Effects of heavy-metal and SO2 pollution on the concentrations of carbohydrates and nitrogen in tree leaves

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Abstract
The concentrations of carbohydrates and nitrogen in leaves or needles of Betula pubescens Ehrh., Betula pendula Roth, Picea abies (L.) Karst., and Pinus sylvestris L. were studied in two industrial areas in Sweden. One of the sites, the Gusum brass foundry in SE Sweden, is polluted by Cu and Zn, the other site, the Rönnskär smelter in NE Sweden, by SO2 in addition to several heavy metal elements. Leaves and needles were sampled during the main growing season at different distances from the sources and analysed for starch, sugars, total nitrogen, and heavy metals. In most leaf or needle samples nearest to the sources, the concentrations of starch and total sugars were significantly higher than in the controls. Of the sugars, sucrose concentration was usually elevated, while glucose and fructose were lower than in the controls. The effects observed were already evident at the beginning of the season, but were usually more pronounced later on. Of the tree species sampled, conifers appeared to be more affected than deciduous trees, and pine more than spruce. The mechanisms of the disturbances are probably complex, but heavy metals and SO2 may inhibit several processes such as hydrolysis of starch and sucrose as well as the transport of sucrose. Increased carbohydrate concentrations may also be secondary effects of a disturbed nitrogen metabolism, as nitrogen concentrations were lower in polluted tree leaves or needles than in controls, and severe inhibition of the soil nitrogen mineralization rate has been recorded in other studies. Key words: starch, sucrose, glucose, fructose, nitrogen, birch, pine, spruce, Cd, Cu, Pb, Zn, SO2.
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