Abstract
Water relations were studied in Norway spruce [Picea abies (L.) Karst.] trees grown at ambient (AC, 350 mu mol mol(-1)) and elevated (EC, 700 mu mol mol(-1)) CO2 concentrations under temperate water stress. The results suggested that both crown position and variability in atmospheric CO2 concentration are responsible for different patterns of crown water relations. Mean hourly sap flux density (FSA) showed higher values in upper crown position in comparison with the whole crown in both AC and EC treatments. Mean soil-to-leaf hydraulic conductance (G(Tsa)) was 1.4 times higher for the upper crown than that calculated across the whole crown for the trees in AC. However, G(Tsa) did not vary significantly with crown position in EC trees, suggesting that elevated CO2 may mitigate differences in hydraulic supply for different canopy layers. The trees in EC treatment exhibited significantly higher values of F-SA measured on the whole crown level and slightly higher soil water content compared to AC treatment, suggesting more economical use of soil water and therefore an advantage under water-limited conditions.
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