Effects of Nitrogen Addition and Plant Identity on Ground-Dwelling Arthropod Community Structure in Green Roofs

Green roofs are a key component of urban green infrastructure and can support diverse urban biota. However, the effects of global change factors, such as nitrogen (N) deposition, on arthropod communities in green roofs remain poorly understood. We conducted a controlled N addition experiment on an experimental green roof planted with four species. Ground-dwelling arthropods were collected by pitfall traps and identified to the family or genus level. We assigned individuals to functional groups based on feeding habits and analyzed how N addition and plant characteristics affect functional group structure. N addition did not change total arthropod abundance or richness, but it increased predator abundance significantly (p = 0.023) and herbivore abundance marginally (p = 0.060). The interaction between N addition and plant identity affected Shannon–Wiener and Pielou evenness of detritivore arthropods. PCoA and PERMANOVA testing showed that plant identity explained 23.7% of community variation (p = 0.006), whereas N addition was marginal (R2 = 7.7%, p = 0.056). Plant characteristics were closely related to the community structure of different functional groups. These results indicate that N addition caused functional group-specific shifts rather than overall diversity loss, and that plant identity was a major driver of ground-dwelling arthropod communities on green roofs.