Seed-Soil Adhesion A Sticky Remediation for Erosive Soils using Myxospermous Weeds 1,2
2
2
Ashley Gorman , Blair M. McKenzie , Cathy Hawes , John S. Rowan
3
1
Centre for Environmental Change and Human Resilience, University of Dundee, Nethergate, Dundee DD1 4HN, Scotland UK 2 The James Hutton Institute, Invergowrie, Dundee DD2 5DA, Scotland UK 3 School of Social Sciences, University of Dundee, Nethergate, Dundee DD1 4HN, Scotland UK Email: ashley.gorman@hutton.ac.uk. Twitter: @AshG_SeedSoil
Why?
What?
How?
Soil erosion degrades physical and biogeochemical functioning of arable soils, threatening sustainable food production.
The adhesive nature of seed mucilage may physically alter soil, stabilise structure and enhance water retention.
Upon hydration, myxospermous seeds become enveloped in a hydrophyllic mucilage sheath.
Aims •
Mucilage Secretion
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The acidic hydrogel is comprised of two layers: Non-Adherent Mucilage · Pectin · Capable of influencing biogeochemistry and soil structure Adherent Mucilage · Cellulose fibres in a pectinaceous matrix
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Understand biophysical mechanism between seed-soil interactions. Define mucilage structural characteristics across six arable weed species. Can myxospermous seeds be a natural solution to reducing runoff erosion?
Pectin (P), Columella (C), Cellulose Fibres (F)
Can mucilage structure vary between species? Mucilage Release Before
After
Outer Pectin (Soluble)
Inner Cellulose (Insoluble)
Can mucilage structure influence soil adhesion?
MSC Structure
Arabidopsis thaliana
Hexagonal Cells, Central Columellae
Capsella bursapastoris Elongated Columellae
Senecio vulgaris
Viola arvensis
Fig. 1 Diagram illustrating relationship between mucilage secreting cell (MSC) structure [left] and seed-particle adhesion mechanism [right] using Scanning Electron Micrographs (SEM). In confocal images, seeds were stained with ruthenium red and calcofluor white stain to highlight relative mucilage composition of soluble pectin and insoluble cellulose, respectively.
Oval Cells, No Central Columellae
Urtica urens
Plantago lanceolata
No Central Columellae
Conclusions
How will mucilage interact with particles of different sizes? Method Modelled seed-soil adhesion mechanism in sterile system using six myxospermous weed species. Quantified seed mucilage adherence to glass particles (1 mm, 0.5 mm, 0.1mm and a 1:2:7.5 ratio) following two wet-dry cycles.
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Before
Soluble + Insoluble Mucilage B
A
Insoluble Mucilage Only C
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Fig. 2 0.5 mm particles with U. urens in 20 ml aluminium dish (A). Particles adhered to seed by both soluble and insoluble mucilage following wet-dry (B) treatment, and what remains due to only insoluble mucilage after wet-dry-wet-dry (C) treatment. Scale bar: 10 mm.
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Result •
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Larger, heavier seeds produced more mucilage and adhered a greater number of particles. As surface area of particles decreased, the size of mucilageaided aggregates decreased.
A
B
500 µm
C
500 µm
Fig. 3 Confocal images of U. urens adhered to 1 mm (A) and 0.1 mm particles (B) by insoluble mucilage following wet-dry-wet-dry cycle. Close-up of seed-particle adherence by mucilage (C).
Seed-particle adhesion varied due to differences in mucilage solubility between species and may be important for porosity and soil hydrophobicity. Species-specific structures anchored seeds to particles. This can result in seedbank community-specific influences on soil biogeochemistry, thus vital implications for soil health.
Acknowledgements
Evelyne Delbos, Laura-Jane Strachan, Tracy Valentine, Linda Ford, Pete Iannetta. This PhD studentship is funded by CECHR and The James Hutton Institute.