Atmospheric CO 2 concentrations ([CO 2 ]) are continuously rising since the beginning of the industrialization. At the same time, N-deposition is also increasing. The influences of elevated CO 2 and fertilization on the physiology and development of forest trees have been intensively studied. However, the effects of these environmental factors on wood quality, carbon and nitrogen allocation to long-and short-term C-N pools in wood of forest trees are not clear yet. To shed light on these questions, Populus × euramericana, P. alba, and P. nigra clones were grown in ambient air (about 370 ppm CO 2 ) and in air with elevated [CO 2 ] (about 550 ppm CO 2 ) using Free-Air CO 2 Enrichment (FACE) technology in central Italy. FACE was maintained for five years. After three growing seasons, the plantation was coppiced and one half of each experimental plot was fertilized with nitrogen. In secondary sprouts, this investigation was carried out.To characterise wood quality in response to elevated CO 2 and N-fertilization, growth and wood anatomy of the three poplar clones were investigated. In the three poplar genotypes, most of anatomical traits showed no uniform response pattern to elevated CO 2 or N-fertilization. In P. × euramericana, N-fertilization resulted in significant reductions in fiber lengths. In all three genotypes, N-fertilization caused significant decreases in cell wall thickness. In P. × euramericana and P. alba, elevated CO 2 also caused decreases in wall thickness, but less pronounced than nitrogen. In P. nigra and P. × euramericana, elevated CO 2 induced increases in vessel diameters. The combination of elevated CO 2 and Nfertilization resulted in overall losses in cell wall area of 5-12% in all three clones suggesting that in future climate scenarios, the negative effects on wood quality may be anticipated.To quantify carbon allocation between short-and long-term pools in wood in response to elevated CO 2 and N-fertilization, in P. nigra, carbon concentrations and stocks were quantified. Although elevated CO 2 , N-fertilization and season had significant tissuespecific effects on carbon partitioning to the fractions of structural carbon, soluble sugars and starch as well as to residual soluble carbon, the overall magnitude of these shifts was small. The major effect of elevated CO 2 and N-fertilization was on biomass production, resulting in about 30% increases in above ground stocks of cell wall mass. Relative C-VI partitioning between mobile and immobile C-pools was not significantly affected by elevated CO 2 or N-fertilization. These data demonstrate high metabolic flexibility of P. nigra to maintain C-homeostasis under changing environmental conditions.To characterise secondary metabolites and internal N-pools responding to elevated CO 2 and N-fertilization, carbon-based secondary compounds, concentrations of total N and Klason lignin-bound N were measured in P. nigra. Elevated CO 2 had no influence on lignin, cell wall-bound phenolics and soluble condensed tannins. Higher N-supply slightly but marke...