Effect Of Copper Oxide Nanoparticles On Properties And Microbial Ecosystem Of Paddy Soil

Rapid development of nanotechnology has enabled the mass production of metal nanoparticles (MNPs). The wide use of MNPs will inevitably increase their environmental release into soil, which consequently raises concerns about their environmental impacts and ecological risks. Paddy soil is the most typical and widespread agricultural soil in China, and the quality of paddy soil is critical to the national economy and people’s livelihood. To evaluate the ecosystem and environmental risks of MNPs and promote the sustainable development of nanotechnology, CuO nanoparticles (CuO NPs) were chosen to study their speciation transformations in the flooding-drying paddy soils, and the impacts on the soil properties as well. Furthermore, we focused on the toxicity mechanisms of MNPs to microbes and the regulation of CuO NPs to rhizosphere microbial communities and their ecological functions. Primeray results were summarized as follows:(1) We demonstrated the transformation rule of CuO NPs in paddy soils and their impacts on soil properties and constituents. CuO NPs dissoluted ions or combined with soil components immediately after applied into the soils. The CuO NPs tended to develop into complexing or precipitation forms after long-term flooding, and the transformations of CuO NPs depend on the different properties of soils. Moreover, the metal oxide character of CuO NPs could change the environmental indexes, including pH, Eh and Ec, but not the CEC and adsorption capacity of soils. Highly exposure dose of CuO NPs could change the content and component of soil constituents, including minerals, organic matters and microbes, which probably induced by the microbial changes influenced by CuO NPs. Furthermore, organic matters could alleviate the effects of CuO NPs on soils.(2) We compared the distinctive effects of TiO2 NPs and CuO NPs on microbes and their correlations with the available forms of MNPs as well, and confirmed the toxic mechanism of MNPs to microbes in flooded paddy soil. Both TiO2 NPs and CuO NPs were observed to induce distinctive perturbations on the microbes in flooded paddy soil. While TiO2 NPs showed complicated effects on soil enzyme activities and slight impacts on soil microbial biomass and community structures, an overall reduction in the soil microbial biomass, enzyme activities and microbial community composition and biological diversity was observed with the amendment of CuO NPs. The reduced impacts of TiO2 NPs were mainly induced by the particles themselves, whereas the heavy metal characteristics of CuO NPs with high dissolution and bioavailability in flooded paddy soil was demonstrated to induce major toxicity to soil microbes. Meanwhile, elevated stress ratio values suggest that CuO NPs may also indirectly affect soil microbes by changing the nutrient bioavailability.(3) High throughput sequencing technology Miseq was used to study the dynamics of bacterial community in the rhizosphere soils under CuO NPs treatment. We found that the response of different genus to CuO NPs depended on different properties of CuO NPs, and also, we demonstrated the eco-system perturbation induced by CuO NPs. Most bacterial phylums, especially for Chloroflexi, were strongly inhibited by the metal toxicity of CuO NPs. Meanwhile, the nitrogen-cycling involved bacteria were highly sensitive to CuO NPs. However, some other elemental cycling related genus, including cellulose degradation, iron reduction and sulfur reduction bacteria, gradually developed into dominant genus due to the particle properties of CuO NPs. CuO NPs accelerated the attenuation of bacterial diversity and the succession of community during the flooding periods, thus the homeostasis of rhizosphere microbial ecosystem was severely affected by CuO NPs. Moreover, the rhizosphere environment would adjust the microbial effects of CuO NPs.(4) We figured out the coupling regulation of functional microbes under CuO NPs treatment, hence changed the progress of important elements cycling in paddy soil ecosystem. The relative high surface area of CuO NPs facilitated the contact between the microbial cells and the cellulose in soils, resulting an increasing growth and activity of cellulose degradation bacteria, and the production of dissolved organic matters as well. Subsequently, the massive dissolved organic matters would accelerate the growth of iron reduction genus and the activity of methanogens by supplying carbon sources. Moreover, CuO NPs may also participate into the electron transfer process between cells, thus increased the production of CH4 and Fe (Ⅱ) induced by functional microbes. Nitrogen-cycling involved microbes were sensitive to CuO NPs, but different genus make responses differently, hence the emission of N2O was not effected by CuO NPs in this study.