Nitrogen addition changes the trophic cascade effects of spiders on a detrital food web

Abstract

AbstractThe trophic cascade effects of predators on detrital food webs have crucial impacts on ecosystem functioning. However, due to the complexity of detrital food webs, no consistent pattern of cascading effects has emerged. Furthermore, global changes, such as increased nitrogen (N) deposition, likely have significant impacts on detrital trophic interactions but are not well understood. Here, we evaluate how increased N deposition influences trophic cascades using a simplified detrital food web (spider–Collembola) that has previously exhibited trophic cascades in an experimental context. We tested the impact of N addition on the direct and cascading effects of spiders in detritus food web. We manipulated the abundance of spiders with sit‐and‐wait or actively hunting foraging strategies in microcosms. Under ambient N conditions (control treatments), we did not detect trophic cascade effects of spiders on litter decomposition. In contrast, N addition enhanced the negative trophic cascade effects of spiders on decomposition by directly reducing Collembola density. Our findings suggest that understanding how increased N deposition affects trophic interactions and ecosystem functioning is important for predicting the impact of global change on soil ecosystems.