Research On Anatomical Characteristics And Physicochemical Properties Of Compression Wood Of Taxodium Hybrid 'Zhongshanshan'

Taxodium hybrid‘Zhongshanshan'was an excellent species by interspecific hybridization of Taxodium.It was an excellent species for coastal saline afforestation,with the advantages of water resistance,wind resistance,salt resistance and fast growing.It is an excellent tree species for coastal beach afforestation.As a fast-growing species,Taxodium hybrid‘Zhongshanshan'was susceptible to the environment and gravity,and thus formed compression wood.There were a great many differences between compression wood and opposite wood,such as wood anatomy,chemical component,physical and mechanical properties.Therefore,it is necessary to systematically study the anatomical structure and physical and mechanical properties of compression wood of Taxodium hybrid‘Zhongshanshan',which is beneficial to explore the difference between compression wood and opposite wood.The objects of study were compression wood,side wood and opposite wood of Taxodium hybrid‘Zhongshanshan',and anatomical characteristics,lignin distribution,cellulose structure,wood density,shrinkage and tensile mechanical properties were systematic researched,and the correlations between physical and mechanical properties and microfibril angle was analyzed.The main conclusions of this paper are as follows.(1)Macroscopically,the compression wood of Taxodium hybrid‘Zhongshanshan'was brown or dark brown,and was usually formed at the middle or the end of the growth ring.The latewood and early wood at the beginning of the growth ring were the normal wood,instead of compression wood.The greatest difference in anatomical structure between the compression wood and the opposite wood was the tracheid.The tracheids of opposite wood of Taxodium hybrid‘Zhongshanshan'were square or polygon,and the wood tracheids length was 3280.1?m,the radial diameter was 37.0?m,and the radial double wall thickness was 5.6?m.Compression wood tracheids were significantly rounded in cross section,thereby forming a large number of intercellular spaces.Compared with the opposite wood tracheids,the radial double wall thickness of the compression wood tracheids thickened about 95%,the length was reduced by 25%,and the radial diameter is reduced by about 71%.The S2 layer of the secondary wall was divided into the S2 inner layer and the S2L layer,and spiral grooves embedded in the cell wall.The side wood tracheids were approximately square with a small amount of interstitial spaces,and the S2L layer were at the edges and corners of the tracheids.There are no spiral grooves in the inner wall of the side wood tracheids,but there are some fine streaks.Compared with the opposite wood tracheids,the length of the side wood tracheids were shortened by 17%,the radial double wall thickness is increased by 11%,and the radial diameter is reduced by 6%.The circle values of the tracheids of the compression wood were significantly different from the side wood and the opposite wood tracheids(P<0.01).The circle of the side wood and the opposite wood showed a significant difference(P=0.037).(2)Under the fluorescence microscope,the lignin in the S2L layer of compression wood and side wood had the strongest fluorescence effect,and in the opposite wood,the strongest fluorescence effect was at the cell corner.It showed that the area with the highest lignin concentration in the compression wood and the side wood was the S2L layer,and the area with the highest lignin concentration in the opposite wood was the cell corner.The S2L layer of the wood tracheids was thicker and wraped the entire inner S2 layer.The transition zone tracheids in the compression wood were square and had a thinner S2L layer,and the cross-sectional morphology was similar to the normal early wood.The S2L layer of the side wood tracheids was thinner,only located at the corners of the cells.The S2L layer of the secondary wall was not founded in the opposite wood and the late wood.The results of raman microspectroscopy analysis showed that the lignin concentration from high to low of the opposite wood was cell corner,compound middle lamella and secondary wall S2 layer,and the concentration ratio was about 2:1.3:1.The lignin concentration from high to low of the compression wood was S2L layer near the cell corner,cell corner and compound middle lamella,inner S2 layer,and the concentration ratio is about 1.9:1.3:1.Therefore,the response of lignin deposition location to external stress was faster than the change of cell morphology.XRD was used to determine the microfibril angle and relative crystallinity of compression wood and opposite wood of Taxodium hybrid‘Zhongshanshan'.The microfibril angles of compression wood and opposite wood were 38.02°and 30.01°,respectively.The relative crystallinity of the compression wood and opposite wood were 42.01%and 52.08%,respectively.(3)The wood density of compression wood was higher than the opposite wood of Taxodium hybrid‘Zhongshanshan',and there was a significant difference between the both side.The air-dry density,oven-dry density and basic density of compression wood were 0.662 g/cm~3,0.603 g/cm~3,and 0.528 g/cm~3,respectively.The air-dry density,oven-dry density and basic density of opposite wood were 0.430 g/cm~3,0.379 g/cm~3 and 0.326 g/cm~3,respectively.The axial air-drying and oven-drying shrinkage rates of compression wood were 1.801%and 5.973%,respectively,2.9 times and5.9 times that of the opposite wood;while the radial,tangential and volume shrinkage rates of the compression wood were significantly smaller than the opposite wood.The axial shrinkage rate,radial shrinkage rate,tangential shrinkage rate and volume shrinkage rate of compression wood and the opposite wood of Taxodium hybrid‘Zhongshanshan'were very significantly different.Correlation analysis shows that the axial air-drying and oven-drying shrinkage of compression wood were extremely significantly correlated with the microfibril angle,and coefficient of association were 0.588 and 0.667,respectively.While there were no correlation between radial and tangential shrinkage rate and microfilament angle.The R~2 of the linear function fitting equation of the axial air-drying and oven-drying shrinkage rate and the microfibril angle is 0.3581 and 0.4315,respectively.(4)The tensile property of the compression wood of Taxodium hybrid‘Zhongshanshan'were significantly lower than opposite wood.The tensile fracture force of single tracheid of compression wood was 12.91 m N,which was reduced by about 64%compared with that of the opposite wood,and the difference between them was extremely significant(P<0.01).The tensile strength of the compression wood was 64.59 MPa,which was decreased by 40%compared with that of the opposite wood,and there was extremely significant difference between them(P<0.01).The tensile fracture force of 100?m compression wood slice was 16.89 N,which was reduced by37%compared with opposite wood slice,and the difference between the both was extremely significant(P<0.01).The tensile strength of the 100?m compression wood slice was 16.86MPa,which was reduced by 38%compared with opposite wood,and the difference between the compression wood and opposite wood was extremely significant(P<0.01).There is no correlation between the tensile property of single tracheid and the microfibril angle due to the effect of spiral grooves.There is a significant negative correlation between the tensile fracture force along the grain and the microfibril angle of 100?m compression wood slice,and a significant negative correlation between the tensile strength along the grain and the microfiber angle.The R~2 of the linear function fitting equation of the wood slice fracture force along the grain and microfilament angle was 0.3931,and the R~2 of the linear function fitting equation of the tensile strength and microfilament angle was 0.4421.