Spatial variation of eucalyptus fibres considering the structure of annual growth rings

ABSTRACT Background: The fibres dimensions vary along a tree trunk, and these variations are related to the apical meristem and vascular cambium activities; understanding these variations would guide the best use of wood. There have been studies on the pattern of fibres dimensions variation along the tree trunk in the radial and longitudinal directions; however, the vast majority do not take into account the structure of the annual growth rings. Hence, this study aimed to obtain the pattern of fibres dimensions variation and their quality indexes along the tree trunk take into account the structure of the annual growth rings. Two Eucalyptus urophylla x Eucalyptus grandis hybrid clones were used in the study. Ten-year-old trees were selected and discs were removed from 13 longitudinal positions. The disks were prepared and the growth rings were subsequently identified and the samples used for maceration were collected. Twenty fibres were measured in the annual growth rings present in each longitudinal position. Results: In the longitudinal direction, within the annual growth rings, the fibre dimensions and their quality indices did not show a well-defined pattern of variation. In the radial direction, the length, cell wall thickness, wall fraction, and Runkel ratio of the fibres tended to increase following the pith-bark direction, while the lumen diameter and flexibility coefficient decreased. Conclusion: Nevertheless, the fibre width and fibre slenderness index did not present a well-defined pattern of variation in the radial direction.摘要： **背景**：木材纤维尺寸沿树干呈现动态变化，该变化与顶端分生组织（apical meristem）及维管形成层（vascular cambium）的活动密切相关；明晰此类变化规律可为木材的高效利用提供理论指导。已有诸多研究围绕树干径向与纵向的纤维尺寸变化规律展开，但绝大多数未考虑年轮（annual growth rings）结构的影响。鉴于此，本研究旨在结合年轮结构，明确树干全高度上的纤维尺寸变化规律及其品质指标。 本研究选用2个尾叶桉（Eucalyptus urophylla）×巨桉（Eucalyptus grandis）杂交无性系作为试验材料，选取树龄为10年的植株，在13个纵向取样位置截取圆盘试样。对圆盘试样进行制片处理后，识别年轮结构并采集用于纤维离析（maceration）的试样，随后在每个纵向位置的年轮内随机选取20根纤维进行尺寸测量。 **结果**：在纵向方向上，单年年轮内的纤维尺寸及其品质指标未呈现明确的变化规律。在径向方向上，纤维长度、细胞壁厚度（cell wall thickness）、壁积分数（wall fraction）以及伦克尔比（Runkel ratio）随髓心向树皮方向逐渐增大，而胞腔直径与柔度系数（flexibility coefficient）则呈下降趋势。 **结论**：但纤维宽度与纤维细长比（slenderness index）在径向方向上未呈现明确的变化规律。