The Roots of Rhizosphere Development

One way to use fewer resources for sustainable intensification in agriculture is to optimise root function. Roots are a major source of easily decomposed organic matter in soil, and the combination of this with the hydraulic and mechanical stresses they impart to soil impacts soil structure development and the biological activity of the rhizosphere. We have demonstrated that different crop species have different abilities to do this. Using rheological tests, we have found that root exudates from barley disperse soil particles, whereas those from maize act as a gel [Naveed et al. 2017. Eur. J. Soil Sci. 68, 806-816]. Also maize root exudate held onto water as a hydrogel, while barley root exudates acted as a surfactant. These different functions offer different physiological advantage to the plant under drought conditions. Using very high-resolution Synchrotron tomography, we found that the rhizosphere can restructure to recreate macropore volumes lost due to compression induced by roots during growth [Koebernick et al. 2017. New Phyt. 216, 124-135]. Vital to this restructuring was the presence of root hairs, single cell protrusions that increase the zone of influence of the root and anchor it into surrounding soil. We went on to test the impact of the presence of root hairs on the formation of the rhizosphere in the field and the impact on yield, where it was apparent that they were important for maintaining root soil contact and yield in coarser textured soil. In conclusion, root influence on soil structure dynamics varies between species and with the presence of root hairs. There is considerable scope to alter root traits and the select crops to help develop soil structure at the same time as maintaining yields and tolerance to drought.