In this study, we present an on-chip analytical method using a microfluidic device to characterize the mechanical properties in growing roots. Roots are essential organs for plants and grow under heterogeneous conditions in soil. Especially, the mechanical impedance in soil significantly affects root growth. Understanding the mechanical properties of roots and the physical interactions between roots and soil is important in plant science and agriculture. However, an effective method for directly evaluating the mechanical properties of growing roots has not been established. To overcome this technical issue, we developed a polydimethylsiloxane (PDMS) microfluidic device integrated with a cantilevered sensing pillar for measuring the protrusive force generated by the growing roots. Using the developed device, we analyzed the mechanical properties of the roots in a model plant, Arabidopsis thaliana. The root growth behavior and the mechanical interaction with the sensing pillar were recorded using a time-lapse microscopy system. We successfully quantified the mechanical properties of growing roots including the protrusive force and apparent Young's modulus based on a simple physical model considering the root morphology. (c) 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Understanding the anchorage of a complex root system architecture (RSA) in soil upon tree overturning is vital to evaluate tree stability under lateral loads. Empirical correlations between root anchorage capacity and root morphological traits have been established, but the role of soil in these correlations has been ignored. This study developed and validated a threedimensional finite element model and then used it to investigate the underlying mechanisms of root-soil load transfer mechanisms in terms of the evolution of soil stress states and root strength mobilisation during overturning. Two root traits--radial distance and embedded depth--influenced root anchorage capacity remarkably. The pattern of soil stress state evolution near taproots and laterals was remarkably different. Roots that displaced in the direction more aligned with the soil's major principal stress were more effective to mobilise their strength to resist against overturning. The failure envelope defined by the normalised peak moment capacity in the x- and y-direction of the asymmetric RSA was elliptic, displaying anisotropic overturning under combined load conditions.

This study used triaxial tests to examine the impact of the root diameter of Cunninghamia lanceolata (Chinese fir) on the mechanical behavior of sand, including stress-strain development, strength, volumetric strain, and failure envelope. It also revealed the reinforcement mechanisms of roots with different diameters based on root-soil interactions. The results showed the following: (1) The addition of roots significantly enhanced sand strength and reduced volumetric deformation. The average peak strength increased by 31.8%, while the average peak volumetric strain decreased by 34.3%. (2) Roots provided additional cohesion and increased the friction angle of the sand, causing the failure envelope to shift upward and deflect. (3) Smaller-diameter roots improved the mechanical properties of sand more significantly, leading to higher peak strength, shear strength parameters, and smaller volumetric deformation. As the root diameter increased from 1 mm to 5 mm, the peak strength ratio decreased from 1.78 to 1.13, and the peak volumetric strain increased from 0.48 to 0.79. (4) Smaller-diameter roots, which form denser networks, allowing more roots to resist loads, and have a higher elastic modulus providing greater tensile stress, also possess higher tensile strength and critical sliding tensile stress, making them less likely to fail, thereby making the mechanical reinforcement of sand more significant.

Background and aimsUrban trees in coastal cities like Hong Kong may suffer from an uprooting failure when subjected to extreme winds. A proper numerical model for tree uprooting simulation can help to select tree species or soil types that better resist uprooting failure. However, modeling tree uprooting is challenging as it is a cross-disciplinary problem involving complex root system architectures (RSAs) and large deformation of both roots and soils. This study aims to develop a hybrid numerical model that combines truss elements and material point method (MPM) to simulate the entire large-deformation uprooting process of trees with complex RSAs.MethodsThe tree uprooting model is developed by coupling truss elements in finite element method (FEM) with MPM. Laboratory pull-out tests using artificial roots and real root cuttings are adopted to validate the developed model. A comparative study is performed to investigate the difference between using complex and simplified RSAs in tree uprooting simulations.ResultsThe developed model provides consistent predictions of peak load, critical displacement and failure mode when compared with results from laboratory tests. Moreover, the comparative study shows that the uprooting resistance obtained with a complex RSA is higher than that with a simplified RSA. The difference varies with the soil and root mechanical properties.ConclusionThe developed hybrid model offers a novel way for simulating an entire tree uprooting process involving large deformations and complex RSAs. The study shows that using a simplified RSA to approximate the complex RSA might result in misleading failure modes.

Understanding the pore water pressure distribution in unsaturated soil is crucial in predicting shallow landslides triggered by rainfall, mainly when dealing with different temporal patterns of rainfall intensity. However, the hydrological response of vegetated slopes, especially three-dimensional (3D) slopes covered with shrubs, under different rainfall patterns remains unclear and requires further investigation. To address this issue, this study adopts a novel 3D numerical model for simulating hydraulic interactions between the root system of the shrub and the surrounding soil. Three series of numerical parametric studies are conducted to investigate the influences of slope inclination, rainfall pattern and rainfall duration. Four rainfall patterns (advanced, bimodal, delayed, and uniform) and two rainfall durations (4h intense and 168-h mild rainfall) are considered to study the hydrological response of the slope. The computed results show that 17% higher transpiration-induced suction is found for a steeper slope, which remains even after a short, intense rainfall with a 100-year return period. The extreme rainfalls with advanced (PA), bimodal (PB) and uniform (PU) rainfall patterns need to be considered for the short rainfall duration (4 h), while the delayed (PD) and uniform (PU) rainfall patterns are highly recommended for long rainfall durations (168 h). The presence of plants can improve slope stability markedly under extreme rainfall with a short duration (4 h). For the long duration (168 h), the benefit of the plant in preserving pore-water pressure (PWP) and slope stability may not be sufficient.

Biochar amendment have been explored recently for improving hydro-mechanical properties of landfill cover system and enhancing the vegetation for the ecological restoration of post closure landfills. Existing studies have predominantly focused on the hydro-mechanical properties of biochar-amended rooted soils and yet few studies have comprehensively investigated their gas permeability functions in response to unsaturated conditions. The objective of this study is to experimentally and theoretically investigate the coupled effects of biochar and root intensity on CO2 gas permeability in unsaturated soil. Biochar-amended rooted soil was prepared by growing Chrysopogon zizanioides on granite residual soils with biochar at a mas ratio of 5 %. Gas permeability and unsaturated soil properties (i.e., suction and degree of saturation) were monitored simultaneously. Due to the presence of roots, the maximum gas permeability, hydraulic conductivity, and suction increased by 200 %, 600 %, and 50 %, respectively, compared with bare soil. This was attributed to preferential flow, micropore increasement and negative pressure induced by root growth. However, biochar addition decreased the maximum gas permeability and hydraulic conductivity by 21 % and 33 %, respectively. This was attributed to the pore filling function of biochar, increased capillarity due to intrapore of biochar, and presence of surface functional groups in biochar promoting CO2 adsorption. A newly developed model was proposed to predict gas permeability with respected to unsaturated soil properties. It was revealed that the gas permeability function of rooted soils showed a strong dependence on the measured root length density. This study highlights the significance of adopting biochar in mitigation of gas emissions in vegetated landfill cover system.

The interface between plants' roots and soil is strongly affected by rhizodeposits, especially mucilage, that change mechanical and hydrological behaviour. In addition to impacts to aggregation, water capture and root penetration, rhizodeposits may also affect the pull-out resistance of plant roots. Due to the complex architecture of plant roots and an inability to restrict rhizodeposit production, this study used a simplified system of wooden skewers to simulate roots and chia seed mucilage as a model to simulate rhizodeposit compounds. Pull-out tests were then carried out to measure the impacts of mucilage, and one (WD1) or two (WD2) cycles of wetting and drying of soils. Using a mechanical test frame, the maximum pull-out resistance (Fmax) and pull-out displacement (dL) were recorded, allowing for pull-out energy (E), average pull-out force (F over bar $$ \overline{F} $$) and bond strength (tau max) to be calculated. The results showed that all pull-out parameters of the samples with added rhizodeposit compounds tended to decrease between WD1 and WD2, but they were still significantly greater than without the added mucilage. The model rhizodeposit increased all pull-out parameters by a minimum of 30%. With an additional wet-dry cycle, the mucilage tended to cause a decline in pull-out parameters relative to a single wet-dry cycle. This suggests mucilages could enhance the mechanical resistance of roots to pull-out, but resistance decreases over time with cycles of wetting and drying. To conclude, an important role of mucilage is pull-out resistance, which has relevance to plant anchorage and root reinforcement of soils.

A large volume of research reporting the pull-out behaviour of root systems is available, but no study has considered the effects of soil drainage. This work implemented a modified three-dimensional embedded beam element model in a finite element platform that solved model equations by using a fully hydromechanically coupled algorithm. The model was validated against published centrifuge pull-out tests on root analogues, and the validated model was then applied to study parametrically the influence of the ratio of uplift rate to soil hydraulic conductivity on pull-out behaviour. The results demonstrated that the model can well capture the prepeak behaviour of the root systems up to the peak pull-out resistance. The generation of negative pore-water pressure (pex) owing to soil dilation upon root-soil interfacial shearing was the major reason for increased pull-out resistances under partially drained conditions. Compared with other root systems, root systems with smaller branch angles and deeper branch depths mobilised considerably more significant plastic deviatoric strains in the soil in their vicinity, generating more negative pex. Hyperbolic dimensionless backbone curves were derived to explain the transitional pull-out behaviours of root systems of different geometries under drainage conditions that ranged from fully drained to undrained.