Towards modeling the function of root traits for enhancing water acquisition by crops

Drought is a primary limitation for crop production that is projected to become more severe in important agroecosystems as a result of global climate change. Improving the drought tolerance of major crops is increasingly important as water scarcity and salinity problems limit irrigation. An important aspect of drought tolerance is efficient water acquisition from the soil by crop root systems. The complexity and inaccessibility of root systems make them suited to simulation modeling. Models of root structure and function have advanced significantly over the past 20 yr and have begun to provide useful insights into root traits that may be useful for improving drought tolerance. Such traits include root architecture, anatomy, plasticity, metabolic economy, and rhizosphere alteration. For each root trait, metabolic and/or ecological trade-offs may exist which are often poorly understood. Optimization modeling can help in the identification of root ideotypes adapted to multiple environmental constraints. We present a case study demonstrating the value of modeling in understanding the utility of root cortical aerenchyma (RCA) in crop drought tolerance. An integration of a root architectural model (SimRoot) with a crop simulation model (CROPGRO) suggests that RCA may enhance water acquisition from drying soils by decreasing the metabolic costs of soil exploration. We propose that root modeling will make important contributions to the discovery and understanding of traits improving drought tolerance of crops by permitting assessment of the costs and benefits of specific traits in diverse environments.