Abstract
The increased atmospheric deposition of nitrogen (N) may indirectly affect herbivorous insects by deposition-induced changes in host quantity and quality. To avoid the “lamp effect” that can occur in small-scale N fertilizations, large-scale N fertilization (ca. 9 ha, 100 kg N ha−1 year−1) experiments were performed in a deciduous, broad-leaved, cool temperate forest. The initial responses of mature oak canopy trees (Quercus crispula) and their herbivorous insects to N fertilization were evaluated by measuring the growth and leaf qualities of the trees. The feeding guilds and community structures of the herbivorous insects at control and fertilized sites before (2012) and after (2013–2014) N fertilization were then determined. In 2014, N fertilization enhanced plant growth. In 2013 but not 2014, N fertilization increased N content and decreased the carbon/nitrogen (C/N) ratio in leaves. Despite these changes in plant traits in 2013, N fertilization had no effect on either feeding guilds (chewing herbivory, galler density, and miner density) or community structures (species richness, diversity index, and relative abundance) of herbivorous insects in the same year. However, in 2014, the diversity index decreased significantly, whereas species richness and abundance were unchanged. This suggests that species-specific responses to changes in leaf qualities following N fertilization, in the form of altered insect fecundity, impact the diversity index of herbivorous insects, albeit with a 1-year lag time. Thus, our large-scale N fertilization experiment show the time-delayed bottom-up effects of N fertilization on insect community structure.
Published Version
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