Effects of zinc oxide nanoparticles on carbon mineralization kinetics and microbial attributes in plant residue-amended soils

The widespread use of ZnO nanoparticles (ZnO-NPs) will inevitably enhance their discharge into soils, leading to serious concerns about their effects on soil microbial functions essential for sustaining environmental health. This study was designed to determine the impacts of different ZnO-NPs concentrations (100 − 1000 mg kg − 1 soil) on soil carbon (C) mineralization kinetics of soil amended with alfalfa hay and wheat straw. The microbial biomass C (MBC), basal respiration (BR), and metabolic quotient (qCO 2 ) were also compared in the contaminated and control soil samples. The results showed that ZnO-NPs influenced the measured C mineralization criteria of the residue-amended soils, such as the total mineralized C and the C mineralization rates. The results of kinetic analysis using the double first-order model revealed that the addition ZnO-NPs increased the amount of C mineralized during the initial fast phase, while it reduced the C mineralization in the subsequent slow phase. The rate constants associated with the fast and the slow C mineralization phases were also differently affected by ZnO-NPs. Furthermore, the soil contaminated with ZnO-NPs had lower MBC and BR values compared to the uncontaminated soil, indicating that the size and activity of the soil microbial community were suppressed by ZnO-NPs. The qCO 2 value increased in the ZnO-NPs contaminated soils, suggesting that the soil microbial community was subjected to toxicity stress by ZnO-NPs. In conclusion, ZnO-NPs can drastically influence the microbial abundance, maintenance energy demand, and C mineralization process in plant residue-amended calcareous soils.