乔木侧根对土体的斜向牵引效应 Ⅱ野外直测

TRACTION EFFECT OF LATERAL ROOTS OF TREES Ⅱ IN SITU DIRECT REST

根据乔木侧根对土体的斜向率引效应原理和数学模型，以云南松林为例，进行了野外直接剪土测试。结果表明，在表层根际土中（０～２０ｃｍ）松树侧根能在相同的垂直截面上平均提供５７７２３Ｎ的斜向牵拉力，使根际土层的抗滑力提高了３８７８％，把根际土层的抗张强度提高了５７７ｋＰａ。同时发现，侧根牵引效应的量值随根生物量大小的影响。

Lateral roots of trees are provided with mechanical stabilizing effect on the rooted soil,through their traction effect(see detail in the abstract of part one of this series paper).To verify whether or not a traction effect exists in the roots system of Yunnan pine,a direct in situ test was conducted in the Hutiaoxia Gorge area,SW China,taking Yunnna pine forest( Pinus yunnanensis French .)as an example.The method used in this study to examine the traction effect in situ is a new technique,being the first of this kind in the world.Though some improvement still needed,it successfully obtained some preliminary results. To test the traction effect,two groups of soil cuboids were selected,one group with roots and one without.When pulled,the two groups resisted the force pulling force to different extents.This difference is considered to be an indication of the result of the traction effect.The instrument system,consisting four main parts,and their connections were carefully designed.After the experiments with the instrument system,the magnitude of the pine's traction effect could be obtained,using a special group of equations. Based on the sampled soil cuboids,generally,the pulling force of the rooted samples at critical displacement is higher than those of the non_rooted ones;the force on the rooted samples averaging 1488.33N,compared with the one of the non_rooted samples of 911.10N.The rooted cuboids reach their maximum pulling force a bit later (average displacement reaches about 5.0mm)than those of the nonrooted ones(only average 2.5mm).Calculation shows that,most of the rooted samples had received an increased tensile strength,on the set vertical cross_section area of 1000 cm 2 in the uppermost soil layer,ranging from 2.2kPa to 16.9kPa.The mean tensile strength increase at the topmost soil layer was 5.8 kPa,which is considerable.There is certain relationship between the traction force and the biomass of the lateral roots:the former increases positively with the later.