Cellulose decomposition in clay and sandy soils contaminated with heavy metals

Heavy metals at high concentrations affect the activity of soil microorganisms and possibly will have toxic effects on soil ambience health and soil microbiological and biochemical processes. This study estimated the separate specific impacts of heavy metals cadmium, cobalt, nickel and lead on cellulose-decomposing microorganisms and the enzymatic activities of cellulase and -glucosidase in clay and sandy soils representing the main soil great groups prevailing in Egypt. Regardless of metal application rate, the highest microbial and enzymatic activities were observed in the clay soil, treated or untreated, whereas the lowest values detected in the sandy soil. Soil texture and organic matter had intense effect on heavy metals toxicity to microbial activity, where clay soil was more repugnant to metal toxicity and has maximum quantities of soil microbial activity and as a result higher cellulose decomposition rates than sandy soil. Irrespective of heavy metal application rates, cadmium and cobalt suppressed the growth of cellulose-decomposing bacteria and fungi to the highest degree. Also, among the heavy metals investigated, cadmium was the most effective inhibitor of cellulase and -glucosidase enzyme activities followed by cobalt, lead and nickel, depending on the investigated soil physiochemical characteristics. Thus, these metals can be considered the most dangerous to soil microorganisms in particular, the cellulose-decomposing group. In agricultural soils, the presence of these heavy metals at high applications above the recommended permissible levels can cause toxicity to cellulose-decomposing microorganisms and plants.