Main conclusionAtmosphericpCO(2)impactsQuercus petraeabiomass production and cell wall composition of the leaves in favor of cellulose at the expense of lignin, and enhances foliar non-structural carbohydrate levels and sucrose contents in apCO(2)concentration-dependent manner.Sessile oak (Quercus petraea Liebl.) was grown for ca. half a year from seeds at ambient control (525ppm), 750, 900, and 1000ppm atmospheric pCO(2) under controlled conditions. Increasing pCO(2) enhanced biomass production, modified the cell wall composition of the leaves in favor of cellulose at the expense of lignin, and enhanced the foliar non-structural carbohydrate level, in particular the sucrose content; as well as total N content of leaves by increased levels of all major N fractions, i.e., soluble proteins, total amino acids, and structural N. The enhanced total amino acid level was largely due to 2-ketoglutarate and oxalo acetate-derived compounds. Increasing pCO(2) alleviated oxidative stress in the leaves as indicated by reduced H2O2 contents. High in vitro glutathione reductase activity at reduced H2O2 contents suggests enhanced ROS scavenging, but increased lipid peroxidation may also have contributed, as indicated by a negative correlation between malone dialdehyde and H2O2 contents. Almost all these effects were at least partially reversed, when pCO(2) exceeded 750 or 900ppm. Apparently, the interaction of atmospheric pCO(2) with leaf structural and physiological traits of Q. petraea seedlings is characterized by a dynamic response depending on the pCO(2) level.