| A 9 ha poplar plantation (EUROFACE, Italy) was fumigated during 6 years (3+3 years; two rotations) with elevated atmospheric CO2 concentrations ([CO2], 550ppm) by the use of a Free Air Carbon dioxide Enrichment system (FACE). Half of the experimental plots were fertilized to study the possible interactions between elevated CO2 and fertilization. The primary goal of the EUROFACE project was to elucidate whether intensive poplar biomass plantations would produce more biomass in a future high [CO2 ] world, and whether they might serve as a C-sink by an increased C-sequestration in the biomass or soil.; We closely followed the productivity and dynamics of the regrowth of the poplars during the second rotation under elevated [CO2]. The evolution of the leaf area index (LAI) during the growing season was assessed, and vertical profiles of light, leaf photosynthesis and leaf characteristics such as the specific leaf area (SLA), leaf nitrogen and chlorophyll content were measured. At the end of the second rotation, a final harvest determined the total above- and belowground productivity of the plantation.; Poplars produced significantly more and bigger shoots under elevated [CO2], and the increased biomass was equally distributed to the above- and belowground parts. At the end of the second rotation, the total above- and belowground productivity were stimulated up to 29%. The poplar canopy contained more leaves under elevated [CO2], even after canopy closure, and together with the sustained photosynthetic enhancement of the leaves, the C-uptake significantly increased under elevated [CO2]. Because of the historical land-use (agriculture), the soil contained enough nutrients to support the increased growth under elevated [CO2], and fertilization had no significant effect.; In a future high CO2 world, large amounts of carbon could be sequestered in a poplar biomass plantation and help to mitigate the rise in atmospheric [CO2], provided trees are intensively managed and planted in regions with high incident radiation and supplied with sufficient water and nutrients. Substantially more renewable energy could be produced in an economically feasible way whereby the CO2 stimulation might sustain over several rotations. |
