Can root systems redistribute soil water to mitigate the effects of drought?

Context
Plants combine a diverse range of well-studied morphological and physiological mechanisms to adapt to water deficit and drought. In addition to this, plant roots have also been shown to induce preferential flows of water through vegetated soil. However, less is known about the contribution of this particular phenomenon to a plant’s capacity to resist drought.

Objective
This work investigates how root-induced preferential flow redistributes soil water according to the architecture of a root system and how this may influence plant drought resistance. Specifically, we consider how this redistribution of soil water affects the length of time that water remains in the rooted zone and available for uptake following a precipitation event.

Methods
We developed a model for water transport through vegetated soil that incorporates root-induced preferential flow, and then used Bayesian optimisation to calibrate the model against experimental data. A finite element scheme was used to simulate the model and assess how the fate of soil water is impacted by preferential flow strength, soil type, and root system architecture.

Results
As the preferential flow strength induced by a root system was increased, evaporation from the soil surface reduced, but deep percolation from the rooted zone increased. When assessing the effect of root architecture, it was found that a root system with reduced gravitropic response retained the most water in the soil around its roots over a 7-day post-precipitation period.

Conclusion
Our findings indicate that an optimal preferential flow strength exists for minimising water loss from the rooted zone and that this optimum differs with soil type. Furthermore, in instances where crops are rain fed or irrigated from above, results suggest that a reduction in gravitropic response allows a root system to uptake more of the water that enters the soil.

Implications
New insights are provided into the role of root system traits in plant drought resistance and root system architectures are identified for improved water use efficiency within cropping systems.