Single and Combined Effects of Continuous and Discontinuous O₃ and SO₂ Immission on Norway Spruce Needles: I. Histological and Cytological Changes

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.

Key Words:

• Forest die-back
• ozone
• sulphur dioxide
• needle tissue alterations