Effects of Mucilage on Rhizosphere Hydraulic Functions Depend on Soil Particle Size

Kroener, Eva; Holz, Maire; Zarebanadkouki, Mohsen; Ahmed, Mutez Ali; Carminati, Andrea

doi:10.2136/vzj2017.03.0056

Cited by 54 publications

(88 citation statements)

References 48 publications

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“…The latter is explained by the maintained connectivity of the liquid phase during drying, which enables film flow at low water potentials. This result shows that the maintained connectivity of the liquid phase during drying counteracts the expected decrease in permeability caused by the shrinkage of the polymer matrix (Kroener et al, 2018).…”

Section: Resultsmentioning

confidence: 79%

“…To what extent the emerging matrix augments the water retention of soils is still not known. Kroener et al (2018) reported greater water retention of mucilage in fine‐ than in coarse‐textured soils. The pronounced water retention in fine‐textured soils can be explained by the higher specific surface area of these soils and the amplified entanglement of polymers with the soil particles, which favors the formation of the polymer matrix across the pore space.…”

Section: Resultsmentioning

confidence: 99%

“…Extracellular polymeric substances and mucilage can hold water at negative potentials (Chenu, 1993; McCully and Boyer, 1997), but their effect on soil water retention is amplified in fine‐textured soils (Kroener et al, 2018), which suggests that additional forces emerge from the interaction between polymers and soil matrix. Similarly, mucilage separated from soil showed no resistance to drying (McCully and Boyer, 1997), and being in a porous system is a prerequisite to allow the polymer network to utilize its full hydraulic capacity (Deng et al, 2015; Kroener et al, 2018). In summary, there is no conclusive theory on the mechanisms by which EPS and mucilage interact with soil and affect their physical properties.…”

Section: Physical Properties Of Extracellular Polymeric Substances (Ementioning

confidence: 99%

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Microhydrological Niches in Soils: How Mucilage and EPS Alter the Biophysical Properties of the Rhizosphere and Other Biological Hotspots

Benard

Zarebanadkouki

Brax

et al. 2019

Vadose Zone Journal

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Core Ideas Plant mucilage and bacterial extracellular polymeric substances (EPS) prevent the breakup of the soil liquid phase. Formation of continuous structures buffers soil hydraulic properties. The release of viscous polymeric substances represents a universal strategy. Plant roots and bacteria are capable of buffering erratic fluctuations of water content in their local soil environment by releasing a diverse, highly polymeric blend of substances (e.g. extracellular polymeric substances [EPS] and mucilage). Although this concept is well accepted, the physical mechanisms by which EPS and mucilage interact with the soil matrix and determine the soil water dynamics remain unclear. High‐resolution X‐ray computed tomography revealed that upon drying in porous media, mucilage (from maize [Zea mays L.] roots) and EPS (from intact biocrusts) form filaments and two‐dimensional interconnected structures spanning across multiple pores. Unlike water, these mucilage and EPS structures connecting soil particles did not break up upon drying, which is explained by the high viscosity and low surface tension of EPS and mucilage. Measurements of water retention and evaporation with soils mixed with seed mucilage show how these one‐ and two‐dimensional pore‐scale structures affect macroscopic hydraulic properties (i.e., they enhance water retention, preserve the continuity of the liquid phase in drying soils, and decrease vapor diffusivity and local drying rates). In conclusion, we propose that the release of viscous polymeric substances and the consequent creation of a network bridging the soil pore space represent a universal strategy of plants and bacteria to engineer their own soil microhydrological niches where stable conditions for life are preserved.

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Section: Resultsmentioning

confidence: 79%

Section: Resultsmentioning

confidence: 99%

Section: Physical Properties Of Extracellular Polymeric Substances (Ementioning

confidence: 99%

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Microhydrological Niches in Soils: How Mucilage and EPS Alter the Biophysical Properties of the Rhizosphere and Other Biological Hotspots

Benard

Zarebanadkouki

Brax

et al. 2019

Vadose Zone Journal

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“…The soil columns were saturated with water for a period of 48 h by capillary rise, and subsequently a constant water level difference of 2 cm was established between the top and the bottom of the samples, and water outflow was determined. This information (outflow [cm 3 s −1 ], the geometry of soil, and established pressure gradient [cm]) was used to calculate the saturated hydraulic conductivity of the soil ( K s , cm s −1 ) based on Darcy's equation (Kroener et al, 2018). The van Genuchten–Mualem equation was used to parameterize the unsaturated hydraulic conductivity of soil:

K (normalθ) = K_{normals} {normalΘ}^{normalλ} {[1 - {(1 - {normalΘ}^{1 / m})}^{normalm}]}^{2}

where K (θ) is the hydraulic conductivity of the soil as a function of soil water content (cm s −1 ), λ is a unitless fitting parameter describing the tortuosity of the flow path, and m = 1 – 1/ n .…”

Section: Methodsmentioning

confidence: 99%

Mucilage Facilitates Nutrient Diffusion in the Drying Rhizosphere

Zarebanadkouki

Fink

Benard

et al. 2019

Vadose Zone Journal

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Core Ideas Our aim was to test whether mucilage promotes diffusion of nutrients in dry soil. Mucilage favors transport of nutrients in drying soil and their uptake by plant. Mucilage increases the soil moisture in the rhizosphere as soil dries. Mucilage maintains the connectivity of liquid phase in the rhizosphere as soil dries. Despite detailed investigations of its distinct biochemical properties and their effects on the availability of nutrients for plants, the biophysical aspects of the rhizosphere, particularly the effect of mucilage on the transport of water and nutrients, are poorly understood. The aim of this study was to investigate the effect of mucilage on the diffusion of nutrients and consequently their transport through the rhizosphere into the plant roots. Phosphor imaging technique determined the temporospatial distribution of 137Cs in a model rhizosphere (a sandy soil mixed with chia seed (Salvia hispanica L) mucilage. The observed profiles of activities were used to estimate the diffusion coefficient of K in soils. A diffusion–convection equation was numerically solved to predict the transport of K and its uptake by a single plant root in drying soil. The results suggest that mucilage (i) keeps the rhizosphere wet and (ii) maintains the connectivity of the liquid phase in drying soil. In these ways, mucilage moderates the drop in diffusive transport. The modeling results showed that the presence of mucilage in the rhizosphere (i) prevents depletion of nutrients in soils with a low nutrient concentration in the soil solution and (ii) delays the risk of nutrient and/or salt accumulation in the vicinity of the root in soils with a high concentration nutrient and/or salt the soil solution. In conclusion, mucilage appears to mitigate the risk of nutrient deficiency and salinity stress as it enhances the diffusive transport in drying soil. In this way, mucilage may favor the transport of nutrients within the rhizosphere and their uptake by plant roots in drying soil.

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“…It is proposed that bioadhesive mucilage components of exudates are important factors, along with root hairs, in the formation of cylinders of soil around roots known as rhizosheaths. It appears that this will involve differing impacts on soil aggregation through varied viscosities and surface properties, on drying/wetting cycles and the potential for hydrophobicity of mucilage after drying and binding properties in general, including the sequestering of heavy metals (Ray et al, 1988;Watt et al, 1994;Dennis et al, 2010;Naveed et al, 2017;Kroener et al, 2018). Rhizosheath bioengineering by some grass species during periods of drought has been observed, where the grasses increased the thickness of their rhizosheaths (Hartnett et al, 2012).…”

Section: Root Exudates Bioengineer Rhizospheres For Sustained Resourcmentioning

confidence: 99%

Sticky mucilages and exudates of plants: putative microenvironmental design elements with biotechnological value

2019

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Summary Plants produce a wide array of secretions both above and below ground. Known as mucilages or exudates, they are secreted by seeds, roots, leaves and stems and fulfil a variety of functions including adhesion, protection, nutrient acquisition and infection. Mucilages are generally polysaccharide‐rich and often occur in the form of viscoelastic gels and in many cases have adhesive properties. In some cases, progress is being made in understanding the structure–function relationships of mucilages such as for the secretions that allow growing ivy to attach to substrates and the biosynthesis and secretion of the mucilage compounds of the Arabidopsis seed coat. Work is just beginning towards understanding root mucilage and the proposed adhesive polymers involved in the formation of rhizosheaths at root surfaces and for the secretions involved in host plant infection by parasitic plants. In this article, we summarise knowledge on plant exudates and mucilages within the concept of their functions in microenvironmental design, focusing in particular on their bioadhesive functions and the molecules responsible for them. We draw attention to areas of future knowledge need, including the microstructure of mucilages and their compositional and regulatory dynamics.

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Effects of Mucilage on Rhizosphere Hydraulic Functions Depend on Soil Particle Size

Cited by 54 publications

References 48 publications

Microhydrological Niches in Soils: How Mucilage and EPS Alter the Biophysical Properties of the Rhizosphere and Other Biological Hotspots

Microhydrological Niches in Soils: How Mucilage and EPS Alter the Biophysical Properties of the Rhizosphere and Other Biological Hotspots

Mucilage Facilitates Nutrient Diffusion in the Drying Rhizosphere

Sticky mucilages and exudates of plants: putative microenvironmental design elements with biotechnological value

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