摘要
本文阐述了木材微纤丝角的概念及其与木材性质的关系，介绍了微纤丝角的测定方法、变异规律及影响微纤丝角变化的主要因素，分析了微纤丝角研究的发展趋势，并在此基础上对苗期11个无性系、7个无性系的林分及造林密度、修枝处理和立地条件3种处理的杨树微纤丝角、木材密度、纤维形态与纤维素含量进行了研究，并得结果如下：
(1)苗期11个杨树无性系木材微纤丝角的变异达到极显著水平，微纤丝角变化在13°～30°之间；无性系木材纤维长度变化范围在618.88～858.84um之间，平均值为690.42um，纤维长度差异达极显著水平；纤维宽度在21～28um之间，35杨(P.deltoids CL'36／66')最大(27.04um)，四季杨(P.deltoids×P.nigra cv.Chile)最小(21.31um)；维素含量差异不显著，纤维素含量变化范围为41.4～47.4％。
(2)7个无性系杨树胸径处前6、8、11年的微纤丝角、纤维长度差异不显著，微纤丝角平均值为17.836°。11年时比前6年下降了17.5％，7个无性系微纤丝角大小排序为：1-72杨＞I-69杨＞南林-351＞南林-1388＞南林-895＞南林-447＞南林-95。微纤丝角在年轮间差异显著，并且变异以第6年轮为界限。7个无性系胸径处木材密度、纤维宽度和纤维素含量差异显著。I-72杨与南林-447和南林-95木材密度差异显著，南林-95与其它无性系差异较大；纤维宽度南林-95、南林-895较小而I-69杨和南林-1388较大；纤维素含量南林-95、南林-895、南林-447与南林-351、I-69杨、I-72杨、南林-1388差异达显著水平。
(3)杨树微纤丝角、木材密度、纤维长度、纤维宽度和纤维素含量胸径处变异规律为：生长前期也即幼龄期(1～4R)微纤丝角逐渐增大，而当到达一定年龄(4～6R)后，微纤丝角随着年轮的增加而逐渐减小，直至一定年龄后又趋于稳定；第1年轮处木材密度最小，从髓心向外以曲线形式缓慢增大；胸径处纤维长度、纤维宽度和纤维素含量从髓心到树皮都为显著的增加。
杨树微纤丝角、木材密度、纤维长度和纤维宽度纵向变异规律为：杨树微纤丝角的最大值出现在树木基部，并随树高的增加而减小，到树高6m以后基本变得稳定，但还有进一步平缓下降的趋势；从树干基部向上木材密度存在随树木高度的增加而逐渐增大的均势，测定发现木材密度最小值出现在地径处，最大值出现在3.6m的高度；纤维长度在同一年轮内不同高度均是树干基部最小，随树高的增加纤维长度逐渐增加，到5.6m左右达到最大，以后持续保持至17.6m左右又开始下降，即纤维长度在树干基部和树梢处总是较小，而在这两者之间保持在一个较为稳定的范围内波动；纤维宽度在树干基部到9.6m的范围内较大，而超过9.6m后开始减小。这说明树木生理年龄是影响纤维形态的一个主要因子。
(4)对7个杨树无性系木材性质的分析表明，微纤丝角与树木年龄间存在显著的多项式(R~2=0.8263)和指数式(R~2=0.8069)回归关系，微纤丝角与树高主要存在多项式(R~2=0.616)的回归关系。纤维长度与年轮间存在极显著的直线型(R~2=0.8979)、多项式(R~2=0.9828)、对数式(R~2=0.9682)和乘幂式(R~2=0.9737)回归关系。纤维素含量与年轮间存在极显著的对数式
（R’二0．8168）、多项式（R’二0．0．8630）、乘幂式（R‘二0．8178）的回归关系。
以树高、生长年轮为自变量，以微纤丝角为因变量进行二元回归分析得方程为：
y＝22．557056—0．264541XI—0．751337X2
经检验，回归方程，回归系数及相关系数（RI一一0。4480，RZ一一0．4845）均达到极显著水
平。
（）以微纤丝角的变异、木材密度的变化和纤维形态的变化将杨树元性系幼龄材与成
年材的界限界定为第6年轮。树干中央部分（l－6R）的微纤丝角和木材密度低且变化急剧不
稳定，纤维长度逐渐增长构成所谓的幼龄材，树干外围（＞6以微纤丝角达到最大并开始下
降，木材密度高且相对均一，纤维长度变得稳定构成所谓的成熟材。选育或预测杨树材质
时，以6年生以上的木材性质来衡量是较为合理的。
的乃 杨不同林分密度间微纤丝角、纤维长度的差异不显著，但随着林分密度的增大
微纤丝角有减小的趋势。4种密度处理中，年轮间微纤丝角的变异达到显著水平，微纤丝
角随年轮的增加而减小。纤维长度之间差异不显著，几种处理中3mx4m在纤维长度方面
是较好的，纤维长度变幅为663．73－1416．6urn；年轮间纤维长度差异显著，并且随着年轮
的增加差异逐渐减小。351杨不同林分密度间木材密度、纤维宽度和纤维素含量的差异显
著。纤维宽度3mx4m处理好于其它，年轮间纤维宽度差异显著，幼龄期＊一R）与其它年轮
差异明显显著。纤维素含量4mx4m与其它处理差异较大。年轮间纤维素含量差异显著，
且前4年轮与其它年轮间差异最大。树木生长前期＊刁）纤维素含量呈逐渐上升趋势，而
过了这一阶段年轮内纤维素含量变化开始变得不稳定，这说明林分密度对树木的影响是从
定植第5年后才开始的。
OI＊9杨不同强度的修枝措施对木材微纤丝角、纤维长度、木材密度和纤维素含量的
影响均未达到显著水平，但修枝后早晚材间微纤丝角差异减小。微纤丝角、纤维长度、木
材密度和纤维?
Based on the information, the concept of microfibril angle, the relationship between microfibril angle and wood properties, the methodology for measuring microfibril angle, variation dynamics of microfibril angle, the factors affecting microfibril angle variation and future research prospects are discussed. In order to strength the competition capacity and oriental cultivation, more effort is devoted to the genetic improvement and cultivation of tree species, so as to make the timber production combining with demand of end products to wood properties in wood industry. Based on the review of related references, the temporal and spatial variation of microfibril angles and wood properties for 11 one-year-old poplar clones and 7 mature (more than 11 years old) poplar clones, the effects of planting densities, pruning intension and site conditions on microfibril angle and wood properties (wood densities, fiber length, fiber width and cellulose contents), and the relationship between microfibril angle and wood pro
perties were studied in the paper, and the main conclusions are drawn as follows:
1. There exists significant variation in microfibril angles and fiber length among 11 seedling poplar clones, microfibril angle varies from 13°to 30°and fiber length varies from 618.88um to 858.54um with the average 690.42um. Fiber width varies from 21um to 28um with the widest occurring in clone 35(P. deltoids CL'36/66') with 21 um, the least in siji (P. deltoidsx.P. nigra cv. Chile) with 21.3um. Significant differences have not been observed in cellulose contents in 11 one-year-old poplar clones and it varied from 41.4% to 47.4%.
2. The results of variation analysis indicated that there were no significant differences in microfibril angles and fiber length within 6, 8 11 years old at breast height among 7 maturate poplar clones. The average of microfibril angle is 17.84° in 11 years old in 7 clones and it decreases 17.5% within 11 than in 6 years old. It can be ordered I-72> I-69> NL-351> NL-1388>NL-895>NL-447>NL-95 in averages of microfibril angles in 7 poplar clones within 11 years old. Significant differences were observed in wood density, fiber width and cellulose contents at breast height in 7 poplar clones. There exist notable difference between 1-72, NL-447, and NL-95 in wood density. It showed that the widest fiber occurred in 1-69 and NL-1388, the least fiber occurred in NL-95 and NL-895. There exist significant differences between NL-95, NL-895, NL-447 and NL-351, 1-69, 1-72, NL-1388 in cellulose contents.
3. The spatial variation pattern of microfibril angle, wood density, fiber length, fiber width and cellulose contents are as follows:
From pith to bark: The microfibril angle gradually increases from pith to 4-5 rings, after reach the largest in 4~5 rings, it start declining from pith to bark, and then it would be stable to a certain ring. Wood density was the least in the first ring and increased gradually from pith to bark. Fiber length, fiber width and cellulose contents were significantly increased from pith to bark.
Within a single tree: Microfibril angle was lager at base of trees and decreased with the increase of height, and maintained stabilization over 6m height within trees. There existed an increasing trend in wood density from the base to tree top. The least occurred in the base, and the largest wood density occurred at 3.6m of the tree. Fiber length varies as "inverted saddle pattern" from base to tree top in one growth ring. The least fiber length occurred at base of trees and gradually increased with the increase of height, and fiber length reached the longest about 6m. The longest fiber would be stable to 17.6m, then it become declining. Fiber width was wider bellow 9.6m, it would be decreased beyond 9.6m in the tree.
4. It proved from analysis of wood properties that there exist significant polynomial (R2=0.8263) and index (R2=0.8069) regression relationship between microfibril angle and growth rings; and polynomial
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