Effect Of ZnO Nanoparticles On The Growth And Development And Zinc Uptake Of Hibiscus Syriacus L.

Hibiscus（Hibiscus syriacus L.）is a deciduous shrub or small tree of Malvaceae.It is an ornamental plant with edible,medicinal,ornamental and ecological values.As more and more nanotechnology is used in agriculture,nanotechnology has great potential to change traditional agricultural practices,and the application of nanochemicals to enhance the growth and physiological properties of plants is a future application trend.In this study,the effects of different particle sizes and concentrations of ZnO NPs and different treatments on seed germination,seedling growth,color parameters and petal characteristics of H.syriacus were investigated by seed soaking and foliar application of ZnO NPs.The feasibility of ZnO NPs to promote seed germination of H.syriacus and whether it can be used as a more efficient Zn fertilizer or Zn supplement to promote the physiological growth of H.syriacus and provide new applications for the management and application its germplasm resources and enhance the edible and economic value.The results of the study are as follows:1.Effect of seed soaking of ZnO NPs on seed germination and seedlings of H.syriacusThree particle sizes（30,50,90 nm）and five concentrations（10,50,100,500,1000 mg/L）of ZnO NPs were used to soak the seeds of H.syriacus.（1）Seed germination:The germination indexes of the low concentration（10,50,100 mg/L）treatments of the three ZnO NPs were significantly higher than CK,while the high concentration（500 and 1000 mg/L）treatments were significantly lower than those of CK.Among the 16 treatments,the germination rate of the N30C50 treatments reached 68.89%,a significant increase of 51.22%compared with CK.（2）Growth characteristics:The low concentrations of the three particle sizes of ZnO NPs all had a certain promotion effect on growth,and the biomass of above-ground and below-ground parts increased,while the high concentrations of ZnO NPs all had toxic effects on H.syriacus,and seedling growth was inhibited,with slow growth of stems and leaves,loss of green leaves,and short and sparse root systems.（3）Physiological characteristics:As the concentrations of ZnO NPs of three particle sizes increased,the soluble protein content,soluble sugar content and SOD activity of seedlings showed a trend of increasing and then decreasing.（4）Photosynthesis:P_nmax,LSP,R_d,G_s,F_v/F_m,qP,ETR and photosynthetic pigment content all showed a trend of increasing and then decreasing with the increase of ZnO NPs concentration in the three particle sizes.（5）Low concentrations of all three particle sizes of ZnO NPs promoted seed germination,seedling growth,physiological characteristics and photosynthesis of H.syriacus,while high concentrations of ZnO NPs produced toxic effects and inhibited the growth of H.syriacus,and the smaller the particle size of ZnO NPs,the more obvious the inhibitory effect was.The treatments with the highest overall score was N30C50 that 30 nm particle size and 50 mg/L ZnO NPs was the best treatment for promoting seed germination,growth and physiological characteristics of H.syriacus2.Effects of foliar application of ZnO NPs on H.syriacus seedlingsFoliar application of three particle sizes（30,50,90 nm）and three concentrations（10,50,100 mg/L）of ZnO NPs and 50 mg/L ZnSO₄ were applied to H.syriacus at the seedling stage for a total of three times.（1）Growth characteristics:Among the 11 treatments,the N30C10,N50C50 and N90C50 treatments performed well and significantly promoted the growth of H.syriacus seedlings,while the 100 mg/L ZnO NPs treatments of all three particle sizes significantly inhibited the growth of seedlings.（2）Physiological characteristics:The soluble sugar,soluble protein content and SOD activity of the N30C10,N50C50 and N90C50 treatments were significantly higher than those of the CK and ZnSO₄ treatments after the three sprays,while the above indicators were significantly lower than those of the CK in the three ZnO NPs treatments at 100 mg/L.（3）Photosynthesis:P_nmax,LSP,R_d,G_s,F_v/F_m,qP,ETR and photosynthetic pigment content increased in the N30C10,N50C50 and N90C50 treatments compared with CK and ZnSO₄ treatments,and photosynthetic pigment content decreased significantly in the 100 mg/L ZnO NPs treatment compared with CK,and light response curve characteristics and chlorophyll fluorescence parameters indicated that seedlings The light response curve and chlorophyll fluorescence parameters indicated that the photosynthesis of seedlings was weakened.（4）The leaf Zn content of all three ZnO NPs showed an increasing trend with increasing concentration,and the smaller the particle size,the more obvious the increasing trend.30 nm and 50 nm ZnO NPs showed higher leaf Zn content than ZnSO₄ treatment.（5）The foliar application of ZnO NPs was more effective than ZnSO₄ in promoting the growth and physiological characteristics of H.syriacus seedlings,and the best foliar application treatment for promoting the growth and leaf Zn content of H.syriacus seedlings was N50C50 that 50 nm particle size and 50 mg/L ZnO NPs treatment.3.Effect of foliar application of ZnO NPs on color parameters and petal characteristics of H.syriacusThe foliar application treatments that significantly promoted the growth of H.syriacus seedlings were selected and three times foliar applications in the pre-flowering stage.Determined the flower color phenotype,physiological indicators and petal zinc content.No significant differences were observed in the flower color phenotypes of H.syriacus in the N30C10,N50C50,and 50 mg/L ZnSO₄ treatments compared with CK.Foliar application of ZnO NPs promoted more significantly the basic nutrients,antioxidant substances,and petal zinc content of H.syriacus flowers compared to ZnSO₄.soluble sugar content of N30C10 and N50C50 increased significantly by 104.85%and 110.80%,respectively,compared to CK,and by 71.45%and 76.42%,respectively,compared to the ZnSO₄ treatment...