About the Project
Supervisors: Professor Paul Hallett, Dr Gareth Norton and Dr Timonthy George (James Hutton Institute)
Crops can enhance the capture of nutrients and water from soil by manipulating a thin-zone at the root-soil interface termed the rhizosphere (Gregory et al., 2013). Although the presence of the rhizosphere and its significance to plant productivity is well researched, less is known about the drivers that cause its physical formation and the impact of soil and fertiliser management strategies, as well as specific crop traits (Hallett et al., 2013). This PhD studentship will explore the plasticity of rhizosphere formation in response to soil physical conditions, nutrient status and specific plant traits, such as root hairs (Haling et al., 2013). It will also investigate the knock-on benefit of rhizosphere formation to the ease of water capture and dispersion/aggregation processes that could enhance nutrient release and tolerance to abiotic stresses. These same processes stabilise soils against weathering stresses and by aggregating its structure improve the habitat for soil organisms. Microscale sampling and measurement techniques, many unique to the research supervisors, make this research possible.
Objectives:
1. To explore nutrient release and transport in the presence of root exudates.
2. To obtain direct measurements of changes in rhizosphere physical properties from plants grown under a range of nutrient and soil physical conditions.
3. To explore the impact of crop traits, including root hair abundance and rhizosphere formation.
4. To integrate understanding of changes in rhizosphere physical properties to crop productivity, biological habitat formation and soil resistance to abiotic stresses.
Methods:
The end-point of this PhD will be studies using a range of root trait phenotypes, where microscale measurements allow quantification of functionally significant physical and chemical (nutrients) gradients from the root-soil interface into bulk soil. Scale presents a significant challenge to such measurements and their interpretation, therefore to begin with, the student will conduct larger-scale column experiments that ease sampling and allow for more controlled conditions. Using sectioned columns it will be possible to investigate fluxes driven by the combination of root exudate compounds and water transport. We hypothesise that a drop in air-liquid-surface energy by root exudate compounds, combined with particle dispersion, will enhance nutrient capture and soil aggregation. Next the student will use near-isogenic plant lines that express a range of root phenotypic traits, including root hair abundance and exudation. Collections of maize, barley and Arabidopsis thaliana are available. Microscale measuring techniques from the root-soil interface into bulk soil will measure root exudate enhanced fluxes in more realistic conditions. For physical measurements, techniques to assess microscale interparticle bonding and water transport are available. Nutrient measurements at the microscale will use a combination of fine-scale spatial sampling and in situ testing with laser ablation ICP-MS.
This project provides interdisciplinary training in soil physics and chemistry, with direct application to understanding root-soil interactions that could enhance water and nutrient capture from soils. Given the need to reduce inputs in the sustainable intensification of agriculture, combined with decreasing reserves of these resources, such research is of direct interest to commercial breeders who recognise the considerable untapped potential at the root-soil interface.
Funding Notes
This project is eligible for the EASTBIO Doctoral Training Partnership: http://www.eastscotbiodtp.ac.uk/.
This opportunity is only open to UK nationals (or EU students who have been resident in the UK for at least three years immediately prior to the programme start date) due to restrictions imposed by the funding body.
References
Gregory, P.J., George, T.S., Hallett, P.D. and Bengough, A.G. 2012. [In] Enhancing Understanding and Quantification of Soil-Root Growth Interactions (Eds. Timlin, D. & Ahuja,L.) ASA-SSSA-CSSA. p. 1-30.
Haling, R.E., Brown, L.K., Bengough, A.G., Young, I.M., Hallett, P.D., White, P.J. and George, T.S. 2013. Root hairs improve root penetration, root-soil contact and phosphorus acquisition in soils of different strength. Journal of Experimental Botany, 64, 3711-3721.
Hallett, P.D., Karim, K.H., Bengough, A.G. and Otten, W. 2014. Biophysics of the vadose zone: from reality to model systems and back again. Vadose Zone Journal,12, doi:10.2136/vzj2013.05.0090.