<b>Drought eliminates soil pathogens mediated indirect facilitation among exotic plants</b>

Ecosystems worldwide are experiencing escalating accumulations of multiple exotic species. Although direct facilitation among exotic species is known to contribute to this accumulation, indirect interactions, particularly those shaped by changing environmental conditions, remain poorly understood. Here, we examined how native and exotic plant species impact the growth and competition of later arriving natives and exotics through soil microbial legacies generated in different environmental conditions. We found that soils conditioned by exotics under well-watered conditions indirectly facilitated responding exotics over natives but those conditioned by natives did not. This reflected higher abundant pathogens in exotic conditioned soils, which disproportionately reduced the growth of responding natives and increased competitive effects of exotics on natives. However, drought eliminated this pathogen-mediated indirect facilitation among exotics by preventing pathogen accumulation. This study emphasizes the critical importance of considering indirect interactions among native and exotic species for accurately predicting exotic species accumulation under climate change.