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

Many invasive plant species have demonstrated a greater capacity for
tolerating and accumulating heavy metals than their co-occurring native
plants. Given the potential biological toxicity associated with metal
accumulation in plants and its ability to alter the composition of
plant-associated microbial communities, we postulated that heavy metal
contamination could potentially enhance the pathogen resistance of
metal-accumulating invasive plant species when compared with their local
congeneric competitors. This study focused on examining the resistance of
the invasive weed Alternanthera philoxeroides and its native congener
Alternanthera sessilis to infection by a leaf pathogenic fungus under soil
cadmium (Cd) pollution. The findings revealed that despite the detrimental
effects of Cd exposure on the growth of both plant species, A.
philoxeroides exhibited superior growth and accumulated higher
concentrations of Cd in its leaves compared to A. sessilis. Cd stress
reduced leaf lesion in both plant species following leaf pathogen
infection, with A. philoxeroides experiencing less leaf lesion 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 potent
antagonistic properties against the leaf pathogen, potentially elucidating
the enhanced pathogen resistance of A. philoxeroides under soil Cd
pollution. This study advances our understanding of how heavy metal
pollution might augment the pathogen resistance of invasive plants by
influencing plant-associated microbial communities.