Soil bioturbation by earthworms and plant roots- mechanical and energetic considerations

Abstract:

Soil structure is a key factor shaping hydrological and ecological functions including water storage, deep recharge and plant growth. Compaction adversely impacts soil ecosystem services over extended periods (years to decades) until structure and functionality are restored. An important class of soil structural restoration processes are related to biomechanical activity associated with borrowing of earthworms and root proliferation in impacted soils. This study employs a new biomechanical model to estimate stresses required for earthworm and plant root bioturbation under different conditions and the mechanical energy required. We consider steady state plastic cavity expansion to determine burrowing pressures of earthworms and plant roots as linked with models for cone penetration required for initial burrowing into soil volumes. We use earthworm physical and ecological parameters (e.g., population density, burrowing rate, and burrowing behavior) to convert mechanical deformation to estimation of energy and soil organic carbon (energy source for earthworms). Results illustrate a reduction in strain energy with increasing water content and trade-offs between pressure and energy investment for various root and earthworm geometries and soil hydration. The study provides a quantitative framework for estimating energy costs of bioturbation in terms of soil organic carbon or plant assimilates and delineates mechanical and hydration conditions that promote or constrain such activities.