Soil nutrient heterogeneity interacts with elevated CO₂ and nutrient availability to determine species and assemblage responses in a model grassland community

• Interactive effects of atmospheric CO₂ concentration ([CO₂]), soil nutrient availability and soil nutrient spatial distribution on the structure and function of plant assemblages remain largely unexplored. • Here we conducted a microcosm experiment to evaluate these interactions using a grassland assemblage formed by Lolium perenne, Plantago lanceolata, Trifolium repens, Anthoxanthum odoratum and Holcus lanatus. • Assemblages exhibited precise root foraging patterns, had higher total and below-ground biomass, and captured more nitrogen when nutrients were supplied heterogeneously. Root foraging responses were modified by nutrient availability, and the patterns of N capture by interactions between nutrient distribution, availability and [CO₂]. Greater above-ground biomass was observed under elevated CO₂ only under homogeneous conditions of nutrient supply and at the highest availability level. CO₂ interacted with nutrient distribution and availability to determine foliar percentage N and below : above-ground biomass ratios, respectively. Interactions between nutrient distribution and CO₂ determined the relative contribution to above-ground biomass of four of the species. The responses of dominant and subordinate species to [CO₂] were dependent on the availability and distribution of nutrients. • Our results suggest that soil nutrient distribution has the potential to influence the response of plant species and assemblages to changes in [CO₂] and nutrient availability.