Research On The Variation Mechanism Of Autumn Leaf Characteristics And Family Evaluation Of Landscape Application Value Of Sassafras Tsumu

Sassafras tsumu?Hemsl.?Hemsl,a deciduous species of Sassafras Trew in the family Lauraceae,is an excellent ornamental plant that has high and straight stem trunk,wide crown over forest canopy,various leaf shapes,beautiful yellow flowers in early spring and colourful leaves in the fall.In addition,it is a high-grade timber species with pale yellow wood and beautiful wood figure.It has been choiced as one main species in mountainous forest landscape reconstruction engineering.In order to understand the genetic background of selective breeding and autumn leaf color change mechanism of S.tsumu,the leaf phenotypic and genetic diversity,the physiological process and environmentive effects of leaf color changes were studied in this paper.As the analyzation results of genetic variation of seedling growth and autumn leaf characteristics between families,their value as better planting variety in mountainous landscape recongstruction engineering were evaluated.The main results are as follows:1)The phenotypic traits of S.tsumu at different altitudes in Tianmushan Mountain,Zhejiang province vary at different degrees,among which the populations of leaf area?AR?were varied significantly.However,the specific leaf area?SLA?,leaf dry weight,the ratio of leaf length to width,chlorophyll content and nitrogen content among these populations had extremely significant difference;AR had a significant positive correlation with SLA?P<0.01?,but significant negative correlation with the ratio of leaf length to width?P<0.05?.SLA had a significant positive correlation with leaf dry weight?P<0.01?.Significant positive correlation?P<0.01?was found between nitrogen and chlorophyll content of the leaves.Besides,linear regression between leaf traits and temperature showed that AR,SLA,chlorophyll content and nitrogen content decrease with temperature reduction,while leaf dry weight and the ratio of leaf length to width increase with the reduction.2)Expected and observed heterozygosities of natural population of S.tsumu were 0.84 and 0.61 respectively.Gene flow?Nm?reached 3.63,which means that high genetic diversity existed in the natural populations in Tianmushan Mountain.According to Shannon index?I?,the diversity of S.tsumu at middle altitudes?500-800m?was higher than that at low?200m?and high altitudes?1100-1400m?.The coefficient of genetic differentiation and AMOVA analysis showed that genetic variation of S.tsumu was mainly distributed within populations.Genetic structure analysis indicated that S.tsumu populations in Tianmushan Mountain were divided into two groups,high altitudes populations and middle-lower altitudes populations.The differences in genetic distance of S.tsumu populations at middle and low altitudes revealed that natural reserve areas play a positive role in the protection of species diversity.3)The leaf senescence process of S.tsumu included 3 phases.The preparation phase was from late September to early October.The slow phase was from late October to early November.The last phase started from late November to defoliation.The value of leaf color,pigment and nutrient contents of S.tsumu at the preparation and slow phases were greatly different from those at the last phase.Moreover,from the preparation till the last phase,the change trends of chlorophyll and carotinoid contents were opposite to that of anthocyanin content.However,nutrient content decrease in all phases.The value a* of leaf color value represents the redness of leaves.The greater the value a* got,the lower the chlorophyll content in the leaf was,while the greater the anthocyanin content was.Anthocyanin content was inversely proportional to nitrogen content,while carotinoid content was directly proportional to phosphorus content.In addition,When nitrogen content increased,its re-utilization efficiency decreased.On the contrary,when phosphorus content increased,its re-utilization efficiency increased.4)Light quality had different influences on leaf color,pigment content and net photosynthetic rate.Red light could delay leaf color change and promote chlorophyll synthesis.Blue light and purple light accelerated the leaf color change,promoted anthocyanin synthesis and the degradation of chlorophyll,and delayed the decomposition of carotenoids.Comparing to blue and purple lights,red light could increase the net photosynthetic rate of S.tsumu.5)Water stress also had impact on leaf color,pigment contents and net photosynthetic rate.A soil water content of 40% or 100% accelerated the leaf color change,while a soil water content of 60% or 80% was favorable to the accumulation of carotenoid and anthocyanin synthesis.A soil water content of 60% or 80% was more favorable to the growth,the formation and reserve of nutrients of S.tsumu than a soil water content of 40% or 100%.6)AHP was applied to evaluate and select fine autumn leaves of S.tsumu.The results showed that the twenty families of excellent ornamental autumn leaves had a order as follows based on the value of integrated quantitative evaluation : CL₁F>CLF₁₄>NL₄>CL₃D>CL₂D>ZJJ >NP₁>NP₂>NL₁>NL₂>CL₁₂>CL₇A>NL₃>NP₃>JD>FY₉>LY>ES₅>YD>HD?...