Soil strength influences wheat root interactions with soil macropores

Abstract

Deep rooting is critical for access to water and nutrients found in subsoil. However, damage to soil structure and the natural increase in soil strength with depth, often impedes root penetration. Evidence suggests that roots use macropores (soil cavities greater than 75 μm) to bypass strong soil layers. If roots have to exploit structures, a key trait conferring deep rooting will be the ability to locate existing pore networks; a trait called trematotropism. In this study, artificial macropores were created in repacked soil columns at bulk densities of 1.6 g cm−3 and 1.2 g cm−3, representing compact and loose soil. Near isogenic lines of wheat, Rht‐B1a and Rht‐B1c, were planted and root–macropore interactions were visualized and quantified using X‐ray computed tomography. In compact soil, 68.8% of root–macropore interactions resulted in pore colonization, compared with 12.5% in loose soil. Changes in root growth trajectory following pore interaction were also quantified, with 21.0% of roots changing direction (±3°) in loose soil compared with 76.0% in compact soil. These results indicate that colonization of macropores is an important strategy of wheat roots in compacted subsoil. Management practices to reduce subsoil compaction and encourage macropore formation could offer significant advantage in helping wheat roots penetrate deeper into subsoil.

Root Growth of Hordeum vulgare and Vicia faba in the Biopore Sheath

“…This indicates that, in this study, the subsoil roots of spring barley colonized the biopores due to a hard setting soil environment. As Atkinson et al [50] have reported, colonization of macropores is an important strategy of wheat roots to compacted subsoil. Contrary to homorhizous barley, allorhizous faba bean, with its thicker roots [51], less plasticity [52], and independance from nitrogen in the sheath, might be less attracted by the biopore sheath.…”

The effects of long-term fertilizations on soil hydraulic properties vary with scales

“…The pores in the cores are not only hydrologically important for providing quick pathways for fluid to flow through, they are also biologically critical for modulating nutrient cycling as well as root growth ( Atkinson et al, 2020 ). An increase in porosity and permeability of the cores could lead to a rise in yield due to the increase in nitrification and root penetration as our previous work based on the Rothamsted long-term experiments showed that more porous and permeable soils were positively related to abundance of nitrification-related genes ( Neal et al, 2020b ).…”

The interaction between wheat roots and soil pores in structured field soil

“…The biopores not only provided paths with lower mechanical resistance, but also altered the physical, chemical, and biological properties of the surrounding soil that benefit root growth ( Kautz et al , 2013 ; Banfield et al , 2017 ). In previous studies, artificial pores have been created to study root behaviour in soil ( Pfeifer et al , 2014 ; Colombi et al , 2017 ; Atkinson et al , 2020 ). In these examples, the soil was artificially packed; the soil around artificial pores is most likely to have similar chemical properties to the bulk soil.…”

“…Recently, Fradgley et al (2020) demonstrated significant differences in the near-surface architecture of wheat roots on a selection of modern and historic wheat lines, but whether this translates into differences in deep rooting remains to be determined. It is likely that where biopores are not immediately accessible, roots undertake foraging-like behaviour in order to secure an easier passage through the soil ( Atkinson et al , 2020 ). Roué et al (2020) recently demonstrated, for Arabidopsis, that the root cap size and shape can influence the penetration ability of roots; however, by the resolution adopted in our imaging approach, it was not possible to accurately measure root caps to assess this and therefore is suited to future investigations.…”

“… White and Kirkegaard (2010) reported that deep wheat roots were found in pores, implying that soil structure, or the existence of a continuous pore network at depth, might be as important as genotype in determining rooting depth. Recently, we have shown in a laboratory study that, in strong soil, wheat roots will preferentially elongate in macropores ( Atkinson et al , 2020 ). New research to establish and quantify relationships between macropores and root elongation in the field is urgently needed.…”