Abstract
We summarize the impacts of elevated CO 2 on the N concentration of plant tissues and present data to support the hypothesis that reductions in the quality of plant tissue commonly occur when plants are grown under elevated CO 2 . Synthesis of existing data showed an average 14% reduction of N concentrations in plant tissue generated under elevated CO 2 regimes. However, elevated CO 2 appeared to have different effects on the N concentrations of different plant types, as the reported reductions in N have been larger in C3 plants than in C4 plants and N 2 ‐fixers. Under elevated CO 2 plants changed their allocation of N between above‐ and below‐ground components: root N concentrations were reduced by an average of 9% compared to a 14% average reduction for above‐ground tissues. Although the concentration of CO 2 treatments represented a significant source of variance for plant N concentration, no consistent trends were observed between them.