A comparison between water uptake and root length density in winter wheat: effects of root density and rhizosphere properties

Abstract

Background and aims We aim to quantify the variation in root distribution in a set of 35 experimental wheat lines. We also compared the effect of variation in hydraulic properties of the rhizosphere on water uptake by roots. Methods We measured the root length density and soil drying in 35 wheat lines in a field experiment. A 3D numerical model was used to predict soil drying profiles with the different root length distributions and compared with measured soil drying. The model was used to test different scenarios of the hydraulic properties of the rhizosphere. Results We showed that wheat lines with no detectable differences in root length density can induce soil drying profiles with statistically significant differences. Our data confirmed that a root length density of at least 1 cm/cm 3 is needed to drain all the available water in soil. In surface layers where the root length density was far greater than 1 cm/ cm 3 water uptake was independent of rooting density due to competition for water. However, in deeper layers where root length density was less than 1 cm/cm 3 , water uptake by roots was proportional to root density. Conclusion In a set of wheat lines with no detectable differences in the root length density we found significant differences in water uptake. This may be because small differences in root density at depth can result in larger differences in water uptake or that the hydraulic properties of the rhizosphere can greatly affect water uptake.

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

“…Water uptake by wheat roots at depths greater than ~0.5 m is usually very limited ( Gregory et al , 1978 a , b ; Ober et al , 2014 ; Zhang et al , 2020 ). There is a general view that this is at least in part because of a low root density in deeper layers, but Zhang et al (2020) have shown that the hydraulic properties of the rhizosphere can also contribute to low water uptake rates and particularly if any hydrophobicity is induced at the root–soil interface.…”

“…Water uptake by wheat roots at depths greater than ~0.5 m is usually very limited ( Gregory et al , 1978 a , b ; Ober et al , 2014 ; Zhang et al , 2020 ). There is a general view that this is at least in part because of a low root density in deeper layers, but Zhang et al (2020) have shown that the hydraulic properties of the rhizosphere can also contribute to low water uptake rates and particularly if any hydrophobicity is induced at the root–soil interface. Root exudates, root decomposition, soil fauna activity, and related microbial processes could increase soil organic carbon and nutrient concentrations of the surrounding soil, which lead to differences in soil mechanical and hydraulic properties associated with modification to soil structure ( Whalley et al , 2005 ; Helliwell et al , 2017 ; Naveed et al , 2018 ).…”

Root system variation of pulse crops at early vegetative stage

“…The water uptake pattern is uneven throughout the depth of the rooting zone. The water is taken by plants changes depending on soil structure, the existence of water in the soil, root architecture, root density, and different zones of taproot (Pardo et al, 2000;Wasson et al, 2012;Zhang et al, 2020). In general, almost 40% of the total water uptake occurs over the 1 st one-fourth of the root zone, 30% over the 2 nd , 20% over the 3 rd , and 10% over the last 4 th of the total rooting depth under optimum water conditions (Subbarao et al, 1995).…”

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

“…Apart from this, another issue that has been overlooked is hydraulic anisotropy. Soil anisotropy is important not only in hillslope hydrology for lateral water flow but also in plant uptake of water as vertically-dominant roots drive water to flow mainly in the horizontal direction towards the roots ( Zhang et al, 2020 ).…”