Aims

Root hairs are one root trait among many which enables plants to adapt to environmental conditions. How different traits are coordinated and whether some are mutually exclusive is currently poorly understood. Comparing a root hair defective mutant with its corresponding wild-type, we explored if and how the mutant exhibited root growth adaptation strategies and how dependent this was on substrate.

Methods

Zea mays root hair defective mutant (rth3) and the corresponding wild-type siblings were grown under well-watered conditions on two substrates with contrasting texture and hence nutrient mobility. Root system architecture was investigated over time using repeated X-ray computed tomography.

Results

There was no plastic adaptation of root system architecture to the lack of root hairs, which resulted in lower uptake of nutrients especially in the substrate with high sorption capacity. The function of the root hairs for anchoring did not result in different root length density profiles between genotypes. Both maize genotypes showed a marked response to substrate. This was well reflected in the spatiotemporal development of rhizosphere volume fraction but especially in the highly significant response of root diameter to substrate, irrespective of genotype.

Conclusions

The most salient root plasticity trait was root diameter in response to substrate. Coping mechanisms for missing root hairs were limited to a shift in root-shoot ratio in loam. Further experiments are required, to elucidate whether observed differences can be explained by mechanical properties beyond mechanical impedance, root or microbiome ethylene production or differences in diffusion processes within the root or the rhizosphere.