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

Abstract

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 ∼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.

Sweet Sorghum Performance Affected by Soil Compaction and Sowing Time as a Second Crop in the Brazilian Cerrado

“…For the March sowing, the water limitation was greater, regardless of the level of soil compaction and phenological phase, in accordance with Bengough et al (2011) andBetioli Júnior et al (2012). It was observed that the soil compaction brought about by T 7 promoted water conditions (Fwithin) for vegetative growth of sorghum sown in January and February similar to that sown in March when the soil was in ideal structural conditions (Table 2).…”

Mapping soil deformation around plant roots using in vivo 4D X-ray Computed Tomography and Digital Volume Correlation

“…Under limited water and/or nutrient availability, the development of an extensive root system is a key determinant of crop yield (Bengough et al, 2011). To penetrate soil, an individual root must either follow the path of an existing pore network (White and Kirkegaard, 2010), or displace soil material by a combination of rigidbody movement, shear and compression (Bengough et al, 2011).…”

Root distribution and water use in coffee shaded with Tabebuia rosea Bertol. and Simarouba glauca DC. compared to full sun coffee in sub-optimal environmental conditions

“…Other work has demonstrated that compacted soil layers may limit water movement, root penetration and therefore, plant water uptake (Bennie 1996;Bengough et al 2011). In such soil conditions tree roots play an important role in facilitating water flow and crop root penetration (Nair 1984;Van Noordwijk et al 1996).…”