Study On Freezing Resistance Of Introduced Evergreen Broad-leaved Trees In Nanjing

Evergreen broad-leaved trees distribute in the subtropical warm and moist regions of Yangtze River Valley in China. They are the main elements of subtropical forest vegetation. Therefore, temperature as limitation to introduce to higher latitude regions for evergreen broad-leaved trees is one of the important environment factors. In order to change single and inanimate phenomenon of landscape architecture (LA) in the north in winter, by various microclimatic factors, introducing, taming and applying evergreen broad-leaved trees are increasing concerned by constructors of LA. In recent years, there are much fewer evergreen broad-leaved trees; and their expansion of new species is difficult in the LA of higher latitude regions. Introduced trees have not predicted effect, even some species result in economic loss because of freezing of winter. The main reason is that comprehensive and systemic research and evaluation of evergreen trees were lack in wintering compatibility and principle of freezing resistance in the north. In order to put forward scientific consulting for forecasting, choosing, cultivating and applying of subsequently introduced evergreen broad-leaved trees, the article firstly carries on study on wintering compatibility, physiology and ecosystem research of freezing resistance of some evergreen broad-leaved trees in Nanjing of the north subtropics. The main results indicate:1. Morphological observation of evergreen broad-leaved trees for compatibility of winterWintering compatibility of 24 evergreen broad-leaved trees was observed in the introduced region, trees leaves of different freezing resistance appeared different freezing symptoms. Leaves of stronger freezing resistance remained light and green; and leaves layers of weaker freezing resistance appeared brown and dead spot under different low temperature, the former was as Ilex latifolia, the later was as Elaeocarpus decipiens. Some trees appeared symptom of vast effoliation, dead sprig and bud. The deadly freezing period of most trees was coldness of spring.2. Relationship between the temperature and distribution of evergreen broad-leavedtreesOrder of freezing resistance of 24 evergreen broad-leaved trees was well identified by cold indexes, the most'suitable scope and the whole scope, ability of freezing resistance appeared stronger with lower CI and BI of plants. The results indicated that tendency of freezing resistance of these trees by two ecological indexes was consistent with their wintering compatibility in the introduced region. For example, wintering compatibility of Cyclobalanopsis glauca was stronger; the same was that CI and BI of it were lower.3. Electric conductivity changes of the organization of evergreen broad-leaved trees under different low temperatureLow temperature can break osmosis of cell membranes; and cause penetration of electrolyte. Compared with ck, increment of electric conductivities of leaf and sprig was homologous under a series of simulated low temperature; and their electric conductivities were increased greatly along with continuing of the low temperature. Electric conductivities of leaf and sprig were combined with Logistic, lethal temperature 50(LT50) which were calculated could correctly indicate freezing resistance of these trees in quantitative determination. The results of freezing resistance of two nourishment organizations are mostly consistent, and almost corresponding to observation of wintering in the introduced region.4. Content changes of soluble sugars and proline of 6 evergreen broad-leaved trees leaves under different low temperatureRegular changes of the contents of soluble sugars and proline appeared in leaves of 6 trees under low temperature treatment. The contents of soluble sugars and proline of leaves were increased largely with decreasing of the temperature; and increment range of stronger freezing resistance was much greater than that of weaker freezing resistance. The results indicated changes of the contents of soluble sugars and proline could be a characteristic index for freezing resi...