The roots of soil and food security

Plant roots have an important role in manipulating soil to improve conditions for growth (Oleghe et al., 2017). We recently demonstrated that exudates can disperse and gel soil particles, which could be the initiating processes in the production of the thin-zone at the root-soil interface termed the rhizosphere (Koebernick et al., 2017). 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, irrigation and fertiliser management strategies, as well as specific crop traits (e.g. Norton et al., 2017). We have been exploring these processes as part the BBSRC project 'Rhizosphere by Design' and in this PhD project we would like to complement this research by exploring the interaction with soil nutrients.

You will explore the plasticity of rhizosphere formation in response to soil physical conditions, nutrient status and specific plant traits, such as root hairs. You will also investigate the knock-on benefits 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 on rhizosphere formation.
4. To interpret findings on rhizosphere 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. 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. Next the student will use near-isogenic plant lines that express a range of root phenotypic traits, including root hair abundance and exudation. Microscale measuring techniques from the root-soil interface into bulk soil will measure root exudate enhanced fluxes in more realistic conditions, including XRay-CT to describe pore structure. 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, to gain better understanding of how roots capture water and nutrient 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.