Long‐term exposure of Norway spruce,Picea abies(L.) Karst., to ozone in open‐top chambers

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summaryRates of net photosynthesis were measured on Norway spruce,Picea abies(L.) Karst. exposed to three different concentrations of ozone for three seasons (1985–7) in open‐top chambers. The treatments were non‐filtered air + ozone (NF +), non‐filtered air (NF) and charcoal‐filtered air (CF). Ozone was added daily between 11.00–18.00 local time. The study was performed during September and October, 1987. The rate of net photosynthesis was determined using an infrared gas analyser (IRGA) connected to a small cuvette, which was equipped with an artificial light source for unilateral illumination. The measurements were made on shoots of three different age classes: current year, 1 year old and 2 years old. Measurements took place at saturating light intensity (1150 μmol m1s1), at a temperature of 16.6 ±0.7°C, and at a relative humidity of 67.5 ± 5.3%. In current‐year shoots the rate of net photosynthesis expressed on a needle‐area basis was lowest in the CF treatment and highest in the NF treatment. In 1‐ and 2‐year‐old shoots, a decreased rate of the net photosynthetic assimilation rate, expressed on a needle area basis, was observed in trees from the NF and NF+ treatment compared with that of trees from the CF treatment. The effect increased with increasing ozone concentration and shoot age. A significant increase in the rate of respiration, expressed on a dry‐weight basis, was observed in current year shoots from trees exposed to NF+. A significant decrease of the leaf conductance to carbon dioxide was obtained in 2‐year‐old shoots exposed to NF and NF+. A decrease in the content of chlorophyll was observed in 1‐ and 2‐year‐old needles from trees exposed to NF+.