We investigated whether Japanese barberry in forest understory responded to N availability through physiological adjustments at the leaf level or growth components at the plant level. Barberry increased foliar N, photosynthesis at ambient and saturating light and specific leaf area in proportion to N availability. Barberry relative production rate increased with foliar N, leaf biomass, specific leaf area and total canopy N mass. Increases in production and N uptake were proportional and, thus, neither photosynthetic nitrogen-use efficiency nor production per unit of total canopy N differed with treatment or across the range of N status.