Poisonous plants weakens plant-microbe-fauna trait networks across temperature and precipitation gradients.

Trait-based ecology provides a mechanistic framework for predicting how species and trophic interactions respond to environmental change, yet cross-trophic trait linkages remain poorly understood. We investigated how the expansion of poisonous plants reshapes functional traits of plants, soil microbes, and soil fauna along climatic gradients on the Qinghai-Tibet Plateau, and how these shifts affect multitrophic trait networks and ecosystem complexity. To address this, we quantified 36 functional traits covering plants, bacteria, fungi, nematodes, and mites from 150 plots at 15 sites spanning a large climatic gradient. We found that poisonous plants induced coordinated shifts in trait values toward an acquisitive strategy in plants (thinner and softer leaves) and microbes (faster C and N cycling), but toward a conservative strategy in soil fauna (larger body size). Temperature weakened the poisonous plant-induced shift of plant trait values toward acquisitive strategies, whereas precipitation amplified the poisonous plant-induced shift of soil fauna trait values toward conservative strategies. Network analyses revealed that poisonous plants diminished connectivity and complexity among plant-microbe-fauna trait modules. By integrating trait-based and network approaches across plants, microbes, and soil fauna, our study provides the first empirical evidence that poisonous plants can generate cross-trophic trait mismatches and weaken the connectivity of plant-microbe-fauna trait networks across temperature and precipitation gradients. These findings advance trait-based ecology by showing how poisonous plants can reorganize above- and belowground functional relationships, with implications for understanding biodiversity change in alpine grasslands.