Functional- and abundance-based mechanisms explain diversity loss due to N fertilization

TLDR

Human activities have dramatically increased nitrogen availability in terrestrial and aquatic ecosystems, and while nutrient enrichment consistently reduces local plant species diversity, the underlying mechanisms remain unclear. The study aims to demonstrate that both trait‑neutral and trait‑based mechanisms simultaneously drive diversity loss as production increases in nitrogen‑fertilized ecosystems. The authors analyzed responses of over 900 species from 34 nitrogen‑fertilization experiments across nine North American terrestrial ecosystems to assess these mechanisms. They found that rare species were disproportionately lost, with loss risk exceeding 60 % for the rarest species and 10 % for the most abundant, and that perennials, N‑fixing, and native species faced higher extinction risk regardless of abundance, while abundance was consistently important across systems and functional mechanisms varied by system, underscoring the need to target susceptible functional groups and rare species to preserve biodiversity.

Abstract

Human activities have increased N availability dramatically in terrestrial and aquatic ecosystems. Extensive research demonstrates that local plant species diversity generally declines in response to nutrient enrichment, yet the mechanisms for this decline remain unclear. Based on an analysis of >900 species responses from 34 N-fertilization experiments across nine terrestrial ecosystems in North America, we show that both trait-neutral and trait-based mechanisms operate simultaneously to influence diversity loss as production increases. Rare species were often lost because of soil fertilization, randomly with respect to traits. The risk of species loss due to fertilization ranged from >60% for the rarest species to 10% for the most abundant species. Perennials, species with N-fixing symbionts, and those of native origin also experienced increased risk of local extinction after fertilization, regardless of their initial abundance. Whereas abundance was consistently important across all systems, functional mechanisms were often system-dependent. As N availability continues to increase globally, management that focuses on locally susceptible functional groups and generally susceptible rare species will be essential to maintain biodiversity.