Mechanical Properties Of Roots Research Articles

Study on the Mechanical Properties of Roots and Friction Characteristics of the Root–Soil Interface of Two Tree Species in the Coastal Region of Southeastern China

The tensile strength of roots and the friction characteristics of the root–soil interface of tree species are the indicators that play a crucial role in understanding the mechanism of soil reinforcement by roots. To calculate the effectiveness of the reinforcement of soil by tree roots based on essential influencing parameters, typical trees in the coastal region of southeastern China selected for this study were subjected to tests of the tensile mechanical properties of their roots, as well as studies on the friction characteristics of the root–soil interface and the microscopic interfaces. The results indicated that in the 1–7 diameter classes, the root tensile strength of both Pinus massoniana and Cunninghamia lanceolata was negatively correlated with the root diameter in accordance with the power function. The root tensile strength of these two trees, however, was positively correlated with the lignin content but negatively correlated with cellulose and hemicellulose contents. The shear strength at the root–soil interface and the vertical load exhibited a constitutive relationship, which followed the Mohr–Coulomb criterion. As the root diameter increased, both the cohesion and the friction coefficients at the root–soil interface gradually increased, but the growth rate stood at around 15%. The cohesion value of the root–soil interface of the two trees decreased linearly with the increase in soil moisture content within the range of 25 to 45%. At the microinterface, the root surface of C. lanceolata exhibited concave grooves and convex ridges that extended along the axial direction of roots, with their height differences increasing with the enlargement of the root diameter. The rough surface of P. massoniana roots had areas composed of polygonal meshes, with an increase observed in the mesh density with increasing root diameter.

RESEARCH OF THE WORKING PROCESS OF THE CLEANING SYSTEM OF MACHINES FOR HARVESTING ROOT CROPS

Conducted the theoretical and experimental studies of the combined cleaning system functioning process by analyzing the motion of fodder beet through the working surfaces of feeding conveyor and auger installed above it. We have got analytical and empirical process model of fodder beet oblique sub-hiton the augerturn that characterize the dependence of the total rate of sub-hit coefficient of technological interaction of roots and depth of root damage on the main parameters of combined cleaning system. We found out the rational limits of basic structural and kinematic parameters of combined cleaning system by providedminimum offodder beet damage. Particular importance for improving the design and technological level and individual working bodies of the combined cleaning system should be given to issues of general engineering problems of machine design: improvement of working bodies and other structural elements of the combined cleaning system based on a deeper analysis of physical and mechanical properties of roots. Characteristics of fodder beets, as an element of the system "machine-working body-root crop", must be considered as a set of different mechanical qualities and parameters that are decisive in the total mechanical action on the object, their allowable level and range of structural and kinematic parameters of workers bodies. When optimizing the parameters of transport and technological systems of the root of the harvesting machine, which have working bodies of screw mechanisms, at the stage of their design it is advisable to first build a mathematical model of the technological process of root cleaning system parameters.

Roots reinforcement by riparian trees in restored rivers

Riparian vegetation directly and indirectly affects many fluvial processes. In particular, the root system of riparian trees and shrubs may greatly influence river morphodynamics by imparting higher shear strength to riverbanks compared to unvegetated channel margins. Therefore, the bank-stabilizing role of riparian vegetation should be quantitatively considered in river restoration projects. This work aims to quantify the additional strength due to the root systems of naturally established riparian vegetation after two river restoration projects carried out in the Italian Alps (Ahr and Mareit rivers, South Tyrol). These projects represent the largest restoration interventions carried out so far in Italian rivers, and the two sites feature contrasting channel patterns along with varying river-floodplain dynamics.The mechanical properties of roots and their distribution in the floodplain soils in the two sites have been measured to estimate root cohesion distribution associated to gray alder (Alnus incana) and pioneering willows (Salix spp.).Results show that roots of plants colonizing the gravelly substrate of building islands in the Mareit River have less tensile strength than those belonging to trees growing in the floodplain of the Ahr River, rich in fine sediments. However, the higher root contribution to the overall soil strength occurs in the island site, due its lack of fine sediments.

喀斯特坡地拉巴豆地埂篱根及根-土复合体力学特性

PDF HTML阅读 XML下载 导出引用 引用提醒 喀斯特坡地拉巴豆地埂篱根及根-土复合体力学特性 DOI: 10.5846/stxb201901100085 作者: 作者单位: 西南大学资源环境学院,西南大学资源环境学院,西南大学资源环境学院,西南大学资源环境学院,西南大学资源环境学院,西南大学资源环境学院,西南大学资源环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目（2016YFC0502303）；中央高校基本业务费专项资金资助（XDJK2018B044）；岩溶环境重庆市重点实验室开放课题资助（Cqk201803） Study on the mechanic features of root and root-soil matrix of Dolichos lablab L. hedgerows on the slopes of the karst area Author: Affiliation: Key Laboratory of Karst Environment,College of Resources and Environment,Southwest University,Key Laboratory of Karst Environment,College of Resources and Environment,Southwest University,Key Laboratory of Karst Environment,College of Resources and Environment,Southwest University,Key Laboratory of Karst Environment,College of Resources and Environment,Southwest University,Key Laboratory of Karst Environment,College of Resources and Environment,Southwest University,Key Laboratory of Karst Environment,College of Resources and Environment,Southwest University,Key Laboratory of Karst Environment,College of Resources and Environment,Southwest University Fund Project: The National Basic Research Program of China (973 Program) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探索地埂篱在喀斯特坡地水土保持中的价值，在重庆市酉阳县喀斯特顺层坡种植拉巴豆地埂篱，通过对根系灰度扫描、化学成分（木质素、纤维素、半纤维素）测定，单根抗拉试验和根-土复合体抗剪/冲试验，分析拉巴豆地埂篱根及根-土复合体的力学特性及影响因素。结果表明：（1）拉巴豆根系全根指标根长、根表面积、根体积、根重均表现为中坡 > 下坡 > 上坡，优势径级为0.0<d≤1.0 mm径级。全根根系纤维素的平均含量较木质素、半纤维素高，且与根系直径呈显著负相关。（2）根系平均极限抗拉力6.77 N、平均抗拉强度29.57 MPa。极限抗拉力与木质素含量呈对数函数正相关、与木质素/纤维素（木纤比）呈线性正相关，抗拉强度与纤维素含量、木纤比分别为对数函数正相关和负相关。（3）上坡位抗剪土样的根体积密度、根重密度和木纤比显著大于中、下坡；而抗冲土样的根体积密度、根重密度、纤维素和半纤维素含量则中坡较优，但不显著。（4）根系能有效提高土体抗剪性能，根-土复合体的内摩擦角与粘聚力均较对照裸地高，但仅上坡粘聚力存在显著性差异（较对照增大45.67%）。内摩擦角和抗冲指数均中坡、下坡较优，粘聚力最优值位于上坡位。根-土复合体的力学特性主要受根体积、根重、根表面积密度和纤维素的影响。综上，拉巴豆根及根-土复合体的力学特性主要贡献径级为0.0<d≤1.0 mm径级，中、下坡细根量大且根-土复合体抗冲性能表现较优，上坡根-土复合体抗剪切能力最强，但抗冲性能较弱。在推广拉巴豆地埂篱时，尽量种植于地势较低缓的中、下坡，更能凸显水土保持效益。 Abstract:To explore the effect of Dolichos lablab L. hedgerows on soil and water conservation, we planted Dolichos lablab L. at up, middle, and down slopes at bedding slopes of the karst valley in Youyang Chongqing. The roots and root-soil matrix were sampled. The mechanical properties of roots, soil anti-scourability, and soil shear strength of root-soil matrix were tested. To find the factors affecting mechanical properties, we scanned root grayscale and tested root chemical compositions (lignin, cellulose, and hemicellulose), and also performed correlation analysis. The results showed that:(1) The whole root parameters (root length, root surface area, root volume, and root weight) had the highest value in the middle slope portion, followed by down slope portion; the corresponding value of the up slope portion was minimum. Root dominant diameter was in the range of 0.0<d≤1.0 mm. The average content of cellulose in plant root was higher than that of lignin and hemicellulose. The root cellulose content was significantly negatively correlated with root diameter. (2) The root average ultimate tensile force of Dolichos lablab L. was 6.77 N and the average tensile strength was 29.57 MPa. Cellulose and lignin had statistically significant influences on the root mechanical properties. Their regression relations are as follows:the ultimate tensile force increased logarithmically with lignin content and increased linearly with lignin/cellulose(wood fiber ratio); tensile strength increased logarithmically with cellulose content, decreased logarithmically with wood to fiber ratio. (3) The root volume density, root weight density, and wood fiber ratio of the up slope shear strength samples were significantly greater than those of the middle and down slopes. However, for the anti-scour samples, root volume density, root weight density, cellulose content, and lignin content were higher at middle slope portions but there was no significant difference. (4) The root system could effectively improve the shear performance of the soil. The internal friction angle and cohesion of the root-soil matrix were higher than those of the bare ground control. Significant differences in cohesion was only observed for the up slope portion, between the terrace hedgerow and bare ground control, increasing by 45.67%. The internal friction angle and anti-scourability were better at middle and down slopes. Our study showed that the mechanical properties of the root-soil matrix were mainly affected by root volume density, root weight density, root surface area density, and cellulose content. In summary, the root diameter in the range 0.0<d≤ 1.0 mm substantially contributed to the mechanical properties of Dolichos lablab L. root and root-soil matrix. The anti-scourability of root-soil matrix was better at the middle and down slope portions; the shear performance of root-soil matrix was the best at the up slope portion, but anti-scourability was the worst. When promoting the planting of terrace hedgerows of Dolichos lablab L. soil and water conservation would be improved when they are planted in low and flat terrains (such as the middle and down slope portions). 参考文献 相似文献 引证文献

Soil moisture causes dynamic adjustments to root reinforcement that reduce slope stability

AbstractIn steep soil‐mantled landscapes, the initiation of shallow landslides is strongly controlled by the distribution of vegetation, whose roots reinforce the soil. The magnitude of root reinforcement depends on the number, diameter distribution, orientation and the mechanical properties of roots that cross potential failure planes. Understanding how these properties vary in space and time in forests remains a significant challenge. Here we test the hypothesis that spatio‐temporal variations in root reinforcement along a hillslope occur as a function of topographic soil moisture gradients. To test this hypothesis we compared root reinforcement measurements from relatively dry, divergent noses to relatively wet, convergent hollows in the southern Appalachian Mountains, North Carolina, USA. Our initial results showed that root reinforcement decreased in areas of higher soil moisture because the tensile strength of roots decreased. A post hoc laboratory experiment further demonstrated that root tensile strength decreased as root moisture content increased. This effect is consistent with other experiments on stem woods showing that increased water content in the cell wall decreases tensile strength. Our experimental data demonstrated that roots can adjust to changes in the external root moisture conditions within hours, suggesting that root moisture content will change over the timescale of large storm events (hours–days). We assessed the effects of the dynamic changes in root tensile strength to the magnitude of apparent cohesion within the infinite slope stability model. Slopes can be considerably less stable when precipitation‐driven increases in saturated soil depth both increase pore pressures and decrease root reinforcement. Copyright © 2016 John Wiley &amp; Sons, Ltd.

A numerical investigation into factors affecting the anchorage of roots in tension

SummaryThe arrangement of a plant's roots in the soil determines the ability of the plant to resist uprooting. We have investigated the influence of root morphology on anchorage using simple patterns of root systems and numerical simulation. The form and mechanical properties of roots were derived from results found in the literature. Major parameters determining soil characteristics, root patterns and strength were varied so that their influence could be evaluated. The design of the experimental method we used generated an optimal number of configurations of different root systems, the tensile resistances of which were calculated by two‐dimensional finite element analysis. We could quantify the influence of specific parameters, e.g. branching angle, number of lateral roots and soil cohesion, as well as global parameters such as total contact area, basal diameter and volume of the whole root system. We found that the number of roots and the diameter of roots were major components affecting the resistance to uprooting. The combination of topology and biomass explained 70% of the variation of tensile resistance.

The Effects of Mechanical Stimulation on the Morphology and Mechanics of Maize Roots Grown in an Aerated Nutrient Solution

The effects of local mechanical stimulation on local root growth was investigated in maize (Zea mays L.) growing in an aerated nutrient solution. The morphology and mechanical properties of primary nodal roots were compared between those that underwent a program of flexing and those that received no mechanical stimulation. Local mechanical stimulation had limited effects on the morphology of maize nodal roots; there was no significant effect of flexing on the diameter of primary nodal roots when compared with untreated roots. However, there were significant differences in root mass between treatments; there was a large decrease of 43% in the fresh and 41% in the dry mass of the fine roots in the flexed roots compared with the untreated roots. Surprisingly, there was only a small effect on the mass of the primary nodal roots: only at the fifth node was there a significant increase of 15% in the dry mass of flexed roots compared to those that received no mechanical stimulation. The effects of root flexure on the mechanical properties of the roots were more dramatic. Roots at both nodes 4 and 5 were significantly more rigid, stronger, and composed of a stiffer material than those that received no mechanical stimulation. After flexing, the primary nodal roots at the fifth node showed increases of 75% in the rigidity, 60% in the bending strength, and 70% in the bending modulus of the flexed roots compared to unstimulated roots. This study shows that the thigmomorphogenetic response, at least in maize roots, can be localized even down to individual roots and not just to regions of the root system.

Responses of the Root Systems of Sunflower and Maize to Unidirectional Stem Flexure

Abstract Plants of two contrasting species of herbaceous annuals, the dicot sunflower (Helianthus annuusL.) and the monocot maize (Zea maysL.), grown in the glasshouse were subjected to regular unidirectional stem flexure. Differences in morphology and mechanical properties of roots and shoots were then investigated. Root systems were divided into quadrants around the axis of stimulation and differences in root morphology and mechanics between the zones were investigated. There were considerable differences between roots in the leeward and windward zones compared with roots perpendicular to the axis of stimulation. First-order lateral roots in both species were thicker, more rigid and more numerous. These results suggest that plant roots respond locally to mechanical stimulation. There were, however, also differences in the responses of the two species. In sunflower, the tap root and stem base became elliptical in cross section with the major axis lying in the plane of stimulation. The lateral roots of flexed sunflowers in both the leeward and windward zones showed similar growth responses: roots were thicker, more numerous and weighed more than those in the perpendicular zones. However, only leeward roots showed significant differences in their mechanical properties; roots were more rigid, stronger and stiffer. In contrast, the leeward roots of maize were thicker and more numerous, with a greater biomass than the windward roots. However, only roots in the windward zone were stiffer than those in the perpendicular zone. These differences between sunflower and maize are related to their contrasting anchorage mechanics.

Effects of Vibration on Mechanical Properties and Biomass Allocation Pattern ofCapsella bursa-pastoris(Cruciferae)

The herbaceous dicot speciesCapsella bursa-pastoris(Cruciferae) was used to determine the influence of chronic mechanical perturbation on the biomass allocation pattern (i.e. dry weight distribution among roots, stems and reproductive structures) and the mechanical properties of roots and stems (i.e. tensile breaking stress and Young's modulus). It was hypothesized that mechanically stimulated plants would allocate more of their total biomass to root systems and less to shoots compared to control plants and that the breaking stress (a measure of strength) and Young's modulus (a measure of material stiffness) would increase for roots and decrease for stems because these responses would adaptively reduce the bending moment at the base of shoots and increase the anchorage strength of root systems. It was also hypothesized that mechanical perturbation would maladaptively reduce the relative fitness of individuals by reducing biomass allocation to their reproductive organs and the ability to broadcast seeds by means of elastic stem flexure. These hypotheses were tested by vibrating cultivated plants for 60 s every day during the course of growth to maturity and comparing their dry weight distributions and the mechanical properties of their body parts (measured in tension) to those of undisturbed control plants. Based on a total of 51 experimentally manipulated and 44 control plants for which mechanical properties were successfully tested, chronic organ flexure resulted in more massive root systems and less massive vegetative shoots, increased the magnitudes of root breaking stress and Young's modulus and had the reverse effect on stems, reduced the dry weight of reproductive structures at maturity, delayed the formation of the first mature flower and fruit, and accelerated the on-set of plant senescence compared to control plants. These responses to chronic organ flexure are interpreted to be vegetatively adaptive, since they reduce the probability of stem and root failure as a consequence of wind-pressure or foraging, and to be reproductively maladaptive, since they reduce reproductive effort and the ability to mechanically discharge seeds.