Effects Of Four Metal Oxide Nanoparticles On Soil Enzyme Activities And Bacterial Communities In Two Different Soil Types

With the increased availability of nanoparticle-based products,their releases to soil are undoubtedly inevitable.Among the nanoparticle-based products,potential risks of metal oxide nanoparticles（MO-ENPs）have attracted increasing concerns.However,their effects on soil and the interacted organisms remain largely unknown.In this study,four metal oxide NPs,zinc oxide NPs（nZnO）,titanium dioxide NPs（nTiO₂）,cerium dioxide NPs（nCeO₂）,magnetite NPs（nFe₃O₄）were used to evaluate their impacts on four kinds of soil enzyme activities（invertase,urease,catalase and phosphatase）and bacterial communities in two different soil types,i.e.,black soil and saline-alkali soil,which represented the typical soils of northeast China.The community structure and size were analyzed using pyrosequencing and Real-time PCR methods.The soils were exposed to various amounts of MO-ENPs（0.5,1.0and 2.0 mg g-1）for 15 and 30 days,respectively.In general,nZnO had a stronger effect on the four kinds of enzyme activitythan nTiO₂,nCeO₂,and nFe₃O₄,andsaline-alkali soil were more susceptible to MO-ENPs in contrast to black soil.Through real-time PCR analysis,a significant decrease（41.66%,36.34% and 47.99%,respectively）on total bacteria population was only observed in saline-alkali soil treated by 0.5,1.0 and 2.0 mg g-1 nZnO.Meanwhile,pyrosequencing analysis revealed that the samples of saline-alkali soil treated with nZnO showed higher variance in their bacterial community composition.Specifically,relative abundance of Bacilli class increased whereas Alphaproteobacteria and Gammaproteobacteriaclass decreasedinsaline-alkali soil treated withnZnO,but not changed in black soil.The results suggested that MO-ENPs addition could influence soil enzyme activities and change soil bacterial community.And soil type was a key component dictating MO-ENPs effect on the bacterial communitycomposition and size.These findings are of great help towards building a comprehensive understanding of the potential environmental risks of MO-ENPs.