Abstract
Two poplar clones, hybrid Populus deltoides Bartr. Ex Marsh x Populus nigra L. (Populus xeuramericana), clone I-214, and Populus deltoides, clone Lux, were grown from hardwood cuttings for one growing season in either ambient (360 μmol mol-1) or elevated (560 μmol mol-1) [CO 2] in FACE-system rings at Rapolano Terme (Siena, Italy). Both clones I-214 and Lux exhibited a higher aboveground biomass, photosynthesis at light saturation and instantaneous transpiration efficiency (ITE) in CO 2-enriched air. The elevated [CO2]-induced responses of clone I-214 included increased investment in branch and leaf biomass, and enhanced stem volume. The elevated [CO2]-induced responses of clone Lux included an increase in the number of branches (and foliage area). Indication of photosynthetic acclimation under elevated [CO2] was found during the early morning, but only in clone I-214. Stomatal conductance decreased under elevated [CO2] particularly in clone Lux. Clone differences in response to elevated [CO2] should be taken in account when planning future poplar plantations in forecast warmer and drier Mediterranean sites. © 2005 by The Haworth Press, Inc. All rights reserved.