Species-specific impact of protists in controlling litter decomposition

Protists affect soil microbiome composition and functioning, potentially increasing litter decomposition and plant growth. Yet, the role of different protist species, individually or in combinations, in regulating microbial-mediated litter decomposition remains unknown, as well as if these interactions feedback to plant growth. Using a full-factorial design of three protist species combinations with bacterial and fungal communities, we found that only one protist species reduced litter decomposition by 19%, with other species and combinations not affecting litter decomposition. Despite a positive correlation between plant growth and litter decomposition, we did not observe protist-induced changes in plant growth. Overall, our results highlight that protists affect litter decomposition in a species-specific manner, including reducing litter decomposition. • Only 1 of 3 protist species and any combinations reduced litter decomposition. • Protist presence did not affect plant growth. • Litter decomposition positively correlated with plant growth.