Study On The Microscopic Mechanism Of The Interaction Between Tall Festuca Root System And Sandy Soil Based On CT Scanning

In recent years,climate change has intensified the global water cycle,leading to frequent disasters such as typhoons,droughts,and extreme rainfall,making environmental geological disasters such as landslides and soil erosion increasingly prominent.Climate change has become a serious challenge facing countries.China has been actively participating in international efforts to address climate change,including participating in the Paris Agreement,supporting the work of the United Nations Framework Convention on Climate Change,and proposing strategic goals of carbon peak and carbon neutrality.Vegetation plays a crucial role in mitigating and adapting to climate change and natural disasters.Plant roots enhance soil stability by influencing saturation and pore structure,and have the ability to stabilize slopes,reduce erosion,and improve soil structure.They are an important part of ecological geotechnical engineering.Due to the relatively weak research on the hydraulic effects of roots on soil,the micro mechanisms and macro connections of vegetation’s hydraulic and mechanical effects on soil are still not very clear.The macro characteristics and engineering applications of vegetation soil lack micro theoretical verification.Strengthening research on the interaction between roots and soil at the micro level can reveal the regulatory mechanism of vegetation roots on soil hydraulic and mechanical processes,To provide scientific basis for formulating reasonable land management,ecological restoration strategies,and engineering construction experience in unsaturated soil layers of vegetation slopes.In order to study the interaction between tall fescue roots and sandy soil,a fourdimensional CT scanning experiment(3D+time)was conducted using microfocal CT scanning technology.The growth process of young roots of tall fescue in sandy soil was tracked within 2,4,6 and 8 days after seed transplantation.In order to solve the problem of partial volume effect(PVE)in images and the similarity of root water grayscale in CT images,a semi-automatic segmentation process was designed to accurately segment root soil CT images.Using the results of four phase segmentation,the evolution of root three-dimensional parameters with the growth process was analyzed.In addition,porosity evolution analysis based on pore network models,representative volume element(RVE)meshes,and local RVE,as well as saturation evolution analysis based on RVE meshes and local RVE,have been conducted to quantify root soil interaction from a four-dimensional structure.In addition,considering the combination of CT images and finite element models,a three-dimensional finite element model based on real root morphology was established,and based on this model,the water absorption process of root morphology during four growth periods was simulated.The main conclusions of this article are as follows:(1)Microfocal CT is a powerful tool for non-destructive imaging of plant roots and their surrounding soil,which can visualize the detailed spatial structure of roots,soil particles,and water clusters with high spatial resolution.An 8-day growth study was conducted to gain insight into the evolution of root structure and soil characteristics over time.The effects of different root growth times on soil water distribution in tall fescue were studied by designing a 48 hour interval irrigation model.The accuracy of microanalysis was evaluated by comparing the growth and evaporation of tall fescue in the control group.It has been verified that X-ray radiation has no effect on the growth of roots and plants in the short term.(2)A semi-automatic quaternization segmentation process for root soil CT images is proposed,especially for water and roots in images with similar PVE and gray levels.This process combines interactive threshold and morphological filters to separate particles and gas phases and eliminate PVE at the solid gas interface.The marker based watershed method is used for particle segmentation,and the shape factor difference method and image interpolation method are used for separating the root phase and the liquid phase.The particle gradation distribution and water phase volume changes after segmentation are consistent with the macroscopic test results,which proves the accuracy of the segmentation process.This image processing process can determine each phase in the root soil system at different times,thereby enabling more accurate quantification of the evolution process of three-dimensional root characteristic parameters with root growth.(3)Using a pore network model,RVE mesh based,and local RVE method,the evolution process of porosity in root soil CT images was analyzed,and it was found that initial porosity had a significant impact on the root development of tall fescue.The change of soil porosity is significant within 300-400px from the root surface.The evolution process of saturation was analyzed using both RVE based grids and local RVE methods.It was found that saturation decreased with root growth globally,indicating an increase in root water uptake.The local saturation distribution is mainly affected by the pore distribution,and soil saturation changes significantly within 800 px of the root surface.This conclusion can provide reference for the rationalization and economy of planting density.By clarifying the influence range of tall fescue roots on soil porosity and saturation,adjusting the planting density and distribution of roots,and enhancing soil permeability and water storage capacity,planting strategies can be provided for greening and vegetation slope design in practical engineering.(4)By constructing a three-dimensional finite element model of the rooted sand based on root CT images,simulating four different growth times of bare sand and tall fescue roots,the changes in the isosaturation surface of the bare sand column and the root containing sand column within 48 hours of watering were obtained.Unlike the one-dimensional root system water uptake model,this model considers the effect of spatial heterogeneity of root structure on soil water distribution.The error analysis between the simulation results and the data based on RVE mesh saturation proves that the finite element model matches well.In principle,this numerical model can be extended to mature tall fescue with much larger roots,and root growth can be estimated through root parameters,clarifying the water demand of tall fescue at different growth stages and environmental conditions,and reducing water resource waste.At the same time,the water status and hydraulic characteristics of vegetation soil can be evaluated based on root parameters and saturation after watering,guiding the design and construction process of engineering construction plans.