A Study On The Ability Of Resistance To Heavy Metal And Cold Stress Of Landscape Trees

Nanjing is located in the north of subtropics.The typical vegetation of zonality is evergreen and deciduous broadleaved mixed forest with a deciduous broadleaved forest base.The ever-green trees is important to improve landscape in winter. At the present time, the tree species , especially shade-trees in garden are singular, and the landscape is flat.So,it is important to find evergreen tree species which can adapt the soil and climate of Nanjing and increase variety of plants in garden. The purpose of this paper is to study the ability of resistance to heavy metal and cold stress of ?landscape trees, for guiding the choice of tree species and introduction in urban planting. Shade-trees , the main tree species in load planting,are touched by Pb and Cd easily.So, in this paper,four tree species of 1-age,which have high ornamental value and can be shade-trees, were selected for this experiment. The purpose is to study the physiological and ecological effect of four tree species on the Pb and Cd stress in the soil, and to overally evaluate the heavy metal resistance of the trees,for guiding the choice of tree species in urban planting. The results have shown that the harmfulness of lesves under the stress of different Pb and Cd concentrations is effected by concentration main effect and tree species×concentration , tree species×concentration×time interactive effect. On basis of variance analysis , multiple-factor comparison (SPSS11.5)and overall evaluation by subordinate function method,the resistance of four tree species to Pb stress could be ordered as : Cinnamomum longepaniculatum >Michelia platypetala>Manglietia chingi >Michelia foveolata . The part tree species of Magnoliaceae are large evergreen broadleaved trees,having a fine poise, exuberant foliage and strong scent of flowers. It has a bright prospect that these tree species should be tree species especially shade-trees in urban planting.The success of intro-duction Magnoliaceae tree species in the north of subtropics is up to the cold resistance. Five of different aged Magnoliaceae tree species and one of different aged Aquifoliaceae tree species were selected to study the cold resistance under different low temperature to guide naturalizing and cultivating in Nanjing,and the relative electric conductivity in leaves of the trees were determined.The semilethal temperature of the trees were got from Logistic equation. The results showed that the semilethal temperature of the trees in the end of Dec.2003 was lower than that at the beginning of Sept.2003.That is to say,the cold resistance of these trees had raised by exercise in winter. The difference of the semilethal temperature of the trees at the beginning of Sept.2003 was slight(-5.03～-6.08℃). That is to say, the cold resistance of these trees were close.But the difference of the semilethal temperature of the trees in the end of Dec.2003 was remarkable(-9.86～-13.48℃). The difference of the cold resistance of different tree species raised by exer-cise in winter. The results showed that the semilethal temperature of the trees were below -11℃except 3-aged Michelia chapaensis, Michelia foveolata (little higher than -10℃) by exercise in winter. With the increase of the age of trees , the cold resistance increase. The cold resistance of the trees could be ordered as : Michelia maudiae, Michelia platypetala, Manglietia yuyuanensis>Ilex latifolia>Michelia foveolata, Michelia chapaensis. At the same time,the article inquiried into the successful possibility of introduction of these trees in Nanjing .