Heavy metal pollution enhances pathogen resistance of an invasive plant species over its native congener

Abstract Many invasive plant species have demonstrated a better ability to tolerate and accumulate heavy metals than their co‐occurring native plants. Given the potential biological toxicity of heavy metals to phytopathogens, we postulated that heavy metal contamination could enhance the pathogen resistance of metal‐accumulating invasive plant species over their local congeneric competitors. Here, we compared the resistance of the invasive Alternanthera philoxeroides and its native congener Alternanthera sessilis to infection by a leaf pathogenic fungus under soil cadmium (Cd) contamination. The findings revealed that A. philoxeroides exhibited superior growth and accumulated superior amounts of Cd in its leaves compared with A. sessilis . Cd exposure decreased leaf lesions in both plant species following artificial infection by the leaf pathogen, with A. philoxeroides experiencing fewer leaf lesions than A. sessilis . Subsequent analysis of the phyllosphere microbiome and toxicity tests suggested that the increased pathogen resistance of A. philoxeroides following Cd exposure could be attributed to both the direct toxic effects of Cd and the Cd‐induced alterations in the microbial composition of the epiphytic phyllosphere. We further isolated a bacterial strain with a strong antagonistic effect against the leaf pathogen, potentially elucidating the enhanced pathogen resistance of A. philoxeroides under soil Cd pollution. Collectively, these findings indicate that heavy metal contamination may promote plant invasion by altering interactions between plants and pathogens. Read the free Plain Language Summary for this article on the Journal blog.