Plant-soil feedback (PSF) and interspecific variations of its strength determine plant community structure. Understanding which traits control species’ PSF strength is a critical issue for plant ecology. Studies have highlighted either nutrient cycling (litter-mediated PSF) or soil biota (microbial-mediated PSF) as important PSF mechanisms, with each study focusing on different sets of plant traits. However, this separation neglects the complex indirect interactions between plant litter and diverse root-associated microbes. We developed a model coupling litter- and microbial-mediated PSFs to identify the relative importance of different traits in controlling PSF strength, and its dependency on soil microbial composition (i.e. pathogens and/or mycorrhizal fungi). We showed that while litter decomposability was not a major determinant of PSF in pathogen-rich soils, its importance increased with the relative abundance of mycorrhizal fungi as the positive effects of higher decomposability were amplified by the indirect interaction between microbes and litter dynamics. Our results can provide new perspectives to invasion ecology and trait-based ecology.