A quantitative method for the high throughput screening for the soil adhesion properties of plant and microbial polysaccharides and exudates

Abstract

Background and aimsUnderstanding the structures and functions of carbon-based molecules in soils is an important goal in the context of soils as an ecosystem function of immense importance. Polysaccharides are implicated in maintaining soil aggregate status but have not been extensively dissected in terms of their structures and soil adhesion properties. This is largely because of the technical difficulties in identifying polysaccharide structures and quantifying any functional properties.MethodsHere, we describe the use of a novel nitrocellulose-based adhesion assay to determine the relative capacities for soil adhesion of over twenty plant and microbial polysaccharides that are likely to be present in soil and to contribute to organic matter content and properties. Weights of soil adhered to spots of known amounts of specific polysaccharides were quantified by scanning of the nitrocellulose sheets.ResultsThe most effective polysaccharides identified from this survey included chitosan, β-1,3-glucan, gum tragacanth, xanthan and xyloglucan. We also demonstrate that the soil adhesion assay is suitable to assess the soil-binding properties of plant exudates.ConclusionsThe soil adhesion assay will be useful for the functional dissection of the organic matter components of soils and also of the factors involved in soil attachment to plant roots and in rhizosheath formation.

Micro-scale interactions between Arabidopsis root hairs and soil particles influence soil erosion

“…Future work will explore the physical and biochemical aspects unique to root hairs that contribute to their soil-root binding abilities. In this respect, it is interesting to note that Akhtar et al 33 used a novel assay to identify polysaccharides important for soil cohesion, including chitosan, β-1,3-glucan, gum tragacanth, xanthan and xyloglucan. Similarly, Galloway et al 15 found that xyloglucan, a component secreted by a wide range of angiosperm roots, can increase soil particle aggregation.…”

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

“…However, other reports indicate that higher amounts of mucilage could be secreted than what would be predicted from lysing cells (Guinel & McCully, 1986). The isolation of rootderived high-molecular-weight polymers from hydroponic media has provided a more reliable and scalable sampling method (Akhtar et al, 2018) but uses an artificial environment removed from soil. An important future goal will be to untangle the polysaccharide secretions from root tips and the possible secretion from root hairs that promote rhizosheath formation.…”

“…The adhesive properties of both groups of molecules are well documented, particularly with their use as emulsifiers in industry (Nakauma et al, 2008). Xyloglucan along with b-1,3-glucans have recently been shown to have soil-binding properties (Akhtar et al, 2018;Galloway et al, 2018) and are target polymers for our understanding of rhizosheath formation. Nanostructure analysis of climbing plant and insectivourous plant mucilages has revealed highly ordered structures that contribute to extreme tensile strengths.…”

Cereal root exudates contain highly structurally complex polysaccharides with soil‐binding properties

“…Using sets of polysaccharide-directed MAbs, recent work has identified that a range of soluble polysaccharides are released from roots when plants are grown hydroponically, and this has in turn led to the identification of the cell wall polysaccharide xyloglucan as being widely released from land plants (Galloway et al, 2018). Moreover, using tamarind seed xyloglucan as a proxy for root-exuded xyloglucan, evidence indicates that xyloglucan and other polysaccharides of plant and microbial origin have strong soil-binding properties and can act to promote soil particle aggregation (Akhtar et al, 2018;Galloway et al, 2018). While these findings represent an advancement in wider understanding of HMW root exudates, questions remain regarding their biochemical composition and structure, and the potential for release of HMW exudates from regions other than root tips including the surface of root axes.…”