Simulating form and function of root systems: efficiency of nitrate uptake is dependent on root system architecture and the spatial and temporal variability of nitrate supply

1. 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 nitrate-uptake 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 ion-transport characteristics of soil, but is also influenced by the transitory nature of the nutrient source and the structure of the root system.