Root anatomical traits contribute to deeper rooting of maize under compacted field conditions

© The Author(s) 2020. To better understand the role of root anatomy in regulating plant adaptation to soil mechanical impedance, 12 maize lines were evaluated in two soils with and without compaction treatments under field conditions. Penetrometer resistance was 1–2 MPa greater in the surface 30 cm of the compacted plots at a water content of 17–20% (v/v). Root thickening in response to compaction varied among genotypes and was negatively associated with rooting depth at one field site under non-compacted plots. Thickening was not associated with rooting depth on compacted plots. Genotypic variation in root anatomy was related to rooting depth. Deeper-rooting plants were associated with reduced cortical cell file number in combination with greater mid cortical cell area for node 3 roots. For node 4, roots with increased aerenchyma were deeper roots. A greater influence of anatomy on rooting depth was observed for the thinner root classes. We found no evidence that root thickening is related to deeper rooting in compacted soil; however, anatomical traits are important, especially for thinner root classes

Spectral and growth characteristics of willows and maize in soil contaminated with a layer of crude or refined oil

Remote sensing holds great potential for detecting stress in vegetation caused by hydro-carbons, but we need to better understand the effects of hydrocarbons on plant growth and specific spectral expression. Willow (Salix viminalis var. Tora) cuttings and maize (Zea mays var. Lapriora) seedlings were grown in pots of loam soil containing a hydrocarbon-contaminated layer at the base of the pot (crude or refined oil) at concentrations of 0.5, 5, or 50 g·kg−1 . Chlorophyll concen-tration, biomass, and growth of plants were determined through destructive and nondestructive sampling, whilst reflectance measurements were made using portable hyperspectral spectrometers. All biophysical (chlorophyll concentration and growth) variables decreased in the presence of high concentrations of hydrocarbons, but at lower concentrations an increase in growth and chlorophyll were often observed with respect to nonpolluted plants, suggesting a biphasic response to hydrocarbon presence. Absorption features were identified that related strongly to pigment concentration and biomass. Variations in absorption feature characteristics (band depth, band area, and band width) were dependent upon the hydrocarbon concentration and type, and showed the same biphasic pattern noted in the biophysical measurements. This study demonstrates that the response of plants to hydrocarbon pollution varies according to hydrocarbon concentration and that remote sensing has the potential to both detect and monitor the variable impacts of pollution in the landscape.Atmospheric Remote Sensin

Root hairs aid soil penetration by anchoring the root surface to pore walls

The physical role of root hairs in anchoring the root tip during soil penetration was examined. Experiments using a hairless maize mutant (Zea mays: rth3–3) and its wild-type counterpart measured the anchorage force between the primary root of maize and the soil to determine whether root hairs enabled seedling roots in artificial biopores to penetrate sandy loam soil (dry bulk density 1.0–1.5g cm(−3)). Time-lapse imaging was used to analyse root and seedling displacements in soil adjacent to a transparent Perspex interface. Peak anchorage forces were up to five times greater (2.5N cf. 0.5N) for wild-type roots than for hairless mutants in 1.2g cm(−3) soil. Root hair anchorage enabled better soil penetration for 1.0 or 1.2g cm(−3) soil, but there was no significant advantage of root hairs in the densest soil (1.5g cm(−3)). The anchorage force was insufficient to allow root penetration of the denser soil, probably because of less root hair penetration into pore walls and, consequently, poorer adhesion between the root hairs and the pore walls. Hairless seedlings took 33h to anchor themselves compared with 16h for wild-type roots in 1.2g cm(−3) soil. Caryopses were often pushed several millimetres out of the soil before the roots became anchored and hairless roots often never became anchored securely.The physical role of root hairs in anchoring the root tip may be important in loose seed beds above more compact soil layers and may also assist root tips to emerge from biopores and penetrate the bulk soil

Quantifying soil reinforcement by fibrous roots

Reinforcement of soil by fibrous roots is crucial for preventing soil erosion and degradation,yet the underlying mechanisms are poorly understood. Without fully understanding root enmeshment within the soil matrix, and root biomechanical properties key for increasing soil shear strength, adoption in main stream civil engineering, understanding of natural systems and implications to agricultural soil management will be limited. Within this thesis theunderlying processes that drive root reinforcement of soils were assessed through a variety oflaboratory and field based experiments. This included recent advances in geotechnical engineering and model plant lines with specific root traits. Plant lines were barley (Hordeum vulgare) from a mapping population where differences in root hairs, tortuosity and lignin biosynthesis were previously identified by screening large numbers of mutants.The initial hypothesis was that root numbers and area would control shear reinforcement, this was tested by altering planting density in both glasshouse and field experiments using one barley variety. After 5 weeks in the field, planting density was related to both reinforcement and root area ratio (RAR), with a 6.7 ?1.40 kPa, or 190%, increase in shear strength between 0 and 950/m2. By 20 weeks in the field shear strength increased by only 29%. The glasshouse study showed an increase of 53%, with a positive correlation to planting density.Relationships between root number and shear strength were not explicit, however, highlighting further possible interactions between soil shear strength and root inclusions. Various underlying processes were then investigated. Barley mutants, with differences in root hairs and tortuosity, were compared to parent lines. Hairless mutants had different root tensile strength characteristics, but experimental difficulties (malfunctioning logging hardware) prohibited detection of impacts on shear strength. A refined study was then performed that also incorporated the influence of abiotic stress from compaction and waterlogging. Barley with down-regulated lignin biosynthesis (Bowman 140) had increased nodalroot tensile strength of 37% compared to the parent line (Bowman Line) under good growth conditions, but this changed to -31% for compacted and 26% for water-logged soil. In addition to abiotic stress, the age of the roots (measured as distance from root tip) type of root (seminal, nodal or lateral) had a large impact on biomechanical behaviour.EThOS - Electronic Theses Online ServiceBBSRC [BBS/S/K/2005/12211A]GBUnited Kingdo

3D deformation field in growing plant roots reveals both mechanical and biological responses to axial mechanical forces

Strong regions and physical barriers in soils may slow root elongation, leading to reduced water and nutrient uptake and decreased yield. In this study, the biomechanical responses of roots to axial mechanical forces were assessed by combining 3D live imaging, kinematics and a novel mechanical sensor.[br/] This system quantified Young's elastic modulus of intact poplar roots (32 MPa), a rapid <0.2 mN touch-elongation sensitivity, and the critical elongation force applied by growing roots that resulted in bending. Kinematic analysis revealed a multiphase bio-mechanical response of elongation rate and curvature in 3D. Measured critical elongation force was accurately predicted from an Euler buckling model, indicating that no biologically mediated accommodation to mechanical forces influenced bending during this short period of time. Force applied by growing roots increased more than 15-fold when buckling was prevented by lateral bracing of the root. The junction between the growing and the mature zones was identified as a zone of mechanical weakness that seemed critical to the bending process.[br/] This work identified key limiting factors for root growth and buckling under mechanical constraints. The findings are relevant to crop and soil sciences, and advance our understanding of root growth in heterogeneous structured soils

Root reinforcement: continuum framework for constitutive modelling

The mechanical contribution of plant roots to soil strength has typically been studied at the ultimate limit state only. Since many geotechnical problems are related to serviceability, such as deformation of infrastructure, a new constitutive modelling framework is introduced. The rooted soil is treated as a composite material with separate constitutive relationships for soil and roots, and a comprehensive stress-strain relationship for the root constituent is presented.The model is compared to direct shear experiments on field soil reinforced with gorse, grass and willow roots, as well as an existing root reinforcement model based on Winkler-spring supported beam theory.The results show that both the newly developed model and the beam-type model yield good predictions for the evolution of root-reinforced shear strength as a function of increasing shear displacements. Both successfully capture the large deformations required to reach peak reinforcement, the reduction in reinforcement due to root breakage and the presence of significant reinforcement even after very large deformations, associated with root slippage.Since both fibre and beam models only require physically meaningful input parameters, they can be useful tools to study the mobilisation of rooted soil strength and simulate the response of rooted soil in continuum-based numerical simulations