The trees sampled in this study came from two stands of Norway spruce, Picea abies (L.) Karst., near Stockholm, Sweden, differing in mean age and height. Holes were bored perpendicular to the stem surface, and gas samples were taken from the outer part of the sapwood throughout one growing season. Endogenous levels of molecular oxygen (O2), carbon dioxide (CO2) and ethylene in the outer sapwood were determined by combined gas chromatography — mass spectrometry (GC-MS) and GC. O2 concentrations began to decrease as growth started in spring. The lowest levels (<5%) were recorded around mid-summer. In the younger stand concentrations remained below 5% until September. In October, O2 concentrations in the sapwood were similar to those of air. Concentrations of CO2 were below 1% in spring, but began to rise in May, peaking a month later at approximately 10%. Thereafter a slow decrease occurred until October, by which time levels had returned to those recorded in spring. Ethylene concentrations in the older stand reached 75 ppm early in May, while levels in the younger stand peaked at around 30 ppm later in May. Thereafter ethylene levels in both stands started to decrease down to ppb levels. The correlation between determined gas levels and physiological events associated with the seasonal growth cycle in temperate zones is discussed.

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