Growth often involves a trade-off between the performance of contending tasks; metabolic plasticity can play an important role. Here we grow 97 Arabidopsis thaliana accessions in three conditions with a differing supply of carbon and nitrogen and identify a trade-off between two tasks required for rosette growth: increasing the physical size and increasing the protein concentration. We employ the Pareto performance frontier concept to rank accessions based on their multitask performance; only a few accessions achieve a good trade-off under all three growth conditions. We determine metabolic efficiency in each accession and condition by using metabolite levels and activities of enzymes involved in growth and protein synthesis. We demonstrate that accessions with high metabolic efficiency lie closer to the performance frontier and show increased metabolic plasticity. We illustrate how public domain data can be used to search for additional contending tasks, which may underlie the sub-optimality in some accessions. L iving organisms perform many different and sometimes contending tasks, leading to trade-offs in which optimal performance of one task comes at the cost of a sub-optimal performance of another task. Trade-offs are influenced by the environment and their resolution depends on metabolic resources and plasticity 1,2 . One important environmental variable affecting plant growth is resource availability 3-6 . We first ask whether there is a trade-off between two tasks during vegetative growth of Arabidopsis thaliana: the maximization of physical size and the maximization of protein concentration. We then apply two methods to rank accessions: the first based solely on the performance of tasks, and the second based on the efficiency with which metabolic resources are deployed to perform tasks. In addition, we investigate whether the trade-off and the ranking of accessions are affected by the availability of carbon (C) and nitrogen (N) and the way in which it shapes the accession-specific metabolic profiles.Plants use light energy to transform CO 2 and inorganic nutrients into a plethora of metabolic precursors that are used to drive growth. As plants are sessile, resource acquisition is constrained by their physical size. In land plants, the majority of a mature cell is occupied by the vacuole, allowing the generation of a much larger physical size per unit protein than is usually obtained by microbes or animals 7 . For simplification, we do not consider the impact of shape and phenology on the relation between physical size and resource acquisition. On the other hand, proteins are required to catalyse the transformation of resources into biomass. In particular, the majority of the protein in a plant leaf is involved in photosynthesis [8][9][10] . We hypothesize that there is a trade-off between physical size and protein concentration. While production of leaves with a higher protein concentration will allow higher rates of photosynthesis and metabolism per unit biomass, it also increases the costs of growth a...