Differentiation Mature Process Of Xylem Cells In Fast-growing Poplar

In order to make clear of xylem cell differentiation model, cell shape and accumulation, cell wall accumulation, chemical composition distribution of cell walls and their mechanical property of fast-growing Populusxeuram ericana cv.'74/76' during the differentiation and mature process. The method of quantitative anatomy, computer graphics simulation technology, fractal method, polarized microscopic technology, confocal microscopy Raman spectra technology and nanoindentation technique were used to estimate and analyze and in different differentiation stage.The main achievements and conclusions were obtained as follows:1.From early April to early October, the changes of cambium and xylem cells anatomical characteristics were significantly of Populusxeuram ericana cv.'74176'during the active phase. The changes of tissue proportions were significantly, and the changes of wood fiber were more notable than that of vessel element. The microfibril angle presented a decrease trend and crystallinity showed an increase trend. The correlation of cambium anatomical characteristics and xylem cell morphology was notable. The correlations between external climatic factors and cambium and xylem cell were also significantly.2.The results of fractal characterization xylem cells group patterns showed that the fractal dimension of xylem cells cross section presented an increase trend and the changes of tangential section was first decreased then increased. The fractal dimension of cross section was large than that of tangential section. The fractal dimension of cross section xylem cells group has a remarkable correlation with xylem cells' anatomical characteristics.3.It was determined that secondary cell wall of xylem cells differentiated S1 layer and S2 layer in May and S3 in July from cell wall appearing layers images with light and shade in the polarization microscope. The thickness of S1 layer, S2 layer and S3 layer were gradually increased during the active phase. The thicknesses of late wood secondary cell wall were significantly greater than that of early wood.4.The visualization of morphology and quantity changes of cambium and xylem cells and cell wall layers accumulation intuitively shows the cambium and xylem cells anatomical characteristics and the accumulation process of secondary cell wall during the development and maturation process.5.The results of chemical composition distribution in different position of wood fiber cell wall layers in the same stage during the active phase showed that the cellulose distribution was S2>CML>CC and the lignin was CC＞CML＞S2. It was found that lignin and cellulose distribution was vessel element> wood fiber＞parenchyma in the same stage. The lignin and cellulose concertration of late wood were larger than that of early wood in different position of wood fiber and vessel elemen.6.The longitudinal elastic modulus of secondary cell wall S2 layer, CML and CC were increased during the active phase. The longitudinal rigidity of secondary cell wall S2 layer was increased; however, the changes rigidities of CC and CML were not significantly. The longitudinal elastic modulus of xylem cells was S2>CML> CC, and the longitudinal hardness was CC> CML> S2. Cell wall longitudinal elastic modulus had a close relationship with cellulose concentration, and the longitudinal hardness had a close relationship with lignin concentration.