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P. D. Hallett - One of the best experts on this subject based on the ideXlab platform.
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Surface tension, rheology and hydrophobicity of rhizodeposits and seed Mucilage influence soil water retention and hysteresis
Plant and Soil, 2019Co-Authors: Muhammad Naveed, M. A. Ahmed, P. Benard, L. K. Brown, T. S. George, A. G. Bengough, T. Roose, N. Koebernick, P. D. HallettAbstract:Aims Rhizodeposits collected from hydroponic solutions with roots of maize and barley, and seed Mucilage washed from chia, were added to soil to measure their impact on water retention and hysteresis in a sandy loam soil at a range of concentrations. We test the hypothesis that the effect of plant exudates and Mucilages on hydraulic properties of soils depends on their physicochemical characteristics and origin. Methods Surface tension and viscosity of the exudate solutions were measured using the Du Noüy ring method and a cone-plate rheometer, respectively. The contact angle of water on exudate treated soil was measured with the sessile drop method. Water retention and hysteresis were measured by equilibrating soil samples, treated with exudates and Mucilages at 0.46 and 4.6 mg g^−1 concentration, on dialysis tubing filled with polyethylene glycol (PEG) solution of known osmotic potential. Results Surface tension decreased and viscosity increased with increasing concentration of the exudates and Mucilage in solutions. Change in surface tension and viscosity was greatest for chia seed exudate and least for barley root exudate. Contact angle increased with increasing maize root and chia seed exudate concentration in soil, but not barley root. Chia seed Mucilage and maize root rhizodeposits enhanced soil water retention and increased hysteresis index, whereas barley root rhizodeposits decreased soil water retention and the hysteresis effect. The impact of exudates and Mucilages on soil water retention almost ceased when approaching wilting point at −1500 kPa matric potential. Conclusions Barley rhizodeposits behaved as surfactants, drying the rhizosphere at smaller suctions. Chia seed Mucilage and maize root rhizodeposits behaved as hydrogels that hold more water in the rhizosphere, but with slower rewetting and greater hysteresis.
Muhammad Naveed - One of the best experts on this subject based on the ideXlab platform.
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Surface tension, rheology and hydrophobicity of rhizodeposits and seed Mucilage influence soil water retention and hysteresis
Plant and Soil, 2019Co-Authors: Muhammad Naveed, M. A. Ahmed, P. Benard, L. K. Brown, T. S. George, A. G. Bengough, T. Roose, N. Koebernick, P. D. HallettAbstract:Aims Rhizodeposits collected from hydroponic solutions with roots of maize and barley, and seed Mucilage washed from chia, were added to soil to measure their impact on water retention and hysteresis in a sandy loam soil at a range of concentrations. We test the hypothesis that the effect of plant exudates and Mucilages on hydraulic properties of soils depends on their physicochemical characteristics and origin. Methods Surface tension and viscosity of the exudate solutions were measured using the Du Noüy ring method and a cone-plate rheometer, respectively. The contact angle of water on exudate treated soil was measured with the sessile drop method. Water retention and hysteresis were measured by equilibrating soil samples, treated with exudates and Mucilages at 0.46 and 4.6 mg g^−1 concentration, on dialysis tubing filled with polyethylene glycol (PEG) solution of known osmotic potential. Results Surface tension decreased and viscosity increased with increasing concentration of the exudates and Mucilage in solutions. Change in surface tension and viscosity was greatest for chia seed exudate and least for barley root exudate. Contact angle increased with increasing maize root and chia seed exudate concentration in soil, but not barley root. Chia seed Mucilage and maize root rhizodeposits enhanced soil water retention and increased hysteresis index, whereas barley root rhizodeposits decreased soil water retention and the hysteresis effect. The impact of exudates and Mucilages on soil water retention almost ceased when approaching wilting point at −1500 kPa matric potential. Conclusions Barley rhizodeposits behaved as surfactants, drying the rhizosphere at smaller suctions. Chia seed Mucilage and maize root rhizodeposits behaved as hydrogels that hold more water in the rhizosphere, but with slower rewetting and greater hysteresis.
Mutez Ali Ahmed - One of the best experts on this subject based on the ideXlab platform.
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Coupled model of root water uptake, Mucilage exudation and degradation
2017Co-Authors: Eva Kroener, Mutez Ali Ahmed, Andrea CarminatiAbstract:Although the prominent role of root Mucilage plays a prominent in soil-plant water relations is becoming more and more accepted, many aspects of how Mucilage distribution and root water uptake interact with each other remain unexplored. The aims of this study were: i) to measure the effect of soil moisture on Mucilage decomposition; ii) to develop a coupled model of root water uptake and Mucilage diffusion and degradation during root growth. Mucilage decomposition was measured by adding C4 root Mucilage from maize as single pulses to a C3 soil at two different moisture levels. Drought significantly suppressed Mucilage mineralization. Opposed to classical solute transport models the water flow in the rhizosphere is affected by the local concentration of Mucilage. The model accounts for an increased equilibrium water retention curve, a reduction of hydraulic conductivity at a given water content and a non-equilibrium water retention curve caused by swelling and shrinking dynamics of Mucilage. The dispersion coefficient, on the other hand, depends on the water content. The parameters of Mucilage diffusion have been fitted to observations on real plants. The model shows that Mucilage exuded in wet soils diffuses far from the roots and it is rapidly degraded. On the contrary, Mucilage of plants growing in dry soil is not easily degradable and it remains at higher concentrations in a narrow region around the roots, resulting in a marked increase in water content towards the roots as well as to the formation of stable rhizosheath observed in dry soils. This model shows how feedbacks between root water uptake and root exudation could result in adaptation mechanisms of plants to drought.
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Utilisation of Mucilage C by microbial communities under drought
Biology and Fertility of Soils, 2017Co-Authors: Mutez Ali Ahmed, Callum C. Banfield, Muhammad Sanaullah, Anna Gunina, Michaela A. DippoldAbstract:Root Mucilage modulates soil-plant-water dynamics, but its interactions with microbial community functioning remain poorly understood. The aims of this study were to estimate (I) the impacts of Mucilage and soil water content on the microbial community composition and (II) the Mucilage consumption by individual microbial groups. C4 root Mucilage from maize (at 40 and 200 μg C per gram dry soil, corresponding to 10 and 50% of soil microbial biomass, respectively) was added in single pulses to a C3 soil at two moisture levels: optimum (80% of water-holding capacity (WHC)) and drought (30% of WHC). After 15 days of incubation, the microbial community composition was studied by phospholipid fatty acids (PLFA) analysis and incorporation of Mucilage-derived 13C into individual microbial groups was determined by compound-specific isotope analysis. Microbial community composition remained largely unaffected by Mucilage addition but was affected by moisture. Whereas an increase in water content reduced Mucilage 13C recovery in PLFA for the low-dose Mucilage amendment from 19 to 9%, it had no effect under the high-dose amendment (11–12%). This suggests that the role of Mucilage for microbial functioning is especially pronounced under drought conditions. The fungal PLFA 18:2ω6,9 was present only under drought conditions, and fungi profited in their Mucilage C utilisation from the lower competitiveness of many bacterial groups under drought. In this study, Gram-negatives (G−, characterised by PLFA 18:1ω9c, 18:1ω7c, 16:1ω7c and cy17:0) showed the highest Mucilage-derived 13C in PLFA, especially at the high-dose amendment, suggesting them to be the major decomposers of Mucilage, especially when the availability of this C source is high. Gram-positives (G+) included different sub-groups with distinct responses to moisture: G+ 1 (a15:0) were only competitive for Mucilage C under drought, whereas G+ 3 (i17:0) were only able to utilise Mucilage-derived C under optimal moisture conditions. During the 15-day incubation, they built up more than 40% of their membranes from Mucilage-derived C, suggesting that in the case of high availability, Mucilage can act as an important C source for this microbial group. However, under drought, G− 1 and fungi were incorporating the most Mucilage C into their membranes (approx. 20% of PLFA-C). The observation that, for some groups, the high-dose Mucilage amendments under drought led to higher 13C incorporation into PLFA than under optimum moisture suggests that Mucilage can compensate drought effects for particular microbial groups. Thus, Mucilage may not only act as a C source for microorganisms but may also mitigate drought effects for specific rhizosphere microbial groups.
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Pore‐Scale Distribution of Mucilage Affecting Water Repellency in the Rhizosphere
Vadose Zone Journal, 2017Co-Authors: Pascal Benard, Mutez Ali Ahmed, Maire Holz, Mohsen Zarebanadkouki, Clemens Hedwig, Andrea CarminatiAbstract:The hydraulic properties of the rhizosphere are altered by plants, fungi and microorganism. Plant roots release different compounds into the soil. One of these substances is Mucilage, a gel which turns water repellent upon drying. We introduce a conceptual model of Mucilage deposition during soil drying and its impact on the soil wettability. We hypothesized that as soil dries, water menisci recede and draw Mucilage towards the contact region between particles where it is deposited. At high Mucilage content, Mucilage deposits expand into the open pore space and finally block water infiltration when a critical fraction of the pore space is occupied. To test this hypothesis, we mixed Mucilage and particles of varying grain size, let them dry and measured the contact angle (CA) using the sessile drop method. Mucilage deposition was visualized by light microscopy imaging. Contact angle measurements showed a distinct threshold-like behavior with a sudden increase in apparent contact angle at high Mucilage concentrations. Particle roughness induced a more uniform distribution of Mucilage. The observed threshold corresponds to the concentration when Mucilage deposition occupies a critical fraction of the pore space, as visualized with the microscope images. Particle roughness induced a more uniform distribution of Mucilage. In conclusion, water repellency is critically affected by the distribution of Mucilage on the pore-scale. This microscopic heterogeneity has to be taken into account in the description of macroscopic processes, like water infiltration or rewetting of water repellent soil.
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drying of Mucilage causes water repellency in the rhizosphere of maize measurements and modelling
Plant and Soil, 2016Co-Authors: Mutez Ali Ahmed, Pascal Benard, Mohsen Zarebanadkouki, Eva Kroener, Anders Kaestner, Andrea CarminatiAbstract:Although maize roots have been extensively studied, there is limited information on the effect of root exudates on the hydraulic properties of maize rhizosphere. Recent experiments suggested that the mucilaginous fraction of root exudates may cause water repellency of the rhizosphere. Our objectives were: 1) to investigate whether maize rhizosphere turns hydrophobic after drying and subsequent rewetting; 2) to test whether maize Mucilage is hydrophobic; and 3) to find a quantitative relation between rhizosphere rewetting, particle size, soil matric potential and Mucilage concentration. Maize plants were grown in aluminum containers filled with a sandy soil. When the plants were 3-weeks-old, the soil was let dry and then it was irrigated. The soil water content during irrigation was imaged using neutron radiography. In a parallel experiment, ten maize plants were grown in sandy soil for 5 weeks. Mucilage was collected from young brace roots growing above the soil. Mucilage was placed on glass slides and let dry. The contact angle was measured with the sessile drop method for varying Mucilage concentration. Additionally, capillary rise experiments were performed in soils of varying particle size mixed with maize Mucilage. We then used a pore-network model in which Mucilage was randomly distributed in a cubic lattice. The general idea was that rewetting of a pore is impeded when the concentration of Mucilage on the pore surface (g cm−2) is higher than a given threshold value. The threshold value depended on soil matric potential, pore radius and contract angle. Then, we randomly distributed Mucilage in the pore network and we calculated the percolation of water across a cubic lattice for varying soil particle size, Mucilage concentration and matric potential. Our results showed that: 1) the rhizosphere of maize stayed temporarily dry after irrigation; 2) Mucilage became water repellent after drying. Mucilage contact angle increased with Mucilage surface concentration (gram of dry Mucilage per surface area); 3) Water could easily cross the rhizosphere when the Mucilage concentration was below a given threshold. In contrast, above a critical Mucilage concentration water could not flow through the rhizosphere. The critical Mucilage concentration decreased with increasing particle size and decreasing matric potential. These results show the importance of Mucilage exudation for the water fluxes across the root-soil interface. Our percolation model predicts at what Mucilage concentration the rhizosphere turns hydrophobic depending on soil texture and matric potential. Further studies are needed to extend these results to varying soil conditions and to upscale them to the entire root system.
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An efficient method for the collection of root Mucilage from different plant species : A case study on the effect of Mucilage on soil water repellency
Journal of Plant Nutrition and Soil Science, 2016Co-Authors: Ina-maria Zickenrott, Susanne K. Woche, Jörg Bachmann, Mutez Ali Ahmed, Doris VetterleinAbstract:Root Mucilage may play a prominent role in understanding root water uptake and, thus, there is revived interest in studying the function of root Mucilage. However, Mucilage research is hampered by the tedious procedures of Mucilage collection. We developed a Mucilage separator which utilizes low centrifugal forces (570 rpm) to separate the Mucilage from seminal roots without the need of handling individual seeds or removing the germinated seeds from the tray/mesh to a centrifuge tube. For the different plant species, between 1 and 3.7 mL tray−1 of hydrated Mucilage could be produced, with 6 trays being handled successively within 45 min. For Triticum aestivum, which showed a dry matter content of 0.5%, this was equivalent to 98.6 mg Mucilage dry matter. The lowest total production was found for Zea mays with just 34 mg dry matter. The amounts of Mucilage produced normalized to root tip agree well with literature data. The Mucilage obtained by the new method was used to measure its effect on repellency of soil as this property directly relates to the phenomenon of lower rhizosphere soil water content during rewetting. It could be shown that repellency of the rhizosphere is affected by the quantity as well as by species-dependent quality of Mucilage in the rhizosphere. Among the species tested (Lupinus albus, Vicia faba, Zea mays, Triticum aestivum), the largest differences were observed between the two legumes. For Zea mays seminal root Mucilage obtained with the new system was compared to Mucilage of air born brace roots. The differences between these two Mucilages, representing different root orders, indicate clearly that there is still a need for methods which enable the investigation of roots from older plants.
Peter J. Gregory - One of the best experts on this subject based on the ideXlab platform.
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Surface tension and viscosity of axenic maize and lupin root Mucilages
New Phytologist, 1997Co-Authors: D. B. Read, Peter J. GregoryAbstract:summary In many plants, Mucilage permeates the interface between root and soil, yet little is known about its physical properties or its influence on the physical properties of the rhizoasphere. Mucilage was collected from 3–4-d-old, axenically-grown maize (Zea mays L. cv. Freya) and lupin (Lupinus angustifolius L. cv. Merrit) seedlings. Surface tension and viscosity were measured over a range of Mucilage hydration, and neutral sugar analyses of the hydrolysed Mucilages were obtained by gas chromatography. Surface tension of both maize and lupin Mucilage was reduced to ∼ 48 mN m−1 at total solute concentrations > 0.7 mg ml−1, indicating the presence of powerful surfactants. Mucilage viscosity increased with increasing solute concentration and decreasing temperature. At a total solute concentration of 0.7 mg ml−1, the viscosity of maize Mucilage at 20 °C was 2.1 mPa s (approx. double that of pure water), increasing to 3.3 mPa s at 5 °C. Both maize and lupin Mucilage showed viscoelastic behaviour. The major component of maize Mucilage was found to be glucose, but in lupin it was fucose. The surface tension and viscosity results support the idea that Mucilage plays a major role in the maintenance of root-soil contact in drying soils. As surface tension decreases, the ability of the Mucilage to wet the surrounding soil particles becomes greater. Also, as viscosity and elasticity increase, the resistance to movement of any soil particles in contact with the Mucilage increases, a degree of stabilization of the rhizosphere structure is achieved and hydraulic continuity is maintained. It is unclear whether the surfactant is actively secreted by the root or is present simply as a result of leakage from root cells.
L. K. Brown - One of the best experts on this subject based on the ideXlab platform.
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Surface tension, rheology and hydrophobicity of rhizodeposits and seed Mucilage influence soil water retention and hysteresis
Plant and Soil, 2019Co-Authors: Muhammad Naveed, M. A. Ahmed, P. Benard, L. K. Brown, T. S. George, A. G. Bengough, T. Roose, N. Koebernick, P. D. HallettAbstract:Aims Rhizodeposits collected from hydroponic solutions with roots of maize and barley, and seed Mucilage washed from chia, were added to soil to measure their impact on water retention and hysteresis in a sandy loam soil at a range of concentrations. We test the hypothesis that the effect of plant exudates and Mucilages on hydraulic properties of soils depends on their physicochemical characteristics and origin. Methods Surface tension and viscosity of the exudate solutions were measured using the Du Noüy ring method and a cone-plate rheometer, respectively. The contact angle of water on exudate treated soil was measured with the sessile drop method. Water retention and hysteresis were measured by equilibrating soil samples, treated with exudates and Mucilages at 0.46 and 4.6 mg g^−1 concentration, on dialysis tubing filled with polyethylene glycol (PEG) solution of known osmotic potential. Results Surface tension decreased and viscosity increased with increasing concentration of the exudates and Mucilage in solutions. Change in surface tension and viscosity was greatest for chia seed exudate and least for barley root exudate. Contact angle increased with increasing maize root and chia seed exudate concentration in soil, but not barley root. Chia seed Mucilage and maize root rhizodeposits enhanced soil water retention and increased hysteresis index, whereas barley root rhizodeposits decreased soil water retention and the hysteresis effect. The impact of exudates and Mucilages on soil water retention almost ceased when approaching wilting point at −1500 kPa matric potential. Conclusions Barley rhizodeposits behaved as surfactants, drying the rhizosphere at smaller suctions. Chia seed Mucilage and maize root rhizodeposits behaved as hydrogels that hold more water in the rhizosphere, but with slower rewetting and greater hysteresis.
