Root Tensile Strength Research Articles

Methods to measure the mechanical behaviour of tree roots: A review

The presence of forests on hillslopes significantly reduces the slopes susceptibility to rainfall triggered shallow landslides. This is due largely to the reinforcement of the hillslope soil by tree roots which increase the shear strength of the soil, and in some instances, anchor the soil mantle to the underlying bedrock by deeply penetrating roots. Quantifying the reinforcing effects of tree roots within soils and the evaluation of hillslope stability using geomechanical and numerical models relies on a realistic representation of the characteristics of tree roots distribution within the hillslope and the mechanical strength of those roots. The variety of experimental methods that have been developed since the 1960s and are used to generate these root strength and rooted-soil shear-strength data are reviewed. The majority of these studies have focused on determining the tensile strength of individual roots by loading the root in a pulling device until it breaks and/or determining the shear-strength of rooted soil in comparison to non-rooted soil in a Coulomb-type shear-box test. These studies have also generally either examined mature root systems in the field or relatively young plants grown in special containers specifically designed for tensile tests or laboratory shear-box tests. A particular difficulty that most studies have encountered is fixing or securing the ends of roots in the attachment device of the testing apparatus (so called root-pullers or tensile testing machines) as the various styles of clamping employed can easily damage the root which reduces the measured strength or otherwise results in an unrealistic test result. Laboratory shear-box tests encounter a similar difficulty in that the roots are not generally fixed or constrained at the base of the shear-box; field shear-box tests tend to avoid this problem as the roots are present in their natural anchoring characteristics in the soil and rock substrate. A result universally reported in rooted soil shear-box test studies is that the peak shear-strength of rooted soil significantly exceeds the peak shear-strength of that soil in a non-rooted condition and that the rooted-soil peak strength is typically recorded at a shear-displacement distance several times that of the non-rooted soil. This result fundamentally explains the reduced susceptibility of forested hillslopes to shallow landslides. A variety of solutions developed to deal with the difficulties that root and rooted-soil tests present are outlined. A set of suggested protocols for conducting root tensile tests and field pullout tests are also presented. It is intended that the adoption of these protocols will enable more effective and direct comparisons of test results and more confident interpretation with respect to the similarities and differences between test results generated from different species and field sites.

Scaling of the reinforcement of soil slopes by living plants in a geotechnical centrifuge

Understanding root-reinforcement of vegetated slopes is hindered by the cost and practicality of full scale tests to explore global behaviour at the slope scale, and the idealised nature of smaller-scale testing to date that has relied on model root analogues. In this study we investigated the potential to use living plant roots in small scale experiments of slope failure that would use a geotechnical centrifuge to achieve soil stress states comparable to those in the field at homologous points. Three species (Willow, Gorse and Festulolium grass), corresponding to distinct plant groups with different root architecture and ‘woodiness’ were selected and cultivated for short periods (2 months for Willow and Festulolium grass, 3 months for Gorse). The morphologies, tensile strength and Young’s modulus of these juvenile root samples and their effects on increasing soil shear strength were then measured (via tensile tests and direct shear tests) and compared with published results of more mature field grown specimens. Our test results show that when all juvenile root samples of the three species are considered, the commonly used negative power law does not fit the data for the relationship between root tensile strength and root diameter well, resulting in very low R2 values (R2<0.14). No significant differences in tensile strength were observed between roots with different diameter for Willow and Gorse, and the average root tensile strength for all juvenile root samples was 8.70±0.60MPa (Mean±SE), 9.50±0.40MPa, 21.67±1.29MPa for Willow, Festulolium grass and Gorse, respectively. However, a strong linear relationship was observed between tensile strength and Young’s modulus of the roots of the juvenile plants (R2=0.55, 0.69, 0.50 for Willow, Festulolium grass and Gorse, respectively). From a centrifuge modelling perspective, it was shown that using juvenile plants could potentially produce prototype root systems that are highly representative of corresponding mature root systems both in terms of root mechanical properties and root morphology when a suitable growing time (2 months) and scaling factor (N=15) are selected. However, it remains a challenge to simultaneously simulate the distribution of root biomass with depth of the corresponding mature plant. Therefore, a compromise has to made to resolve the conflicts between the scaling of rooting depth and root reinforcement, and it is suggested that 1:15 scale would represent a suitable compromise for studying slope failure in a geotechnical centrifuge.

Root morphology and biomechanical characteristics of high altitude alpine plant species and their potential application in soil stabilization

Glacial forefields host young, poorly developed soils with highly unstable environmental conditions. Root system contribution to soil stabilization is a well-known phenomenon. Identifying the functional traits and root morphology of pioneer vegetation that establish on forefields can provide information useful in the practical application of plants in land restoration of high altitude mountain sites.This study aims to gather information on the root morphology and biomechanical characteristics of the 10 most dominant pioneer plant species of the forefield of Lys Glacier (NW Italian Alps).X-ray Computed Tomography (X-ray CT) was used to visualize and quantify non-destructively the root architecture of the studied species. Samples were cored directly from the forefield. Data on root traits such as total root length, rooting depth, root diameter, root length density and number of roots in relation to diameter classes as well as plant height were determined and compared between species. Roots were also tested for their tensile strength resistance.X-ray CT technology allowed us to visualize the 3D root architecture of species intact in their natural soil system. X-ray CT technology provided a visual representation of root–soil interface and information on the exact position, orientation and elongation of the root system in the soil core. Root architecture showed high variability among the studied species. For all species the majority of roots consisted of roots smaller than 0.5mm in diameter. There were also considerable differences found in root diameter and total root length although these were not statistically significant. However, significant differences were found in rooting depth, root length density, plant height and root tensile strength between species and life forms (dwarf shrub, forb, graminoid). In all cases, root tensile strength decreased with increasing root diameter. The highest tensile strength was recorded for graminoids such as Luzula spicata (L.) DC. and Poa laxa Haenke and the lowest for Epilobium fleischeri Hochst.The differences in root properties among the studied species highlight the diverse adaptive and survival strategies plants employ to establish on and thrive in the harsh and unstable soil conditions of a glacier forefield. The data determined in this study could provide a significant contribution to a database that allow those who are working in land restoration and preservation of high altitude mountain sites to employ native species in a more efficient, effective and informed manner.

Root biomechanical properties during establishment of woody perennials

Background and aimsSoil bio-engineering using vegetation is an environmentally friendly solution to stabilise soil slopes. This study investigates tensile strength, Young’s modulus, and root diameter relationships for establishing woody perennials. MethodsSpecimens of ten woody European shrubs and small trees were transplanted into sandy loam soil to establish for six months. Root tensile strength and Young’s modulus were measured as well as the root length-diameter distribution. The effect of root water status on root diameter was evaluated for Scotch Broom. ResultsMore than half of the root length for all species was thinner than 0.5mm diameter. Typical tensile strengths were <40MPa, with Young’s modulus <600MPa. Negative power relationships between root strength and root diameter existed only for Gorse and Spindle, whilst Blackthorn, European Box and Holly showed slight increase in tensile strength with diameter. Hawthorn, Hazel and Privet showed rapid initial increase in strength with diameter followed by strength decrease with diameter, post-peak. Young’s modulus was linearly related to tensile strength for all ten species (P<0.001; R2 values 17%–64%). Root diameter, investigated for Scotch Broom, depended strongly on root water potential and root water content by mass. Root water content could influence considerably the calculations of tensile strength. Discussion and conclusionRoot tensile strength-diameter relationships often do not follow a negative power law, and depends strongly on taxa. Young’s modulus was strongly related to tensile strength of roots for certain species. Water status of roots strongly influences root diameter and hence strength and Young’s modulus properties, and must be controlled carefully in experiments.

The effect of Bahiagrass roots on soil erosion resistance of Aquults in subtropical China

Herbaceous species, especially their roots, are believed to have an important role in enhancing soil strength and protecting soil against erosion. This study evaluated the effects of root distribution characteristics on soil shear resistance and soil detachment rates, correlations among root mechanical properties, root chemical composition and root parameters, and whether the Wu-Waldron model can accurately estimate soil reinforcement by roots. Bahiagrass (Paspalum notatum) was planted in planter boxes by overlapping four rectangle frames (0.4×0.1×0.1m). A series of laboratory tests of direct shear strength and soil detachment were conducted on two soils that were derived from granite and shale with different soil depths and sowing densities. The results indicated that soil aggregate stability was positively correlated with root characteristics. Over 70% of the total measured root parameters were distributed in the upper 20cm of the soil, and they decreased with increasing soil depth and decreasing sowing density. The tensile properties (root tensile strength and root tensile force) were significantly correlated with root diameter. The contents of root main chemical compositions were significantly correlated with root diameter while hemicellulose showed no obvious trend with root diameter (P=0.12). Root tensile strength and root tensile force were also significantly correlated with the contents of these four compositions, except hemicellulose. The relative soil detachment demonstrated a significant negative correlation with root parameters with sowing densities from 5 to 30gm−2, and it remained at a relatively low value when the sowing density was >20gm−2. The soil detachment rate, erodibility factor and critical flow shear stress were well correlated with the root area ratio, sowing density, and soil depth. The Wu-Waldron model was found to be inappropriate for these soils, as it overestimated additional soil shear strength due to roots by 152–366% in the upper 20cm, and 11–48% in deeper soil layers. This study demonstrated that the root area ratio was a more suitable root characteristic parameter that contributes to soil reinforcement.

STRENGTH CHARACTERISTICS OF SINGLE ROOT TENSILE TEST OF HERBS AND SHRUBS IN COLD AND ARID ENVIRONMENTS

This paper is to further explore the mechanical effects of plants in slope protection in cold and arid environments. It selects five kinds of native herbs and shrubs as the test samples. They are suitable for the local climate conditions. They are planted in the self-built test area in this research. The single tensile tests are carried out to systematically analyze the strength characteristics of plant roots of the five kinds of herbs and shrubs. The results show the follows. The single root tensile resistances increases with the diameter increasing. Power relations exist between single root tensile resistances and root diameters of the herbs and shrubs respectively. Meanwhile, the single root tensile strengths increase with the diameter decreasing. Power relations exist between single root tensile strengths and root diameters of five kinds of herbs and shrubs respectively. The single root tensile strength of Elymus nutans Griseb is bigger than that of Agropyron trachycaulum(Linn.) Gaertn, while the sequence of the single tensile strengths of shrubs from big to small is Caragana korshinskii Kom,Zygophyllum xanthoxylon(Bunge) Maxim. and Nitraria tangutorum Bobr. Besides, some phenomena are shown by comparing and analyzing the stress-strain relationship curves of tensile tests of three kinds of shrubs in the vegetative period of 1a and 2a. That is,in the early single root tensile test of shrubs, there is a linear relationship between stress and strain, which shows the elastic material properties. Until the middle and late stage of the test, the relationship between stress and strain is nonlinear and shows the elastic-plastic material properties. Further research shows a downward trend of the largest elongation of the shrub single root with the increasing of vegetative period. The results of the study have a theoretical researching and practical guiding significance in the prevention and treatment of geological disasters such as shallow landslide and soil erosion in the study area and in the protection of the regional ecological geological environment.

How gauge length and loading rate influence the root tensile strength of Betula platyphylla

The presence of vegetation is beneficial for slope stabilization. Root tensile strength is crucial for the enhancement of soil shear resistance by vegetation. In this study, using Betula platyphylla as the model species, we focused on the mechanisms by which loading rate, root gauge length, and diameter affected single-root tensile strength. This study involved factors influencing root tensile strength including root diameter, gauge length, and loading rate, as well as root moisture content. The results demonstrated that (1) loading rate had little influence on root tensile strength as a whole; (2) using the roots in gauge length of 50 mm (2 in) as examples, the effect of root diameter on tensile strength was significant at the loading rate of 10 mm min−1 (0.4 in min−1), but was minor at the rates of 100 and 200 mm min−1 (3.4 and 7.8 in min−1); (3) gauge length and root tensile strength showed a significant negative linear correlation but with high variability; (4) root diameter and tensile strength showed a negative power function correlation; (5) the increase of loading rate reduced the effect of diameter on tensile strength; and (6) the difference in root weight within one month was not significant, and we therefore ignored the effect of moisture content on root mechanical characteristics. This study can serve as a point of reference for the further studies on mechanics of root system.

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 Tensile Strength of Bermuda Grass and Vetiver Grass in Terms of Root Reinforcement Ability Toward Soil Slope Stabilization

An examination on root characteristics and root properties has been implemented in this study. Two types of bioengineering were chose which are Vetiver grass and Bermuda grass as these grasses were widely applied for slope stabilization. The root samples were taken to the laboratory to investigate its classification, characteristics and strength. The root of both grasses was found grow with fibrous root matrix system. In terms of root anchorage, the root matrix system of Vetiver grass was exhibits more strengthen than the Bermuda grass. However, observation on root image from Scanning Electron Microscope test reveals that the root of Vetiver grass becomes non-porous as the moisture content reduced. Meanwhile, the root tensile strength of Bermuda grass was obtained acquired low value with higher percentage of moisture content, root morphology and bonding strength. The results indicated that the root tensile strength is mainly influence by percentage of moisture content and root morphology.

Grapevine root system strength in an area susceptible to shallow landslides for slope stability assessment

During the last few years, several rainfall-induced shallow landslides affected the Oltrepo Pavese (northern Italy) hilly slopes cultivated with vineyards, causing in many cases the destruction of the cultivated areas. A study of the contribution of the grapevines, and in particular of their roots, is thus fundamental for slope stability analyses and consequently for the slope preservation. In this work, the preliminary results of some experimental investigations on grapevine root system contribution to soil reinforcement are presented. The density of grapevine roots shows great variations between the different sites, with highest values in the first 0.6 m. Roots are usually present till the contact between soil and weathered bedrock. The trends obtained showed that the number of grapevine roots seemed lower in slopes affected by shallow landslides. Despite the differences in the soil features, type of bedrock, grapevine age and vineyard practices, a unique relationship between root diameter and root tensile strength can be identified. The root reinforcement was evaluated applying the Fiber Bundle Model and through back analysis on slopes previously affected by shallow stability failures. Additional root reinforcement reached values till 18.3 kPa in slopes with cultivated vineyards. The root reinforcement in correspondence of the sliding surface reaches values till 8 kPa for vineyards and between 0.9 and 1.5 kPa for abandoned vineyards.

Quantifying the contribution of grapevine roots to soil mechanical reinforcement in an area susceptible to shallow landslides

Hilly slopes cultivated with vineyards are often affected by rainfall-induced shallow landslides that cause destruction and loss of the cultivations. For this reason, the assessment of mechanical contribution from grapevine roots is fundamental for slope stability analyses and consequently for the slope preservation. In this context, our work aims to quantitatively evaluate the soil reinforcement given by grapevine roots. The selected study area (13.4km2), located in the region of Oltrepò Pavese in Northern Italy, is characterized by a high shallow landslides density and is constituted by vineyards in steep slopes. The tested soils are Haplic Calcisols, Petric Calcisols and Calcic Gleysols, with silt loamy or silty clay loamy textures, from high to very high carbonate content and low organic carbon and nitrogen contents. The rootstock of the grapevine is a combination of Vitis berlandieri and Vitis riparia with root systems, which reach average depths of up to 1.5m. The grapevine root density (number of roots and Root Area Ratio) is rather variable and is strongly correlated to soil permeability. In fact, the results show that low permeable soils have small number of roots and occur near recent shallow slides. Despite the differences of soil features, type of bedrock, grapevine plants age, vineyards row orientation and season collection, a unique relationship between root diameter and root tensile strength has been identified. Root reinforcement, related to the grapevine root system and evaluated using Fiber Bundle Model, shows the lowest values in correspondence of sites characterized by the lowest soil permeability, as in the study case Calcic Gleysols. The sites with these soil features, actually, are also those most affected by shallow instability in the past, indicating that their great susceptibility to shallow landslides. The results of this study also highlight the role played by different amounts of grapevine root reinforcement on the slope stability during rainfall conditions, which could lead to triggering, on the study area.

Direct Shear Testing of Clayey Sand Reinforced With Live Stake

Large direct shear tests were conducted on compacted clayey sand, reinforced with Jatropha live stakes of various ages, under saturated and unsaturated conditions. The relationship between root cohesion and the side root area ratio appeared linear. For samples with stake stabilization but no fibrous roots, a stake installed in a larger drilled hole appeared to contribute lower strength increase and greater shear displacement than a stake in a smaller hole. All the unsaturated samples at a suction of approximately 23 kPa exhibited strain-hardening behavior. The rate of strength increase due to the root was affected by the soil's suction. The additional strength due to live stake and fibrous root could be reduced by a factor of 3.5 if the conditions change from unsaturated (at about 23 kPa suction) to fully saturated. A new model was proposed to account for the influence of suction on root cohesion considering the suction effects on bond stress, root tensile strength, root tensile modulus, and shear zone thickness.

Symbiosis of Arbuscular Mycorrhizal Fungi and Robinia pseudoacacia L. Improves Root Tensile Strength and Soil Aggregate Stability.

Robinia pseudoacacia L. (black locust) is a widely planted tree species on Loess Plateau for revegetation. Due to its symbiosis forming capability with arbuscular mycorrhizal (AM) fungi, we explored the influence of arbuscular mycorrhizal fungi on plant biomass, root morphology, root tensile strength and soil aggregate stability in a pot experiment. We inoculated R. pseudoacacia with/without AM fungus (Rhizophagus irregularis or Glomus versiforme), and measured root colonization, plant growth, root morphological characters, root tensile force and tensile strength, and parameters for soil aggregate stability at twelve weeks after inoculation. AM fungi colonized more than 70% plant root, significantly improved plant growth. Meanwhile, AM fungi elevated root morphological parameters, root tensile force, root tensile strength, Glomalin-related soil protein (GRSP) content in soil, and parameters for soil aggregate stability such as water stable aggregate (WSA), mean weight diameter (MWD) and geometric mean diameter (GMD). Root length was highly correlated with WSA, MWD and GMD, while hyphae length was highly correlated with GRSP content. The improved R. pseudoacacia growth, root tensile strength and soil aggregate stability indicated that AM fungi could accelerate soil fixation and stabilization with R. pseudoacacia, and its function in revegetation on Loess Plateau deserves more attention.

Estimation of soil reinforcement by the roots of four post-dam prevailing grass species in the riparian zone of Three Gorges Reservoir, China

Soil erosion and bank degradation is a major post-dam concern regarding the riparian zone of the Three Gorges Reservoir. The development and succession of vegetation is a main countermeasure, especially to enhance bank stability and mitigate soil erosion by the root system. In this study, the roots of four prevailing grass species, namely, Cynodon dactylon, Hemarthria altissima, Hemarthria compressa, and Paspalum paspaloides, in the riparian zone were investigated in relation to additional soil cohesion. Roots were sampled using a single root auger. Root length density (RLD) and root area ratio (RAR) were measured by using the WinRHIZO image analysis system. Root tensile strength (T-R) was performed using a manual dynamometer, and the soil reinforcement caused by the roots was estimated using the simple Wu's perpendicular model. Results showed that RLD values of the studied species ranged from 0.24 cm/cm(3) to 20.89 cm/cm(3) at different soil layers, and RLD were significantly greater at 0-10 cm depth in comparison to the deeper soil layers (> 10 cm). RAR measurements revealed that on average 0.21% of the reference soil area was occupied by grass roots for all the investigated species. The measured root tensile strength was the highest for P. paspaloides (62.26 MPa) followed by C. dactylon (51.49 MPa), H. compressa (50.66 MPa), and H. altissima (48.81 MPa). Nevertheless, the estimated maximum root reinforcement in this investigation was 22.5 kPa for H. altissima followed by H. compressa (21.1 kPa), P. paspaloides (19.5 kPa), and C. dactylon (15.4 kPa) at 0-5 cm depth soil layer. The root cohesion values estimated for all species were generally distributed at the 0-10 cm depth and decreased with the increment of soil depth. The higher root cohesion associated with H. altissima and H. compressa implies their suitability for revegetation purposes to strengthen the shallow soil in the riparian zone of the Three Gorges Reservoir. Although the soil reinforcement induced by roots is only assessed from indirect indicators, the present results still useful for species selection in the framework of implementing and future vegetation recovery actions in the riparian zone of the Three Gorges Reservoir and similar areas in the Yangtze River Basin.

The role of the vineyards on slope stability: a case study from an area susceptible to shallow landslides

Hilly slopes cultivated with vineyards of Oltrepo Pavese (northern Italy) are often affected by rainfall-induced shallow landslides, which cause destruction and loss of the cultivations. The assessment of soil reinforcement of grapevine roots is then fundamental for slope stability analyses. In sites affected by shallow landslides, root density is lower, probably due to the lowest soil permeability. Despite the differences of soil features, type of bedrock, grapevine age and vineyards row orientation, an unique relationship between root diameter and root tensile strength can be identified. The total root reinforcement follows the trend of the root density. Grapevine roots can give a good reinforcement on soil, usually in the first 0.9-1.0 m from ground level.

Experimental Study on Native Plant Root Tensile Strength for Slope Stabilization

The use of plants for protection of slopes or river embankments against water and wind erosion is spreading in civil and environmental engineering. Naturalistic approach for slope stabilization has been more and more studied and experimented, and a genuine discipline, that integrates traditional geotechnical engineering methods, has been created: Bioengineering. To evaluate plants roots effect on soil shear strength and slope stability, theoretical and experimental studies about biotechnical and mechanical characteristics are needed, to better understand soil-root interaction mechanism. This work provides indications on mechanical strength parameters of some species of native plant roots. Tensile strength of two Mediterranean species have been analyzed caring out a series of experimental tests. Results indicate that tensile strength of roots is influenced by many factors, among which, the most important are root diameter, its moisture and the location where plants had grown up.

Evaluating soil reinforcement by plant roots using artificial neural networks

AbstractSoil reinforcement by plant roots and its response to influencing factors are very important for bank stability evaluation and control. Models with improved accuracy are urgently needed for evaluating soil reinforcement. Using a back‐propagation (BP) learning algorithm, an artificial neural network (ANN) model with five input variables, including the number of roots, root area ratio, root tensile strength, soil shear strength, and soil moisture content, was developed to simulate the response of soil reinforcement to these factors. A connection weight approach was used to understand the relative importance of each factor. Using a data set published in 2003 and collected in Australia, soil reinforcement of four trees, Casuarina glauca, Eucalyptus amplifolia, Eucalyptus elata and Acacia floribunda, was simulated using three models: BP‐ANN, one described by Wu et al. in 1979 and the 2005 fibre bundle model (FBM) of Pollen and Simon. Comparisons of results from these models showed that the BP‐ANN model most accurately estimated the soil reinforcement. The simulated results indicated that only the effect of soil moisture content on soil reinforcement was negative. The influence of the other four factors was positive, and the relative importance was in the order: root area ratio &gt; root tensile strength &gt; the number of roots &gt; soil shear strength. This study provides a new approach to soil reinforcement estimation and improves our understanding of soil resistance and bank stability.

Effect of root age on the biomechanics of seminal and nodal roots of barley (Hordeum vulgare L.) in contrasting soil environments

The biomechanics of root systems influence plant lodging resistance and soil structural stabilisation. Tissue age has the potential to influence root biomechanical properties through changes in cell wall chemistry, root anatomy and morphology. Within a root system the internal structures of roots are known to vary markedly within different root types. Nodal, seminal and lateral roots of Barley (Hordeum vulgare) have differing biomechanical behaviour in tension. This study examines the effects of root age on biomechanical properties of barley root types (Hordeum vulgare) under abiotic stress. Root age was determined as a function of the distance from root tip with abiotic stresses consisting of waterlogging and restriction to root elongation rate through increased soil bulk density. Linear regression analyses were performed on log-transformed tensile strength and Young’s modulus data with best fits determined for single and multiple parameter models to root morphological properties. Regression co-efficients and Akaike values showed that distance from root tip (taken as a proxy of root age) was the best single variable for prediction of both root tensile strength and Young’s modulus. Incorporation of both distance from root tip and root diameter and root type increased the reliability of predictions for root biomechanical properties from 47 to 57 % for tensile strength and 35 to 62 % for Young’s modulus. The age effect may partly explain some scatter in both Young’s modulus and tensile strength to diameter relationship, commonly cited in the literature.

Reducing soil erosion by improving community functional diversity in semi‐arid grasslands

Summary Great efforts have been made to control soil erosion by restoring plant communities in degraded ecosystems world‐wide. However, soil erosion has not been substantially reduced mainly because current restoration strategies lead to large areas of mono‐specific vegetation, which are inefficient in reducing soil erosion because of their simple canopy and root structure. Therefore, an advanced understanding of how community functional composition affects soil erosion processes, as well as an improved restoration scheme to reduce soil erosion, is urgently needed. We investigated the effect of community functional composition on soil erosion in restored semi‐arid grasslands on the Loess Plateau of China. Community functional composition of 16 restored grasslands was quantified by community‐weighted mean (CWM) and functional diversity (FD) trait values, which were calculated from nine plant functional traits of thirteen locally dominant plant species. Species richness and evenness were also measured. Soil erosion rates were measured using standard erosion plots. The multimodel inference approach was used to estimate the direction and the relative importance of these biodiversity indices in reducing soil erosion. A robust and strong negative effect of functional divergence (FDiv) on soil erosion was found. The prevalence of particular trait combinations can also decrease soil erosion. The greatest control over soil erosion was exerted when the community mean root diameter was small and the root tensile strength was great. Synthesis and applications: These findings imply that community functional diversity plays an important role in reducing soil erosion in semi‐arid restored grasslands. This means that current restoration strategies can be greatly improved by incorporating community functional diversity into restoration design. We propose a trait‐based restoration framework for reducing soil erosion, termed ‘SSM’ (Screening–Simulating–Maintaining). SSM aims to translate the target of community functional diversity into community assemblages that can be manipulated by practitioners. Based on this framework, a comprehensive procedure, highlighting functional diversity as the primary concern in determining optimal community assemblages, was developed to meet the pressing need for more effective restoration strategies to reduce soil erosion.

Root anatomical phenes predict root penetration ability and biomechanical properties in maize (Zea Mays).

The ability of roots to penetrate hard soil is important for crop productivity but specific root phenes contributing to this ability are poorly understood. Root penetrability and biomechanical properties are likely to vary in the root system dependent on anatomical structure. No information is available to date on the influence of root anatomical phenes on root penetrability and biomechanics. Root penetration ability was evaluated using a wax layer system. Root tensile and bending strength were evaluated in plant roots grown in the greenhouse and in the field. Root anatomical phenes were found to be better predictors of root penetrability than root diameter per se and associated with smaller distal cortical region cell size. Smaller outer cortical region cells play an important role in stabilizing the root against ovalization and reducing the risk of local buckling and collapse during penetration, thereby increasing root penetration of hard layers. The use of stele diameter was found to be a better predictor of root tensile strength than root diameter. Cortical thickness, cortical cell count, cortical cell wall area and distal cortical cell size were stronger predictors of root bend strength than root diameter. Our results indicate that root anatomical phenes are important predictors for root penetrability of high-strength layers and root biomechanical properties.