Single and Combined Effects of Continuous and Discontinuous O3and SO2Immission on Norway Spruce Needles: I. Histological and Cytological Changes

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Abstract
For 22 months young Norway spruces (Picea abies Karst.) were separately and simultaneously exposed to a fumigation program, which was selected after the natural pollution values of O3 and SO2, both in clean-air areas and in industrial urban areas, had been determined. In all fumigation experiments we observed decreases in all histological parameters studied. Reductions in tissue areas and cell numbers of spruce needles were antagonistic after simultaneous exposures, simulating the clean-air area; those representing the industrial urban area were less than additive. Discontinuous fumigation with O3 separately and low constant-concentration exposure to SO2, overlapped by occasional peak concentration of SO2, had stronger reducing effects on vascular tissues than continuous fumigation with O3 of the same concentration or continuous fumigation with SO2, even with a higher concentration.