Unveiling the Role of Protists: Species-Specific and Size-Dependent Regulation of Litter Decomposition

Samenvatting

Litter decomposition is an important process for carbon and nutrient cycling. Litter decomposition is mainly driven by bacterial and fungal decomposers that are subsequently controlled by their predators, particularly the highly diverse protists. However, the role of different protist species individually and in combinations, as well as the potential protist trait differences, in determining microbial-mediated litter decomposition, remain largely unknown. To study the role of protists as top-down regulators in litter decomposition and carbon cycling, we first investigated the role of three phylogenetically distant protist species and their combinations in litter decomposition. Our findings revealed that protists generally did not affect litter decomposition except for one protist species that decreased litter decomposition. Furthermore, we tested whether the body size determines protists’ role in litter decomposition. We found that larger protists decreased litter decomposition by 29% and also increased cumulative carbon respiration in the later phases of litter decomposition by altering bacterial composition and abundance of specific bacterial taxa. Overall, our results highlight that protists affect litter decomposition in a species-specific and size-dependent manner by shaping the microbiome. Studies on litter decomposition and the overall carbon cycle should include protists to obtain a comprehensive understanding of the biodiversity underlying these processes.