Trees (2005) 19: 109–118 DOI 10.1007/s00468-004-0369-0 ORIGINAL ARTICLE Zhi-Bin Luo . Rosemarie Langenfeld-Heyser . Carlo Calfapietra . Andrea Polle Influence of free air CO 2 enrichment (EUROFACE) and nitrogen fertilisation on the anatomy of juvenile wood of three poplar species after coppicing Received: 16 January 2004 / Accepted: 29 July 2004 / Published online: 22 September 2004 # Springer-Verlag 2004 Abstract Populus × euramericana, P. alba, and P. nigra clones were exposed to ambient or elevated (about 550 ppm) CO 2 concentrations under field conditions (FACE) in central Italy. After three growing seasons, the plantation was coppiced. FACE was continued and in addition, one-half of each experimental plot was fertilised with nitrogen. Growth and anatomical wood properties were analysed in secondary sprouts. In the three poplar clones, most of the growth and anatomical traits showed no uniform response pattern to elevated [CO 2 ] or N- fertilisation. In cross-sections of young poplar stems, tension wood amounted to 2–10% of the total area and was not affected by elevated CO 2 . In P. nigra, N- fertilisation caused an about twofold increase in tension wood, but not in the other clones. The formation of tension wood was not related to diameter or height growth of the shoots. In P. × euramericana N-fertilisation resulted in significant reductions in fibre lengths. In all three genotypes, N-fertilisation caused significant decreases in cell wall thickness. In P. × euramericana and P. alba elevated [CO 2 ] also caused decreases in wall thickness, but less pronounced than nitrogen. In P. nigra and P. × euramericana elevated [CO 2 ] induced increases in vessel diameters. These results show that elevated [CO 2 ] and N- fertilisation affect wood structural development in a clone specific manner. However, the combination of these environmental factors resulted in overall losses in cell wall area of 5–12% in all three clones suggesting that in future climate scenarios negative effects on wood quality are to be anticipated if increases in atmospheric CO 2 concentration were accompanied by increased N avail- ability. Keywords Climate change . Elevated CO 2 . N-fertilisation . Wood anatomy . Populus Introduction Forest ecosystems cover 43% of the terrestrial biosphere (Melillo et al. 1993). During the past century human activities, such as combustion of fossil fuels, deforestation, wide application of nitrogen-containing fertilisers, etc., have resulted in a dramatic increase in the atmospheric CO 2 concentration and enhanced nitrogen deposition (Huang et al. 1999). Increased [CO 2 ] is expected to increase biomass accumulation and net primary produc- tivity of forest ecosystems (Melillo et al. 1993; Wulls- chleger et al. 1995; Gielen and Ceulemans 2001; Calfapietra et al. 2003a). Increasing nitrogen deposition also has been observed to stimulate wood production (Brix 1981; McGuire et al. 1992, 1993). Despite compelling evidence that these environmental factors can result in enhanced above-ground biomass and increased annual ring width (Hättenschwiler et al. 1996; Telewski et al. 1999; Yazaki et al. 2001; Ceulemans et al. 2002; Mäkinen et al. 2002), there is no clear picture how CO 2 and nitrogen affect the anatomical properties of wood. For example, Atkinson and Taylor (1996) found that elevated [CO 2 ] significantly increased both vessel number and mean vessel size of Quercus seedlings, but had no influence on the vessel number and size of Prunus seedlings. In Pinus radiata CO 2 enrichment caused no differences in tracheid length, lumen diameter or wall thickness (Donaldson et al. 1987). In contrast to these results, Conroy et al. (1990) reported that tracheid wall thickness increased by 44% in Pinus radiata, whereas Yazaki et al. (2001) found reduced wall thickness in Larix sibirica under elevated [CO 2 ]. Ceulemans et al. (2002) found that the wood of Pinus sylvestris grown at elevated Z.-B. Luo . R. Langenfeld-Heyser . A. Polle (*) Institut für Forstbotanik, Georg-August Universität, Büsgenweg 2, 37077 Göttingen, Germany e-mail: apolle@gwdg.de Tel.: +49-551-393480 Fax: +49-551-392705 C. Calfapietra Department of Forest Environment and Resources (DISAFRI), Universita degli Studi della Tuscia, Via S. Camillo de Lellis, 01100 Viterbo, Italy