Pathways to deeper roots: anatomical phenes of maize under impedance

Vanhees, Dorien J. (2020) Pathways to deeper roots: anatomical phenes of maize under impedance. PhD thesis, University of Nottingham.

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Abstract

When roots grow through soil they experience mechanical impedance to varying extents. When levels of mechanical impedance become greater, for instance when soils become compacted or soil moisture decreases, roots can become obstructed. As a consequence the uptake of nutrients and water from the soil reduces, which can reduce plant growth and ultimately negatively impact yield. In this work field trials were conducted at two different field sites (one at the Apache Root Biology Centre in Willcox, Arizona and one at the Russell E. Larson Agricultural Research Center in Rock Springs, Pennsylvania) to study the differential distribution of maize roots following the interaction with a compacted soil profile. In soils with compacted plots the rooting depth of coarse roots was not correlated with coarse root length, which indicated that nodal roots of some genotypes were able to grow under impeding conditions while other genotypes were not capable of growing through impeding conditions. Furthermore genotypes were identified which had similar rooting depths but contrasting coarse root lengths, these genotypes were equally able to reach to deeper depths. The amount of roots formed by the root system therefore does not determine the ability of roots to grow deeper under impeded conditions. Root thickening, a response of roots often seen when submitted to mechanical impedance, varied among genotypes. The same field trial were also used to investigate the role of root anatomy and adaptation to soil mechanical impedance. Root anatomy varied according to genotype and nodal position. Deeper rooting was facilitated by root anatomical phenes such as reduced cortical cell file number in combination with greater middle cortical cell area for node 3 and increased aerenchyma for node 4.

In a separate pot trial the hypothesis that radial expansion was related to the ability of roots to cross a compacted layer in four different genotypes was tested. Radial expansion of roots was mainly attributed to the cortex. Cortical expansion of a single root axis was caused by cellular expansion and not an increase in cell file number. The ability of roots to reach the compacted layer was dependent on the root growth angle. Genotypic variability was present for the ability to cross the compacted layer, and genotypes that did not radially expand in response to impedance had more roots crossing the layer and reached deeper past the layer. The same genotypes were tested in a hydroponics experiment, which showed that genotypes that did not thicken in response to ethylene were the same as those that were able to overcome impedance.

It can be concluded that radial thickening should be seen as a response to mechanical impedance rather than a positive adaptation. Genotypic variation was related to rooting depth, and anatomical adaptation was more important for thinner than thicker root classes. Understanding the functional utility of root anatomical phenotypes under abiotic stress, such as impedance, is important for the breeding of new crop cultivars with superior adaptation to edaphic stress. Furthermore this work illustrates that root systems are highly adaptive across genotypes but also within an individual plant. The understanding of such adaptability is important, as edaphic stresses such as impedance influence global agriculture.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Lynch, Jonathan P.
Mooney, Sacha J.
Bengough, Anthony G.
Loades, Kenneth W.
Keywords: Maize roots; Compacted soil; Root anatomy; Root growth
Subjects: Q Science > QK Botany > QK640 Plant anatomy
Faculties/Schools: UK Campuses > Faculty of Science > School of Biosciences
Item ID: 59994
Depositing User: Vanhees, Dorien
Date Deposited: 15 Jul 2020 04:40
Last Modified: 15 Jul 2020 04:40
URI: http://eprints.nottingham.ac.uk/id/eprint/59994

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