Effects of Nitrogen Enrichment on the Competition Network of Above-Ground Species in Inner Mongolia Steppe

Nitrogen enrichment affects and changes the community structure of terrestrial ecosystems. Recently, intransitivity competition networks have been widely considered to in maintaining coexistence and biodiversity. However, whether the structure and function of the species competition network changes under nitrogen enrichment remains unclear. In this paper, we applied the Apriori algorithm to find dominant species assemblies to simulate competition matrices. We found that (1) intransitive competition networks derived by a species-dominant assembly accounted for a relatively large proportion of the derived networks, and the species acting as mediators constituted a nested pattern; (2)Under N enrichment, the complexity of the networks varied from an intransitive network to a sub-competition structure, and transitive networks was a transition structure between these two structures; (3) the negative effect of N-enrichment on species network was counteracted by mowing and rainfall; and (4) increasing the number of loops enhances the diversity in a community, while high competition among species is a representation of an intransitive competition network.