华北护坡阔叶树种根系抗拉性能与其微观结构的关系

为了研究乔木单根抗拉性能与其微观结构和纤维的关系,为筛选合适的水土保持、边坡防护树种提供理论基础,对白桦、榆树、蒙古栎3种北方常见阔叶树种的根系进行了抗拉力、抗拉强度、根系解剖结构以及根系分子离析等一系列的试验,并运用多元回归的方法对两者之间的关系进行定量的分析。试验结果表明:3种阔叶树种的根系显微结构基本和其树材相同;根系显微结构中木纤维所占根系横截面积的百分比、韧皮部所占根系横截面积的百分比、木纤维的尺寸因素影响单根的抗拉特性;其中木纤维所占根系横截面积的百分比对单根抗拉力的影响因子最大且呈正相关,韧皮部所占根系横截面积的百分比对单根抗拉强度的影响因子最大且呈正相关;同时单根抗拉特性与木纤维的长度、木纤维的长宽比以及壁腔比均成正相关,但影响因子小于木纤维所占根系横截面积的百分比、韧皮部所占根系横截面积的百分比;3个树种中榆树在相同直径下的各项测定指标都高于白桦和蒙古栎,表现出单根具有更好的抗拉特性。研究结果可为固土护坡阔叶树种的选择提供参考。

Relationship between tensile properties and microstructures of three different broadleaf tree roots in North China

Abstract: Forest vegetation is known to increase slope stability by reinforcing soil shear resistance, and root tensile properties are important factors to consider when choosing suitable species for reinforcing soil on an unstable slope. The macroscopic properties are determined by the microscopic structure; as a result, the microscopic structure of roots needs to be further observed to help us understand the relationship between the soil's mechanical properties and the microstructure of roots. We chose three common broadleaf species (Betula platyphylla, Quercus mongolica, Ulmus pumila) in North China and carried out several experiments, including single-root tensile tests, root anatomical-structure tests, and wood-fiber segregation experiments. To analyze data from those experiments, we used multiple regression and analysis of variance (ANOVA) in order to determine the relationship between root tensile properties and selected anatomical structure. Results showed that in all species a significant power relationship existed between tensile properties and root diameter (R2>0.8). The root tensile force increased with increasing root diameter, but root tensile strength increased with decreasing root diameter. According to the results of root tensile tests, we found that Ulmus pumila was the most resistant to failure, followed by Betula platyphylla and Quercus mongolica. Through the observation of microscopic sections, the root anatomical features of three kinds of broadleaf species were the same as those of their trunk, and wood fiber was the main anatomical feature in the root. According to the multiple regression models, the area percentage of wood fiber in the root cross-section (short for the area percentage of wood fiber), the area percentage of phloem in root cross section (short for the area percentage of phloem), and fiber dimensions affected single roots' tensile properties. The percentage of wood fiber area was the most important impact factor on root tensile force, exhibiting positive correlation. The percentage of phloem area had the biggest influence on root tensile strength. Wood fiber length, the length-width ratio of wood fiber, and the ratio of cell wall to cell cavity also affected tensile properties, but their quantitative influence was less than other factors. Although the area percentage of phloem affected root tensile strength, within a given species there was no significant difference in different root diameter. From the measurement of wood fiber in roots, we found that wood fiber size and type were different in the three selected species. The quantity of wood fiber increased with increasing root diameter, but the size of wood fiber varied only slightly. In three different broadleaf species' roots, the related index (including the percentage of wood fiber area, the percentage of phloem area, and the fiber dimensions) of Ulmus pumila was higher than that of Betula platyphylla and Quercus mongolica in the same diameter; that is to say, Ulmus pumila had better tensile properties than the other species. In accordance with the root anatomical features, fiber dimension, and tensile properties, Ulmus pumila, the roots of which have a better ability to reinforce soil on unstable slopes, is an appropriate broadleaf species for soil and water conservation.