High resolution synchrotron imaging of wheat root hairs growing in soil and image based modelling of phosphate uptake

Abstract

SummaryRoot hairs are known to be highly important for uptake of sparingly soluble nutrients, particularly in nutrient deficient soils. Development of increasingly sophisticated mathematical models has allowed uptake characteristics to be quantified. However, modelling has been constrained by a lack of methods for imaging live root hairs growing in real soils.We developed a plant growth protocol and used Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM) to uncover the three-dimensional (3D) interactions of root hairs in real soil. We developed a model of phosphate uptake by root hairs based directly on the geometry of hairs and associated soil pores as revealed by imaging.Previous modelling studies found that root hairs dominate phosphate uptake. By contrast, our study suggests that hairs and roots contribute equally. We show that uptake by hairs is more localized than by roots and strongly dependent on root hair and aggregate orientation.The ability to image hair-soil interactions enables a step change in modelling approaches, allowing a more realistic treatment of processes at the scale of individual root hairs in soil pores.

Phenotyping for Root Traits

“…Using synchrotron radiation X-ray tomographic microscopy (SRXTM) technique, Keyes et al (2013) uncovered the 3D interactions of wheat root hairs in soil (Fig. 8.4), leading to the development of a model of phosphate uptake by root hairs based on the geometry of hairs and associated soil pores.…”

Challenges in imaging and predictive modeling of rhizosphere processes

“…This raises substantial issues with producing representative samples that can be related to higher scale systems. Recent work by Keyes et al (2013) has shown that it is possible to grow single roots in soil at a scale amenable to synchrotron imaging. By guiding roots into polymer soil chambers of diameter~4 mm using rapid-prototyped mesocosms, an intact rhizosphere (albeit for a young plant <3 weeks) can be imaged rapidly enough to suppress motion artifacts visible to the naked eye.…”

“…Thus, the high-detail 'gold standard' models help to make sure that simplifications do not introduce mathematical artefacts and distort scientific interpretation. However, the emergence of these models also highlights the need for more accurate and detailed characterisation of the soil chemistry; for example, buffer-power-style equilibrium characterisation of bulk soil chemistry is not very informative for the pore scale processes as described in Keyes et al (2013).…”

“…In these models root surfaces are explicitly represented without any a priori averaging, and boundary conditions are applied for the root-soil interface domain rather than the root system being represented by a volumeaveraged sink term. Following this development, Keyes et al (2013) imaged and conducted image-based porescale modelling of plant P uptake by root hairs in which the root, root hair, and soil particle surfaces were all explicitly accounted for, resulting in the first ever image based rhizosphere model that included such structural information. A hierarchy of different models is ultimately necessary since high levels of detail and complexity in models require computational resources and time, which contraindicate high-throughput approaches.…”

Image-based modelling of skeletal muscle oxygenation

“…Most importantly, the results provided by the mathematical model need to be validated experimentally, which-in some cases-can be used to provide (refined) parameters for mathematical modelling. Apart from the geometric information that is provided by the imaging of the system, based on which the system will be modelled [15], image data can supply information on material properties that feed directly into the mathematical model. The link between greyscales in computed tomography data and bone mineralization is well established [16], which for example can be used for modelling of structural mechanics.…”