Bayreuther Institut für Terrestrische Ökosystemforschung
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Michalzik, B; Müller, T; Stadler, B: Aphids on Norway spruce and their effects on forest floor solution chemistry, Forest Ecology and Management, 118, 1-10 (1999)
Many species of aphids on spruce excrete large quantities of honeydew. As providers of carbohydrates, it is likely that they affect several ecosystem functions by fuelling biological processes, which are energy limited. In a rainfall simulation experiment we manipulated the level of aphid infestation on spruce and studied the effects of honeydew on forest floor solution chemistry collected underneath infested and uninfested trees. A non-destructive sampling method was used to allow repeated measurements using the same forest floor during the experimental period. Although the input of dissolved organic carbon (DOC) underneath infested trees to the forest floor was considerably higher compared to uninfested trees, carbon concentrations of forest floor leachates did not differ between treatments. Concentrations of dissolved organic nitrogen (DON), NO3-N and Ntotal of forest floor leachates, underneath infested and uninfested trees followed a marked seasonal trend with low concentrations recorded in June and after frost treatment of the forest floor, while highest concentrations were recorded in July/August. Statistically significant differences in soil solution properties underneath infested and uninfested trees were recorded in July when honeydew affected forest floor leachates had lower concentrations of NH4-N, Ntotal, a lower conductivity and a higher pH. Discriminant function analysis showed that forest floor leachates can be classified according to the experience of frost and nitrogen concentrations, which were affected by the honeydew of aphids. At the end of the experiment, the number of micro-organisms present in the forest floor was not significantly different between treatments but was higher in the Oh compared to the Ol+f horizon. Microbial communities did not appear to be severely influenced by deep temperatures. It seems likely that in coniferous forests aphids can considerably reduce local fluxes of nitrogen from the forest floor.
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