Root elongation, water stress, and mechanical impedance: a review of limiting stresses and beneficial root tip traits

A. Glyn Bengough*, B. M. McKenzie, P. D. Hallett, T. A. Valentine

*Corresponding author for this work

Research output: Contribution to journalLiterature reviewpeer-review

648 Citations (Scopus)


Root elongation in drying soil is generally limited by a combination of mechanical impedance and water stress. Relationships between root elongation rate, water stress (matric potential), and mechanical impedance (penetration resistance) are reviewed, detailing the interactions between these closely related stresses. Root elongation is typically halved in repacked soils with penetrometer resistances > 0.8-2 MPa, in the absence of water stress. Root elongation is halved by matric potentials drier than about -0.5 MPa in the absence of mechanical impedance. The likelihood of each stress limiting root elongation is discussed in relation to the soil strength characteristics of arable soils. A survey of 19 soils, with textures ranging from loamy sand to silty clay loam, found that similar to 10% of penetration resistances were > 2 MPa at a matric potential of -10 kPa, rising to nearly 50% > 2 MPa at - 200 kPa. This suggests that mechanical impedance is often a major limitation to root elongation in these soils even under moderately wet conditions, and is important to consider in breeding programmes for drought-resistant crops. Root tip traits that may improve root penetration are considered with respect to overcoming the external (soil) and internal (cell wall) pressures resisting elongation. The potential role of root hairs in mechanically anchoring root tips is considered theoretically, and is judged particularly relevant to roots growing in biopores or from a loose seed bed into a compacted layer of soil.

Original languageEnglish
Pages (from-to)59-68
Number of pages10
JournalJournal of Experimental Botany
Issue number1
Publication statusPublished - Jan 2011


  • penetration resistance
  • soil compaction
  • soil strength
  • maize zea-mays
  • water potential
  • penetrometer resistance
  • seminal roots
  • root growth
  • plant-roots
  • growth pressure
  • seedling roots
  • frictional resistance
  • arabidopsis-thaliana


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