Canopy nitrogen addition affects ground‐dwelling spider assemblages and trophic position

Abstract

1. While it is clear that nitrogen (N) deposition impacts the plant diversity of major terrestrial ecosystems, how ground-dwelling fauna respond to N deposition is less understood.2. Here, we use a novel experimental methodology of canopy addition of N (CAN) to simulate realistic N deposition and contrast this method to standard understory addition of N (UAN) in a temperate forest and a subtropical forest. We investigated the shifts in community composition and trophic position for ground-dwelling spiders under different N deposition treatments.3. We found that the CAN deposition treatment increased the diversity of sit-andwait spiders and the abundance of actively hunting spiders at the subtropical forest, but N treatments had no effect on spider abundance or diversity at the temperate forest. In contrast, UAN treatments had no significant impact on spider communities compared to control treatment. Furthermore, N treatments had significant effects on spider assemblage at subtropical forest. Overall, spiders in the CAN treatment had a higher trophic position as indicated by δ 15 N isotopic signatures at both forest types. 4. In conclusion, our study suggests that the effects of N deposition on grounddwelling spider assemblages depend on N addition approaches. Furthermore, our results suggest that CAN is a more realistic method for understanding the effects of atmospheric N deposition on soil arthropods in forest ecosystems. K E Y W O R D S 15 N and 13 C stable isotope, atmospheric nitrogen, canopy and understory, foraging strategy, global change, subtropical and temperate forest Shengjie Liu and Yuanyuan Meng contributed equally to this work.