Respiration of Woody Tissues of Norway Spruce in Elevated CO₂ Concentration

Abstract

Eight open top chambers (OTCs) were constructed around trees in situ in 1992 with one tree per chamber in a Norway spruce stand (Picea abies (L.) Karst.) planted in 1982. The trees were exposed to the following three treatments: OTCs with ambient atmospheric CO₂ concentration (350 ppm), OTCs with doubled CO₂ concentration (700 ppm) and freely growing trees. The respiration rate of stems, branches and coarse roots was measured during the season 1995. The respiration was measured using a closed IRGA system with several types of cuvettes attached to the trees, and CO₂ efflux was related to tissue temperature. The measurements were carried out during the growing season and also after and before the active growing period, to assess the maintenance respiration. Stem respiration was found to be significantly lower in the elevated treatment in comparison to ambient in terms of total annual respiration related to sapwood volume and respiration related to dry stem wood mass. The respiration rate of branches was larger compared to stem respiration and the same differences between treatments occurred. High intensities of CO₂ efflux from coarse roots suggested that coarse roots have a very important role in tree carbon budget, but for coarse roots, no differences between treatments were found.