| In this research, growth strain and main wood properties of Eucalyptus urophylla ×E. grandis plantation widely planted in south China were investigated, the relationship between growth strain and wood properties and high growth strain formation mechanism of normal wood were obtained. The results were provided with important theoretic and realistic values for forest oriented cultivation and wood processing utilizing. The paper adopted Strain Guage Method for the first time in China to measure surface longitudinal growth strain (SLGS) of standing trees, and the differences between Strain Guage Method and CIRAD-Foret method was compared. It and discussed The relationship between SLGS and wood physical and mechanical properties of fallen wood and between radial distribution of internal longitudinal residual strain (ILRS) and wood properties was analyzed, a new approach for classifying juvenile wood and mature wood was brought forward, according to radial distribution of ILRS and tree diameter. Using advanced transmission electronic microscope, visible light micro-spectrophotometer and scanning electron microscope and energy dispersive X-ray analysis(SEM-EDXA), especially using cell and histo-chemical method (lignin bromazition etc.), lignin distribution regulation in different micro-morphological regions of cell wall was opened out during lignification process.The relationship between high growth strain formation and lignification process was discussed, a new viewpoint that there was"deficient lignification "phenomenon in wood fiber cell wall of high growth strain normal wood was brought forward. The results were as the followings, 1. It took about three minutes using Strain Gauge Method to test SLGS at 1.3m height for standing trees. The value of SLGS was between 651×10-6 and 1100×10-6. Single factor variation analysis showed, there was no significant difference between two families, south and north and among different heights in tree; consequently, SLGS at 1.3m height should be as a reference criterion to evaluate the level of growth stress of the whole tree. 2. CIRAD-Foret Method and Strain Gauge Method were used to measure SLGS for fallen woods at the same point and at two points. The values obtained from the CIRAD-Foret method were bigger than those from strain gauge method. The former was 1.3 time as high as the latter for the measurement at two points, and it was 2.0 times as high as the latter for the measurement at the same point. 3. Along tree height increasing,there was similar changing tendency of volume shrinkage, longitudinal shrinkage, tangential shrinkage and radial shrinkage; Basic density showed little change while MOR displayed no obvious changing regulation and MOE increased obviously with tree height increasing. Single factor variation analysis showed, there was no distinct difference in volume, longitudinal and tangential shrinkage, basic density and MOR, while there was very significant difference in radial shrinkage and MOE at different heights. SLGR and longitudinal shrinkage was tightly related despite of single tree and different height. 4. The radial distribution of ILRS was symmetrical across the diameter.The largest tensile strain was near the bark, to the pith direction, tensile strain absolute value declined and turned zero at certain radius, after that tensile strain changed into compressive strain which presented obvious increasing tendency to the pith direction. The regression equation of radial distribution of ILRS was y = -21.075x2 + 4.5297x + 890.75, significantly correlated at 0.01level (correlation coefficient was 0.87). Tree radius of crossover point from tensile strain to compressive strain was 0.618R. Radial distribution pattern of ILRS at different heights was similar, but the correlation coefficient decreased with tree height increasing. 5. There was different changing tendency for wood anatomical properties(fiber length, fiber width, fiber wall thickness, ratio of length to width, microfibril angle, ratio of different tissue, cell wall percentage etc.), wood physical property(basic density) and wood chemical properties(alpha-cellulose content, Klason lignin content, hollocellulose content and degree of crystallinity) from the pith to bark. Single factor variation analysis showed, there were great differences among 5 radial positions in fiber length, fiber width, fiber wall thickness, distributing frequency of vessel, T-diameter of vessel element, alpha-cellulose content, hollocellulose content and basic density. However, there were no significant differences in microfibril angle, ratio of length to width, ratio of wall to lumen, ratio of lumen to diameter, ratio of different tissue, cell wall percentage, degree of crystallinity among 5 radial positions. There was positive correlation between tensile residual strain and fiber length, fiber width, T-diameter of vessel element and hollocellulose content, and between compressive residual strain and fiber wall thickness and distributing frequency of vessel. There was great positivecorrelation between tensile residual strain and alpha-cellulose content. 6. Radial distribution Changing gradient of ILRS was greatly affected by tree diameter, the curve of the smaller tree was much steeper. For Eucalyptus urophylla ×E. grandis in this study, when tree diameter was larger than 19.9cm, effect of diameter on radial distribution of ILRS became weak.It indicated that tree grow enters mature period while tree diameter reaches 19.9cm.So a new approach for classify juvenile wood and mature wood was brought forward, according to radial distribution of ILRS and tree diameter. 7. There was no significant difference between high growth strain material and low growth strain material for lignin deposition. After the appearance of S1 layer, lignin deposited with a style of patches firstly at the middle lamellae of cell corner. Accompanying with S2 layer deposition, lignification extended from corner to the rest regions of middle lamellae and secondary cell wall at the same time, and lignin content at cell corner increased sharply. After S3 layer appeared, lignin with irregular patches deposited on the entire secondary cell wall. 8. The results of histo-chemical dyeing showed, Syringyl(S) lignin and Guaiacyl(G) lignin were main component in micro-morphological regions of wood fiber cell wall for high growth strain and low growth strain material during lignification process. S lignin and G lignin content increased firstly and then leveled off. With lignification process, S lignin content was higher than G lignin content. S lignin and G lignin content decreased with growth strain increasing, at the same time, the difference of S lignin content among micro-morphological regions of wood fiber cell wall became smaller, but the difference of G lignin content became bigger. 9. The results of lignin bromazation method showed, lignin content in micro-morphological regions of wood fiber cell wall increased firstly and then leveled off during lignification process. Lignin content in sequence was cell corner, compound middle lamellae, S1, S2, S3.With growth strain increasing, lignin content decreased, lignification rate was slowed down and lignification process was delayed. Thereout, a new viewpoint that there was"deficient lignification"phenomenon in wood fiber cell wall of high growth strain normal wood was brought forward. This phenomenon was intrinsic response for trees adapting and counteracting outside circumstance changes.
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