Young spruce (Picea abies [L.] Karst; 2-yr) and beech trees (Fagus sylvatica L.; current-year and 1-yr-old seedlings) were grown under field conditions at a rural site near the city of Basel (Schönenbuch; 400 m above sea level) and 2-yr-old spruce trees at an elevated montainous site (Wengernalp; 1890 m above sea level). The plants were exposed in open-top-chambers (OTC) either to charcoal-filtered air or ambient air with ozone being the predominant air pollutant at both sites. The exposures lasted up to 1 yr. At the end of the growth period the plants were harvested and the pool sizes of the major non-structural carbohydrates were determined. Exposure to ambient air compared with filtered air controls caused an increase of glucose, fructose, pinitol, starch and, in some cases, sucrose in needles whereas carbohydrate contents in roots and twigs of spruce were reduced, in particular at Wengernalp. In beech saplings at Schönenbuch, a significant rise of sucrose and, in some cases, of raffinose, together with a significant reduction of glucose and fructose was observed in buds, leaves, twigs, and roots in ambient air compared with filtered air. In phloem exudates of current year beech seedlings, a 54–160% higher content of carbohydrates was found in ambient air than in filtered air. In roots of the beech saplings, the amount of soluble carbohydrates increased and starch contents mostly decreased. In general, starch storage in roots and stems was more abundant in beech trees. Spruce, especially at the mountainous site, accumulated high amounts of soluble carbohydrates in needles, in particular glucose.