Elevated pCO2 affects N-metabolism of young poplar plants (Populus tremula x P. alba) differently at deficient and sufficient N-supply

Abstract

Summary • The effects of N‐availability and elevated atmospheric CO 2 partial pressure ( pCO2) on growth, allometry and N‐metabolism of poplar plants are reported here. • Poplar plants were grown hydroponically at deficient and sufficient N‐supply under ambient and elevated pCO2. The N‐fluxes within the plants were estimated by comparing the fate of newly acquired 15N‐NO3− in plants either severely N‐limited or with sufficient N‐supply. • At deficient N‐supply, plants accumulated less biomass and exhibited an increased root : shoot ratio compared with sufficient N‐supply; a larger fraction of newly acquired 15 N was allocated to the youngest leaves immediately after exchange of the nutrient solution. Increasing the external N‐supply from deficient to sufficient shifted the site of nitrate reduction from roots to leaves. • Elevated pCO2 increased total biomass and the root : shoot ratio at deficient N‐supply, but had no effect at sufficient N‐supply. Elevated pCO2 decreased rates of N‐uptake in both treatments. Increased root : shoot ratio at deficient N‐supply coincided with enhanced nitrate reduction in the root and elevated pCO2 also enhanced the allocation of newly acquired 15N to the youngest leaves. Root nitrate reduction as a possible factor controlling the root : shoot ratio and N‐allocation is discussed.