Study On The Variation Of Wood Properties And Optimal Selection Of Chinese Fir Families And Clones

Chinese fir(Cunninghamia lanceolate[Lamb.]Hook.),the most important conifer species for timber production and has wide geographic distribution in southern China.It is an important fast-growing wood species accounting for 20–30%of the total commercial timber production which has important commercial significance for timber and pulp industry.The study of wood anatomical properties,wood physical properties,wood chemical properties and wood mechanical properties is of great significance for efficient wood processing,utilization and forest breeding.In this paper,26 Chinese fir families and4 Chinese fir clones in Kaihua forest farm in Zhejiang Province were selected as experimental materials.Referring to relevant national standards,wood structural factors such as cell morphology,wood physical properties wood mechanical properties and cell wall ultrastructure of Chinese fir,including microfibril angle,crystallinity and three major chemical elements content of cell wall,were measured by optical microscope,X-ray diffraction(XRD),universal strength testing machine and UV spectrophotometer,the growth characters,anatomical,physical,mechanical and chemical indexes of Chinese fir from 26 families and 4 clones were measured,the radial variation of wood properties of Chinese fir families and clones was systematically analyzed as well.At the same time,the transformation years of juvenile wood and mature wood of Chinese fir were determined by hierarchical K-means clustering method,and the differences in anatomical,physical and chemical properties between juvenile wood and mature wood were compared and analyzed.Using principal component analysis(PCA)and hierarchical K-means(Hk-means)clustering method,five families and two elite trees of the clones with excellent wood properties were screened for future breeding.The results showed that:1.The five families with the longest tracheid length wereⅢ-SHANG-3(X55×124),Ⅲ-SHANG-17(X55×109),Ⅲ-XIA-23(J032×C44),Ⅲ-SHANG-24(J032×A029),Ⅲ-SHANG-27(J032×127),the average value of tracheid length reached 2610.63μm,2451.60μm,2532.06μm,2483.65μm,2489.86μm,respectively.The tracheid width was mainly distributed in 29.06μm-42.41μm,and the tracheid aspect ratio is mainly distributed in 75.73-53.37.The tracheid length and tracheid width increase linearly and rapidly along the radial direction,which conforms to the y=a+b*x pattern;The basic density distribution range of each family was 0.29 g/cm~3-0.38 g/cm~3,and the crystallinity distribution range was 36.83°-49.76°;The distribution range of cellulose photometric value is 0.69°-1.96°,hemicellulose photometric value is 0.11°-0.46°,and lignin photometric value is 0.86°-1.82°.There were significant differences in anatomical,physical and chemical characteristics among 26 Chinese fir families(P<0.05).2.The growth rate of tracheid length of 20-year-old Chinese fir increased rapidly along the radial direction at first,and then slowed to a steady state,which conformed to the change pattern of y=a–b*ln(x+c)function(R~2>0.97).The microfibril angle of the clones along the pith to bark decreased rapidly at first and then gradually stabilized.The double-index cluster analysis of tracheid length and microfibril angle showed that the transition year between juvenile wood and mature wood was 16 a.The transition zone of earlywood and latewood was different between different clones.There was no need for separate studies on early and latewood when defined the demarcation of juvenile wood and mature wood by tracheid length and microfibril angle.3.Compared with juvenile wood,the tracheid of mature wood was longer and wider,thecell wall was thicker,and the angle of microfibrils was smaller.In terms of chemical composition content,compared with juvenile wood,mature wood had higher holocellulose content andα-cellulose content and less extract content,but there is no significant difference in lignin content.The stability of chemical components was earlier than that of anatomical properties.Correlation analysis showed that there was a strong correlation between chemical composition and anatomical characteristics in juvenile wood and mature wood,but in different parts(juvenile wood or mature wood),the correlation between anatomical characteristics and chemical composition was different.4.Ⅲ-XIA-12,Ⅲ-XIA-14,Ⅲ-SHANG-11,Ⅲ-XIA-15 andⅢ-SHANG-24 had higher contribution values in the first four principal components than the other 21 families.KAI241 and k AI35 had much higher contribution values in principal components 1-3 than the other 18 individual trees of clones,indicating that the comprehensive quality of the five families and two trees of clones is better than that of other Chinese fir.The family parents A029,J032 and Long 15 expressed excellent heritability and had the potential for further cultivation and utilization.