Photosynthesis, chloroplast pigments, and antioxidants in Pinus canariensis under free-air ozone fumigation

High O₃ levels, driving uptake and challenging defense, prevail on the Canary Islands, being associated with the hot and dry summers of the Mediterranean-type climate. Pinus canariensis is an endemic conifer species that forms forests across these islands. We investigated the effects of ozone on photosynthesis and biochemical parameters of P. canariensis seedlings exposed to free-air O₃ fumigation at Kranzberg Forest, Germany, where ambient O₃ levels were similar to those at forest sites in the Canary Islands. The twice-ambient O₃ regime (2xO₃) neither caused visible injury-like chlorotic or necrotic spots in the needles nor significantly affected violaxanthin, antheraxanthin and zeaxanthin levels and the de-epoxidation state of the xanthophyll cycle. In parallel, stomatal conductance for water vapour, net photosynthesis, intercellular CO₂ concentration, chlorophyll fluorescence parameters, as well as antioxidant levels were hardly affected. It is concluded that presently prevailing O₃ levels do not impose severe stress on P. canariensis seedlings.