Photosynthetic performance, chloroplast pigments and mineral content of Norway spruce (Picea abies (L.) Karst.) exposed to SO2 and O3 in an open-air fumigation experiment

Photosynthetic performance, mineral content and chloroplast pigments were investigated in August-September 1988 and 1989 in Norway spruce trees (Picea abies (L.) Karst.) exposed to SO₂, and O₃ in an open-air fumigation facility at Liphook, England. The data do not suggest a treatment effect on the mineral content of the needles in terms of nutrient leaching from the foliage. In addition, there were no direct SO₂ and/or O₃ effects on the content and/or composition of the chloroplast pigments. However, the long-term application of SO₂ resulted in a depression of net photosynthesis under light saturation and ambient CO₂ (A ₃₄₀) which was probably caused by a treatment-related depression of the carboxylation efficiency (CE). In 1989, the supposed treatment effects were apparently masked by an insufficient N-supply and probably also by low water availability during summer. However, fumigation appeared to accelerate an N-deficiency-related decrease of CE, stomatal closure and the age-dependent development of the chlorophyll content of the needles. In 1989, an observed depression of the photosynthetic capacity (A₂₅₀₀) was in part accompanied by a decrease in light use efficiency (α), suggesting an enhanced photosensitivity resulting from the impact of several possible interacting stresses (drought, N deficiency and fumigation). The results support the general conclusion that long-term low-level SO₂ dosage adversely affects the photosynthetic performance of the needle, whether directly or indirectly, and may also interact with other environmental stresses. The findings of our investigations are discussed with regard to the hypothesis of forest decline in the mountain regions of the Fichtelgebirge (north-eastern Bavaria, Germany).