Long-term effects of elevated CO2 on woody tissues respiration of Norway spruce studied in open-top chambers

In an open-top chamber experiment located in a mountain stand of 14-years;old Norway spruce (Picea abies [L.] Karst.), trees were continuously exposed to either ambient CO2 concentration (A),or ambient + 350 mu mol mol(-1) (E) over four growing seasons. Respiration rates of different woody parts (stem, branches, coarse roots) were measured during the last growing season. The calculated increase in the respiration rate related to a 10 degrees C temperature change (Q(10)) was different in stem compared to branches and roots. Differences between the E and A variants were statistically significant only for roots in the autumn. Stem maintenance respiration (R-Ms) measured in April and November (periods of no growth activity) were not different. The stem respiration values (R-s) were recalculated to a standard temperature of 15 degrees C to estimate the seasonal course. The obtained R-s differed significantly between used variants during July and August. At the end of the season, R-s in E decreased slower than in A, indicating some prolongation of the physiological activity under the elevated CO2 concentration. The total stem respiration carbon losses for the investigated growing season (May - September) were higher for A (2.32 kg(C) m(-2) season(-1)) compared to E (2.12 kg(C) m(-2) season(-1)). The respiration rates of the whorl branches (R-b) were lower compared with the stem respiration but not significantly different between the used variants. The root respiration rate was increased in E variant.