TY - JOUR

T1 - How do roots elongate in a structured soil?

AU - Jin, Kemo

AU - Shen, Jianbo

AU - Ashton, Rhys W.

AU - Dodd, Ian C.

AU - Parry, Martin A. J.

AU - Whalley, William R.

PY - 2013/11

Y1 - 2013/11

N2 - In this review, we examine how roots penetrate a structured soil. We first examine the relationship between soil water status and its mechanical strength, as well as the ability of the soil to supply water to the root. We identify these as critical soil factors, because it is primarily in drying soil that mechanical constraints limit root elongation. Water supply to the root is important because root water status affects growth pressures and root stiffness. To simplify the bewildering complexity of soilroot interactions, the discussion is focused around the special cases of root elongation in soil with pores much smaller than the root diameter and the penetration of roots at interfaces within the soil. While it is often assumed that the former case is well understood, many unanswered questions remain. While low soilroot friction is often viewed as a trait conferring better penetration of strong soils, it may also increase the axial pressure on the root tip and in so doing reduce the rate of cell division and/or expansion. The precise trade-off between various root traits involved in root elongation in homogeneous soil remains to be determined. There is consensus that the most important factors determining root penetration at an interface are the angle at which the root attempts to penetrate the soil, root stiffness, and the strength of the soil to be penetrated. The effect of growth angle on root penetration implicates gravitropic responses in improved root penetration ability. Although there is no work that has explored the effect of the strength of the gravitropic responses on penetration of hard layers, we attempt to outline possible interactions. Impacts of soil drying and strength on phytohormone concentrations in roots, and consequent root-to-shoot signalling, are also considered.

AB - In this review, we examine how roots penetrate a structured soil. We first examine the relationship between soil water status and its mechanical strength, as well as the ability of the soil to supply water to the root. We identify these as critical soil factors, because it is primarily in drying soil that mechanical constraints limit root elongation. Water supply to the root is important because root water status affects growth pressures and root stiffness. To simplify the bewildering complexity of soilroot interactions, the discussion is focused around the special cases of root elongation in soil with pores much smaller than the root diameter and the penetration of roots at interfaces within the soil. While it is often assumed that the former case is well understood, many unanswered questions remain. While low soilroot friction is often viewed as a trait conferring better penetration of strong soils, it may also increase the axial pressure on the root tip and in so doing reduce the rate of cell division and/or expansion. The precise trade-off between various root traits involved in root elongation in homogeneous soil remains to be determined. There is consensus that the most important factors determining root penetration at an interface are the angle at which the root attempts to penetrate the soil, root stiffness, and the strength of the soil to be penetrated. The effect of growth angle on root penetration implicates gravitropic responses in improved root penetration ability. Although there is no work that has explored the effect of the strength of the gravitropic responses on penetration of hard layers, we attempt to outline possible interactions. Impacts of soil drying and strength on phytohormone concentrations in roots, and consequent root-to-shoot signalling, are also considered.

KW - Root elongation

KW - root penetration

KW - root stiffness

KW - soil drying

KW - soil strength

KW - soil structure

KW - LOW WATER POTENTIALS

KW - TRITICUM-AESTIVUM L.

KW - MAIZE PRIMARY ROOT

KW - MECHANICAL IMPEDANCE

KW - PENETROMETER RESISTANCE

KW - HYDRAULIC CONDUCTIVITY

KW - GROWTH DYNAMICS

KW - AUXIN TRANSPORT

KW - PLANT-ROOTS

KW - WAX LAYERS

U2 - 10.1093/jxb/ert286

DO - 10.1093/jxb/ert286

M3 - Literature review

VL - 64

SP - 4761

EP - 4777

JO - Journal of Experimental Botany

JF - Journal of Experimental Botany

SN - 0022-0957

IS - 15

ER -