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

In a seminatural manipulation experiment with artificial irrigation we followed throughfall and forest floor solution chemistry collected underneath aphid infested and uninfested Norway spruce. Solutions underneath infested trees 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 (NH4-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. Differences in throughfall were more pronounced than in forest floor leachates. It is likely that honeydew is fuelling the metabolism of micro-organisms and thus critically affects above and below ground nutrient cycles. We emphasize the importance of linking the biology of herbivores and micro-organisms with geochemical processes.