Soil Mechanics Research Articles

Zinc and Phosphate Solubilizing by Rhizobacteria Promotes Lettuce (Lactuca sativa L.) Growth in Salty Conditions

Due to climate change, the world is negatively affected by drought, temperature, salinity, and flood stress, leading to a significant decline in crop production. Lettuce is particularly significant when considering salt stress. To increase plant tolerance to salinity, various strategies are employed to support the development of agriculture. Rhizobacteria play a key role in regulating phosphorus (P) and zinc (Zn) homeostasis in plants. According to the study results, Rhizobium bacteria supported plant growth by improving the solubility of zinc and phosphate. These findings highlight the beneficial effects of plant growth-promoting rhizobacteria (PGPR) on the antioxidant system, which helps detoxify reactive oxygen species. The relationship between proline accumulation and antioxidant enzyme activities showed that PGPR inoculation enhanced the plant's defense mechanism against salt stress. In establishing this tolerance, increases in chlorophyll content, repair of membrane repair, and higher leaf relative humidity under salt stress were observed. PGPR also improved seedling height, diameter, and fresh and dry weight under stress by 70%, 51.4%, 55%, and 109%, respectively, due to the stress-mitigating effects of P and Zn. In conclusion, it is predicted that there will be a need to develop fertilization programs containing different rhizobacteria and Zn+P combinations. These programs would activate the antioxidant mechanism in saline soils, stabilize physiological processes, and positively impact plant growth.

Determination of the Ultimate Bearing Capacity of a Single Barrette Wall using FEA and Cubic Nonlinear Regression

This study analyzes the mechanical behavior of barrette walls under various load levels, a critical issue in the design and construction of structures subjected to large loads. The primary objective of the research is to determine the nonlinear relationship between load and settlement of barrette walls, as well as to assess the maximum load-bearing capacity of the walls under diverse loading conditions. The finite element analysis method was employed to simulate the detailed interaction between the barrette wall and the soil, combined with cubic and linear regression analysis techniques to establish the model of the relationship between load and settlement displacement. The research results reveal a nonlinear relationship between load and settlement of the wall, with an inflection point occurring at a load level of approximately 12,000 kN, where the change in settlement becomes more pronounced. The cubic regression equation achieved a coefficient of determination R² = 0.999, demonstrating the high accuracy of the model. The maximum load-bearing capacity of the barrette wall was determined to be 15,745.59 kN, providing a clear scientific basis for evaluating the load-bearing capacity of structures. The conclusions from this study affirm the importance of using finite element simulations in soil mechanics analysis and the design of structures subjected to large loads. The achieved results not only enhance understanding of the behavior of Barrette walls but also contribute to the development of new technical solutions and design methods, with the potential for wide application in the construction and geotechnical engineering sectors.

On stress ratio equations in three-dimensional stress space for modelling soil behaviour

Constitutive models and failure criteria of soils, rocks, and other materials often need to be extended beyond the triaxial state where they are usually defined, for plane strain, axisymmetric, or three-dimensional analyses. This extension is commonly done by making the stress ratio a function of the Lode angle. This process turns two-dimensional yield, plastic potential, bounding, dilatancy and similar surfaces into three-dimensional shapes such as cones and bullets. The equations used have a range of shapes on the octahedral or π-plane between Mohr-Coulomb’s irregular hexagon and Drucker-Prager’s circle. Nine stress ratio generalization equations popular in soil mechanics are evaluated based on numerical stability, agreement with available data, and ease of implementation. The computed limits on their convexity, and the flexibility they offer in the calibration process are discussed. At the end, a new equation that satisfies all these criteria while remaining simple and easy to calibrate is proposed, implemented in a finite element model, and demonstrated to improve numerical stability and efficiency.

Numerical and Experimental Study of the Interaction between Surface Swelling Soil and Gas Well Casing, Based on Unsaturated Soil Mechanics

This research presents an in-depth analysis of the volumetric and mechanical behavior of expansive soils surrounding the Khangiran gas well in Sarakhs, emphasizing the effects of matric suction and confining pressures on soil mechanical properties. The study employs both laboratory and numerical approaches, utilizing an unsaturated triaxial apparatus and GeoStudio software, to assess (1) the influence of matric suction and confining pressure on volumetric deformation and shear strength, (2) the impact of annual precipitation on soil swelling, and (3) the tensile stresses exerted on the well casing due to soil expansion. Laboratory results reveal that shear strength increases from 195 kPa to 235 kPa as confining stress rises from 100 to 200 kPa, while cohesion climbs from 68 kPa in saturation to 95 kPa under 100 kPa of matric suction, signifying enhanced resistance in drier soil conditions. Numerical modeling indicates that annual precipitation induces a maximum tensile force of 163 kN at a depth of 13 m, with the expansive zone extending approximately 15 m from the well. The thickness of the steel used for tensile strength resistance against soil swelling is sufficient, and if extensive corrosion of the steel casing is not a concern, tensile strength failure will not occur. These findings offer critical insights into soil-structure interaction in expansive soils and provide practical guidance for the design of resilient gas well casings in similar geotechnical settings.

Changes in selenium bioavailability in selenium-enriched paddy soils induced by different water management and organic amendments

Combined effects of water management and agricultural organic waste return on selenium (Se) bioavailability and mechanisms in Se-enriched paddy soils remain unclear. We investigated the effects of continuous flooding (CF) and alternating wet and dry (AWD), two types (cotton straw biochar [BC] and sheep manure [SM]) and concentrations (10 and 50 g·kg−1) of organic amendments on soil Se bioavailability, bacterial community structure in naturally Se-enriched soils (1.69 mg·kg−1). Results showed that 10 g·kg−1 SM treatment was the most effective in increasing Se bioavailability, especially under AWD treatment, whereas BC treatment reduced it. Compared with CF treatment, AWD treatment increased the Se content of root surface iron plaque and rhizosphere affinity for Se, and promoted the conversion of soil weakly organic matter bound Se to soluble-Se and exchangeable-Se. BC and SM addition significantly altered soil solution Fe(II), dissolved organic carbon, and soil bacterial community structure and function, including sulfur-oxidizing bacteria (Thiobacillus) and Se-reducing bacteria (Pseudarthrobacter), under different water management regimes. Notably, these bacteria showed a significant correlation with bioavailable Se. The present study provides theoretical guidance for agronomic practices in Se-enriched paddy soils.

Rational eucalypt logging site management patterns enhance soil phosphorus bioavailability and reshape phoD-harboring bacterial community structure

Continuous planting of eucalypt plantations negatively affects soil nutrient effectiveness, especially soil phosphorus (P) availability. Therefore, exploring the response characteristics of soil P-mineralising microbial communities and the distribution mechanism of soil P fractions under different transformation patterns on eucalypts logging sites holds great practical significance for improving soil nutrient effectiveness in plantations. This experiment investigated the effects and correlations between four different transformation patterns on soil phoD-harboring bacterial communities, alkaline phosphatase (ALP) activity, and P fractions. Management patterns mainly included non-forest area formed upon eucalypt stump germination suppression after two generations of Eucalyptus afforestation (TWE), the third generation of pure plantation planting (THE), mixing of Eucalyptus with Manglietia glauca (EM), and rotation of pure M. glauca plantation (MM), with previous mixed coniferous and broadleaf forest (CK) as the control. The results showed that, TWE and THE significantly reduced soil (0–10 cm and 10–20 cm) organic carbon (SOC), total nitrogen (TN), bioavailable P, and labile Po, and increased the occluded P and ALP activity compared to CK; however, SOC, TN, bioavailable P, and labile Po indices improved in plantations of EM or MM compared to TWE and THE. Meanwhile, the four management patterns on the logging site caused significant differences in phoD gene community structure and diversity. TWE and THE significantly increased the relative abundances (RAs) of Pseudomonadaceae and Comamonadaceae, which correlated negatively with soil bioavailable P and HCl-P and positively with ALP activity, suggesting a positive effect on Po mineralization and insoluble P mobilization. In contrast, Streptomycetaceae and Oxalobacteraceae were significantly enriched in EM or MM, implying that not all microorganisms carrying phoD genes play important roles in synthesizing ALP. The structure equation model showed that TN, resin-Pi, NaHCO3-Pi, and HCl-P had indirect effects on ALP through phoD-harbouring bacterial diversity and community composition. These findings provide a basis for understanding the soil P cycling mechanism after eucalypt plantations logging site transformation.

How Does the Largest Cluster in the Strong Network Rule Granular Soil Mechanics? A DEM Study

ABSTRACTThe contact network of granular materials is often divided into strong and weak subnetworks, which play different roles in micromechanics. Within the strong contact network, there exists the largest connected component, that is, the largest cluster, which may connect system boundaries and could be the most important structure in force transmission of the whole system. This paper concerns the particular features of the largest cluster in the strong contact network of granular materials, by considering the combining effects of loading path and particle shape. A series of true triaxial tests with various intermediate principal stress ratios are conducted for granular assemblies of different shaped particles using the discrete element method (DEM). Both the macroscopic stress–strain responses and the microscopic topological changes of the contact network are investigated. It is found that both particle shape and loading path will influence the shear strength and the topological features of the strong network. The threshold (the ratio to the average force) is used to distinguish the strong and weak networks, and a critical threshold can be identified by comparing the network‐based metrics. The largest cluster within the strong network approaching the critical threshold can span the boundaries in each direction with minimum contacts, which occupies a small portion of particles and contacts but transmits a considerable portion of the applied stress. In addition, the similar contribution weight of the largest cluster to the deviatoric stress is identified for granular materials with different particle shapes.

Deformation evolution and failure mechanism of rainfall-induced granite residual soil landsliding event in Northern Guangdong, China

Deformation evolution and failure mechanism of rainfall-induced granite residual soil landsliding event in Northern Guangdong, China

Impact of glyphosate on soil bacterial communities and degradation mechanisms in large-leaf tea plantations

This study investigated the impact of glyphosate on bacterial communities and their degradation mechanisms in large-leaf tea soil, through exposure microcosm and enrichment culture experiments. Soils from three tea gardens in Yunnan, China, were used: two glyphosate-free (JM and KL) for microcosm study and one long-term exposed (G2) for enrichment culture experiment. The results revealed a two-phase degradation process with half-lives of 12.7 to 268 days, while the metabolite AMPA was notably persistent. The acidic conditions and high organic content of tea soils may retard glyphosate microbial availability and degradation. Glyphosate initially stimulated bacterial growth but led to abundance declines with prolonged exposure. It tended to enhance bacterial diversity at lower doses. Network complexity increased in JM soil where strong adsorption moderated glyphosate exposure, yet decreased in KL soil where weak adsorption enabled greater microbial-glyphosate interactions. Community structure analysis revealed soil-specific responses, with decreased Proteobacteria in JM soil and Actinobacteria in KL soil, while several phyla including Proteobacteria, Acidobacteriota, Chloroflexi, Myxococcota, and Verrucomicrobiota showed increased abundance. PICRUSt2 analysis indicated enhanced biosynthesis and cell growth pathways, while carbohydrate metabolism, nitrogen metabolism, and xenobiotics biodegradation pathways were reduced. LEfSe analysis identified potential degrading biomarkers primarily from Proteobacteria, Acidobacteriota, Myxococcota, Chloroflexi, and Actinobacteriota, suggesting their putative role in degradation. The enriched consortium G2 efficiently degraded 400mg/L glyphosate within 7 days, with notable increases in Afipia, Dokdonella, and Cohnella abundance. This study provides insights into bacterial interactions with glyphosate in tea soils, suggesting strategies for contamination mitigation and environmental restoration.

Printed Potentiometric Ammonium Sensors for Agriculture Applications.

Ammonium (NH4 +) concentration is critical to both nutrient availability and nitrogen (N) loss in soil ecosystems but can be highly variable across spatial and temporal scales. For this reason, effectively informing agricultural practices such as fertilizer management and understanding of mechanisms of soil N loss require sensor technologies to monitor ammonium concentrations in real time. Our work investigates the performance of fully printed ammonium ion-selective sensors used in diverse soil environments. Ammonium sensors consisting of a printed ammonium ion-selective electrode and a printed Ag/AgCl reference were fabricated and characterized in aqueous solutions and three different soil types (sand, peat, and clay) under the range of ion concentrations likely to be present in soil (0.01-100 mM). The response of ammonium sensors was further evaluated under variable gravimetric moisture content in the soil to reflect their reliability under field conditions. Ammonium sensors demonstrated a sensitivity of 53.6 ± 5.1 mV/decade when tested in aqueous solution, and a sensitivity of 55.7 ± 11 mV/dec, 57.5 ± 4.1 mV/dec, and 43.7 ± 4 mV/dec was measured in sand, clay, and peat soils, respectively.

Salinization and salt expansion mechanism of soda residue soil at subgrade

The solid waste soda residue (SR) exhibits a high content of soluble salts, and the liquid phase soluble salts in soda residue soil (SRS) undergo phase transition crystallization during cooling process, leading to subgrade salt expansion and deformation damage. In order to explore the salt mechanisms of SRS, this paper systematically analyzes the impact of SR content on the salinization and salt expansion characteristics of SRS using soluble salt tests and salt expansion experiments. Combined with X-ray diffractometry (XRD) and low-temperature frost shrink tests, the study analyzed the salt expansion process of SRS. The results indicate that under different SR content, SRS is classified as chloride saline soil. The SRS is categorized into weak saline soil, moderate saline soil, strong saline soil, and over-saline soil with different soda residue dosage. During cooling from 20°C to −25°C, all SRS groups exhibit initial salt expansion followed by frost shrink deformation characteristics. As the SR content increases within the 0 % – 40 % range, the temperature range for severe salt expansion gradually decreases from 5°C to −15°C. At 25 % SR content, SRS exhibits the most severe salt expansion, while excessively high SR content inhibits the crystallization of sulfate salt phase transitions. The study identifies three stages in the salt expansion process of SRS: promotion stage, severe stage, and inhibition stage. The research findings provide valuable insights for the prevention of salt expansion in SRS and the widespread utilization of SR in road applications.

Field‐based estimation of cation exchange capacity using induced polarization methods

AbstractThis study investigates the potential of field‐based induced polarization (IP) methods to provide in‐situ estimates of soil cation exchange capacity (CEC). CEC influences the fate of nutrients and pollutants in the subsurface. However, estimates of CEC require sampling and laboratory analysis, which can be costly, especially at large scales. Induced polarization (IP) methods offer an alternative approach for CEC estimation. The sensitivity of IP measurements to the surface properties of geological materials ought to make them more appropriate than DC resistivity and electromagnetic induction methods, that are sensitive to bulk electrical properties . Such abilities of IP are well demonstrated in the laboratory; however, applications are lacking at field scales. In this work, the ability of field‐based IP to characterize the CEC of floodplain soils is assessed by implementing a methodology that allows for direct comparison between IP and soil parameters. In one field, soil polarization and CEC exhibited the expected positive correlation; but multi‐frequency measurements showed no clear advantage over single‐frequency measurements. In another field, coarser soils (with low CEC) exhibited a high polarization. These coarser soils were characterized by anomalous magnetic susceptibility values, and hence the polarization was attributed to the presence of magnetic minerals. Although better than order‐of‐magnitude estimates of CEC were possible in soils without substantial magnetic minerals, better characterization of porosity, saturation, cementation and saturation exponents, and pore fluid conductivity would improve predictions. However, the measurement of these parameters would require similar efforts as direct CEC measurements. This study contributes to bridging the gap between laboratory‐derived relationships and their applicability in field applications. Overall, this work provides valuable insight for future studies seeking to understand polarization mechanisms in soils at the field scale.

Formulation and Implicit Numerical Integration of a Kinematic Hardening Model for Unsaturated Soils

ABSTRACTCurrently, our understanding of material‐scale deterioration resulting from meteorologically induced variations in pore water pressure and its significant impact on infrastructure slopes is limited. To bridge this knowledge gap, we have developed an extended kinematic hardening constitutive model for unsaturated soils that refines our understanding of weather‐driven deterioration mechanisms in heterogeneous clay soils. This model has the capability of predicting the irrecoverable degradation of strength and stiffness that has been shown to occur when soils undergo wetting and drying cycles. The model is equipped with a fully coupled and hysteretic water retention curve and a hysteretic loading–collapse curve and has the capability to predict the irrecoverable degradation of strength and stiffness that occurs during cyclic loading of soils. Here, we employ a fully implicit stress integration technique and give particular emphasis to deriving a consistent tangent operator, which includes the linearisation of the retention curve. The proposed algorithm is evaluated for efficiency and performance by simulating various stress and strain‐driven triaxial paths, and the accuracy of the integration technique is evaluated through the use of convergence curves.

Unsaturated Soil Mechanics Topics for All Geotechnical Engineers

Unsaturated Soil Mechanics Topics for All Geotechnical Engineers

Effects of freeze–thaw on the detachment capacity of soils with different textures on the Loess Plateau, China

Soil detachment capacity (Dc) is a crucial indicator for quantifying erosion intensity. However, the combined actions of freeze–thaw and water flow complicate the erosion process, leaving the variation mechanism of Dc under this condition systematically unexplored. This study examined five loess soils from a seasonal freeze–thaw area. The mechanism driving changes in Dc was quantified through freeze–thaw simulation combined with flow scouring tests, and a Dc prediction model was established. The results revealed that the shear strength (τm), cohesion (Coh), and internal friction angle (φ) in silt loam were higher than in sandy loam. After freeze–thaw cycles (FTC), τm, Coh, and φ of the five loess soils decreased by 1.02–1.37, 1.07–9.15, and 0.92–1.05 times, respectively. As FTC increased, τm and Coh gradually stabilized, while φ showed minimal fluctuation, indicating that FTC had a cumulative effect on the deterioration of soil mechanical properties. During FTC, Dc in Wuzhong sandy loam was the largest, being 1.14–3.24 times greater than in other soils, suggesting a significant main effect of soil type on Dc variation, with a contribution rate of 19.27 %. Dc eventually stabilized with increasing, indicating a critical FTC of around 10 for its impact on Dc. Compared to unfrozen soils, Dc increased by 33.69 %–102.40 % under the combined effects of freeze–thaw and water flow, clarifying that FTC aggravated soil instability. Effective stream power was the optimum hydraulic parameter, contributing the most to Dc (45.94 %). FTC (6.41 %) and initial soil moisture content (8.59 %) were less influential, as FTC initially degraded soil properties, and then the combined action with water flow intensified soil damage, causing the role of freeze–thaw factors to be obscured by other variables. A Dc prediction model using a general flow intensity index estimated well Dc, with both R2 and NSE at 0.94. Model performance comparison emphasized the need for validation when extending the application range beyond development conditions. These findings provide new insights into the detachment mechanisms of different textured soils under compound freeze–thaw and hydrodynamic influence in freeze–thaw region.

Study on micromechanical behavior and energy evolution of granular material generated by latent diffusion model under rotation of principal stresses

In this study, advanced image processing technology is used to analyze the three-dimensional sand composite image, and the topography features of sand particles are successfully extracted and saved as high-quality image files. These image files were then trained using the latent diffusion model (LDM) to generate a large number of sand particles with real morphology, which were then applied to numerical studies. The effects of particle morphology on the macroscopic mechanical behavior and microscopic energy evolution of sand under complex stress paths were studied in detail, combined with the circular and elliptical particles widely used in current tests. The results show that with the increase of the irregularity of the sample shape, the cycle period and radius of the closed circle formed by the partial strain curve gradually decrease, and the center of the circle gradually shifts. In addition, the volume strain and liquefaction strength of sand samples increase with the increase of particle shape irregularity. It is particularly noteworthy that obvious vortex structures exist in the positions near the center where deformation is severe in the samples of circular and elliptical particles. However, such structures are difficult to be directly observed in sample with irregular particles. This phenomenon reveals the influence of particle morphology on the complexity of the mechanical behavior of sand, providing us with new insights into the understanding of the response mechanism of sand soil under complex stress conditions.

Goethite introduction strengthens balck soil carbon sequestration under various water management conditions and its microbial mechanisms

Natural and anthropogenic disturbances lead to degradation of (soil organic carbon) SOC content black soil in northeast china. Goethite (α-FeO (OH)) as widely distributed mineral, has a sequestration effect on SOC. With the diversification of crop cultivation in northeast china, various water management are becoming important. However, SOC sequestration mechanism by goethite under varying water management conditions is still unclear. In our study, we set up 3 groups of experiments: 1) 60% water-holding capacity (60% WHC), 60% water-holding capacity with goethite (60% WHCG), 2), waterlogging (W), waterloggin with goethite (WG), 3) alternation of wetting and drying (AWD), alternation of wetting and drying with goethite (AWDG) to elucidate the sequestration mechanism of SOC by goethite under three water management conditions. Results shows introducing goethite can sequester SOC under three water management conditions, with WG SOC sequestration capacity more than AWDG and 60% WHCG. The main sequestration mechanism of SOC has two aspects, on the one hand, goethite introduction increased significantly SOC functional groups, Fe-bound OC, iron molar ratio and Fe-bound OC/SOC, made SOC was bound to goethite by adsorption and co-precipitation. On the other hand, goethite introduction increased the diversity and abundance of bacteria and fungi by affecting soil pH, iron morphology and valence, induced the enrichment of Bryobacter, Gemmatimonas, Conexibacter, Streptomyces, Gaiella, Rubrobacter and Talaromyces potential carbon sequestrating microorganisms, further contributing to SOC sequestration. This study offers a significant theoretical foundation for elucidating the SOC sequestration mechanism of northeastern black soil.

Denitrifying Anaerobic Methane Oxidation Activity and Microbial Mechanisms in Riparian Zone Soils of the Yulin River, a Tributary of the Three Gorges Reservoir

Riparian zones are recognized as major sources of greenhouse gas emissions, particularly methane (CH4). Denitrifying anaerobic methane oxidation (DAMO) has garnered growing attention due to its significant contribution to mitigating CH4 emissions in wetland environments. Nonetheless, the specific role and microbial mechanisms of DAMO in controlling CH4 release within riparian zones are still not well comprehended. This study employed isotopic labeling experiments to measure the nitrate-dependent anaerobic methane oxidation (NaDAMO) and nitrite-dependent anaerobic methane oxidation (NiDAMO) potential of soil samples from riparian zones that were collected during different hydrological cycles. Moreover, soil physicochemical properties, DAMO activity, and microbial abundance were integrated to analyze the key factors and mechanisms influencing DAMO in riparian zone soils. The isotope tracer results showed that NaDAMO activities (1.4–11.93 nmol 13CO2 g-1day-1) were significantly higher than NiDAMO activities (0.66–9.19 nmol 13CO2 g-1day-1) in the riparian zone (p<0.05). NiDAMO activities were more strongly influenced by hydrological variations compared to NaDAMO activities, exhibiting higher levels during the discharge period (2.78–9.19 nmol 13CO2 g-1day-1) compared to the impoundment period (0.66–4.10 nmol 13CO2 g-1day-1). The qPCR analysis showed that the gene copies of NaDAMO archaeal mcrA (107 copies g-1) were approximately ten times greater than those of NiDAMO bacterial pmoA (106 copies g-1) in the majority of the sampling sites. Correlation analyses revealed that NiDAMO activity was influenced by soil pH (p<0.05), while NaDAMO microbes were influenced by temperature, organic carbon, and ammonia nitrogen concentrations (p<0.05). In summary, this research explored how hydrological changes in the riparian zone influence DAMO activities and their underlying mechanisms, providing a theoretical basis for mitigating CH4 emissions in riparian zones of reservoir regions.

The role of microbiomes in cooperative detoxification mechanisms of arsenate reduction and arsenic methylation in surface agricultural soil.

Microbial arsenic (As) transformations play a vital role in both driving the global arsenic biogeochemical cycle and determining the mobility and toxicity of arsenic in soils. Due to the complexity of soils, variations in soil characteristics, and the presence and condition of overlying vegetation, soil microbiomes and their functional pathways vary from site to site. Consequently, key arsenic-transforming mechanisms in soil are not well characterized. This study utilized a combination of high-throughput amplicon sequencing and shotgun metagenomics to identify arsenic-transforming pathways in surface agricultural soils. The temporal and successional variations of the soil microbiome and arsenic-transforming bacteria in agricultural soils were examined during tropical monsoonal dry and wet seasons, with a six-month interval. Soil microbiomes of both dry and wet seasons were relatively consistent, particularly the relative abundance of Chloroflexi, Gemmatimonadota, and Bacteroidota. Common bacterial taxa present at high abundance, and potentially capable of arsenic transformations, were Bacillus, Streptomyces, and Microvirga. The resulting shotgun metagenome indicated that among the four key arsenic-functional genes, the arsC gene exhibited the highest relative abundance, followed by the arsM, aioA, and arrA genes, in declining sequence. Gene sequencing data based on 16S rRNA predicted only the arsC and aioA genes. Overall, this study proposed that a cooperative mechanism involving detoxification through arsenate reduction and arsenic methylation was a key arsenic transformation in surface agricultural soils with low arsenic concentration (7.60 to 10.28 mg/kg). This study significantly advances our knowledge of arsenic-transforming mechanisms interconnected with microbial communities in agricultural soil, enhancing pollution control measures, mitigating risks, and promoting sustainable soil management practices.

Grass species and mycorrhizal fungi improved aggregate stability of compacted and vegetated soils

Abstract Aim Compaction of slope soils can substantially hinder root penetration of grass cover, which may be alleviated through the colonisation of arbuscular mycorrhizal (AM) fungi and aggregate stabilisation. We investigated aggregate stabilisation and breakdown mechanisms in compacted dense mycorrhizal soils. Methods A pot-culture experiment with seven treatments (five replicates per treatment) was implemented. In a local decomposed granitic soil, we inoculated two grass species (Chrysopogon ziaanioides and Cynodon dactylon) with AM fungi. We used loose soil to grow C. dactylon to compare it with compacted dense soil, as well as pots without a plant and/or fungal inoculation for comparison. After 20 weeks of cultivation, we measured root and AM fungal characteristics, soil organic matter and aggregate properties by dry sieving, wet sieving and Le Bissonnais methods. Results Compaction led to the formation of macro-aggregates (&gt; 0.25 mm) but had a negative influence on the aggregate stability. The fungal inoculation increased polysaccharide production and aggregate stability in the compacted soil vegetated with C. dactylon. The inoculated C. ziaanioides showed a similar level of aggregate stability as the inoculated C. dactylon, but the uninoculated group demonstrated higher aggregate stability compared with the inoculated group owing to root decomposition. The aggregate stability against various breakdown mechanisms was related to the established aggregate hierarchy and qualitative organic matter inputs. Conclusion Soil organic matter supplied by grass species together with the mediation of AM fungal hyphae played a crucial role in the systemic enhancement of aggregate stability in the compacted soil.