The emergent rhizosphere: imaging the development of the porous architecture at the root-soil interface

Abstract

The rhizosphere is the zone of soil influenced by a plant root and is critical for plant health and nutrient acquisition. All below ground resources must pass through this dynamic zone prior to their capture by plant roots. However, researching the undisturbed rhizosphere has proved very challenging. Here we compare the temporal changes to the intact rhizosphere pore structure during the emergence of a developing root system in different soils. High resolution X-ray Computed Tomography (CT) was used to quantify the impact of root development on soil structural change, at scales relevant to individual micro-pores and aggregates (µm). A comparison of micro-scale structural evolution in homogenously packed soils highlighted the impacts of a penetrating root system in changing the surrounding porous architecture and morphology. Results indicate the structural zone of influence of a root can be more localised than previously reported (µm scale rather than mm scale). With time, growing roots significantly alter the soil physical environment in their immediate vicinity through reducing root-soil contact and crucially increasing porosity at the root-soil interface and not the converse as has often been postulated. This ‘rhizosphere pore structure’ and its impact on associated dynamics are discussed.

Imaging microstructure of the barley rhizosphere: particle packing and root hair influences

“…However, the current study used soil sieved to < 250 μm, whereas previous research used soil sieved to < 2 mm (e.g. Feeney et al ., ; Helliwell et al ., ; Koebernick et al ., ). Our smaller particle size and the resulting packing condition produced a soil environment more typical of intra‐aggregate structure.…”

“…The present study confirms previous observations of increased pore volume fraction at the soil–root interface (Helliwell et al ., ; Koebernick et al ., ). The radial porosity distribution about the root surface showed very different patterns for individual replicates suggesting that even in a relatively homogeneous soil there can be very different porosity distributions for individual roots.…”

“…Recent observations by Helliwell et al . (), using time‐lapse computed tomography (CT) imaging, have shown that densification of rhizosphere soil may not be the general trend. They showed that soil porosity decreased with distance from the root surface of tomato.…”

Root‐induced soil deformation influences Fe, S and P: rhizosphere chemistry investigated using synchrotron XRF and XANES

“…Recent work has shown that soil porosity varies with distance from the root surface, with an increased porosity directly adjacent to the root surface (Hinsinger et al, 2005;Helliwell et al, 2017;Koebernick et al, 2019; see also Supporting Information Fig. Recent work has shown that soil porosity varies with distance from the root surface, with an increased porosity directly adjacent to the root surface (Hinsinger et al, 2005;Helliwell et al, 2017;Koebernick et al, 2019; see also Supporting Information Fig.…”

Multilab EcoFAB study shows highly reproducible physiology and depletion of soil metabolites by a model grass

“…However, investigation of root morphology in soil is challenging due to its opacity, and investigation of exudation in soil is challenging due to soils physiochemical complexity (Cai et al ., ). Specialized imaging techniques, such as magnetic resonance imaging, computed tomography (Metzner et al ., ; Helliwell et al ., ), or the use of labeled plants (Rellán‐Álvarez et al ., ), have been developed, but they are not widely accessible or amenable to high‐throughput experimentation (Metzner et al ., ). Similarly, approaches for the investigation of root exudation in soils include the use of in situ soil drainage systems (lysimeters) in fields (Strobel, ), which are low throughput and require complex installations, or of laboratory‐based extraction methods that are based on flushing the soil with large volumes of liquids (Swenson et al ., ; Pétriacq et al ., ).…”