Superoxide dismutase activity in needles of Scots pine and Norway spruce under field and chamber conditions: lack of ozone effects

Abstract

Spruce [Picea abies (L.) Karst.] and pine (Pinus sylvestris L.) trees were exposed to various ozone regimes ranging from short‐term fumigation of twigs for some hours up to long‐term exposures of young plants for 20 wk in environmental chambers. At the end of the experimental treatments needles of spruce trees exposed to episodes with moderate ozone mixing rations (10–150 nl l−1) showed no visible symptoms of injury; needles exposed to high ozone mixing ratios (300 and 600 nl l−1) were bleached. None of the treatments affected the soluble protein content and superoxide dismutase activity. When the same stocks used in the chamber experiments were exposed in pots at a forest site to ambient conditions with an average of 30 nl l−1ozone, the specific superoxide dismutase activities were increased by factors ranging from 1–4 to 3–7. The needles of old field‐grown pine and spruce trees contained 1.5‐ to 60‐fold higher specific superoxide dismutase activities than the needles of young plants kept under chamber conditions. Mature trees with decline symptoms were also investigated. Current year's bleached needles of field‐grown spruce did not contain increased superoxide dismutase activities. Only in older needle age classes of damaged spruce orpine trees were moderate increases (1.2‐ to 1.3‐fold) of superoxide dismutase activities observed, as compared to needles from healthy trees. The results indicate that superoxide dismutase activity in needles of spruce and pine growing outdoors responds to factors different from ozone.