Rooting around soil constraints

View of a wheat root and surrounding soil, the rhizosphere, and root hairs extending into a pore space. Root was frozen in the field in liquid nitrogen, and viewed frozen with a cryo-scanning electron microscope.

ROOTS INFLUENCE the soil around them, a region known as the rhizosphere. Root influence on the rhizosphere is determined by their water and nutrient uptake, and by the exudation of many soluble compounds (e.g. sugars, amino acids, organic acids, steroids, surfactants etc), and tissue residues, by the roots themselves. The carbon added to the rhizosphere in these forms can represent 30 per cent of the total fixed by photosynthesis by each plant.

View inside a wheat root and its surrounding soil, the rhizosphere, anchored with root hairs. Root was frozen in the field ill liquid nitrogen, sliced in half and viewed frozen with a cryo-scanning electron microscope.

Root exudates and residues influence the activities and diversity of microbes and soil fauna that inhabit the rhizosphere, which in turn affect the nutrient supply, health and vigour of the crop. The materials added to the rhizosphere by the roots differ with crop species and variety, and also with the age, growth rate and environment of each root.

When roots die they leave behind, as channels (biopores), the spaces they occupied while alive. Any roots of subsequent crops that grow through these channels will encounter a very different environmen to that of the bulk soil. The processes that occur at interfaces between roots and soil in these pores in field soil are complex and are not well understood. However, they can have profound effects on crop productivity.

This GRDC-supported project is aimed at understanding these processes better, linking them to crop performance and then applying this knowledge to soil management and targeted breeding for root traits adapted to particular soi1 environments.

We are applying a range of new and old techniques to study field-grown crop roots and their rhizospheres. New techniques include cryo-scanning electron microscopy for observation and analysis of roots in their undisturbed rhizosphere, and molecular microbiology for quantification and identification of associated rhizosphere microbes.

The old techniques include extensive spadework and coring in the field to reveal the architecture and placement of the crop roots.