Growth performance of Populus exposed to "Free Air Carbon dioxide Enrichment" during the first growing season in the POPFACE experiment

Abstract

Stem diameter, total plant height and number of sylleptic branches of three poplar (Populus) genotypes were followed during the first growing season of a high density intensively cultured plantation (in Central Italy) both under ambient CO 2 (Control) and under elevated atmospheric CO 2 (550 ppm) using the FACE technique. The three poplar genotypes belonged to different species of Populus alba L., Populus nigra L. and Populus x euramericana Dode (Guinier). All three genotypes responded by an enhanced growth performance but the extent of their response to the FACE treatment was different. A stem volume index was calculated considering the stem composed by a truncated cone in the lower part and by a cone in the upper part. At the end of the first growing season, stem volume index was increased in the FACE treatment by 54% to 79% as compared to Control treatment, depending on the genotype. This increased stem volume index was caused by an increase of basal stem diameter rather than by an enhancement of plant height. Number of sylleptic branches was stimulated by more than 35% in the P. nigra genotype. The results confirm the optimal performance of this new POPFACE experiment and show the positive response of this fast-growing tree species to elevated CO 2 conditions at an ecosystem scale even if considering the genotypic differences. elevated CO 2 / FACE / short-rotation intensive culture / Populus / growth Rsum -Performance de croissance de plants de Populus exposs une atmosphre enrichie en dioxide de carbone durant la premire saison de croissance dans l'exprimentation POPFACE. Le diamtre du tronc, la hauteur totale et le nombre des branches sylleptiques de trois gnotypes de peuplier (Populus) ont t suivis durant la premire saison de croissance d'une plantation de haute densit en culture intensive (en Italie Centrale), la fois sous air ambiant (350 ppm, plantes tmoins), et sous atmosphre enrichie en CO 2 (550 ppm) en utilisant la technique FACE. Les trois gnotypes de peuplier utiliss font partie d'espces diffrentes : Populus alba L., Populus nigra L. et Populus x euramericana Dode (Guinier). Les trois gnotypes ont tous rpondu au traitement FACE par une augmentation de la croissance, mais avec des intensit diffrentes. Un index de volume du tronc a t calcul en considrant le tronc comme tant compos d'un cne tronqu pour sa partie infrieure, et d'un cne pour la partie suprieure. la fin de la saison de croissance, l'index de volume du tronc tait suprieur de 54 % 79 %, en fonction du gnotype, pour le traitement FACE par rapport aux plants tmoins. Cette augmentation de l'index de volume du tronc est principalement due l'augmentation du diamtre basal des troncs, plus qu'

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