华北典型植被根系抗拉力学特性及其与主要化学成分关系

为了解植被根系化学成分对根系力学性能的影响，该研究对华北地区常见的2种针叶树油松（Pinus tabulaeformis Carr.）和华北落叶松（Larix principis-rupprechtii Mayr.）以及3种阔叶树白桦（Betula platyphylla Suk.）、蒙古栎（Quercus mongolicus Fisch. ex Ledeb）和榆树（Ulmus pumila Linn.）5种树直径为0.75～7.65mm，共473根系进行了单根抗拉试验，并将拉伸后的根系按7个直径级归类后测定其纤维素含量、木质素含量、半纤维素含量及综纤维素含量。结果表明，5种树根系抗拉力范围为8～954 N，抗拉强度范围为6～53 MPa。不同树种间抗拉力、抗拉强度差异显著，从大到小依次为榆树＞白桦＞蒙古栎＞油松＞华北落叶松。抗拉力随直径增大以幂函数增大；抗拉强度随直径减小以幂函数和逆函数减小。根系的极限延伸率范围为6.95%～15.50%，不同树种间差异显著。5种树7个径级根系纤维素质量分数范围为20.09%～37.67%，木质素质量分数范围为18.03%～41.67%，半纤维素质量分数范围为1.29%～14.90%，综纤维素质量分数范围为26.20%～52.09%，木质素与纤维素质量分数比值（简称木纤比）为0.53～1.81。根系抗拉力与纤维素含量、半纤维含量、综纤维素含量正相关，与木质素含量、木纤比负相关；根系抗拉强度与纤维素含量、半纤维含量、综纤维素含量负相关，与木质素含量、木纤比正相关。但对于不同的树种，显著影响抗拉力、抗拉强度的化学成分不同。因此，根系中某一化学成分含量的变化并不能完全解释根系力学性能与直径的尺寸效应，或许根系其他内在因素如显微结构等也有着重要的贡献。

Relationship between root tensile mechanical properties and its main chemical components of tipical tree species in North China

Abstract: In order to understand the effect of root chemical components on its mechanical properties, root tensile tests were conducted on 473 roots with diameters of 0.75-7.65 mm from two conifers and three broadleaf, namely Pinus tabulaeformis Carr., Larix principis-rupprechtii Mayr., Betula platyphylla Suk., Quercus mongolicus Fisch. ex Ledeb. and Ulmus pumila Linn, which were very common species in North China. All tested roots were devided into 7 diameter classes to measure the cellulose content, lignin content, hemicellulose content and holocellulose content. The results showed that the root tensile force varied from 8 to 954 N and tensile strength was in the range of 6-53 MPa. There was significant difference in tensile force and tensile strength among roots of five species, with a clear following ranking order: Ulmus pumila Linn. has the largest tensile force and tensile strength, followed by Betula platyphylla Suk, Quercus mongolicus Fisch. ex Ledeb, Pinus tabulaeformis Carr, and Larix principis-rupprechtii Mayr. The tensile force increased with the increasing root diameter at the level of power function, and at the same time, the tensile strength decreased with the decrease in root diameter at the level of power function and inverse function. The range of root ultimate elongation was from 6.95% to 15.50% with significant difference among different tree species. The cellulose contents were from 20.09% to 37.67%, the lignin contents from 18.03% to 41.67%, the hemicellulose contents from 1.29% to 14.90%, the holocellulose contents from 26.20% to 52.09%, and the content ratio of lignin to cellulose was from 0.53 to 1.81. The root tensile force was positively correlated with cellulose content, hemicellulose content and holocellulose content, and was negatively correlated with lignin content and the content ratio of lignin to cellulose. The root tensile strength was negatively correlated with cellulose content, hemicellulose content and holocellulose content, but was positively correlated with lignin content and the content ratio of lignin to cellulose. For different tree species, the root chemical components effecting on the tensile force and tensile strength were different. Therefore, the size effect of root diameter on tensile strength can not be totally explained by the changes in root chemical components. Maybe the other inner factors of the root, such as its microstructure, also make the important contribution to it.