Linking aphid honeydew, throughfall, and forest floor solution chemistry of Norway spruce

In a seminatural manipulation experiment with artificial irrigation we foll owed throughfall and forest floor solution chemistry collected underneath a phid infested and uninfested Norway spruce. Solutions underneath infested t rees showed significantly higher concentrations of dissolved organic carbon (DOC) but lower concentrations of dissolved organic nitrogen (DON), NO3-N, and NH4-N in throughfall solutions and of NH4-N in forest floor solutions. Average concentrations were 40.5% (DON), 27.5% (NO3-N), and 46.2% lower (N H4-N) underneath infested trees in throughfall solutions, and 19.5% (DON), 9.4% (NO3-N), and 42.0% (NH4-N) lower in forest floor solutions. Difference s in throughfall were more pronounced than in forest floor leachates. It is likely that honeydew is fuelling the metabolism of micro-organisms and thu s critically affects above and below ground nutrient cycles. We emphasize t he importance of linking the biology of herbivores and micro-organisms with geochemical processes.