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• Efficient water transport from soil to leaves sustains stomatal opening and steady-state photosynthesis. The aboveground portion of this pathway is well-described, yet the roots and their connection with the soil are still poorly understood due to technical limitations. • Here we used a novel rehydration technique to investigate changes in the hydraulic pathway between roots and soil and within the plant body as individual olive plants were subjected to a range of water stresses. • Whole root hydraulic resistance (including the radial pathway from xylem to the soil–root interface) constituted 81% of the whole-plant resistance in unstressed plants, increasing to >95% under a moderate level of water stress. The decline in this whole root hydraulic conductance occurred in parallel with stomatal closure and contributed significantly to the reduction in canopy conductance according to a hydraulic model. • Our results demonstrate that losses in root hydraulic conductance, mainly due to a disconnection from the soil during moderate water stress in olive plants, are profound and sufficient to induce stomatal closure before cavitation occurs. Future studies will determine whether this core regulatory role of root hydraulics exists more generally among diverse plant species.

To highlight the importance of the soil-root interface in bacterial root colonization, we performed 16S rRNA gene amplicon sequencing on the Illumina MiSeq platform to characterize the bacterial endophytes of rice plants grown by two experiments – soil and hydroponic, considering their soil, solution, and endosphere compartments. We hypothesized that rice plants from both experiments would exhibit dissimilar endophytic bacterial communities. Alpha-diversity (richness (ASVs), Shannon index, Faith’s phylogenetic diversity, and Pielou’s evenness) for bacterial endophytes was lower in the soil experiment than in the hydroponic experiment. However, the rhizospheric soil exhibited higher microbial diversity and richness than the hydroponic solution after 6 weeks. Proteobacteria and Firmicutes were the most dominant phyla in both experiments, while several other bacterial taxa showed major differences at genus levels. A Venn diagram revealed that 5 overlapping bacterial genera were shared by the endosphere and rhizosphere/solution compartments of both experiments. Principal coordinate analysis (PCoA) based on weighted UniFrac distances showed a clear distinction between microbial communities of all sampled compartments. Furthermore, PERMANOVA results showed that the endophyte communities of both experiments differed significantly (p < 0.001). Overall, this study suggests that the soil-root interface plays a significant role in determining the bacterial endophyte community in rice plants, and the different patterns of endophytic colonization of the rice roots in both experiments were likely influenced by factors that may include bacterial motility, biofilm formation, as well as the decreased effects of root exudates due to dissolution in the solution of the hydroponic experiment.

Cereals zinc (Zn) biofortification represents an effective strategy for alleviating human Zn malnutrition. However, understanding how to enhance Zn uptake in shoots by optimizing the soil–root interface, particularly considering Zn availability, microbiome interactions, and plant physiology, remains poorly understood, especially in high-pH soils. In this study, we investigated Zn rhizomobilization, plant Zn uptake, and the composition of bacterial and fungal communities in the rhizosphere and roots of ten high-yielding wheat cultivars with consistently contrasting grain Zn concentrations, within calcareous fields. We found that a range of beneficial bacteria, fungi/mycorrhizas, and their interactions play crucial roles in Zn rhizomobilization and wheat Zn uptake. Zn-solubilizing rhizobacteria demonstrated the ability to enhance Zn rhizomobilization, leading to a 35.4% increase in available Zn concentration and a 0.11 units reduction of soil pH. Increased colonization by arbuscular mycorrhizal fungi, along with reduced the presence of fungal pathogens, significantly promoted Zn uptake, ranging from 22 to 132% per unit of root biomass. Additionally, the enriched bacteria relevant with nitrogen cycle and plant growth-promotion not only optimized soil mineral-N/available-P supply but also potentially suppressed fungal pathogens in root and rhizosphere. Optimizing the microbiome to enhance soil nutrient supply and root health emerges as a promising strategy for improving Zn-efficient wheat cultivars’ ability to uptake Zn in shoots. Combining Zn-efficient cultivars with specific soil bacteria and fungi in the rhizosphere holds potential for realizing Zn biofortification in wheat.

It is important to quantify the effect of the root diameter, the embedment length of the root and load speed on the soil-root interface mechanical properties for studying the root anchorage. The soilroot interface mechanical properties can be obtained through the pullout force and root slippage curve (F-S curve). About 120 Pinus tabulaeformis single roots whose diameters ranged from 1 mm to 10 mm divided into 6 groups based on different root embedment length (50 mm, 100 mm and 150 mm) and different load velocity (10 mm·min -1 , 50 mm·min -1 , 100 mm·min -1 and 300 mm·min -1 ) were investigated using the pullout method. This study aims to explore the mechanical properties of the soil-root interface in the real conditions using the pullout test method. The results showed two kinds of pullout test failure modes during the experimental process: breakage failure and pullout failure. The results showed that the roots were easier to be broken when the root diameter was smaller or the loading speed was larger. The relationship between the maximum anchorage force and root diameter was linear and the linearly dependent coefficient (R 2 ) was larger than 0.85. The anchorage force increased with the root embedment length. An increase of 10%-15% for the maximum anchorage force was found when load speed increased from 10 to 300 mm.min-1. The mean peak slippage of the root was from 13.81 to 35.79 mm when the load velocity varied from 10 to 300 mm.min-1. The study will be helpful for the design of slopes reinforced by vegetation and in predicting risk of uprooting of trees, and will have practical benefits for understanding the mechanism of landslide.

Herbaceous grafting is a propagation method largely used in solanaceous and cucurbit crops for enhancing their agronomic performances especially under (a)biotic stress conditions. Besides these grafting-mediated benefits, recent advances about microbial networking in the soil/root interface, indicated further grafting potentialities to act as soil environment conditioner by modulating microbial communities in the rhizosphere. By selecting a suitable rootstock, grafting can modify the way of interacting root system with the soil environment regulating the plant ecological functions able to moderate soilborne pathogen populations and to decrease the risk of diseases. Genetic resistance(s) to soilborne pathogen(s), root-mediate recruiting of microbial antagonists and exudation of antifungal molecules in the rhizosphere are some defense mechanisms that grafted plants may upgrade, making the cultivation less prone to the use of synthetic fungicides and therefore more sustainable. In the current review, new perspectives offered by the available literature concerning the potential benefits of grafting, in enhancing soilborne disease resistance through modulation of indigenous suppressive microbial communities are presented and discussed.

Grey alder (Alnus incana) and black alder (Alnus glutinosa) stands on forest land, abandoned agricultural, and reclaimed oil-shale mining areas were investigated with the aim of analysing the functional diversity and activity of microbial communities in the soil–root interface and in the bulk soil in relation to fine-root parameters, alder species, and soil type. Biolog Ecoplates were used to determine community-level physiological profiles (CLPP) of culturable bacteria in soil-root interface and bulk soil samples. CLPP were summarized as AWCD (average well color development, OD 48 h-1) and by Shannon diversity index, which varied between 4.3 and 4.6 for soil–root interface. The soil–root interface/bulk soil ratio of AWCD was estimated. Substrate-induced respiration (SIR) and basal respiration (BAS) of bulk soil samples were measured and metabolic quotient (Q = BAS/SIR) was calculated. SIR and Q varied from 0.24 to 2.89 mg C g-1 and from 0.12 to 0.51, respectively. Short-root morphological studies were carried out by WinRHIZO™ Pro 2003b; mean specific root area (SRA) varied for grey alder and black alder from 69 to 103 and from 54 to 155 m2 kg-1, respectively. The greatest differences between AWCD values of culturable bacterial communities in soil-root interface and bulk soil were found for the young alder stands on oil-shale mining spoil and on abandoned agricultural land. Soil–root interface/bulk soil AWCD ratio, ratio for Shannon diversity indices, and SRA were positively correlated. Foliar assimilation efficiency (FOE) was negatively correlated with soil–root interface/bulk soil AWCD ratio. The impact of soil and alder species on short-root morphology was significant; short-root tip volume and mass were greater for black alder than grey alder. For the investigated microbiological characteristics, no alder-species-related differences were revealed.

Available tools to study rhizosphere characteristics at a sub-mm spatial resolution suffer from a number of shortfalls, including geometrically and physiologically ill-defined root layers containing soil or other growth medium. Such designs may result in over-or underestimation of root-induced changes in the rhizosphere. We present a novel rhizobox design that overcomes these shortfalls. Plants are pre-grown in a soil-root compartment with an opening slit at the bottom. As plants reach the targeted physiological stage, this compartment is transferred on top of a rhizosphere soil compartment attached to a vertical root-only compartment. The latter is made up of a membrane (pore size 7 µm to restrict root hair growth into the rhizosphere compartment or 30 µm to restrict only root growth) and a transparent acrylic window which is gently pressed against the membrane and rhizosphere soil compartment using an adjustable screw. This design allows roots to penetrate from the upper soil-root compartment through the slit into the root-only compartment. Root growth and distribution can be monitored through the acrylic window using digital camera equipment. Upon termination of the experiment, the rhizosphere compartment is removed and frozen prior to separation of sub-mm soil layers using microtome techniques. In a test experiment, canola (Brassica napus L. cv. Sprinter) developed a fairly dense root monolayer within 8 days. Using measurement of soil characteristics at 0.5-1-mm increments across the rhizosphere we demonstrate that the proposed rhizobox design is yielding reproducible data. Due to exudation of LMWOC, we found a statistically significant increase of DOC towards the root plane, whereas more stable soil characteristics were not affected by root activity. Limitations and further extensions of this rhizobox design, including the use of micro suction cups and microsensors for pH and redox potential to measure spatial and temporal changes in a non-destructive manner are discussed along with potential applications such as validation of rhizosphere models.

This study investigates the influence of the degree of pectin esterification (DE) on the sorption of aluminium (Al) by plant roots. Ca-pectates, with varying degrees of esterification, are major constituents of the soil-root interface and of the root apoplast. Ca-pectate networks (Ca-PG and Ca-Al-PG) were formed at three DEs (0%, 26%, 65%) with custom-made cells and used as a model system for the root cell wall. Sorption of Al was conducted for 24 h at a range of oxalic acid concentrations (0-500 μM) at pH 4.50 to examine two different metal resistance mechanisms of plants. In fact, plants release organic acids either to desorb or to complex metals to prevent their sorption by plant roots.Thermal analysis showed that Al sorption did not seem to affect the stability of the pectate gels and the presence of hydrophobic groups (-CH₃) at DE > 0% seemed to even increase the stability of the gels decreasing thermal decomposition. Results suggest two potential Al tolerance mechanisms: (a) high oxalic acid concentrations (500 μM) were able to desorb almost 100% and 72% at DE 65 and 0%, respectively; (b) high oxalic acid concentrations (500 μM) and thus molar ratios of 5:1 (oxalate/Al) reduced Al sorption by 98% and 86% at DE 65 and 0%, respectively. In conclusion, both mechanisms indicate that high degrees of esterification as 65% are much more efficient in excluding Al from the apoplast and might therefore contribute to Al resistance in plants.

Spatial distribution characteristics of heavy metals in soil-root system have important significance for the research of soil pollution risk assessment and phytoremediation effect. Taking Ligustrum lucidum plant as an example in this paper, according to the characteristics of adsorption of heavy metals in soil by woody plants, laying out sampling points, using Sufer software for Kiging interpolation analysis, horizontal migration law of heavy metal copper in the soil-root interface system was simulated. Through multi-model statistical regression trend analysis, the horizontal migration mechanism of copper in different section has been discussed. The results showed that under horizontal migration law in the surface soil, the migration capability of Cu by root in soil near the roots is relatively weak; with root extending, the migration capability is strengthened gradually. In the deeper soil, the migration law with the root extension was gradually weaker, and the main range of accumulation ability is 60-90cm in three sections. In addition, its migration law follows the cubic curve mode. Under longitudinal migration law, based on the Kriging method, migration models Z(hi) of heavy metal Cu in any depth of h^sub i^ are constructed. [PUBLICATION ABSTRACT]

The aim of this work was to investigate the effect of aluminium (Al), a toxic metal for plant growth, as well as pH on the mobility of phosphate across a calcium-polygalacturonate (Ca-PG) network used as a soil-root interface model. The Ca-PG fibrils, having acidic properties, are able to complex ions selectively: thus a Ca-PG model could be useful to study the ion uptake by plants. Ca-PG networks were exposed to Al solutions at different concentrations (25, 100 and 200 µM) at pH 3.50, 4.00 and 4.50. These Ca-PG and Ca-Al-PG networks were subsequently used to measure the phosphate flux at pH 3.50, 4.00 and 4.50. The results showed that the phosphate's mobility across the soil-root interface is strongly influenced by pH and aluminium: its mobility is much greater at a low pH. The presence of Al slowed down the phosphate even more leading to a complete flux impedance in the first 3-5 h at pH 4.00 and 4.50. This impedance is probably not only due to interactions between phosphate and Al but it is also due to structural changes: the interaction of Al (hydrolytic and/or polymeric species) at pH 4.00 and 4.50 with the polygalacturonic chains could lead to a collapse of the porous structure. These results suggest that the apoplastic-bound Al hinders, especially at pH 4.00 and 4.50, the phosphate uptake by plants.