Root Exudation Facilitates Water Infiltration and Rewetting of Dry Soil

The way plant roots facilitate water infiltration in soil may be just as important as the efficiency with which the root system in turn extracts it from the soil. Here we studied the mechanisms through which the root system facilitates water infiltration through a dry soil layer. Dye tracing experiments were conducted in model soil microcosms to characterise how root growth and exudation affect the permeability of dry layers of the model soil. Results showed that the growth of plant roots through the dry layers of an artificial soil increased the water infiltration rate. In the absence of roots, dissolved root exudates had a significant effect on water infiltration but penetration of the dry layer by a needle did not. We conclude that in dry soil, root architecture and root exudation act synergistically to increase soil hydraulic conductivity, and this may help decrease the water lost by evaporation. This mechanism could be used to select root traits that match the soil and climate, thereby improving water use efficiency in agriculture.