Influence of urban air pollution on needle litter decomposition and nutrient release

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Abstract
A comparison was made between green needle litter from Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) for the mass loss rate and chemical composition after a one‐year soil incubation period in natural forest stands influenced by urban air pollution. The pollution, which consists mainly of SO2, NOX and heavy metals, did not significantly lower the decomposition rate of pine needle litter in pine stands or spruce needle litter in spruce stands. In the pine needle litter a nearly significant (p<0.1) increase in the release of Mn and a significant enrichment of Fe and Pb were detected. In the spruce needle litter there was a significantly higher release of Mn and a significant enrichment of Fe, Cu and Pb. The urban air pollution had no effects on the content of Ca, Mg, K and Zn in the decomposing pine and spruce needles when the polluted sites were compared to the less polluted controls. The results are also compared with one Scots pine and Norway spruce site which was not exposed to urban pollution. In this comparison the higher release of Mn from the decomposing coniferous needle litter and the enrichment of Fe and Pb into the needle litter of the polluted area becomes even more pronounced.