Emerging effects of root hairs on plant scale soil water relations

• Applicants: Professor Dr. Mutez Ali Ahmed; Professor Dr. Jan Vanderborght
• Subject Area: Soil Sciences
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 403670197

Although the importance of root hairs in nutrient acquisition is well accepted, their role in water uptake remains controversial. In the first phase, we demonstrated, both in the lab and in the field, that maize root hairs exhibited no effects on soil-plant hydraulics in both sandy and loamy soils. This result is opposite to what has been recently reported in barley, which suggests that the role of root hairs is species and soil specific. The overall objective of this renewal proposal is to reveal the role of root hairs in water uptake, from the small scale interactions in the rhizosphere up to the field. We plan to combine experimental and modelling studies to quantify whether, in what soil and climatic conditions, and by which mechanisms hairs of different species impact plant-soil system conductance, and ultimately plant-soil relations. We hypothesize that: (i) hairs length, density, distribution along the root, turnover, shrinkage and recovery and hence root-soil contact is species and soil specific; (ii) hairless mutants develop different root hydraulic architecture and thus might have a different root water uptake pattern to compensate for the lack of root hairs.The project is structured into four work packages (WP). In WP1a, we will use Synchrotron X-ray CT to quantify the spatial distribution of maize and barley root hairs in loam and sand and investigate the temporal dynamics of root hair functions, including turnover (aging) and shrinkage/recovery during soil drying/wetting. In WP1b, we will measure the impact of root hairs on water uptake of two barley genotypes (WT vs brb) grown in sandy and loamy soils and we will compare the results to those obtained with maize in the first phase. A root hair model will be built to functionally represent the impact of root hairs on water uptake (WP1c). In WP2, we plan to utilize neutron radiography to characterize the root architecture and root segment hydraulic conductances of the two maize and barley mutants and investigate whether the hairless mutant developed different root hydraulic architectures to compensate for the lack of hairs. In WP3, we will investigate the impact of maize root hairs on water uptake in long columns under a range of well-controlled conditions that expand the range of conditions that can be considered in the field plot (e.g. interactions between nutrient and water stress). The latter WP would not only facilitate the upscaling between the SEC and SPE, but also provide a system to study the role of root hairs in well-controlled, field-like conditions and hence disentangling the trade-off between root hydraulic architecture and rhizosphere effects (root hairs). In WP4, we will continue to measure and model the effect of root hairs and soil texture on transpiration and leaf water potential in the field and over an entire cropping cycle.The outcome of this project is a mechanistic understanding of the role of root hairs on water uptake from the micro to the field scales.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2089: Rhizosphere Spatiotemporal Organisation - a Key to Rhizosphere Functions
• International Connection: Switzerland
• Co-Investigator: Professor Dr.-Ing. Mathieu Javaux, Ph.D.
• Cooperation Partner: Professor Dr. Andrea Carminati