Cold-Resistance Analysis And Suitability Of Cultivation Areas For D.odorifera Seedlings In Southern Zhejiang

D.odorifera T.Chen,a special redwood plant in China,can be damaged by low temperature,limiting its introduction to the north.In this paper,the effects of paclobutrazol treatment mimicking low temperature on the morphology and physiological characteristics of the seedlings were studied for their resistance.The effects of different temperatures on the wintering of D.odorifera were specifically examined;and the wintering habitats of the seedlings in the experimental sites in south Zhejiang was further assessed.The main findings are:(1)The height-to-diameter ratio and shoot-to-root ratio decreased under paclobutrazol treatments,while lignification of seedlings increased.We found that soluble sugar content,soluble protein content and SOD activity of the leaves increased,but MDA and relative conductivity decreased.The top three treatments,according their importance,are 1000 mg/L soil application,1000 mg/L leaf spray,and 2000 mg/L soil application.The most significant leaf spray time treatment appeared at 1500mg/L on November 30.For practical applications,we recommended the foliage be sprayed with 1000-1500 mg/L paclobutrazol solution in conjunction with wintering actions during mid-to-late November for growth promotion and resistance maintenance.(2)At the three field experiments in Yueqing,Wenzhou and Cangnan,soil water content,capillary water holding capacity and capillary porosity increased while soil bulk density decreased;soil nutrient content was significantly higher than that under "no shading" treatment.With low temperature manipulations,the soluble sugar content of seedlings under the shading and no shading treatment was 54.39%and 10.27%(p<0.05),respectively.The soluble protein content of Wenzhou and Cangnan was increased by 75.32%and 51.61%.p<0.05),the SOD activity was increased by 1.38%,45.24%,and 13.75%(p<0.05)respectively under the shading and no shading treatments,respectively.(3)The damage level of D.odorifera was positively correlated with the latitude and altitude of the plantation site,and negatively correlated with forest age,the lowest temperature and the shading.The correlation from shading(0.28)was significantly negative(p<0.05).(4)Delineating suitable habitats for D.odorifera in southern Zhejiang need attentions in three broad aspects:I Suitable planting areas(>-4℃)cover most parts of southern and northern Cangnan,northeastern Pingyang,eastern Ryan,Ouhai District of northern Wenzhou,Lucheng District and the eastern part of Longwan District,Yuhuan and southern Yueqing;Ⅱ Area with extreme low temperature(-6～-4 ℃)should not be promoted,including southern to central Cangnan,central and western Pingyang,central and western Ryan,northwestern Bohai,Lucheng District,southern Yongjia,and southeastern Yueqing;Ⅲ The area falling on difficult-for-introductions(temperature<-60 C)includes northwestern Cangnan,southwestern Pingyang,Taishun and Wencheng,northwestern Ruian-LuchengYongjia-Yueqin.Finally,the plantation bases should be properly developed in the moderately-cultivated areas.The areas under Ⅲ conditions should be carefully examined and tested prior to gradual expansions as they are not recommended for introduction.