Assessing the Biogeographic Risks of Potentially Toxic Plants—A Case Study for a Novel Locoweed <scp> <i>Sphaerophysa salsula</i> </scp> in China

Climate change-induced grassland degradation has exacerbated the spread of toxic plants, yet many potentially toxic species remain overlooked, undermining rangeland management and causing significant economic losses. Quantifying the toxicity and distribution of potential toxic plants under climate change is critical for mitigating biogeographic risks. As a case study, taking <i>Sphaerophysa salsula</i>, a leguminous plant distributed in Asia and the Americas, historically utilized for erosion control but recently associated with livestock poisoning, this research integrated toxicity identification, species distribution modeling (SDM), and risk assessment to evaluate its biogeographic threats in China. Results suggested for the first time that <i>S. salsula</i> can function as a high-toxicity (chemotype 1) locoweed due to swainsonine (mean content 0.373%), produced by its endophyte <i>Alternaria oxytropis</i> (23.46 pg/ng), which is implicated in locoism-like syndromes in livestock. The Maximum Entropy model identified temperature annual range (43.22°C), mean temperature of the driest quarter (-6.29°C), and soil pH (8.61) as key distribution drivers. Currently, suitable habitats are concentrated in Northern China (Xinjiang, Inner Mongolia, Ningxia). By the 2070s, these habitats are projected to decline by 6.3%-9%, shifting westward toward pastoral regions. Risk assessments integrating grazing intensity revealed high-risk zones in Gansu, Ningxia, and Inner Mongolia, with future scenarios predicting declining risks in eastern Inner Mongolia but increasing threats in western Tibet. These findings clarify <i>S. salsula</i>'s toxic mechanism and biogeographic risks, providing a framework for targeted management of overlooked toxic plants under climate change.