| Loropetalum chinense var. rubrum is an evergreen shrub that belongs to Hamamelidaceae. Because of the characteristics of its graceful branches, colorful leaves, long flowering period, a large number of flowers, easy reproduction, rapid growth and so on, it already becomes a fine specie and has a unique ornamental value. It is widely used in landscaping due to the features of strong ecological adaptability, resistance to cutting, easy modeling.The influence of sulfur dioxide on L. chinense var. rubrum was studied in this experiment with 60 days fumigation and 30 days recovery treatment. There were four concentrations of SO2 treatments, including 0 mg/m3、2.86 mg/m3、7.14 mg/m3、14.28 mg/m3, to analysis the physiological impact of SO2 and restoration capabilities of L. chinense var. rubrum by observing the morphology and physiological characteristics change. The conclusion could provide a theoretical basis for the introduction and cultivation and garden applications of L. chinense var. rubrum and provide a favorable reference for resistance to SO2 pollution. The results were as follows:1. With the increase of the concentration of SO2 and fumigation time, L. chinense var. rubrum leaf damaged area increased gradually.2. After 60 days of stress,2.86 mg/m3 and 7.14 mg/m3 two SO2 concentrations had no significant effect on the total content of chlorophyll (P> 0.05), but had some impact on chlorophyll a/b of L. chinense var. rubrum. After 30 days of recovery, there was a significant difference on the total content of chlorophyll and chlorophyll a/b between the control and treatments (P> 0.05) under 14.28 mg/m3 concentrations of SO2 treatment.3. After 60 days of stress, with increasing concentrations of SO2, the photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) of L. chinense var. rubrum decreased, and CO2 concentration intercellular (Ci) increased. After 30 days of recovery, there was no significant difference (P> 0.05) on photosynthetic parameters between the control and treatments under 2.86 mg/m3 concentrations of SO2 treatment. And under 7.14 mg/m3,14.28 mg/m3 concentrations of SO2 treatment, there was a significant difference (P <0.05)on the photosynthetic parameters between the control and treatments, Pn, Gs, Tr, Ci was 48.56%,59.89%,106.97%,39.95% of the control,respectively.4. After 60 days of stress, with increasing concentrations of SO2, the maximum fluorescence (Fm), maximal photochemical efficiency (Fv/Fm), and potential activity (Fv /Fo) of L. chinense var. rubrum decreased, and initial fluorescence (Fo) increased. Under 14.28 mg/m3 concentrations of SO2 treatment, Fm, Fv/Fm, and Fv/Fo was decreased by 40.66%,30.92%,71.91%, respectively. Fo increased by 45.89% compared with the control. After 30 days of recovery, the Fm, Fv/Fm, Fv/Fo rised up and close to the control under 2.86 mg/m3 concentrations of SO2 treatment,but under 7.14 mg/m3 and 14.28 mg/m3 concentrations of SO2 treatment increased to a lesser extent, still significantly lower than the control (P<0.05).5. After 45 days of stress, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activity increased with increasing concentrations of SO2. After 60 days of stress, POD and CAT activity decreased, SOD activity increased under 14.28 mg/m3 concentrations of SO2 treatment. In recovery stage, SOD, POD and CAT activity decreased. SOD, CAT activity returned to the control, however, SOD activity was significantly higher than the other treatments (P<0.05) under 14.28 mg/m3 of SO2 treatment.6. In recovery stage, the proline (Pro), soluble sugar content (SS), soluble protein (SP) were increased with the SO2 concentration and stress time increasing. After 30 days of recovery, Pro and SS decreased to the control, and SP was significantly higher than the control (P<0.05) under 2.86 mg/m3 of SO2 treatment. Pro content was 5.66 times of the control under 14.28 mg/m3 of SO2 treatment.7. After 60 days of stress, malondialdehyde (MDA) content in various concentrations reached a maximum. After 30 days of recovery, MDA content returned to the control under 2.86 mg/m3 of SO2 treatment. However, the MDA content under 14.28mg/m3 concentrations was 1.28 times of the control.8. Following the increase of SO2, the sulfur content of leaf of L. chinense var. rubrum increased. After 60 days of stress, the sulfur content under 2.86 mg/m3,7.14 mg/m3,14.28 mg/m3 was 2.50 times,4.23 times,6.11 times of the control,respectively. In recovery stage, sulfur content decreased with increasing of recovery time. After 30 days of recovery, the sulfur content was 1.65 times,2.89 times,3.72 times of the control, respectively.According to all indexes discussed above, indicated that there were some influences on leaf morphology, photosynthesis, physiological effects of L. chinense var. rubrum under 2.86 mg/m3 and 7.14 mg/m3 of SO2 treatment. In a short term, L. chinense var. rubrum had some repair functions, and it could resist and adapt to SO2 pollution through adjusting a variety of substances under SO2 concentrations below 7.14 mg/m3. However, L. chinense var. rubrum leaf blades appeared injury symptoms under 14.28 mg/m3 of SO2 treatment, and its physiological functions could not be fully restored to normal levels through its own restoration in a short time. |
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