The effect of elevated CO2 and soil type on non-structural carbohydrates in beech leaves and Norway spruce needles growing in model ecosystems

Young beech and Norway spruce trees from two Swiss provenances were both planted in an acidic and calcareous soil in 16 open-top chambers. Half of the plants were exposed to elevated CO2 (ambient, ambient + 200 mu l l(-1), 24 hrs/day, 365 days/year) and enhanced nitrogen deposition (2.5, 25 kg ha(-1) yr(-1)) throughout a single growing season. Leaf and needle samples from all 64 trees were collected (2 provenances x 2 soil types x 4 treatments x 4 replications) at the end of July and September. These were analysed for starch, soluble carbohydrates and total non-structural carbohydrates (TNC). Increased starch and TNC levels were found in plants under elevated CO2 and those growing on the acidic soil. These effects were not consistent in both species or on both sampling dates. Soluble carbohydrates were only effected significantly by sail type. So far no interactions have been found between CO2, N or soil type on any date and in any fraction. It is concluded that soil type should be considered when discussing the effects of elevated CO2 on starch, soluble carbohydrate or TNC contents in beech and spruce trees.