Copper dynamics and impact on microbial communities in a vineyard soil. Influence of the soil organic status

摘要

In a coupled microcosm and lysimeter study, the effect of the soil organic status (SOS) on copper dynamics and impact was investigated in a vineyard soil that had been amended with varying types of organic matter during a previous long-term field experiment. Soil microcosms and lysimeters were contaminated at 240 mg Cu/kg and incubated for 12 months. Copper distribution and dynamics were assessed in the solid matrix by size fractionation and sequential extraction procedures and in the soil solution by measuring total and free exchangeable copper concentrations. Copper bioavailability was also measured with a whole-cell biosensor. Variations in microbial communities were assessed by means of bacteria enumeration and characterization of genetic structure using ARISA (Automated-Ribosomal-Intergenic-Spacer-Analysis). Results showed that copper distribution, speciation and bioavailability are strongly different between organically amended and non-amended soils and largely driven by the SOS. Unexpectedly, in solution, bioavailable copper correlated with total-copper, suggesting that non-free copper remains bioavailable to microorganisms. Similarly the observed differential copper impact on micro-organisms suggested that organic matter controlled coppertoxicity through the control of the structure of the microbial communities in the different soils. In the two soils, microorganisms were dominantly distributed in the <20mu m fraction, where native and spiked copper also accumulate. This soil smallest size fraction is also the one that more releases free and bioavailable copper, explaining thus the important amount of copper-resistant bacteria inhabiting this fraction. A clear relation between copper speciation, bioavailability, distribution and impactwas established in the present study and will permit better predicting the fate and impact of trace elements in complex heterogeneous soils.