Impact of contrasted maize root traits at flowering on water stress tolerance â A simulation study

Water stress is among the dominant yield limiting factors in global crop production. Better drought resistance is therefore a key challenge for breeding and crop management. Avoidance of water stress by effective root water uptake is considered a promising approach to yield stability in water limiting environments. Water uptake efficiency is the result of multiple plant root traits that dynamically interact with site hydrology. Root models are therefore an essential tool to identify key root traits for water efficient crops in a certain target cropping environment.We present a novel combination of a dynamic root architecture model (RootBox) with a functional model of root xylem hydraulic properties and soil water flow (R-SWMS). This model integrates structural and functional root traits to simulate water uptake under variable hydrological conditions. Application of the model is exemplified for three different maize root phenotypes. We evaluate the role of root architectural and functional traits to deal with water stress at the flowering stage under two contrasted hydrological conditions (deep water storage vs. moist upper profile layer in silt loam) for a 7-day period. The phenotypes include a reference phenotype (P1), one phenotype with steeper main roots (P2), and one with steep main roots and with longer lateral roots (P3) We showed that generally those phenotypes whose root axes allocation matched with available water distribution were able to transpire more. This synchronization is a result of root architecture (structural root traits). The temporal dynamics of water depletion on the contrary were essentially determined by root hydraulic properties. We showed that lower equivalent root conductance is essentially related to a water saving behaviour of the plant, while high root conductance contributes to a water spending type with high initial transpiration that decreases quickly over time.). We also showed the dramatic importance of root hydraulic property distribution, and their relation to root order and root age, in determining equivalent root conductance and water uptake behaviour. In our simulations, increasing the radial conductivity of lateral roots by a factor 10 had more impact in the total transpiration than having different root architecture traits. It emphasizes the importance to consider not only architectural traits but also hydraulic properties in defining ideotypes and to use quantitative methods to build and test them.Our results confirmed that functional-structural root models are appropriate to better understand the role of roots in whole plant adaptation to different drought scenarios and their contribution to distinct drought response types. The newly developed model contains all basic components to further refine complex root processes such as architectural plasticity, dynamic root conductance (xylem vulnerability, composite radial transport) and root exudation. These results could feed into cropping system models to see the effect of these processes on crop yield