Warming intensifies soil pathogen negative feedback on a temperate tree

The soil pathogen‐induced Janzen–Connell (JC) effect is considered as a primary mechanism regulating plant biodiversity worldwide. As predicted by the framework of the classic plant disease triangle, severity of plant diseases is often influenced by temperature, yet insufficient understanding of how increasing temperatures affect the JC effect contributes uncertainty in predictions about how global warming affects biodiversity. We conducted a 3‐yr field warming experiment, combining open‐top chambers with pesticide treatment, to test the effect of elevated temperatures on seedling mortality of a temperate tree species, Prunus padus, from a genus with known susceptibility to soil‐borne pathogens. Elevated temperature significantly increased the mortality of P. padus seedlings in the immediate vicinity of parent trees, concurrent with increased relative abundance of pathogenic fungi identified to be virulent to Prunus species. Our study offers experimental evidence suggesting that global warming significantly intensifies the JC effect on a temperate tree species due to increased relative abundance of pathogenic fungi. This work advances our understanding about changes in the JC effect linked to ongoing global warming, which has important implications for predicting tree diversity in a warmer future.