Limits...
Soil Penetration by Earthworms and Plant Roots--Mechanical Energetics of Bioturbation of Compacted Soils.

Ruiz S, Or D, Schymanski SJ - PLoS ONE (2015)

Bottom Line: The critical earthworm or root pressure increases with increased diameter of root or earthworm, however, results are insensitive to the cone apex (shape of the tip).The invested mechanical energy per unit length increase with increasing earthworm and plant root diameters, whereas mechanical energy per unit of displaced soil volume decreases with larger diameters.Estimated energy requirements for earthworm biopore networks are linked to consumption of soil organic matter and suggest that earthworm populations are likely to consume a significant fraction of ecosystem net primary production to sustain their subterranean activities.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Systems Science, ETHZ, Zurich, Switzerland.

ABSTRACT
We quantify mechanical processes common to soil penetration by earthworms and growing plant roots, including the energetic requirements for soil plastic displacement. The basic mechanical model considers cavity expansion into a plastic wet soil involving wedging by root tips or earthworms via cone-like penetration followed by cavity expansion due to pressurized earthworm hydroskeleton or root radial growth. The mechanical stresses and resulting soil strains determine the mechanical energy required for bioturbation under different soil hydro-mechanical conditions for a realistic range of root/earthworm geometries. Modeling results suggest that higher soil water content and reduced clay content reduce the strain energy required for soil penetration. The critical earthworm or root pressure increases with increased diameter of root or earthworm, however, results are insensitive to the cone apex (shape of the tip). The invested mechanical energy per unit length increase with increasing earthworm and plant root diameters, whereas mechanical energy per unit of displaced soil volume decreases with larger diameters. The study provides a quantitative framework for estimating energy requirements for soil penetration work done by earthworms and plant roots, and delineates intrinsic and external mechanical limits for bioturbation processes. Estimated energy requirements for earthworm biopore networks are linked to consumption of soil organic matter and suggest that earthworm populations are likely to consume a significant fraction of ecosystem net primary production to sustain their subterranean activities.

No MeSH data available.


Related in: MedlinePlus

Fracture toughness vs water content. [50–52].Continuous curve was plotted through the data points in order to approximate fracture toughness values at different water contents.
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pone.0128914.g005: Fracture toughness vs water content. [50–52].Continuous curve was plotted through the data points in order to approximate fracture toughness values at different water contents.

Mentions: The fracture toughness changes as a function of soil water content. Values for fracture toughness for lower water contents were collected from Hanson et al. [51] and Wang et al. [52]. For a soil with clay content of 15–25% and saturated conditions (water content of θm = 0.44 kg kg−1), the mechanical shear modulus is equivalent to that of gelatine used in the study by Dorgan et al. [50] (G = 1.4 kPa). The fracture toughness parameters were fit to a continuous curve plotted against water content in order to estimate mechanical energy investments for a wider range of water contents (seen in Fig 5).


Soil Penetration by Earthworms and Plant Roots--Mechanical Energetics of Bioturbation of Compacted Soils.

Ruiz S, Or D, Schymanski SJ - PLoS ONE (2015)

Fracture toughness vs water content. [50–52].Continuous curve was plotted through the data points in order to approximate fracture toughness values at different water contents.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4472233&req=5

pone.0128914.g005: Fracture toughness vs water content. [50–52].Continuous curve was plotted through the data points in order to approximate fracture toughness values at different water contents.
Mentions: The fracture toughness changes as a function of soil water content. Values for fracture toughness for lower water contents were collected from Hanson et al. [51] and Wang et al. [52]. For a soil with clay content of 15–25% and saturated conditions (water content of θm = 0.44 kg kg−1), the mechanical shear modulus is equivalent to that of gelatine used in the study by Dorgan et al. [50] (G = 1.4 kPa). The fracture toughness parameters were fit to a continuous curve plotted against water content in order to estimate mechanical energy investments for a wider range of water contents (seen in Fig 5).

Bottom Line: The critical earthworm or root pressure increases with increased diameter of root or earthworm, however, results are insensitive to the cone apex (shape of the tip).The invested mechanical energy per unit length increase with increasing earthworm and plant root diameters, whereas mechanical energy per unit of displaced soil volume decreases with larger diameters.Estimated energy requirements for earthworm biopore networks are linked to consumption of soil organic matter and suggest that earthworm populations are likely to consume a significant fraction of ecosystem net primary production to sustain their subterranean activities.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Systems Science, ETHZ, Zurich, Switzerland.

ABSTRACT
We quantify mechanical processes common to soil penetration by earthworms and growing plant roots, including the energetic requirements for soil plastic displacement. The basic mechanical model considers cavity expansion into a plastic wet soil involving wedging by root tips or earthworms via cone-like penetration followed by cavity expansion due to pressurized earthworm hydroskeleton or root radial growth. The mechanical stresses and resulting soil strains determine the mechanical energy required for bioturbation under different soil hydro-mechanical conditions for a realistic range of root/earthworm geometries. Modeling results suggest that higher soil water content and reduced clay content reduce the strain energy required for soil penetration. The critical earthworm or root pressure increases with increased diameter of root or earthworm, however, results are insensitive to the cone apex (shape of the tip). The invested mechanical energy per unit length increase with increasing earthworm and plant root diameters, whereas mechanical energy per unit of displaced soil volume decreases with larger diameters. The study provides a quantitative framework for estimating energy requirements for soil penetration work done by earthworms and plant roots, and delineates intrinsic and external mechanical limits for bioturbation processes. Estimated energy requirements for earthworm biopore networks are linked to consumption of soil organic matter and suggest that earthworm populations are likely to consume a significant fraction of ecosystem net primary production to sustain their subterranean activities.

No MeSH data available.


Related in: MedlinePlus