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Little is known about root architectural attributes that aid the capture of nitrate from coarse-textured soil profiles of high leaching potential. In this study, a range of root architectures from the herringbone to the dichotomous structure were simulated, and their capacity to take up nitrate leaching through a sandy profile was recorded. All root systems had equal total volume at each point in time, and so were considered cost equivalent. These simulations showed that the root architecture likely to maximize nitrate capture from sandy soils (under the Mediterranean rainfall pattern experienced in Western Australia) is one that quickly produces a high density of roots in the top-soil early in the season, thereby reducing total nitrate leached with opening season rains, but also has vigorous taproot growth, enabling access to deep-stored water and leached nitrate later in the season. This is the first published, spatially explicit attempt to assess the ability of different root architectures equivalent in cost, to capture nitrate from a spatially and temporally heterogeneous soil environment.

Abstract.A semi-hydroponic bin system was developed to provide an efficient phenotyping platform for studying root architecture. The system was designed to accommodate a large number of plants in a small area for screening genotypes. It was constructed using inexpensive and easily obtained materials: 240 L plastic mobile bins, clear acrylic panels covered with black calico cloth and a controlled watering system. A screening experiment for root traits of 20 wild genotypes of narrowleafed lupin (Lupinus angustifolius L.) evaluated the reliability and efficiency of the system. Root architecture, root elongation rate and branching patterns were monitored for 6 weeks. Significant differences in both architectural and morphological traits were observed among tested genotypes, particularly for total root length, branch number, specific root length and branch density. Results demonstrated that the bin system was efficient in screening root traits in narrow-leafed lupin, allowing for rapid measurement of two-dimensional root architecture over time with minimal disturbance to plant growth and without destructive root sampling. The system permits mapping and digital measurement of dynamic growth of taproot and lateral roots. This phenotyping platform is a desirable tool for examining root architecture of deep root systems and large sets of plants in a relatively small space.

Summary1. Root-system architecture, and plastic variation in architecture and physiological function, influence the capacity of plants to acquire nutrients from non-uniform soil. Previous theoretical analyses of the relationship between root architecture and nutrient acquisition have largely assumed uniform soils and unresponsive root systems. We extend these studies by considering non-uniform nutrient supply and plasticity in root growth and uptake physiology. 2. Using modelling, we investigated the growth and nitrate uptake of two extreme theoretical architectural types: dichotomous (highly branched) and herringbone (sparsely branched). Root systems with plastic or non-plastic root-growth and nitrateuptake responses, supplied with non-uniform distributions of soil nitrate, were simulated. 3. The simulated herringbone root system had a higher nitrate-uptake efficiency (NUE, nitrate-N m − 3 soil) when supply varied spatially and temporally (compared with variation in space alone), and NUE was affected only by the capacity to elevate uptake kinetics locally. In contrast, the efficiency of the dichotomous root system decreased under spatially and temporally dynamic nitrate supply (compared with static supply), and was influenced only by the capacity to proliferate roots in nitrate patches. 4. These results suggest that root-system NUE is not solely a function of the iontransport characteristics of soil, but is also influenced by the transitory nature of the nutrient source and the structure of the root system.