Changes in quantity rather than palatability of alpine meadow species induce cascading effects of long‐term nitrogen fertilization on phytophagous insect abundance

Abstract

AbstractQuestionsDo changes in plant tissue quality mediated by long‐term N enrichment cascade to affect the palatability and thus abundance of phytophagous insects? Do shifts in the abundance of plant functional groups mediated by long‐term N enrichment cascade to affect abundance of phytophagous insects?LocationAn alpine meadow on the Tibetan Plateau, China.MethodsWe measured the abundance of larvae of a phytophagous moth (Gynaephora menyuanensis) in plots subjected to 8 years of fertilization with different N rates and chemical forms in an alpine meadow. In a feeding experiment with the larvae, we tested whether N rate and N form affected leaf consumption of six abundant plant species in the alpine meadow through leaf quality.ResultsHigh N rate increased larval density by 45.6%. It increased leaf N concentration and decreased leaf C:N of four plant species, but did not affect leaf consumption on any of the six species. High N increased the abundance of more favoured graminoids, but decreased that of less favoured legumes and some forbs. Larval density was positively related to graminoid abundance and negatively related to forb abundance.ConclusionsLong‐term N fertilization induced changes in both leaf quality and abundance of plant species in the community. However, the abundance of phytophagous insects was associated with shifts in plant functional group abundance but not with changes in plant palatability. These findings suggest that N‐mediated changes in plant community composition may have cascading effects on insect quantity.