Study On The Formation Rule Of Secondary Tissues In Compression Wood Of Taxodium Hybrid ’Zhongshanshan’ Induced By Artifical Nclination

The purpose of this experiment is to provide theoretical support for the wide spread of Zhangshanshan,promote the efficient cultivation of plantation,improve the universality of compression wood,overcome the defects of processing and utilization,reduce the loss of wood,and improve the economic benefits of products.In this experiment,Zhongshanshan at different inclined angles（0°,15°,30°,60°）were taken as the research objects.It produced compression wood by artificial inclination.The secondary growth in compression wood and opposite wood was observed.Optical microscope,fluorescence microscope and electron microscope were used to observe the activity of wood cambium and the anatomical characteristics of secondary tissues（phloem and xylem）at different periods and different inclined angles.The morphological indexes of xylem tracheid and phloem fiber were counted by Franklin dissociation method,and the cell wall layer was observed by transmission electron microscope.Ultrastructure（crystallinity,microfibril angle）of wood was characterized by X-ray diffraction.The main conclusions of this paper are as follows:（1）Different inclined angles affect degree of cambium activity.During the period of cell division in the cambium zone（from June to August）:the number of cambium cells in the compression wood increased with the increase of inclined angle;the number of cell layers in the opposite wood decreased with the increase of inclined angle.At the end of the activity period of the cambium zone cells（in October）:with the increase of the inclined angle,the number of cambium zone cells in the compression wood increased.With the increase of inclined angle,the number of cell layers in the opposite wood had a downward trend.At this time,the opposite wood at 30°and 60°inclined had been into dormancy.（2）Different inclined angles affect the number of xylem cell division of compression wood.As of June:there was no significant difference in xylem cell growth in the compression wood as the inclined angle increased,and there was no significant difference in xylem cell growth in the opposite wood as the inclined angle increased.At this time,the cell growth of the opposite wood under the same tilt angle was slightly greater than that of the compression wood.As of August:with the increase of the inclined angles,the xylem cell growth in the compression wood had a significant upward trend,of which the cell growth was slightly greater than that of normal wood when at 15°,the cell growth amount was significantly greater than that of normal wood when at30°,the cell growth amount was less than the cell growth when at 60°,and the cell growth rate in the opposite wood xylem was decreasing with the increase of inclined angle,of which the cell growth amount was closer to normal wood when at 15°,and the cell growth was inclined to 30°and 60°.The amount of cell growth was much smaller than normal.As of October:with the increase of the inclined angle,the growth of xylem cells in the compression wood had a significant upward trend,of which the cell growth was slightly greater than that of normal wood when at 15°,and the cell growth was significantly greater than that of normal wood when at 30°and 60°;with the increase of inclined angle,the growth of xylem cells in the opposite wood had a downward trend,the cell growth amount was slightly close to normal wood when at 15°,and the cell growth amount was significantly less than that of normal wood when at 30°and 60°.From June to August,it was a period of mass meristem of compression wood cells,and the cells in the compression wood were faster than those of normal wood and opposite wood.（3）Different inclined angles affect the morphological characteristics of xylem tracheid,such as length,width,wall thickness and roundness.With the increase of the inclined angle,the characteristics of the compression wood of the Zhongshanshan tracheids were more obvious.When inclination at 15°,the morphology of the tracheid appeared partially compression wood,of which the length and width of the tracheids were slightly reduced compared with the normal wood,the double wall thickness of the tracheid was slightly larger than the normal wood,the wall cavity ratio and the cavity diameter were not significantly different from the normal wood,the roundness value is 0.87,and the spiral grooves had appeared on the tracheid wall.When inclination at 30°,the compression wood characteristics of zhongshanshan was the most obvious,compared with other inclined angles.At this time,the tracheid length was the smallest.The width was the smallest.The double wall thickness was the largest.The wall cavity ratio was the largest.The cavity diameter ratio was the smallest.The roundness value was 0.94,and the spiral grooves on the tracheid wall had been significantly deepened.When inclination at 60°,the characteristics of compression wood of Zhongshanshan were similar to those at 30°.（4）Different inclined angles affect the conducting phloem cell tissue ratio,cell composition and phloem fiber morphology.The conduction phloem of Zhongshanshan after inclined treatment was the same as that of normal wood,which was composed of phloem fiber（PF）,sieve cell（Se）and parenchyma cell（PP）.The arrangement of phloem cells in the compression wood of 15°,30°and 60°Zhongshanshan generally appeared’PF-Se-PP-Se-PP-Se-PF’,while the normal wood and the opposite wood after inclined treatment was mostly’PF-Se-PP-Se-PF’,and occasionally’PF-Se-PP-Se-PP-Se-Se-PF’.On the compression wood,from 0°to 30°,with the increase of inclined angle,the tissue ratio of sieve cells and parenchyma cells showed an increasing trend.The maximum tissue ratio of sieve cells to parenchyma cells was 80.60%in the compression wood at 30°,and the tissue ratio of sieve cells and parenchyma cells in the conducting phloem in compression wood at 60°was 78.48%lower than that in the compression wood at 30°.On the opposite wood,from 0°to 30°,the tissue ratio of sieve cells to parenchyma cells decreased with the increase of inclined angle.The minimum tissue ratio of sieve cells to parenchyma cells in the opposite wood at 30°was 69.93%.The tissue ratio of sieve cells and parenchyma cells in the conducting phloem in the opposite wood at 60°was74.86%higher than that at 30°.In the compression wood and the opposite wood,the length of the phloem fiber decreased with the increase of inclined angle.And the length of phloem fiber in compression wood was less than that in the opposite wood.（5）Different inclined angles affect the tracheid ultrastructure in the compression wood of Zhongshanshan.The normal wood cell wall layer was P+S₁+S₂+S₃;when the inclined angle was 15°,the cell wall layer was composed of P+S₁+S₂（S₂L）,and a highly lignification S₂L layer appeared near the corner of the cell in the S₂ layer.When the inclined angle was 30°and 60°,the cell wall layer in the compression wood was composed of P+S₁+S₂（S₂L）.At this time,a complete highly lignification S₂L layer was formed near the outer side of S₂.Different inclined angles affected the crystallinity and microfibril angle.From 0°to 30°,the crystallinity of cellulose decreased with the increase of inclined angle.The lowest crystallinity of cellulose was 25.13%when inclined angle was 30°.From 0°to 30°,with the increase of inclined angle,the microfibril angle had an increasing trend.When the inclined angle was 30°,the microfibril angle was the largest,which is 40.76°.In summary,when the inclined angle was 15°,the compression wood degree was not serious,which was mild compression wood.Severely compressed wood was formed when 30°and above.Typical compression wood tracheids were produced in the period of vigorous cell division from June to August.