Ecological thresholds of poisonous plants encroachment in grassland ecosystems of the Qinghai-Tibetan Plateau

Climate change and overgrazing are accelerating grassland degradation and the concomitant encroachment of poisonous plants worldwide. Effective restoration of degraded grassland and management of poisonous plants rely critically on identifying the ecological thresholds of poisonous plants encroachment, but this information remains uncertain. Here, we analyzed the responses of 20 structural and functional grassland variables to the increasing coverage of poisonous plants across 465 standardized field plots in alpine grasslands on the Qinghai-Tibetan Plateau. Asynchronous responses emerged across ecosystem variables: root productivity declined at 10% poisonous plants coverage, biodiversity decreased at 30%, but soil nutrients increased beyond 50%. In addition, ecosystem multifunctionality and plant–soil network also recovered slightly after 50%. We propose that 50% coverage represents a critical threshold where poisonous plants transition from a driver to a mitigator of degradation. We suggest stage-specific management strategies to mitigate poisonous plants encroachment in grasslands based on these thresholds. Poisonous plants encroachment in grasslands shows stage-dependent ecological thresholds, with early losses in root productivity and biodiversity but partial recovery of multifunctionality beyond 50% coverage, based on analyses of 20 ecosystem variables across 465 standardized field plots.