Influence of free air CO2 enrichment (EUROFACE) and nitrogen fertilisation on the anatomy of juvenile wood of three poplar species after coppicing

Abstract

Populus × euramericana, P. alba, and P. nigra clones were exposed to ambient or elevated (about 550 ppm) CO2 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 (CO2 )o r 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 CO2 .I nP. 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 (CO2) also caused decreases in wall thickness, but less pronounced than nitrogen. In P. nigra and P. × euramericana elevated (CO2) induced increases in vessel diameters. These results show that elevated (CO2) 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 CO2 concentration were accompanied by increased N avail- ability.