Effects Of Three Metal Oxide Nanomaterials On Growth And Rhizospheric Microbial Community Structure Of Rice Seedling

With the wide application of nanomaterials in people's production and life,more and more nanomaterials have spread into the environment and have impacted on the organisms in it.In order to reveal the ecological effects of metal oxide nanomaterials in the environment,the effects of different concentrations of three metal oxide nanomaterials?nSiO₂,nTiO₂ and nZnO?on germination of rice seed were investigated by hydroponic culture.When nSiO₂ was mixed with nTiO₂ and nZnO respectively,the alleviated effects of nSiO₂ on the other two nanomaterials and the toxic mechanism of nTiO₂ and nZnO were discussed.Then three concentrations of the above nanomaterials in soil were applied to rice seedling cultured with pot experiment.The effects of seedling growth,main nutrient absorption,soil fertility and rhizosphere microbial community structure were carried on research.The distribution of Zn in subcellular fractions of rice roots and leaves and the chemical fractions in soil were conducted to further study after treated with nZnO so that it could provide theoretical basis for the environmental ecological effect and toxic mechanisms of metal oxide nanomaterials.The main research results are listed as follows:1.The effects of three metal oxide nanomaterials on rice seed germination:With the increase of nTiO₂ and nZnO concentration in nutrient solution,the root length and shoot length of rice decreased,the inhibition increased,and the maximum inhibition;When the treatment concentration was 1000 mg/L,the inhibitory effect of nSiO₂ on the growth of rice seed roots was not significant,and the treatment of four concentrations of nSiO₂ did not significantly affect the growth of rice seed shoots.The inhibitory effects of 1000 mg/L nZnO on the growth of rice seed roots and shoots were enhanced by different concentrations of three metal oxide nanomaterials,and the inhibition rates were 22.97%and 27.62%.2.The effect of nSiO₂ treatment with nTiO₂ or nZnO on the growth of rice roots and shoots:The inhibition effect of combined treatment of nSiO₂ and nTiO₂ on the growth of rice roots and shoots was significantly less than that of single treatment of nTiO₂ and single treatment of nSiO₂?not significant?.The root length and bud length were 1.31 times,1.20 times,1.21 times and 1.16times of the 2000 mg/L and 1000 mg/L nTiO₂ treatment.The inhibitory effect of nSiO₂ combined with nZnO on the growth of rice roots and shoots was significantly lower than that of nZnO alone,and the root length and bud length were 1.15,1.15,1.13 and 1.20 times of those of nZnO alone treatment at 2000 mg/L and 1000 mg/L,but significantly higher than that of nSiO₂ alone.3.The effect of agglomeration on toxicity of nTiO₂ and nZnO:The inhibitory effect of agglomerated nTiO₂ treatment on root growth of rice was significantly smaller than that of dispersed treatment,and the inhibitory effect on buds was also reduced.The effect of agglomeration treatment on nZnO toxicity was not significant.4.Determination of Zn²⁺concentration in nZnO treatment with different concentrations:as the concentration of nZnO in the dispersion increased,the concentration of Zn²⁺dissolved gradually decreased.After 7 days of standing,the dissolved Zn²⁺was significantly increased.5.The effects of metal oxide nanomaterials on physiological and biochemical indexes of rice seedlings:fresh weight,dry weight and plant height of rice seedlings treated with 0.5 mg/g nZnO increased by 24.95%,12.42%and 9.71%.The fresh weight,dry weight and plant height of rice treated with 1,2 mg/g nZnO decreased.The dry weight and plant height of rice treated with 2 mg/g nSiO₂ decreased significantly by 15.56%and 7.12%.The content of N in rice treated with 0.5 and2 mg/g nSiO₂ was significantly decreased.The content of P in rice treated with three concentrations of nZnO increased by 12.75%-20.59%?P<0.05?,and the content of K in rice decreased by 13.08%-17.08%?P<0.05?.Compared with the control,the SOD activity of rice seedlings treated with nSiO₂and nTiO₂ increased by 2.41%-17.44%;The SOD activity of 0.5mg/g and 1 mg/g rice seedlings treated with nZnO decreased by 22.76%and 13.99%?P<0.05?;The concentration of?2 mg/g?nZnO treated SOD activity increased by 10.33%?P<0.05?.The POD activity of rice seedlings treated with nSiO₂ and nZnO increased by 14.40%-36.70%?P<0.05?.The POD activity of rice seedlings treated with 0.5 mg/g nTiO₂ was the highest and the difference was significant?P<0.05?.The other nTiO₂ treatments did not significantly differ from the control.The treatment of three different concentrations of nanomaterials significantly increased the CAT activity of rice seedlings,and the effect of nZnO treatment on the CAT activity of rice seedlings was more obvious than that of nSiO₂ and nTiO₂ treatments.6.The effect of adding metal oxide nanomaterials on soil fertility:Soil pH and organic matter content decreased after treatment with three concentrations of nSiO₂ and nTiO₂,and soil available N and available P were significantly increased after treatment with 1,2 mg/g nSiO₂.Soil available P and available K contents decreased by 3.57%-7.36%and 3.12%-13.82%respectively after nZnO treatment at three concentrations.The soil acid phosphatase and soil catalase activities were significantly inhibited?inhibition rate 7.37%-17.49?and significantly promoted?promotion rate4.81%-16.00%?after treatment with all nanomaterials.At the same time,different concentrations of nZnO were treated.Soil sucrase and urease activities were significantly inhibited,while soil invertase activity was enhanced in different concentrations of nTiO₂.7.The effects of adding metal oxide nanomaterials to soil on soil microbial community structure:Three nanomaterials treatment will cause changes in soil community structure;The addition of nanomaterials significantly reduced the number of soil microorganisms and microbial species?except for 0.5 mg/g nSiO₂ treatment?.The microorganisms in the 10 treatments mainly belong to the following 11 phylum:Proteobacteria,Acidobacteria,Chloroflexi,Bacteroidetes,Actinobacteria,Firmicutes,Gemmatimonadetes,TM7,Verrucomicrobia,Nitrospirae,Cyanobacteria,however,the proportion of microorganisms treated with different conditions was different in each phylum.The effect of nSiO₂ and nTiO₂ treatment on soil microbial richness was not significant,but it had a great impact on the composition of soil microbial community,especially the high concentration of nSiO₂ and low concentration of nTiO₂ treatment.Both nZnO treatment reduced soil microbial richness,and low and high concentration nZnO treatment also reduced soil microbial Alpha diversity.At the same time,medium and high concentration of nZnO treatment also had a significant impact on soil microbial community composition.8.The distribution of zinc in soil and rice after treatment with different concentrations of nZnO:The content of Zn in rice leaves increased with the increase of nZnO concentration in soil.The zinc content in rice roots was higher than that in leaves.The main distribution of Zn in the cell wall and cell fluid of rice roots and leaves,and the content of Zn in the organelles is relatively low.The nZnO added to the soil mainly exists in the form of Fe-Mn oxide.The content of total zinc and available zinc in the soil increases significantly with the increase of nZnO concentration in the soil.The proportion of bioavailable zinc?available zinc and carbonate exchange zinc?in the soil also increases gradually,but the proportion of residual zinc decreases.