Abstract

Leaves of up to eleven different plant species (terrestrial moss: Hylocomium splendens and Pleurozium schreberi; blueberry: Vaccinium myrtillus and Vaccinium uliginosum; cowberry: Vaccinium vitis-idaea; crowberry: Empetrum nigrum; birch: Betula pubescens and Betula nana; willow: Salix spp.; pine: Pinus sylvestris; and spruce: Picea abies) have been collected from up to nine catchments (size 14–50 km2) spread over a 1 500 000 km2 area in northern Europe and analysed for ‘total’ (digestion by 16M HNO3) sulphur concentrations. Soil samples were taken of the O- and C-horizon at each plant sample site. The soil samples were analysed for ‘total’ (digestion by 16M HNO3 for O-horizon, aqua regia for C-horizon) and ‘soluble’ (ammonium acetate extraction buffered at pH 4.5, O-horizon only) S concentrations. The overall median S concentration for all plants is 1290 mg kg−1. The median S concentration is 965 mg kg−1 in moss; 990 mg kg−1 in conifers; 1490 mg kg−1 in shrubs; and 1900 mg kg−1 in deciduous trees. Total S concentrations in the leaves of the 11 plant species are very different within and between the catchments. Compared to the total regional variance, the local variance within just one catchment is very high. One of the nine catchments was located directly adjacent (5–10 km S) to the nickel smelter and refinery at Monchegorsk, Kola Peninsula, Russia, one of the largest SO2 (and metal) emitters in Europe. Only spruce needles returned significantly higher S concentrations (by a factor of 2) in all samples collected near Monchegorsk. Otherwise pollution is reflected in a higher variance rather than in high concentrations. Willow leaves show by far the highest total S concentrations. They are, however, not related to pollution but were observed in the catchment nearest to the coast of the Barents Sea. The measured S concentrations in the leaves do not correlate well either with ‘available’ or total S in the soils. Several different pathways must be considered for leaf uptake of S in all plants. The important role of S as a major plant nutrient and the consequently high background concentrations and variations prohibit the use of leaves as reliable indicators of SO2 pollution levels in air. It is not possible to establish general ‘background’ S concentrations in plant leaves for a very large area.

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