Tropical Peatlands as Hotspots of Hidden Arcellinida Diversity: Insights from Maludam National Park, Borneo (Sarawak, Malaysia)

Recent investigations on tropical peatlands have shown their extremely high efficiency as carbon sinks, far beyond better studied boreal bogs. The microbial diversity found in those ecosystems, as well as their corresponding ecological and metabolic processes, are just starting to be revealed, and differ considerably from high latitudes systems. However, these efforts have been concentrated almost exclusively towards prokaryotes and fungi, leaving protist communities virtually unknown. Arcellinida (testate amoebae) are well acknowledged to play an important role in boreal and temperate peatland ecology by driving microbial community composition as top predators, but also as nutrient recyclers and carbon fixers. Yet, to our knowledge, no community–level study has addressed their diversity and its drivers in tropical peatlands. In this study, we surveyed Arcellinida communities' diversity across five functionally distinct vegetation–hydrological zones situated along a hydrological transect in a coastal tropical peatland in the Maludam National Park, Malaysia. Taxonomic composition of Arcellinida communities, characterized by a high diversity of Trigonopyxis-related taxa, indicated fundamental differences in diversity and community composition from extratropical ecosystems. Species richness was significantly higher in the zones with developed understory vegetation. Furthermore, the composition of diversity varied significantly among vegetation-hydrological zones. Altogether, this study shows unique Arcellinida communities in a Southeastern Asian peatland and suggests the importance of vegetation-hydrological characteristics for protist diversity.