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

Rates of photosynthesis at different concentrations of CO2 (0-1850 μmol mol-1 ) were measured using one clone of Norway spruce, Picea abies (L.) Karst. exposed to three different concentrations of ozone for four seasons (1985-8) in open-top chambers. The treatments were non-filtered air+ozone (NF+), non-filtered air (NF) and charcoal-filtered air (CF). The measurements were made on shoots of four different age classes. No significant effects were found on photosynthesis or on leaf conductance to CO2 in current year shoots. In 1- to 3-yr-old shoots, leaf conductance to CO2 and rates of net photosynthesis at both 330 μmol mol-1 CO2 (Pn 330), and saturating concentrations of CO2 (Pn max), decreased with increasing shoot age and ozone concentration, although this was only significant for Pn 330 in 3-yr-old shoots. In current year shoots the intercellular concentration of CO2 was significantly higher in NF+-treated shoots compared with CF- and NF-treated shoots, while in the 2- and 3-yr-old shoots it was significantly higher in NF- and NF +-treated shoots compared with CF-treated shoots. The carboxylation efficiency significantly decreased in 2- and 3-yr-old shoots from the NF and NF+ treatments compared with shoots from the CF treatment. The gas phase limitation of photosynthesis decreased with increasing shoot age and ozone concentration.