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The main objective of the study was to evaluate inter-annual ring-width variation and cumulative growth of aspen (Populus tremula L.) trees growing on the spots of different soil CO2 concentration at natural mofette site. We hypothesized that growth rate of trees is affected by CO2 concentration within their rooting zone. The study site was situated in the flood plain of Plesná stream near Hartoušov (Western Bohemia). Trees growing in a pure aspen stand were selected according to the CO2-gas regime within their rooting zone. Five high [CO2] trees (10-25% CO2 in the soil) and five low [CO2] trees (up to 3% CO2 in the soil) were sampled. Stem growth analysis of each trunk was carried out to study growth pattern in detail. High and low [CO2] trees significantly differed in a growth rate. At the age of 25 years, the basal area of high [CO2] trees exceeded low [CO2] trees by 39 %. The positive effect of CO2 on annual increment was pronounced particularly in the years with optimal growing conditions. Results suggest that trees can be fertilized not only by elevated atmospheric CO2 but also when fed with CO2 via the roots. [ABSTRACT FROM AUTHOR]