Root-soil Interface Research Articles

Root-soil interface friction jointly amplified by high root density and shear deflection

Plant roots significantly enhance the stability of shallow slopes. However, the mechanism of the root-soil interaction at root-bundle scale remains unclear. The objective of this study is to reveal the factors that control root-soil interface frictional stress at root-bundle scale. Through theoretical analysis, it is clarified that spatiotemporal inhomogeneity exists in root-soil interface frictional stress, and it could be amplified by root density and root deflection angle. Large-scale shear tests with 160 mm and 10 mm shear zones were then conducted to verify this hypothesis, where variations in shear zone thicknesses corresponded to different shear deflections. The number of roots was measured within the sheared zone. Results reveal that the average root-soil interface frictional stress of rooted soils with 10 mm shear zone is 66% higher than that for rooted soils with 160 mm shear zone. During the shear process, the state of roots transitions from stretching to sliding, accompanied by increasing root-soil interface friction. This study confirms that root-soil interface frictional stress is jointly amplified by root density and root deflection angle, providing robust evidence for constructing physics-based mechanical reinforcement models.

Plant-specific microbial diversity facilitates functional redundancy at the soil-root interface

Abstract Aims Plant-specific microbial diversity reflecting host-microbe coevolution was frequently shown at the structural level but less on the functional scale. We studied the microbiome of three compartments at the soil root interface (root endosphere, rhizosphere, bulk soil) of medicinal plants cultivated under organic management in Egypt. The study aimed to examine the impact of the rhizosphere on microbial community composition and diversity in desert agricultural soil, as well as to identify specific functions associated with the rhizosphere. Methods The microbiome community structure, diversity, and microbial functioning were evaluated through the utilization of 16S rRNA gene amplicon and shotgun metagenome sequencing. Results We found the typical rhizosphere effect and plant-species-specific enrichment of bacterial diversity. The annual plants Calendula officinalis and Matricaria chamomilla (Asteraceae) were more similar than the perennial Solanum distichum (Solanaceae). Altogether, plant species explained 50.5% of the variation in bacterial community structures in the rhizosphere. Our results indicate a stronger effect of the plant species in terms of modulating bacterial community structures in the rhizosphere than in root endosphere samples. The plant-driven rhizosphere effect could be linked to redundant plant beneficial functions in the microbiome, while enrichment of specific genes related to amino acid ion transport and metabolism, carbohydrate transport and metabolism, defense mechanisms, and secondary metabolites biosynthesis were more specific. Conclusions The study explores the microbiome continuum at the soil-root interface of medicinal plant species, revealing significant bacterial community structure shifts and plant specificity. The study provides insights into the essential microbiome components contributing to rhizosphere functionality.

Root exudates simultaneously form and disrupt soil organo-mineral associations

Organic compounds exuded by plant roots can form organo-mineral associations through physico-chemical interactions with soil minerals but can disrupt existing organo-mineral associations by increasing their microbial decomposition and dissolution. The controls on these opposing processes are poorly understood, as are the chemical and spatial characteristics of these associations which may explain gain or loss of organic matter at the root-soil interface termed the rhizosphere. By pulse-labeling with 13C-carbon dioxide, we found that maize root exudates increased organic matter in the rhizosphere clay size fraction and decreased organic matter in the silt size fraction, and that organic matter loss was mitigated by dry conditions. Organic matter associated with rhizosphere clay particles was linked to microbial metabolism of exudates and was more spatially and chemically heterogeneous than non-rhizosphere clay particles. Our findings show that root exudates can simultaneously form and disrupt organo-mineral associations, mediated by mineral size and composition, and soil moisture.

Advancing hyperspectral imaging techniques for root systems: a new pipeline for macro- and microscale image acquisition and classification

BackgroundUnderstanding the environmental impacts on root growth and root health is essential for effective agricultural and environmental management. Hyperspectral imaging (HSI) technology provides a non-destructive method for detailed analysis and monitoring of plant tissues and organ development, but unfortunately examples for its application to root systems and the root-soil interface are very scarce. There is also a notable lack of standardized guidelines for image acquisition and data analysis pipelines.MethodsThis study investigated HSI techniques for analyzing rhizobox-grown root systems across various imaging configurations, from the macro- to micro-scale, using the imec VNIR SNAPSCAN camera. Focusing on three graminoid species with different root architectures allowed us to evaluate the influence of key image acquisition parameters and data processing techniques on the differentiation of root, soil, and root-soil interface/rhizosheath spectral signatures. We compared two image classification methods, Spectral Angle Mapper (SAM) and K-Means clustering, and two machine learning approaches, Random Forest (RF) and Support Vector Machine (SVM), to assess their efficiency in automating root system image classification.ResultsOur study demonstrated that training a RF model using SAM classifications, coupled with wavelength reduction using the second derivative spectra with Savitzky-Golay (SG) smoothing, provided reliable classification between root, soil, and the root-soil interface, achieving 88–91% accuracy across all configurations and scales. Although the root-soil interface was not clearly resolved, it helped to improve the distinction between root and soil classes. This approach effectively highlighted spectral differences resulting from the different configurations, image acquisition settings, and among the three species. Utilizing this classification method can facilitate the monitoring of root biomass and future work investigating root adaptations to harsh environmental conditions.ConclusionsOur study addressed the key challenges in HSI acquisition and data processing for root system analysis and lays the groundwork for further exploration of VNIR HSI application across various scales of root system studies. This work provides a full data analysis pipeline that can be utilized as an online Python-based tool for the semi-automated analysis of root-soil HSI data.

Microbes in Agriculture: Prospects and Constraints to Their Wider Adoption and Utilization in Nutrient-Poor Environments.

Microbes such as bacteria and fungi play important roles in nutrient cycling in soils, often leading to the bioavailability of metabolically important mineral elements such as nitrogen (N), phosphorus (P), iron (Fe), and zinc (Zn). Examples of microbes with beneficial traits for plant growth promotion include mycorrhizal fungi, associative diazotrophs, and the N2-fixing rhizobia belonging to the α, β and γ class of Proteobacteria. Mycorrhizal fungi generally contribute to increasing the surface area of soil-root interface for optimum nutrient uptake by plants. However, when transformed into bacteroids inside root nodules, rhizobia also convert N2 gas in air into ammonia for use by the bacteria and their host plant. Thus, nodulated legumes can meet a high proportion of their N requirements from N2 fixation. The percentage of legume N derived from atmospheric N2 fixation varies with crop species and genotype, with reported values ranging from 50-97%, 24-67%, 66-86% 27-92%, 50-92%, and 40-75% for soybean (Gycine max), groundnut (Arachis hypogea), mung bean (Vigna radiata), pigeon pea (Cajanus cajan), cowpea (Vigna unguiculata), and Kersting's groundnut (Macrotyloma geocarpum), respectively. This suggests that N2-fixing legumes require little or no N fertilizer for growth and grain yield when grown under field conditions. Even cereals and other species obtain a substantial proportion of their N nutrition from associative and endophytic N2-fixing bacteria. For example, about 12-33% of maize N requirement can be obtained from their association with Pseudomonas, Hebaspirillum, Azospirillum, and Brevundioronas, while cucumber can obtain 12.9-20.9% from its interaction with Paenebacillus beijingensis BJ-18. Exploiting the plant growth-promoting traits of soil microbes for increased crop productivity without any negative impact on the environment is the basis of green agriculture which is done through the use of biofertilizers. Either alone or in combination with other synergistic rhizobacteria, rhizobia and arbuscular mycorrhizal (AM) fungi have been widely used in agriculture, often increasing crop yields but with occasional failures due to the use of poor-quality inoculants, and wrong application techniques. This review explores the literature regarding the plant growth-promoting traits of soil microbes, and also highlights the bottle-necks in tapping this potential for sustainable agriculture.

Mucilage facilitates root water uptake under edaphic stress: first evidence at the plant scale.

Mucilage has been hypothesized to soften the gradients in matric potential at the root-soil interface, hereby facilitating root water uptake in dry soils and maintaining transpiration with a moderate decline in leaf water potential. So far, this hypothesis has been tested only through simplified experiments and numerical simulations. However, the impact of mucilage on the relationship between transpiration rate (E) and leaf water potential (ψleaf) at the plant scale remains speculative. We utilized an automated root pressure chamber to measure the E(ψleaf) relationship in two cowpea genotypes with contrasting mucilage production. We then leveraged a soil-plant hydraulic model to reproduce the experimental observations and inferred the matric potential at the root-soil interface for both genotypes. In wet soil, the relationship between the leaf water potential and transpiration rate (E) was linear for both genotypes. However, as the soil progressively dried, the E(ψleaf) relationship exhibited nonlinearity. Genotype with low mucilage production exhibited nonlinearity earlier during soil drying, i.e. in wetter soil conditions, (soil water content < 0.36cm3 cm-3) compared to Genotype with high mucilage production (soil water content < 0.30cm3 cm-3). The incidence of nonlinearity was concomitant with the decline in matric potential across the rhizosphere. High mucilage production attenuated water potential diminution at the root-soil interface with increased E. This shows, for the first time at the plant scale, that root mucilage softened the gradients in matric potential and maintained transpiration in drying soils. The model simulations indicate that a plausible explanation for this effect is an enhanced hydraulic conductivity of the rhizosphere in genotype with higher mucilage production. Mucilage exudation maintains the hydraulic continuity between soil and roots and decelerates the drop in matric potential near the root surface, hereby postponing the hydraulic limitations to transpiration during soil drying.

Rhizosheath Formation and Its Role in Plant Adaptation to Abiotic Stress

The rhizosheath, the layer of soil tightly attached to the roots, protects plants against abiotic stress and other adverse conditions by providing a bridge from the plant root system to the soil. It reduces the formation of air gaps between the root and soil and facilitates the transportation of water at the root–soil interface. It also serves as a favourable niche for plant-growth-promoting rhizobacteria in the surrounding soil, which facilitate the absorption of soil water and nutrients. This review compares the difference between the rhizosheath and rhizosphere, and summarises the molecular and physiological mechanisms of rhizosheath formation, and identifying the causes of rhizosheath formation/non-formation in plants. We summarise the chemical and physical factors (root hair, soil-related factors, root exudates, and microorganisms) that determine rhizosheath formation, and focus on the important functions of the rhizosheath in plants under abiotic stress, especially in drought stress, phosphorus deficiency, aluminium stress, and salinity stress. Understanding the roles played by the rhizosheath and the mechanisms of its formation provides new perspectives for improving plant stress tolerance in the field, which will mitigate the increasing environmental stress conditions associated with on-going global climate change.

Serendipita indica Drives Sulfur-Related Microbiota in Enhancing Growth of Hyperaccumulator Sedum alfredii and Facilitating Soil Cadmium Remediation.

Endophytic fungus Serendipita indica can bolster plant growth and confer protection against various biotic and abiotic stresses. However, S. indica-reshaped rhizosphere microecology interactions and root-soil interface processes in situ at the submicrometer scale remain poorly understood. We combined amplicon sequencing and high-resolution nano X-ray fluorescence (nano-XRF) imaging of the root-soil interface to reveal cadmium (Cd) rhizosphere processes. S. indica can successfully colonize the roots of Sedum alfredii Hance, which induces a remarkable increase in shoot biomass by 211.32% and Cd accumulation by 235.72%. Nano-XRF images showed that S. indica colonization altered the Cd distribution in the rhizosphere and facilitated the proximity of more Cd and sulfur (S) to enter the roots and transport to the shoot. Furthermore, the rhizosphere-enriched microbiota demonstrated a more stable network structure after the S. indica inoculation. Keystone species were strongly associated with growth promotion and Cd absorption. For example, Comamonadaceae are closely related to the organic acid cycle and S bioavailability, which could facilitate Cd and S accumulation in plants. Meanwhile, Sphingomonadaceae could release auxin and boost plant biomass. In summary, we construct a mutualism system for beneficial fungi and hyperaccumulation plants, which facilitates high-efficient remediation of Cd-contaminated soils by restructuring the rhizosphere microbiota.

RhizoMAP: a comprehensive, nondestructive, and sensitive platform for metabolic imaging of the rhizosphere

BackgroundElucidating the intricate structural organization and spatial gradients of biomolecular composition within the rhizosphere is critical to understanding important biogeochemical processes, which include the mechanisms of root-microbe interactions for maintaining sustainable plant ecosystem services. While various analytical methods have been developed to assess the spatial heterogeneity within the rhizosphere, a comprehensive view of the fine distribution of metabolites within the root-soil interface has remained a significant challenge. This is primarily due to the difficulty of maintaining the original spatial organization during sample preparation without compromising its molecular content.ResultsIn this study, we present a novel approach, RhizoMAP, in which the rhizosphere molecules are imprinted on selected polymer membranes and then spatially profiled using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI). We enhanced the performance of RhizoMAP by combining the use of two thin (< 20 μm) membranes (polyester and polycarbonate) with distinct MALDI sample preparations. This optimization allowed us to gain insight into the distribution of over 500 different molecules within the rhizosphere of poplar (Populus trichocarpa) grown in rhizoboxes filled with mycorrhizae soil. These two membranes, coupled with three different sample preparation conditions, enabled us to capture the distribution of a wide variety of molecules that included phytohormones, amino acids, sugars, sugar glycosides, polycarboxylic acids components of the Krebs cycle, fatty acids, short aldehydes and ketones, terpenes, volatile organic compounds, fertilizers from the soil, and others. Their spatial distribution varies greatly, with some following root traces, others showing diffusion from roots, some associated with soil particles, and many having distinct hot spots along the plant root or surrounding soil. Moreover, we showed how RhizoMAP can be used to localize the origin of the molecules and molecular transformation during root growth. Finally, we demonstrated the power of RhizoMAP to capture molecular distributions of key metabolites throughout a 20 cm deep rhizosphere.ConclusionsRhizoMAP is a method that provides nondestructive, untargeted, broad, and sensitive metabolite imaging of root-associated molecules, exudates, and soil organic matter throughout the rhizosphere, as demonstrated in a lab-controlled native soil environment.

Study on the Mechanical Properties of Roots and Friction Characteristics of the Root–Soil Interface of Two Tree Species in the Coastal Region of Southeastern China

The tensile strength of roots and the friction characteristics of the root–soil interface of tree species are the indicators that play a crucial role in understanding the mechanism of soil reinforcement by roots. To calculate the effectiveness of the reinforcement of soil by tree roots based on essential influencing parameters, typical trees in the coastal region of southeastern China selected for this study were subjected to tests of the tensile mechanical properties of their roots, as well as studies on the friction characteristics of the root–soil interface and the microscopic interfaces. The results indicated that in the 1–7 diameter classes, the root tensile strength of both Pinus massoniana and Cunninghamia lanceolata was negatively correlated with the root diameter in accordance with the power function. The root tensile strength of these two trees, however, was positively correlated with the lignin content but negatively correlated with cellulose and hemicellulose contents. The shear strength at the root–soil interface and the vertical load exhibited a constitutive relationship, which followed the Mohr–Coulomb criterion. As the root diameter increased, both the cohesion and the friction coefficients at the root–soil interface gradually increased, but the growth rate stood at around 15%. The cohesion value of the root–soil interface of the two trees decreased linearly with the increase in soil moisture content within the range of 25 to 45%. At the microinterface, the root surface of C. lanceolata exhibited concave grooves and convex ridges that extended along the axial direction of roots, with their height differences increasing with the enlargement of the root diameter. The rough surface of P. massoniana roots had areas composed of polygonal meshes, with an increase observed in the mesh density with increasing root diameter.

Rhizosphere hydraulic regulation in maize: tailoring rhizosphere properties to varying soil textures and moistures

Abstract Aims Motivated by recent studies highlighting the active role of plants in influencing the hydraulic properties of the rhizosphere through mucilage exudation, this study explored the effect of plant rhizosphere regulation on the emergent hydraulic properties of the rhizosphere under varying soil texture and moisture levels. Methods Maize (Zea mays) plants were cultivated in sand and loam soils exposed to varying moisture levels. Neutron radiography was employed to quantify the profile of water content ($${\theta }_{r})$$ θ r ) around lateral and crown roots. The $${\theta }_{r}$$ θ r were used to derive rhizosphere hydraulic indices such as rhizosphere extension ($${d}_{rh}$$ d rh ), water content at the root-soil interface ($${\theta }_{rs}$$ θ rs ), and water content in the rhizosphere ($${\theta }_{rh}$$ θ rh ). The latter two attributes were normalized by the respective bulk soil water contents ($${\theta }_{rs}^{*}$$ θ rs ∗ , $${\theta }_{rh}^{*}$$ θ rh ∗ ). Results Results showed a higher $${\theta }_{rs}^{*}$$ θ rs ∗ , $${\theta }_{rh}^{*}$$ θ rh ∗ and $${d}_{rh}$$ d rh in coarse-textured soil versus fine-textured soil. This indicates a more pronounced rhizosphere development in sand compared to loam, possibly via mucilage exudation to maintain better root-soil contact. In contrast, soil water content did not impact the rhizosphere properties of crown roots but impacted the rhizosphere properties of lateral roots. The derived rhizosphere water retention curves revealed a higher water-holding capacity of the rhizosphere in both soils compared to bulk soil. Conclusions Our study underscores that soil-grown maize plants dynamically adjust the hydraulic properties of their rhizosphere in response to external factors, primarily aiming to optimize root-soil contact. That leads to a more pronounced rhizosphere in coarser textures, interacting with the soil moisture.

Interaction Mechanisms between Blades and Maize Root–Soil Composites as Affected by Key Factors: An Experimental Analysis

To design a high-performance stubble-breaking device, studying the interaction mechanisms between blades and root–soil composites is urgent. A simplified experimental method was proposed to investigate the cutting process and the effects of key factors on cutting by conducting cutting experiments on remolded root–soil composites and maize root–soil composites. The results showed that the soil support force and root–soil interface force significantly impacted cutting. Higher soil compaction and root–soil interface forces helped avoid root dragging, but higher soil compaction and thicker roots led to greater resistance. The superposition and accumulation effects significantly increased the cutting force, especially when root distribution was denser; as the oblique angle and bevel angle increased, the root-cutting force and dragging distance first decreased and then increased. Compared with orthogonal cutting, the optimal angles were both 45° and reduced the root-cutting force by 60.47% and 15.12% and shortened the dragging distance by 22.33 mm and 8.76 mm, respectively. Increasing the slide-cutting angle and cutting speed helped reduce the root-cutting force and dragging distance; however, it also faced greater pure-cutting force. Consequently, the interaction mechanisms between blades and root–soil composites revealed in this study provide a design and optimization basis for stubble-breaking devices, thus promoting the development of no-till technology.

Metabolites of blueberry roots at different developmental stages strongly shape microbial community structure and intra-kingdom interactions at the root-soil interface

The rhizosphere microorganisms of blueberry plants have long coexisted with their hosts under distinctively acidic soil conditions, exerting a profound influence on host performance through mutualistic symbiotic interactions. Meanwhile, plants can regulate rhizosphere microorganisms by exerting host effects to meet the functional requirements of plant growth and development. However, it remains unknown how the developmental stages of blueberry plants affect the structure, function, and interactions of the rhizosphere microbial communities. Here, we examined bacterial communities and root metabolites at three developmental stages (flower and leaf bud development stage, fruit growth and development stage, and fruit maturation stage) of blueberry plants. The results revealed that the Shannon and Chao 1 indices as well as community composition varied significantly across all three developmental stages. The relative abundance of Actinobacteria significantly increased by 10 % (p < 0.05) from stage 1 to stage 2, whereas that of Proteobacteria decreased significantly. The co-occurrence network analysis revealed a relatively complex network with 1179 edges and 365 nodes in the stage 2. Niche breadth was highest at stage 2, while niche overlap tended to increase as the plant developed. Furthermore, the untargeted metabolome analysis revealed that the number of differential metabolites of vitamins, nucleic acids, steroids, and lipids increased between stage 1 to stage2 and stage 2 to stage 3, while those for differential metabolites of carbohydrates and peptides decreased. Significant changes in expression levels of levan, L-glutamic acid, indoleacrylic acid, oleoside 11-methyl ester, threo-syringoylglycerol, gingerglycolipid B, and bovinic acid were highly correlated with the bacterial community structure. Collectively, our study reveals that significant alterations in dominant bacterial taxa are strongly correlated with the dynamics of root metabolites. These findings lay the groundwork for developing prebiotic products to enhance the beneficial effects of root microorganisms and boosting blueberry productivity via a sustainable approach.

Effect of repeated pulling loads on Norway spruce (Picea abies (L.) Karst.) trees

Artificial pulling tests are the most practical method of assessing the maximum resistance of trees to lateral forces (e.g., from the wind), particularly in relation to their anchoring capacity in the ground. The traditional method is to pull the tree monotonically until failure. However, there are still many uncertainties regarding the possibility of mimicking wind gusts in such a tree pulling test. More specifically, it is supposed that a succession of wind gusts during a windstorm may cause fatigue to the root system, leading to a propagation of damage at the root-soil interface which will eventually lead to the collapse of the tree. This work aims to provide initial insights into the biomechanical response of shallow-rooted Norway spruce (Picea abies (L.) Karst.) growing in mineral soils by repeatedly pulling to failure six trees with increasing load magnitude. The mechanical behaviour of the tested trees was first analysed using a classical equilibrium approach by calculating peak applied loads, stem base rotation, equivalent stiffness trend over subsequent cycles and residual rotations. Then, the biomechanics of the trees were analysed using an energetic approach, focusing on the energy absorbed and dissipated during either the single load cycle or the complete cyclic test, by applying consolidated procedures used in the field of mechanical engineering.Results show how small but measurable residual rotations were measured after each load repetition, indicating permanent damage even in seemingly undamaged trees. Additionally, loads producing base rotations about 0.3–0.4 times those corresponding to the peak resistance dissipate less than 1 % of the maximum dissipated energy calculated at the same peak point. Additionally, this peak energy is found to be strongly correlated to both the peak moment and a typical stem volume predictor such as diameter at breast height squared times height.All these outcomes are intended to provide a starting point for the development of a different characterisation of tree resistance as an alternative to the current methodologies, especially when it is important to consider the effects of repeated loading on trees.

Nanoparticles and root traits: mineral nutrition, stress tolerance and interaction with rhizosphere microbiota.

This review article highlights a broader perspective of NPs and plant-root interaction by focusing on their beneficial anddeleterious impacts on root system architecture (RSA). The root performs a vital function by securing itself in the soil, absorbing and transporting water and nutrients to facilitate plant growth and productivity. In dicots, the architecture of the root system (RSA) is markedly shaped by the development of the primary root and its branches, showcasing considerable adaptability in response to changes in the environment. For promoting agriculture and combating global food hunger, the use of nanoparticles (NPs) may be an exciting option, for which it is essential to understand the behaviour of plants under NPs exposure. The nature of NPs and their physicochemical characteristics play a significant role in the positive/negative response of roots and shoots. Root morphological features, such as root length, root mass and root development features, may regulated positively/negatively by different types of NPs. In addition, application of NPs may also enhance nutrient transport and soil fertility by the promotion of soil microorganisms including plant growth-promoting rhizobacteria (PGPRs) and also soil enzymes. Interestingly the interaction of nanomaterials (NMs) with rhizospheric bacteria can enhance plant development and soil health. However, some studies also suggested that the increased use of several types of engineered nanoparticles (ENPs) may disrupt the equilibrium of the soil-root interface and unsafe morphogenesis by causing the browning of roots and suppressing the growth of root and soil microbes. Thus, this review article has sought to compile a broader perspective of NPs and plant-root interaction by focusing on their beneficial or deleterious impacts on RSA.

Drought stress impacts soil microbial nutrient limitation more strongly than O3 pollution

Summer drought conditions generally coincide with exposure to high ground-level concentrations of ozone (O3). These two stressors compromise the availability of water, energy, and nutrients to vegetation and microbial communities present within the soil. However, relatively little is known regarding the responses of rhizosphere and non-rhizosphere soil microbial nutrient acquisition to conditions of drought and O3 exposure. Here, we used ecoenzymatic stoichiometry modeling and vector analyses to decipher the resource constraints on rhizosphere and non-rhizosphere soil microbial metabolic limitation within the soil of hybrid poplars exposed to two watering regimens (well-watered or reduced water of 40 %) and two chronic O3 treatments (charcoal-filtered air or ambient air +40 ppb of O3). Results show that, simulated drought stress resulted in stronger effects on the structure of soil microbial communities and associated enzymatic activity relative to exposure to elevated O3 levels. Exposure to these two stressors induced a microbial phosphorus (P) limitation response, with these limitation effects being more pronounced in the rhizosphere soil relative to non-rhizosphere soil. Structural equation modeling revealed that drought-associated declines in soil water availability and pH values were the primary factors influencing this microbial P limitation. Reduced soil water levels resulted in the exacerbation of microbial P limitation as a consequence of the inhibition of P mineralization and availability of C and N, whereas declining soil pH values had the opposite effect, alleviating microbial P limitations by reducing soil alkalinity and thereby aiding in the dissolution of the insoluble P present in alkaline soil. These results emphasize the complex responses of rhizosphere and non-rhizosphere soil microbial metabolic activity to elevated O3 levels and drought stress, providing invaluable insight into the importance of elemental stoichiometry-driven microbial metabolic variability of nutrient cycling activity at the root-soil interface in O3-polluted and drought-exposed ecosystems.

Effects of vegetation growth on soil microstructure and hydro-mechanical behaviour

Literature studies are presenting counterposed effects of vegetation on soil hydraulic behaviour. Besides, root impacts at the micro-scale are rarely correlated to phenomenological observations due to the complexity of adopting up-scaling factors. In this study, the microstructural causes behind observed changes in vegetated compacted clayey sand’s hydraulic and volume change behaviour were explored. Laboratory experiments were carried out on compacted samples seeded with Cynodon dactylon. Significant changes in soil water-saturated permeability, water retention and shrinkage upon drying were observed after root growth. Laboratory measurements were complemented by the quantification of root morphological features and observations at the micro-scale for different soil hydraulic states. X-ray scans and mercury intrusion porosimetry allowed to cover seven orders of magnitude of pore sizes, shedding light on soil fabric changes at the soil–root interface and the clay aggregate scale. The effects of roots on the soil pore size distribution consisted of Multiphysics phenomena: fissure generation, void clogging and soil aggregation due to roots’ chemical interaction. Furthermore, a good correlation was found between the normalised volume of roots and the micro-pores volume. This new expression was included in a framework to predict soil water retention behaviour considering the aggregated structure and soil–root hydro-chemical interactions.

Observations of root hair patterning in soils: Insights from synchrotron-based X-ray computed microtomography

Background And AimsRoot hair emergence is affected by heterogeneities in water availability in the growth medium. Root hairs preferentially emerge into air, whereas their emergence into water is inhibited. Yet, these results were based either on destructive methods or on roots grown on an agar-air interface. Additionally, there is a lack of knowledge about the spatial distribution of root hairs as hairs elongate radially across the rhizosphere. Therefore, root hair growth in soils remains largely unexplored.MethodsMaize (Zea Mays L.) plants were grown in microcosms which were scanned with a synchrotron-based X-ray μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu $$\\end{document}CT. The distribution of root hairs along the root epidermis and radially across the rhizosphere (i.e. as function of distance from the root epidermis) was analysed using spatial point pattern analysis.ResultsWhile hairs emerged randomly in air-filled pores, their emergence was inhibited where the root was in contact with the soil matrix. As hairs elongated radially into the soil, they were preferentially located in the close proximity of soil particles. In maize, we rarely observed root hairs penetrating into soil aggregates.ConclusionWe conclude that in maize, root hairs grow in air-filled pores at the root-soil interface, where the flow of nutrients and water is impeded. Across the rhizosphere, hairs establish contact to the soil by growing in the proximity to soil particles. The effect of hairs on uptake processes, plant anchorage and rhizosheath formation might be limited (in maize) as they hardly penetrate into soil aggregates.

Role of particle size-dependent copper bioaccumulation-mediated oxidative stress on Glycine max (L.) yield parameters with soil-applied copper oxide nanoparticles

Increased impetus on the application of nano-fertilizers to improve sustainable food production warrants understanding of nanophytotoxicity and its underlying mechanisms before its application could be fully realized. In this study, we evaluated the potential particle size-dependent effects of soil-applied copper oxide nanoparticles (nCuO) on crop yield and quality attributes (photosynthetic pigments, seed yield and nutrient quality, seed protein, and seed oil), including root and seed Cu bioaccumulation and a suite of oxidative stress biomarkers, in soybean (Glycine max L.) grown in field environment. We synthesized three distinct sized (25 nm = S [small], 50 nm = M [medium], and 250 nm = L [large]) nCuO with same surface charge and compared with soluble Cu2+ ions (CuCl2) and water-only controls. Results showed particle size-dependent effects of nCuO on the photosynthetic pigments (Chla and Chlb), seed yield, potassium and phosphorus accumulation in seed, and protein and oil yields, with nCuO-S showing higher inhibitory effects. Further, increased root and seed Cu bioaccumulation led to concomitant increase in oxidative stress (H2O2, MDA), and as a response, several antioxidants (SOD, CAT, POX, and APX) increased proportionally, with nCuO treatments including Cu2+ ion treatment. These results are corroborated with TEM ultrastructure analysis showing altered seed oil bodies and protein storage vacuoles with nCuO-S treatment compared to control. Taken together, we propose particle size-dependent Cu bioaccumulation-mediated oxidative stress as a mechanism of nCuO toxicity. Future research investigating the potential fate of varied size nCuO, with a focus on speciation at the soil-root interface, within the root, and edible parts such as seed, will guide health risk assessment of nCuO.Graphical

Sweet specificities of the root extracellular trap of perennial ryegrass (Lolium perenne), a fructan accumulating plant

Perennial ryegrass (Lolium perenne) is a fructan-accumulating plant constituting one of the most important grassland species with high herbage production, nutritive value and digestibility for grazing cattle. Although fructans were reported to be involved in plant defense acting as antioxidants or stress signals, their contribution in root protection is still to be explored. In roots, atypical defense is provided by the “Root Extracellular Trap” or “RET” at the root-soil interface. The molecular composition and structural organization of the RET are essential to provide root defense against pathogen attacks and abiotic stresses. The RET was reported to be mainly composed of polysaccharides (homogalacturonan, xylogalacturonan, xyloglucan) and proteoglycans such as arabinogalactan proteins (AGPs). Our aim is to characterize the RET composition of L. perenne using cell imaging techniques and a wide range of monoclonal antibodies directed against epitopes from cell wall glycomolecules and to investigate the potential presence of fructans. Interestingly, we found that both mucilage and cell wall surface of border cells were enriched in AGP epitopes. An increased amount of the AGP-containing mucilage was produced by L. perenne root tip in response to both elicitor and osmotic stress. Fructan epitopes were also detected in root cap cells and appeared to be released in the RET under stress conditions. Taken together our findings suggest that AGPs together with fructans are involved in root response of L. perenne to environmental stresses.