Soil Root Research Articles

Synergistic effects of AMF and PGPR on improving saline-alkaline tolerance of Leymus chinensis by strengthening the link between rhizosphere metabolites and microbiomes

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) can synergistically enhance their promotional effects on plants. The positive effects are closely related to their modulation on rhizosphere microbiomes. Leymus chinensis is widely used in restoration of saline-alkaline grasslands. However, the information is unavailable on mechanisms of inoculating AMF and PGPR in enhancing saline-alkaline tolerance of L. chinensis. We conducted a pot experiment to examine effects of separate and combined inoculation of AMF and PGPR, with a focus on the pathways of AMF and PGPR effects by regulating complex interactions in plant rhizosphere. The combined inoculation significantly increased plant biomass (by 40.18–193.18 %) and Na+ accumulation, and decreased soil EC and pH to a greater extent than the separate inoculation did, and it was also superior in terms of multiple nutrient accumulation, root ion homeostasis ratios and soil enzyme activities. The combined inoculation significantly enriched beneficial bacterial and symbiotic mycorrhizal taxa, and increased complexity and stability of rhizosphere microbiome. Coexistence of AMF and PGPR activated beneficial secondary metabolic pathways and higher expression of beneficial metabolites, which regulates plant growth and stress response. The inoculation of AMF and PGPR synergically promoted interactions among keystone microbial species from different cluster modules and rhizosphere soil metabolites, and strengthened the roles of core microorganisms and core metabolites, and their interrelations and their relations with host plant. These results implies that the synergistic positive effects of AMF and PGPR on saline-alkaline tolerance of L. chinensis is realized by strengthening the links between rhizosphere metabolites and microbiomes.

Nitrogen cycling and associated grey water footprint in croplands under different irrigation practices

The pervasive application of nitrogen (N) fertilisers in agriculture poses a significant threat to freshwater ecosystems. The grey water footprint (GWF) is a measure of the volume of freshwater required to assimilate the relative water pollutants resulted from N leaching-runoff processes. The responses of N cycling and associated regional GWF to crop production under different irrigation methods have not been investigated. In this study, the N leaching-runoff rate, N₂O, and NH₃ emissions in croplands and the associated GWF per unit crop yield (UGWF) and annual total GWF (TGWF) of winter wheat-summer maize crop rotations across the Hebei, Shandong, and Henan Region (HSHR) of China were simulated and evaluated at the prefecture level over the 2004–2020 period. Four irrigation scenarios were modelled: furrow, sprinkler, surface drip, and subsurface drip irrigation. The results showed significant spatial and temporal heterogeneity in N leaching-runoff rates and emissions of N2O, and NH3. The N leaching-runoff rates for winter wheat and summer maize ranged from 3.9% to 10.9% and 15.0%–32.3%, respectively. With changing different irrigation methods, N leaching-runoff rates exhibited greater sensitivity than N₂O and NH₃ emissions; this sensitivity was more pronounced in winter wheat than in summer maize. Findings reveal that N pollution is influenced not only by irrigation methods but also by weather conditions, crop-specific rooting characteristics, sowing time, and soil texture. Winter wheat UGWF under the four irrigation methods mostly followed the order of furrow > sprinkler irrigation > surface drip irrigation > subsurface drip irrigation. Conversely, for summer maize, subsurface drip irrigation resulted in a higher UGWF compared to furrow irrigation, mainly due to increased water percolation thus higher N leaching-runoff rate in near-saturated soil with higher rainfall. This result reveals the potential conflict between water-saving irrigation and N pollution control. This analysis underscores the necessity of recognising the combined effects of agricultural management practices on water conservation and environmental safeguarding.

Co-application of cadmium-immobilizing bacteria and organic fertilizers alter the wheat root soil chemistry and microbial communities

Cadmium contamination poses a significant risk to soil ecosystems in certain parts of the world. Using eco-friendly fertilizers alongside beneficial microorganisms offers a viable solution to mitigate Cd pollution in agricultural soil. This study used an outdoor experiment to evaluate the impact of administering a Cd-immobilizing bacterial (Bacillus) inoculant with two biologically-enriched organic fertilizers (either fermentative edible fungi residue or fermented cow dung) on wheat plants and associated microbial populations in a field contaminated with Cd. The mixed application of fermentative cow dung with the Cd-immobilizing bacterium reduced the effective Cd content of wheat root-soil by 13,0 %. Application of Cd-immobilizing Bacillus inoculant reduced the Cd enrichment of wheat roots by 0.07 mg/kg. Co-application of fermentative cow dung with the bacterial inoculant reduced the Cd enrichment of wheat seeds by 20,0 %. Co-application of the two organic fertilizers could improve some of the nutrients related to wheat and soil fertility; however, the diversity of the soil microbial community changed less and its species richness decreased. Applying the Bacillus inoculant inhibited the growth of native pathogenic bacteria, such as Proteobacteria. Whether administering it with either fermented cow manure or fermented edible fungus residue, the relative abundance of nitrate-reducing bacteria such as Rhodobacter increased, which should promote the soil nitrogen cycle. The main factors influencing soil microbial community structure of wheat plants were pH, available potassium, and available Cd content. Symbiotic network analysis revealed bacterial inoculant and organic fertilizer inoculum further altering the ecological relationships of microbial communities. According to the FAPROTAX functional prediction, Rhodanobacter may play a key role in nitrate respiration in the soil nitrogen cycle. In conclusion, this study provides a comprehensive, timely reference for understanding microbial changes caused by the combined application of this type of bacterial inoculant and organic soil amendments in Cd-contaminated fields.

Spatial variability of hydraulic parameters of a cropped soil using horizontal crosshole ground penetrating radar

AbstractSoil hydraulic parameters (SHP) play a crucial role controlling the spatiotemporal distribution of water in the soil–plant continuum and thus affect water availability for crops. To provide reliable information on the SHP at different scales, measurement techniques with a good spatial resolution and low labor costs are required. In this study, we used crosshole ground penetrating radar (GPR)‐derived soil water contents (SWCs) measured along horizontal rhizotubes under a controlled experimental test site cropped with winter wheat to estimate the unimodal and dual‐porosity soil hydraulic characteristics with different soil layer setups. Therefore, sequential inversion of the GPR‐derived SWCs was performed using the hydrological model HYDRUS‐1D, whereby the SWC data were either averaged prior inversion or used in a spatially distributed way. To analyze if the time‐lapse gathered GPR data contain enough information to estimate the SHP, additional synthetic studies were performed increasing the data resolution to daily GPR measurements. The results showed that the time‐lapse data contained enough information to estimate the SHP accurately. Additionally, spatially distributed soil hydraulic characteristics differed from the one estimated based on averaged SWCs derived from spatially distributed GPR data. Finally, we derived spatially resolved SHP, which can be used for 3D process rhizosphere processes and root–soil interaction modeling.

Optimizing Voltage for Effective X-ray Computed Tomography Scan: A Study on Varied Soil Bulk Densities and Container Sizes

Numerous studies have highlighted the role of X-ray computed tomography (X-ray CT) in understanding root architecture. Nevertheless, setting definitive scanning parameters for diverse soils in varied container sizes remains challenging. This study investigates the influence of X-ray CT system voltage on the penetration capability in diverse soils and container sizes, focusing on two key parameters: (1) gray values, which indicate X-ray attenuation and contribute to image contrast, and (2) signal-to-noise ratio, a measure of image clarity. Five soil samples were collected from various depths within a soil profile to encompass bulk density values ranging from 1.34 to 1.84 g·cm−3 to conduct the experiment. Containers with dimensions of 6 × 6 × 6 cm³, 8 × 8 × 6 cm³, 10 × 10 × 6 cm³, 12 × 12 × 6 cm³, 14 × 14 × 6 cm³, and 16 × 16 × 6 cm³ were used. Voltage levels spanning 75 to 225 kV, in 25-kV increments, were applied to each sample. The observed gray values of the X-ray images were fitted using a logistic model of three parameters. Results showed that increasing voltage leads to enhanced penetration up to a plateau point, irrespective of soil density or container size. This plateau could potentially yield higher quality scans, given that lower voltages result in subdued gray values and reduced image contrast. Notably, it was observed that soil properties, including mineral composition, directly affect image gray values. This study established optimal voltage settings for specific soil types at fixed densities, offering valuable insights for researchers investigating soil–root interactions. Although the current findings are based on five soils, a more extensive sampling encompassing diverse soil textures and densities is necessary for a comprehensive understanding of X-ray penetration behavior across various soil types.

Roles of straw return in shaping denitrifying bacteria in rice rhizosphere soils through effects on root exudates and soil metabolites

Roles of straw return in shaping denitrifying bacteria in rice rhizosphere soils through effects on root exudates and soil metabolites

Facile Mechanochemical Functionalization of Hydrophobic Substrates for Single-Walled Carbon Nanotube Based Optical Reporters of Hydrolase Activity.

Single walled carbon nanotubes (SWCNT) have recently been demonstrated as modular, near-infrared (nIR) probes for reporting hydrolase activity; however, these have been limited to naturally amphipathic substrate targets used to noncovalently functionalize the hydrophobic nanoparticles. Many relevant substrate targets are hydrophobic (such as recalcitrant biomass) and pose a challenge for modular functionalization. In this work, a facile mechanochemistry approach was used to couple insoluble substrates, such as lignin, to SWCNT using l-lysine amino acid as a linker and tip sonication as the mechanochemical energy source. The proposed coupling mechanism is ion pairing between the lysine amines and lignin carboxylic acids, as evidenced by FTIR, NMR, SEM, and elemental analyses. The limits of detection for the lignin-lysine-SWCNT (LLS) probe were established using commercial enzymes and found to be 0.25 ppm (volume basis) of the formulated product. Real-world use of the LLS probes was shown by evaluating soil hydrolase activities of soil samples gathered from different corn root proximal locations and soil types. Additionally, the probes were used to determine the effect of storage temperature on the measured enzyme response. The modularity of this mechanochemical functionalization approach is demonstrated with other substrates such as zein and 9-anthracenecarboxylic acid, which further corroborate the mechanochemical mechanism.

Impact of iron sulfate (FeSO4) foliar application on growth, metabolites and antioxidative defense of Luffa cylindrica (Sponge gourd) under salt stress

Salt stress is becoming a major issue for the world’s environment and agriculture economy. Different iron [Fe] sources can give an environmentally friendly alternative for salt-affected soil remediation. In this study the effects of Iron sulfate on Luffa cylindrica (Sponge gourd) cultivated in normal and saline water irrigated soil were examined. When FeSO4 (0.01, 0.025, 0.05, 0.1 ppm) were applied to salt affected soil, the length, fresh and dry biomass of sponge gourd plant roots and shoots inclined by an average of 33, 28, 11, 21, 18 and 22%, respectively. In plants irrigated with saline water, leaf count was raised successively (23–115%) with increasing concentration of FeSO4 (0.025-0.1 ppm) compared to stress only plants. The use of FeSO4 boosted sponge gourd growth characteristics in both normal and salt-affected soils compared to respective controls. The application of Iron sulfate under salt stress boosted photosynthetic indices such as chlorophyll a (22%), chlorophyll b (34%), carotenoids (16%), and total chlorophyll levels (22%). Iron sulfate application also exhibited incline in primary (total free amino acids, 50%; total soluble proteins, 46%) and secondary (total phenolics, 9%; flavonoid content, 51%) metabolites in salt-affected soils. Oxidative enzymatic activities such as catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO) and DPPH scavenging activity (36%) were also increased by foliar spray of FeSO4 in control and salt stressed L. cylindrica plants. FeSO4 had a considerable impact on the growth and development of Luffa cylindrica in normal and salt-affected soils. It is concluded that FeSO4 application can effectively remediate salt affected soil and improve the production of crop plants.

Root Circumnutation Reduces Mechanical Resistance to Soil Penetration.

Root circumnutation, the helical movement of growing root tips, is a widely observed behaviour of plants. However, our mechanistic understanding of the impacts of root circumnutation on root growth and soil exploration is limited. Here, we deployed a unique combination of penetrometer measurements, X-ray computed tomography and time-lapse imaging, and cavity expansion modelling to unveil the effects of root circumnutation on the mechanical resistance to soil penetration. To simulate differences in circumnutation amplitude and frequency occurring among plant species, genotypes and environmental conditions, we inserted cone penetrometers with varying bending stiffness into soil samples that were subjected to orbital movement at different velocities. We show that greater circumnutation intensity, determined by a greater circumnutation frequency in conjunction with a larger circumnutation amplitude, decreased the mechanical resistance to soil penetration. Cavity expansion theory and X-ray computed tomography provided evidence that increased circumnutation intensity reduces friction at the cone-soil interface, indicating a link between root circumnutation and the ability of plants to overcome mechanical constraints to root growth. We conclude that circumnutation is a key component of root foraging behaviour and propose that genotypic differences in circumnutation intensity can be leveraged to adapt crops to soils with greater mechanical resistance.

Effect of layered fertilizer strategies on rapeseed (Brassica napus L.) productivity and soil macropore characteristics under mechanical direct-sowing

Layered fertilization parameters affects crop root system configuration and growth distribution, which in turn affects soil pore properties and aggregate structure. Therefore, understanding the spatial distribution of the root system and soil pore space is helpful in choosing a reasonable fertilization ratio in production practice, which ensures high and stable crop yields and at the same time improves fertilizer utilization and soil health. Albeit the impact of layered fertilization ratio at varied rates on soil pore characteristics in the soil profile at a microscale level remains limited. This study quantifies the impacts of layered fertilization ratio under on rapeseed root distribution and soil pore characteristics using the root analysis system and X-ray computed tomography (XCT). A new fertilization pattern that shallow-deep layer synchronized mechanical sowing was using, rotary tillage mixed fertilization in the shallow layer and 10 cm side-deep band fertilization in the deeper layer. It set five ratios of fertilizer amounts between shallow and deep layers as 0:4 (FD), 1:3 (FL), 2:2 (FM), 3:1 (FH), and 4:0 (F0), with non-fertilization (CK) as the control treatment. The results indicated that layered fertilization effectively improved the rape root conformation and spatial distribution, significantly increased total soil porosity and moisture content, and reduced soil bulk density and resistance (P < 0.05). Additionally, root configuration is closely related to soil pore structure and crop yield. Notably, compared with other treatments, the macroscopic porosity, equivalent pore diameter, hydraulic radius and roundness of FM treatment are significantly improved, and it effectively improves the yield and quality of rapeseed. Correlation analysis showed that the root system configuration parameters were negatively correlated with soil bulk density and resistance but positively correlated with soil moisture content, and macropore morphology parameters and rapeseed yield. Our study demonstrate that layered fertilization can improved rape growth and soil macropore porosity, but its effect depends on good tillage macropore characteristics and distribution created by reasonable fertilization ratio, which provided a theoretical basis for high-yield, efficient, green, and sustainable mechanized direct-sowing production of rapeseed.

2023: a soil odyssey–HeAted soiL-Monoliths (HAL-Ms) to examine the effect of heat emission from HVDC underground cables on plant growth

BackgroundThe use of renewable energy for sustainable and climate-neutral electricity production is increasing worldwide. High-voltage direct-current (HVDC) transmission via underground cables helps connect large production sides with consumer regions. In Germany, almost 5,000 km of new power line projects is planned, with an initial start date of 2038 or earlier. During transmission, heat is emitted to the surrounding soil, but the effects of the emitted heat on root growth and yield of the overlying crop plants remain uncertain and must be investigated.ResultsFor this purpose, we designed and constructed a low-cost large HeAted soiL-Monolith (HAL-M) model for simulating heat flow within soil with a natural composition and density. We could observe root growth, soil temperature and soil water content over an extended period. We performed a field trial-type experiment involving three-part crop rotation in a greenhouse. We showed that under the simulated conditions, heat emission could reduce the yield and root growth depending on the crop type and soil.ConclusionsThis experimental design could serve as a low-cost, fast and reliable standard for investigating thermal issues related to various soil compositions and types, precipitation regimes and crop plants affected by similar projects. Beyond our research question, the HAL-M technique could serve as a link between pot and field trials with the advantages of both approaches. This method could enrich many research areas with the aim of controlling natural soil and plant conditions.

Relationship between root characteristics and saturated hydraulic conductivity in a grassed clayey soil

Soil saturated hydraulic conductivity plays a crucial role in the fields of hydrology, geotechnical and geological engineering. This study investigated the relationship between root characteristics and soil saturated hydraulic conductivity in a grassed soil. The saturated hydraulic conductivity of soil specimens with varying soil dry densities and planting densities were experimentally determined. Root parameters of each specimen were measured, and the relationship between root parameters and soil saturated hydraulic conductivity was determined through the stepwise multiple regression analysis. Experimental results show that both soil dry density and planting density significantly influence root growth and the saturated hydraulic conductivity of the grassed soil. Root length ratio (>4 cm), root length, and root weight density exhibit a positive correlation with planting density, while root length density and root length ratio (>4 cm) are negatively correlated with dry density. Higher dry density leads to lower soil saturated hydraulic conductivity and the permeable effects become more pronounced with increased planting density. When planting density is higher, roots create more preferential flow channels in the soil, resulting in increased soil saturated hydraulic conductivity. Root length density exerts the most significant effect on soil saturated hydraulic conductivity (|r| = 0.82, p＜0.01), followed by root length ratio (>4 cm) and root weight density. This study provides insights into the relationship between root parameters and soil saturated hydraulic conductivity, and identifies key root parameters that govern the saturated hydraulic conductivity of soil. These findings hold significant implications for enhancing the understanding of slope protection using vegetation.

Optimal Water and Nitrogen Regimes Increased Fruit Yield and Water Use Efficiency by Improving Root Characteristics of Drip-Fertigated Greenhouse Tomato (Solanum lycopersicum L.)

The growth of root system directly affects the absorption and utilization of soil water and nitrogen, and understanding the responses of root characteristics to water and nitrogen regimes is thus crucial for optimizing water and nitrogen management. The root characteristics of each soil layer, i.e., root length, root surface area, and root volume, as well as fruit yield and water use efficiency of greenhouse tomato under drip fertigation in response to different irrigation levels and nitrogen rates were explored in northwest China. There were four irrigation levels, i.e., 50% ETC (W1), 75% ETC (W2), 100% ETC (W3), and 125% ETC (W4), where ETC is the crop evapotranspiration, and four nitrogen rates, i.e., 0 kg ha−1 (N1), 150 kg ha−1 (N2), 250 kg ha−1 (N3), and 350 kg ha−1 (N4). The results showed that reasonable irrigation and nitrogen regimes (W3N3) significantly increased fruit yield by 31.64% and root length, root surface area, and root volume by 45.03%, 61.24%, and 148.21% compare to W3N1, respectively. The promoting effect of increasing irrigation level on root characteristics increased with soil depth and had the greatest increases in root volume by 27.07%, 123.43%, and 211.47% for the 0–10, 10–20, and 20–30 cm soil layers, respectively. In addition, reducing irrigation level significantly increased the percentages of roots in the top soil by 29.71%, 26.77%, and 18.53% for root length, root surface area, and root volume, respectively. The reasonable nitrogen rate (N3) significantly increased fruit yield by 41.11%, water use efficiency by 34.42%, and root length, root surface area, and root volume by 40.42%, 41.44%, and 112.76%, respectively. The over-application of nitrogen (N4) reduced root characteristics of all soil layers, fruit yield, and water use efficiency. The promoting effect of increasing nitrogen rate on root length of each soil layer decreased with soil depth, by 71.01%, 48.96%, and 15.71% for 0–10, 10–20, and 20–30 cm soil layers, respectively. Irrigation level was the main factor dominating the root growth of each soil layer. The correlation analysis showed that fruit yield had significantly positive correlations with root characteristics in all soil layers, while water use efficiency had significantly positive correlations with the percentages of root length and root surface area in the 0–10 cm soil layer. In conclusion, rational water and nitrogen regimes achieved better fruit yield by promoting root growth of greenhouse tomato, and the water use efficiency of greenhouse tomato was improved by increasing the root percentage in the topsoil layer to alleviate the adverse effects under water stress conditions. This study reveals how irrigation volume and nitrogen application can enhance tomato yield and water use efficiency by regulating root characteristics and vertical root distribution, providing support for understanding the response of root systems to changes in soil water and nitrogen conditions.

Effects of Grafting on the Structure and Function of Coffee Rhizosphere Microbiome

Heterologous double-root grafting represents an effective strategy to mitigate challenges associated with continuous coffee cropping and reduce soil-borne diseases. However, its specific regulatory mechanism remains unclear. Therefore, a field experiment was conducted including six different grafting combinations for C. canephora cv. Robusta (Robusta) and Coffea Liberica (Liberica): Robusta scion with a homologous double root (R/RR), Liberica scion with a homologous double root (L/LL), Robusta scion with a heterologous double root (R/RL and L/RL), and Liberica scion with a heterologous double root (L/LR and R/LR); these combinations were conducted to clarify the effects of heterologous double-root grafting combinations on the root exudates and soil microbial diversity, structure, and function of Robusta and Liberica. The results demonstrated notable differences in root exudates, rhizosphere microbial structure, and function between Robusta and Liberica. Despite Liberica having lower diversity in its rhizosphere microbial communities and relatively higher levels of potential pathogenic bacteria, it showed stronger resistance to diseases. Roots of Robusta in heterologous double-root coffee seedlings significantly enhanced the secretion of resistance compounds, increased the relative abundance of potentially beneficial bacteria, and reduced the relative abundance of potential pathogenic fungi. This enhances the rhizosphere immunity of Robusta against soil-borne diseases. The results indicated that grafting onto Liberica roots can strengthen resistance mechanisms and enhance the rhizosphere immunity of Robusta, thereby mitigating challenges associated with continuous cropping.

Antibiotics Resistance and PGPR Traits of Endophytic Bacteria Isolated in Arid Region of Morocco

This study aimed to characterize endophytic bacteria isolated from legume nodules and roots in the rhizosphere soils of Acacia trees in Morocco’s arid regions. The focus was on identifying bacterial strains with plant growth-promoting rhizobacteria (PGPR) traits and antibiotic resistance, which could enhance legume productivity under various abiotic stresses. Autochthonous legumes were used to harbor the endophytic bacteria, including chickpea (Cicer arietinum), faba bean (Vicia faba), lentil (Lens culinaris), and common bean (Phaseolus vulgaris). In a previous study, seventy-two isolates were obtained, and molecular characterization grouped them into twenty-two bacterial isolates. These twenty-two bacterial isolates were then further analyzed for their antibiotic resistance and key PGPR traits, such as phosphate solubilization, indole-3-acetic acid (IAA) production, and siderophore production. The results revealed that 86.36% of the isolates were resistant to erythromycin, 45.45% to ciprofloxacin, 22.73% to ampicillin-sulbactam, and 9.09% to tetracycline, with ciprofloxacin and tetracycline being the most effective. All isolates produced IAA, with HN51 and PN105 exhibiting the highest production at 6 µg of IAA per mg of protein. The other isolates showed varying levels of IAA production, ranging from moderate to low. Siderophore production, assessed using CAS medium, indicated that the strains PN121, LR142, LNR146, and HR26 exhibited high production, while the rest demonstrated moderate to low capacities. Additionally, 18.2% of the isolates demonstrated phosphate solubilization on YED-P medium, with PR135 and LNR135 being the most efficient, achieving solubilization indices of 2.14 and 2.13 cm, respectively. LR142 and LNR146 showed a moderate solubilization efficiency. Overall, these findings indicate that these isolated endophytic bacteria possess significant potential as biofertilizers, owing to their antibiotic resistance, IAA production, siderophore production, and phosphate solubilization abilities. These characteristics position them as promising candidates for enhancing legume growth under abiotic stress and contributing to sustainable agriculture in arid regions.

Chemical profiling and bioactivity analysis of shoots and roots essential oil of Indian Blumea mollis (D. Don) Merr.

Aromatic plants contain essential oils, potent extracts renowned for therapeutic benefits. Essential oils are commonly utilized due to their diverse range of phytochemicals that possess therapeutic properties. The present study analyses the chemical composition of the essential oil obtained from shoots and roots of Blumea mollis (Family: Asteraceae), using GC-FID and GC-MS techniques. A total of 49 and 46 compounds were identified from shoots and roots accounting for 95.6 % and 88.4 % respectively. β-caryophyllene is reported as major compound 36.2 ± 0.50 % in essential oil of the shoots and 33.8 ± 0.55 % in essential oil of the roots. Both essential oils of shoots and roots were dominated by sesquiterpene hydrocarbons (59.2–76.4%), followed by oxygenated sesquiterpene (14.9–20.3%). The in vitro antioxidant activity was determined using DPPH radical scavenging activity, H2O2 radical scavenging activity, and Iron(II) complexing activity. The highest antioxidant activity was observed in root essential oil of B. mollis. The oils also inhibited the activity of α-amylase with IC50 of 3.53 ± 0.04 μg/ml (shoot), 3.45 ± 0.04 μg/ml (root). Root oil also showed good activity for protein denaturation with IC50 of 3.02 ± 0.03 g/ml as compared to shoot essential oil. This is first time that essential oil constituent and biological activity of B. mollis roots and shoots have been characterized from India.

Relationship between root system-soil C:N:P and soil microbial diversity at different evolutionary stages of Caragana tibetica scrub in arid desert grassland, Northern China.

Scrub root systems play a crucial role in preventing soil erosion and nutrient loss. However, the effects of the root system configuration on soil nutrient dynamics and microbial changes at various evolutionary stages remain poorly understood. In this study, we investigated the relationship between soil physical and chemical properties and the diversity of bacteria and fungi throughout the evolutionary stages of the scrub root systems. This was achieved through a combination of whole-root excavation and root tracing techniques. The results indicated that root diameter was the main factor contributing to the continuous increase in carbon (C): phosphorus (P) and nitrogen (N): P ratios as the scrub sand pile developed. The soil organic carbon (SOC), total soil nitrogen (TN), and total soil phosphorus (TP) contents in the soil in the four evolutionary stages were the highest during the developmental stage, but the change in TP content was not statistically significant (P > 0.05). Partial least squares path modeling and redundancy analysis (RDA) indicated that root system stoichiometric C and N contents were positively correlated with microbial diversity (R2 = 0.85). There was no correlation between the evolutionary stage and soil nutrient TN, whereas soil nutrient TN was negatively correlated with microbial diversity (R2 = -0.92). These findings elucidate the relationship between the evolutionary stage of root chemical measurement characteristics, soil elements and microorganisms, and their subsequent effects on root elemental composition and microbial diversity. This study enhances the current understanding of plant-soil interactions in desert steppe ecosystems.

Hydromechanical behaviour of a slope reinforced by grass roots under rainfall conditions

Soil bioengineering using vegetation has been considered an environmentally friendly solution to improve slope stability. Although several studies have demonstrated the contribution of vegetation to slope stability, a gap in understanding the mechanisms of grass root–soil interactions under rainfall conditions remains. This study investigates the effects of the roots of vetiver grass (Chrysopogon zizanioides) on the hydromechanical behaviour of an unsaturated soil slope using the centrifuge modelling technique. The changes in pore water pressure and slope deformation were monitored during the test. The monitored data were subsequently back-analysed and interpreted using seepage–stability analyses. In addition, this study focused on evaluating the effect of roots on slope stability, considering safety and pore water pressure during rainfall. Results revealed that the vetiver roots remarkably affected the initial suction of the slope by increasing the soil's air-entry value. The increased suction and the additional cohesion provided by the roots enhanced slope stability under rainfall conditions.

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.

Persistent biogeochemical signals of land use-driven, deep root losses illuminated by C and O isotopes of soil CO2 and O2

Replacing long-lived, rarely disturbed vegetation with short-lived, frequently disturbed vegetation is a widespread phenomenon in the Anthropocene that can influence ecosystem functioning and soil development by reducing the abundance of deep roots. We explore how sources and fate of soil CO2 vary with organic substrate source, abundance of respiring biota (i.e., roots and soil microbes), season, and soil depth. We quantified multiple isotopic signatures of CO2 (δ13C, Δ14C, δ18O) as well as concentrations and δ18O of free O2 in the upper 5 m of soil at sites where root abundances and soil organic C have been previously quantified: in late-successional forests, cultivated fields, and ~ 80 y old regenerating pine forests growing on previously cultivated land. We hypothesized that soil CO2sources would vary across soil depth and land cover, reflecting varying abundances of organic substrates, and seasonally as the dominance of root vs. microbial CO2 production changes through the year. δ13C–CO2 revealed respiration of C4-derived substrates in cultivated fields particularly during the growing season. This effect was not evident in soils of regenerating pine or older hardwood forests, suggesting that ~ 80 y of pine inputs to reforested soils have been sufficient to dominate microbial substrate selection over any remnant, historic agricultural C4 inputs. Δ14C–CO2 diverged by land use at 3 and 5 m, indicating that more recently-produced photosynthate is available for mineralization in forests compared to cultivated plots, and in late-successional forests compared to regenerating pine forests. At 1.5, 3, and 5 m in forested plots we observed evidence of respiratory demands on soil pore space O2. In these soils, we observed declines in [O2] compared to other depths and to the agricultural plots and concurrent increases in δ18O of free O2, consistent with the idea that roots and heterotrophic soil microbes are more active where photosynthate is more available. The δ18O–CO2 values, a likely proxy for δ18O of soil porewater, exhibited 18O enrichment during the winter, when many sampling wells were flooded, compared to growing season values. These data suggest an isotopically-distinct and laterally-flowing source of CO2-laden porewater during winter months. Combined, these datasets document how ~ 80 y of forest regeneration can provide sufficient C inputs to mask any microbial mineralization of decades-old organic inputs, but belowground C inputs still lag those of late successional forests. We also infer that lateral and vertical flows of water can serve as a sink for biotically-generated CO2, and that where deep soil [CO2] is lower due to lower root and microbial activities, production of carbonic acid is also diminished. Where reaction rates are weathering limited, a paucity of deep roots imposed by anthropogenic land cover change thus may limit the production of this agent of soil development and the C sink represented by the silicate weathering it can promote. The data suggest deep and persistent effects of the loss of deeply rooted long-lived vegetation on deep soil C storage and transformations that promote acid-dissolution weathering reactions that help form soil itself.