Genotypic variation in soil penetration by maize roots is negatively related to ethylene-induced thickening

Abstract

Radial expansion is a classic response of roots to mechanical impedance that has generally been assumed to aid penetration. We analysed the response of maize nodal roots to impedance to test the hypothesis that radial expansion is not related to the ability of roots to cross a compacted soil layer. Genotypes varied in their ability to cross the compacted layer, and those with a steeper approach to the compacted layer or less radial expansion in the compacted layer were more likely to cross the layer and achieve greater depth. Root radial expansion was due to cortical cell size expansion, while cortical cell file number remained constant. Genotypes and nodal root classes that exhibited radial expansion upon encountering the compacted soil layer also thickened in response to exogenous ethylene in hydroponic culture, i.e. radial expansion in response to ethylene was correlated with the thickening response to impedance in soil. We propose that ethylene insensitive roots, i.e. those that do not thicken and are able to overcome impedance, have a competitive advantage under mechanically impeded conditions as they can maintain their elongation rates. We suggest that prolonged exposure to ethylene could function as a stop signal for axial root growth.

Harnessing root architecture to address global challenges

“…It has been proposed that the plasticity of root growth in response to mechanical impedance may be adaptive by reallocating root foraging to softer, presumably wetter, soil domains (Lynch et al, 2021b). In support of this proposal, genotypes that thicken in response to impedance are less able to cross a hard soil layer than those for which the anatomical phenotype is unchanged (Vanhees et al, 2020, 2021). This response is mediated by ethylene (Vanhees et al., 2021), which recently has been shown to be a ‘stop signal’ for root growth into hard soil (Pandey et al, 2021).…”

“…In support of this proposal, genotypes that thicken in response to impedance are less able to cross a hard soil layer than those for which the anatomical phenotype is unchanged (Vanhees et al, 2020, 2021). This response is mediated by ethylene (Vanhees et al., 2021), which recently has been shown to be a ‘stop signal’ for root growth into hard soil (Pandey et al, 2021). In the topsoil, this sort of plasticity may be advantageous by preventing root foraging into soil domains that are hard because of surface drying, whereas, in both the topsoil and the subsoil, growth plasticity in response to impedance may be beneficial by redirecting root growth to biopores and low resistance pathways at the interface of soil structural units (Lynch et al, 2021b).…”

De invloed van bodemverdichting op dewater- en luchthuishouding in de bodem en op de plantontwikkeling : literatuuronderzoek

“…Het vermogen van wortels om de bodem in te dringen, wordt beïnvloed door zowel de diameter als door anatomische kenmerken van de wortel. Tot de laatste behoren de diameter van de stengel van de plant en de vorming van luchtkanalen (aerenchyma) Vanhees et al, 2021). Bij gelijke worteldiameter bleken primaire wortels van erwtenplanten een grotere maximale lengtegroei te hebben dan zijwortels (Misra, 1997).…”

“…Het ontstaan van zijwortels wordt vertraagd in verdichte grond in tomaat (Tracy et al, 2012), tarwe (Colombi en Walter, 2017), triticale en soja (Colombi en Walter, 2015). Daarnaast zijn de vorm van de wortelpunt (Bengough et al, 1997a;, de wortelharen, wortelslijm en andere wortelexudaten (Bengough et al, 1997b) én de anatomie van wortels (Schneider et al, 2021;Vanhees et al, 2021) allemaal van invloed op het indringingsvermogen van wortels (Figuur 14).…”

“…Niet alleen de mechanische indringingsweerstand ten gevolge van verdichting vormt een belemmering voor wortelgroei, ook de afwezigheid van (voldoende) zuurstof kan een belangrijke reden hiervoor zijn, hoewel plantenwortels in staat zijn inwendige luchtkanalen te ontwikkelen, de zogenaamde aerenchyma, om op die manier een onvoldoende aanvoer van zuurstof door de bodem te compenseren Vanhees et al, 2021). Dit vergt wel weer extra energie van de plant die niet in de vruchtontwikkeling kan worden gestoken, wat weer negatief werkt op de opbrengst.…”