Abstract
The ability of roots to penetrate hard soil is important for crop productivity but specific root phenes contributing to this ability are poorly understood. Root penetrability and biomechanical properties are likely to vary in the root system dependent on anatomical structure. No information is available to date on the influence of root anatomical phenes on root penetrability and biomechanics. Root penetration ability was evaluated using a wax layer system. Root tensile and bending strength were evaluated in plant roots grown in the greenhouse and in the field. Root anatomical phenes were found to be better predictors of root penetrability than root diameter per se and associated with smaller distal cortical region cell size. Smaller outer cortical region cells play an important role in stabilizing the root against ovalization and reducing the risk of local buckling and collapse during penetration, thereby increasing root penetration of hard layers. The use of stele diameter was found to be a better predictor of root tensile strength than root diameter. Cortical thickness, cortical cell count, cortical cell wall area and distal cortical cell size were stronger predictors of root bend strength than root diameter. Our results indicate that root anatomical phenes are important predictors for root penetrability of high-strength layers and root biomechanical properties.
Highlights
Soil compaction adversely affects crop production in many parts of the world
Results of the principal components analyses (PCA) showed that the first axis explained 61.4% of the variation among the eight phenes and was mostly associated with total cortical area (TCA), cortex thickness (CT), cortical cell count (CCC), and stele diameter (SD) (Fig. 3)
Cortical phenes: TCA, CCC, cortical cell file number (CCFN), inner cortical region (INN) and mid-cortical region (MID) were positively correlated with RD (Fig. 3, Supplementary Table S1), while DIS was negatively correlated with RD (r=−0.41, P
Summary
Soil compaction adversely affects crop production in many parts of the world. The formation of strong or compacted soil layers restricts root exploration and access to nutrients and water thereby promoting early onset of stress (Barraclough and Weir, 1988). Soil strength and mechanical impedance to root growth typically increases with decreasing soil moisture (Cairns et al, 2004; Iijima and Kato, 2007; Whitmore and Whalley, 2009). Soil strength increases nonlinearly with decreasing soil moisture, which may result in mechanical impedance limiting root growth to a relatively greater extent than water stress per se (Bengough et al, 2011). Deep rooting is important for drought adaptation by improving utilization of water in deep soil strata (Lynch, 2013) but the presence of strong or compacted soil layers often precludes the exploitation of deep water and nutrients. Deep roots that are capable of penetrating hard soil are important for improving crop productivity in compacted soils
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