Relationships between root diameter, root length and root branching along lateral roots in adult, field-grown maize

Abstract

Background and Aims Root diameter, especially apical diameter, plays an important role in root development and function. The variation in diameter between roots, and along roots, affects root structure and thus the root system's overall foraging performance. However, the effect of diameter variation on root elongation, branching and topological connections has not been examined systematically in a population of high-order roots, nor along the roots, especially for mature plants grown in the field.Methods A method combining both excavation and analysis was applied to extract and quantify root architectural traits of adult, field-grown maize plants. The relationships between root diameter and other root architectural characteristics are analysed for two maize cultivars.Key Results The basal diameter of the lateral roots (orders 1-3) was highly variable. Basal diameter was partly determined by the diameter of the bearing segment. Basal diameter defined a potential root length, but the lengths of most roots fell far short of this. This was explained partly by differences in the pattern of diameter change along roots. Diameter tended to decrease along most roots, with the steepness of the gradient of decrease depending on basal diameter. The longest roots were those that maintained (or sometimes increased) their diameters during elongation. The branching density (cm -1 ) of laterals was also determined by the diameter of the bearing segment. However, the location of this bearing segment along the mother root was also involved -intermediate positions were associated with higher densities of laterals.Conclusions The method used here allows us to obtain very detailed records of the geometry and topology of a complex root system. Basal diameter and the pattern of diameter change along a root were associated with its final length. These relationships are especially useful in simulations of root elongation and branching in source-sink models.

A New Phenotyping Pipeline Reveals Three Types of Lateral Roots and a Random Branching Pattern in Two Cereals

“…Previous efforts to classify lateral roots in cereal species have been reported Watt et al, 2008;Rebouillat et al, 2009;Henry et al, 2016;Passot et al, 2016), but these classifications were often based on anatomical traits, mainly root diameter and vasculature. A first difficulty comes from the fact that some morphological traits change along lateral roots, typically root diameter (Wu et al, 2016), which was confirmed in our maize data. A different classification method, based on growth rates, was reported in rice (Rebouillat et al, 2009), for which growth rates were highly contrasting among lateral roots but assignment to classes was based on expert knowledge.…”

“…sunflower [Helianthus annuus]; Aguirrezabal et al, 1994), annual monocots (e.g. maize [Zea mays]; Jordan et al, 1993;Wu et al, 2016), and perennials (oak [Quercus robur]; Pagès, 1995; rubber tree [Hevea brasiliensis]; Thaler and Pagès, 1996;and banana [Musa acuminata]; Lecompte et al, 2005). It also has been observed in the model species Arabidopsis (Arabidopsis thaliana; Freixes et al, 2002).…”

Characterization of root traits for improvement of spring wheat in the Pacific Northwest

“…For example, a greenhouse study on winter wheat at the preflowering stage showed that total root length correlated negatively with root diameter (Awad, Byrne, Reid, Comas, & Haley, ). Likewise, a field‐based study in maize found that diameter decreased along the root and change in diameter was correlated with length (Wu, Pages, & Wu, ). However, the average root diameter reported in this study was consistent with the 0.14–0.30 mm range of fibrous wheat root system reported by Manschadi, Manske, and Vlek ().…”

OpenSimRoot: widening the scope and application of root architectural models

“…The vigor factor can also scale the root‐specific root diameter to allow an allometric relation between elongation rate and root diameter expansion within a root class (Pagès, 2000; Wu et al ., 2016). The initial root diameter is otherwise a root class‐specific input parameter.…”

“…The elongation rates of individual roots are predefined in the parameter space, but may be scaled according to a 'root vigor' scaling factor, for example, drawn from a lognormal distribution of elongation rates (scaled to unity), thus creating variation in length. The vigor factor can also scale the root-specific root diameter to allow an allometric relation between elongation rate and root diameter expansion within a root class (Pag es, 2000;Wu et al, 2016). The initial root diameter is otherwise a root classspecific input parameter.…”