| As an important part of landscaping, ground cover plants’ecological adaptability had been paid attention by people.In recent years,the soil heavy metal pollution had be came more and more serious, the research of ecological adaptability could help people to select and configure the garden plants scientifically, as well as exerted its maximum ecological and economic benefits, to provide scientific basis for the selection and appli cation of plant in the urban landscape greening.Potentilla sericea was a wild ground co ver with ornamental value and its cultivation and management was simple, at the same time,it had high value on application in landscape.In this paper, Potentilla sericea was treated as experimental materials, different concentration gradient of heavy metal lead a-nd cadmium stress was simulated,the mechanism of Pb Cd stress was studied from 3 aspects:the structure of plants, physiological and biochemical characteristics and photos ynthetic characteristics.The results show that:1. Different concentrations of heavy metals such as lead, cadmium stress the ultrastructure of Potentilla sericea produced certain effect and the concentration of the impact. When it was under the treatment group Pb300, the chloroplast was in a cyst, and the center of the cell was arched, the structure of chloroplast lamellae appeared loose, but the structure was quite clear.; mitochondrial inner ridge diameter became larger, and the arrangement of the state was loose. In the treatment group Pb600, a large number of starch grains appeared in the chloroplast, which occupied most of the space of the chloroplast, the degree of chloroplast osmiophilic increased, the number of it boomed, its volume was huge, grana layer expanded, even dissolution, grana stack extent declined, the lamellar appeared irregular arrangement wave shape, the mitochondrial bilayer membrane appeared partially dissolved, the number of ridges decreased;the treatment group Pb2000,the chloroplast bilayer membrane system disintegrated, including the logistics distributed, lamellae and grana disarranged and black precipitate, finally disintegrated, mitochondrial vacuolization was serious. When it under the Cd2+stress, in the treatment group,the volume of chloroplast was enlarged, chloroplast stroma lamella is loose, thylakoids swell vesicles, the outflow of the chloroplast stroma and chloroplast membrane system crash. The mitochondria of Control group have double membrane integrity, crest in small volume, inclusions, dense. With the intensive of Cd2+, the mitochondria of treatment group has bigger volume,and the number of the crest was decreased, eventually mitochondrial cavitation on the whole.2. Potentilla sericea under lead stress, with the time prolonging, malondialdehyde content, proline content, chlorophyll content, SOD activity down after rising first, soluble protein content decreased. The treatment concentration of the peak time. Concentration in 300 mg/kg and 600 mg/kg can grow slowly; 2000 mg/kg plant above-ground parts completely dry and dead. Under heavy metals Cd2+stress, along with the extension of time, the content of chlorophyll, soluble protein content is on the decline;The content of proline and malondialdehyde rise, SOD activity lowered after the first. Concentration is 0.5 mg/kg,1 mg/kg can normal growth; 2 mg/kg,5 mg/kg of the plant, the phenomenon of the black dry stems, leaves yellow dry; 10 mg/kg of the plant parts completely dry, Browning, death on the ground.The study showed that plants with low concentrations of heavy metals could maintain normal growth for a long time, and high concentrations could cause the leaves to die.3. The net photosynthetic rate,the stomatal guide, and the transpiration rate of Potentilla sericea, with the extension of time and the concentration of lead, cadmium increases, showed a downward trend, the intercellular CO2 concentration was gradually rising trend. The trend of the changes of Pn, Gs and Tr was opposite to that of Ci in Potentilla sericea. So that, the declining of net photosynthetic rate mainly non stomatal limitation.4. After 50d of lead treatment and 25d of cadmium treatment, potential PSII activity (Fv/Fo)and the maximal photochemical efficiency (Fv/Fm) decreased with the the stress concentration decreased,Treatment group Pb2000photochemical efficiency decreased co-mpared with the control group 38.63%, Cd10 treatment group compared with the contr ol group decreased by 74.26%,the photochemical efficiency (Fv/Fm) decreased gradually with the increase of the concentration, showed that heavy metal stress could lead to t he inactivation of PSII reaction center.5. Through comprehensive comparison test shows, Potentilla sericea can survive within 600mg/kg of the lead concentration and 10mg/kg of cadmium concentration, but slow growth. This study basically defined the heavy metal tolerance range of Potentilla sericea in order to provide a theoretical basis for the screening and appication of metal tolerant plants in landscape. |
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