Modeling the influence of rhizodeposits on root water uptake

The chemical compounds that plant roots release into the soil, referred to as rhizodeposits, affect soil hydraulic properties like the surface tension and viscosity of soil water, and the contact angle between menisci and the pore surface. What remains less clear is how these effects manifest when considering soil water infiltration and retention, and the consequent impact on the availability of water for uptake by roots. A novel model for soil water transport was developed that incorporates the influences of rhizodeposits on soil hydraulics and root water uptake. The finite element method was used to generate model simulations and investigate how the presence of rhizodeposits of wheat (Triticum aestivum L.) affected water uptake of three differently aged root systems under precipitation regimes that varied in total precipitation and delivery pattern. The overriding effect on soil hydraulics of wheat rhizodeposits was to facilitate infiltration. A trade-off was identified in how this could improve water availability to the root system by reducing evaporation but also worsen it by increasing deep percolation. When total precipitation was shared over several rainfall events, the effect of rhizodeposits on root water uptake was positive. However, when higher levels of total precipitation were delivered in a single event, the presence of rhizodeposits reduced the water uptake of shallower root systems. This suggests that the influence of rhizodeposits on soil hydraulics and root water uptake is nuanced and will require careful consideration when developing crops for improved water use efficiency and stress resilience.