Herbivorous insects may have significant impacts on litter decomposition through modification of plant litter quality and quantity. The effects of herbivorous insects on decomposition processes are of growing interest.
Here, experiments were conducted to examine how sap-feeding aphids modify plant litter and whether the aphid-induced modification influences litter decomposition processes, using a plant–herbivore system consisting of soybean [Glycine max (L.)] and soybean aphids (Aphis glycines Matsumura).
First, litter traits produced by aphid-free and aphid-infected plants were compared, and it was found that aphids did not affect litter mass and carbon concentration, but significantly decreased the nitrogen concentration. Such aphid-mediated modification of litter quality may cause deceleration of litter decomposition as the higher C/N ratio inhibits litter decomposition.
A decomposition experiment was then carried out to compare the decomposition of litter between the aphid-free and aphid-infected plants. No impacts of aphid herbivory were found on litter carbon mineralisation but negative impacts were found on nitrogen mineralisation. Litter nitrogen mineralisation of aphid-infected plants decreased by 40% and 28% compared with that of aphid-free plants 1 and 3 months after commencement of the experiment, respectively.
The experimental results clearly showed that aphids decelerated litter nitrogen mineralisation by modifying litter quality.