Study On Cold Resistance Of Two Color-leafed Plants Of Physocarpus Opulifolius Cultivars

Physocarpus opulifolius 'Lutein' and Physocarpus opulifolius 'Summer Wine' are two species of ornamental flowering shrub Rosaceae Physocarpus. They were introduced from abroad in recent years to enrich the landscaping virescence. It has been proved that the two color-leafed tree species are able to be wintering in the open field in parts of North China. But in Harbin region, they haven't been applied widely due to the limit of the low temperature. This paper studies on the cold resistance of the two color-leafed tree species, Physocarpus opulifolius 'Lutein' and Physocarpus opulifolius 'Summer Wine', in order to provide a theory basis for their introductions and applications to the landscape in Harbin region.This paper took the one-year-old detached dormant branches of the two species as the experimental materials. After artificial low-temperature stress, the physiological and biochemical indexes were determined and analyzed. The cold resistance characteristics of the two color-leafed tree species were systematically investigated by the integrating use of variance analysis, main component analysis and cluster analysis of parameter R. The major results were summarized as follows:1. The relative conductivity, MDA content, free proline content, soluble sugar content and soluble protein content of the two color-leafed tree species rise along with the increase of the stress time under artificial low-temperature stress. The SOD and POD activities are raised in the first stage, and then decrease. The budding rate of frozen branches gradually reduces along with the increase of stress time. According to the Logistic equation, the half lethal temperature of Physocarpus opulifolius 'Lutein' is -43.1℃～-40.8℃, and Physocarpus opulifolius 'Summer Wine' is -44.7℃～-41.4℃, which agrees with the results of the growth recovery experiment very well. The sustained low temperature stress causes the increases of damage degree and reductions of cold resistance abilities in the plants.2. With the decrease of the temperature, the changes of physiological and biochemical indexes on the two color-leafed tree species are basically the same at the same stress time. The relative conductivity and soluble sugar content both increase. MDA content and soluble protein content rise in the first stage, and then decrease. The SOD, POD activities and free proline content have the variation trend of a "S" type curve, which means the curve increases and decreases alternately. It peaks at -25℃and -35℃respectively, but still higher than the levels of contrast. The budding rates of frozen branches in the growth recovery experiment decreases as the temperature gets lower. Furthermore, the budding rates of Physocarpus opulifolius 'Summer Wine' are higher than the ones of Physocarpus opulifolius 'Lutein', which agrees with the result of the physiological and biochemical indexes. The relative conductivity and MDA content of the two color-leafed tree species exhibit a negative correlation with the plants'cold resistance ability. On the contrary, the activity of protective enzymes and osmotic substance content exhibit a positive correlation with the cold resistance ability.3. By the comprehensive evaluation, the cell membrane permeability, lipid peroxidation, the activity of protective enzymes, the osmotic substance and the budding rate of frozen branches are proved to be effective as the main indexes of cold resistance ability. Moreover, the budding rate and the relative conductivity can be used as the single cold resistance index of the two colored plants. By holistic marking, the cold resistance ability of Physocarpus opulifolius 'Summer Wine' is proved to be stronger than the Physocarpus opulifolius 'Lutein', which agrees with the results of physiology experiment.4. By the phenophase and the growth rhythm observation, the two color-leafed tree species to be introduced to Harbin region can be normal growing development, the leaf colour, flower types and other ornamental characteristics remain unchanged as the origin, annual growth is slightly lower than the origin. According to the artificial low-temperature stress experiment, the two color-leafed tree species are able to resist -40℃low-temperature with strong cold resistance ability. As the history minimum temperature was -38.7℃in Harbin, the two color-leafed tree species have certain adaptability to the low-temperature of Harbin and can be wintering in the open field. In conclusion, it is feasible for the two color-leafed tree species to be introduced to Harbin region as garden tree species.