Experemental Studies on Soil Enzymes Changes under the Critical Heavy Metals Accumulation in Luvisols and Albeluvisols

Abstract

while fungi and sporeforming bacteria seemed possessing much more effective defence mechanisms leading to higher survival under stress environmental conditions. Due to heavy metals contamination soil enzymes activity found to be decreased in such order: dehydrogenase (95-98%) → urease (65-97%) → sacharase (57-77%) → soil respiration (38-65%). The different soil microorganisms and enzymes response to heavy metals indicate a shift in ratio of microbial groups and suppose about changes in structures of particular microbial communities selecting for more tolerant microorganisms to bioremediate polluted soils. The research is aimed at assessment of critical heavy metals accumulation in undisturbed modelling soil monoliths with respect to determine changes of soil microbial communities and enzymes activity under the conditions of catastrophic soil pollution. In order to simulate heavy metals migration and accumulation in soil profile, a special modelling columns system designed and filled up with natural monoliths of Calcari– Endohypogleyic Luvisol. Three of them were experimentally contaminated with heavy metals (mixture of Pb, Cu and Zn acetates) at the level of sorption capacity, whereas soil monolith in the fourth column saturated with distilled water (uncontaminated control). The experiment has demonstrated a great potential of the modeling Luvisol to accumulate extremely high concentrations of different heavy metals fractions. In particular, catastrophic pollution of Ap horizon (in upper 0-10 cm layer) observed: total Pb – up to 839, Cu – 773 and Zn – 844 mg kg-1. Due to a lower organic mater amount in soil deeper layers (BCkg 95-100 cm), less heavy metals amount was accumulated: total Pb – up to 278, Cu – 429 and Zn – 411 mg kg-1. The constantly rise of heavy metals concentration in solution leached through the soil column determined. However in the separate soil layers, the same as in the whole profile, Pb has showed a highest sorption capacity and Cu the lowest one. Such a high pollution level reduced counts of all investigated microbial groups: organotrophic, spore forming, mineral nitrogen assimilating, oligonitrophylic bacteria, actinomycetes and micromycetes. However, impact of heavy-metal acetates on specific microbial group was related to metal concentrations and properties of soil as well as biological peculiarities of microbes of different groups. High susceptibility of such microorganisms as actinomycetes, oligonitrophylic and mineral N assimilating bacteria suggest about low adaptable possibilities of these microorganisms,.