1 functional-structural root architecture models. 2 The case of root water uptake. Abstract 35Three-dimensional models of root growth, architecture and function are becoming im-36 portant tools that aid the design of agricultural management schemes and the selection of 37 beneficial root traits. However, while benchmarking is common in many disciplines that use 38 numerical models such as natural and engineering sciences, functional-structural root archi-39 tecture models have never been systematically compared. The following reasons might induce 40 disagreement between the simulation results of different models: different representation of 41 root growth, sink term of root water and solute uptake and representation of the rhizosphere.
42Presently, the extent of discrepancies is unknown, and a framework for quantitatively com-43 paring functional-structural root architecture models is required. We propose, in a first step, 44 to define benchmarking scenarios that test individual components of complex models: root 45 architecture, water flow in soil and water flow in roots. While the latter two will focus mainly 46 on comparing numerical aspects, the root architectural models have to be compared at a con-47 ceptual level as they generally differ in process representation. Therefore defining common 48 inputs that allow recreating reference root systems in all models will be a key challenge. In 49 a second step, benchmarking scenarios for the coupled problems are defined. We expect that 50 the results of step 1 will enable us to better interpret differences found in step 2. This bench-51 marking will result in a better understanding of the different models and contribute towards 52 improving them. Improved models will allow us to simulate various scenarios with greater 53 confidence and avoid bugs, numerical errors or conceptual misunderstandings. This work will 54 set a standard for future model development. 55 1 Introduction 56 A growing number of different modelling techniques and software libraries are now available to 57 build functional-structural root architecture models. Different available models of root architec-58 ture and functions have been discussed and qualitatively compared in Dunbabin et al. (2013).
59The available models differ in the way they represent different processes such as root growth, wa-60 ter flow, solute transport are captured and translated into mathematical equations (process-level 61 differences); in how they solve mathematical problems by their choice of analytical or numerical 62 approach, numerical scheme, programming technique (solution-level differences); and in how they 63 couple the different processes to the full model (coupling-level differences). However, the extent of 64 discrepancies is currently unknown. Thus, a framework for quantitatively comparing functional-65 structural root architecture models is required. In addition to the explanatory or predictive power 66 of a model, it is also important to understand the performance of these models, e.g. in terms of 67 ac...