminated soil samples were 63.4, 201.2, 291.2 and 33.2 mg/kg for Cr, Cu, Zn, and Ni respectively. Quantitative analysis of soil microbial populations showed that certain groups of soil microbes (actinomycetes and fungi) were particularly sensitive to long-term contamination and revealed a strong negative correlation with Cr, Cu and Zn. While a notably higher number of cultivable bacteria was observed in the contaminated soil compared to the control.