||The objective of this research was to determine the functional responses of a cultivated, agro-forestry system, namely a poplar plantation, to actual and future atmospheric CO2 concentrations. Hence, this research has combined a fast growing, agro-forestry ecosystem, capable of elevated biomass production, with a large-scale Free Air Carbon Enrichment (FACE) system, one of the few available in the European Union on a forest tree stand. The FACE facility is located close to a natural CO2 source and is drawing scientists from several European countries, and from other continents, to closely cooperate and combine their scientific efforts on the same experimental system. Furthermore, this FACE apparatus utilizes a novel technology, originally developed by Italian institutions, based on the release into the atmosphere, at sonic velocity, of pure CO2 instead of an air-CO2 Mixture. The research activities conducted at the POPFACE site, on the responses of the tree plantation to future atmospheric conditions, have integrated observations at the leaf level, such as photosynthesis, respiration and transpiration, with measures carried out at the whole-tree and stand scale, such as canopy architecture, light interception and biomass production. Finally, the ecosystem dimension has also been analysed by studying root productivity and soil processes, host-parasite interactions, and carbon sequestration throughout a rotation. cycle of the stand.