In belowground environments, labile carbons for soil microorganisms are often limited. Therefore, when sugar is applied to soil, available nitrogen (ammonium and nitrate) to plants decreases because the nitrogen is taken by the increased microorganisms. This effect is known as N-immobilization, which is one of the important decomposition processes.

In terrestrial ecosystems, aphids will bear the N-immobilization because they secrete surplus carbohydrates as honeydew. In addition, sap-sucking by aphids often subsequently alters leaf chemical concentration. If the effects of aphid feeding expand to litter quality, aphids may also influence the litter decomposition. We hypothesize that the aphid is an important ecosystem driver to change belowground decomposition processes.

We carried out a pot-experiment, using soybean (Glycine max) and soybean aphid (Aphis glycines), to examine how aphids alter leaf chemicals and soil nutrients in three levels of aphid density (0, 100, and 1000 aphids per plant, respectively)). We found that available nitrogen in the soil decreased and CN ratio in leaves increased with increasing aphid densities. However, foliar phenolics were unaffected by aphid feeding.