Ecoregional patterns of protist communities in mineral and organic soils: assembly processes, functional traits and diversity of testate amoebae in Northern Eurasia

Abstract

Soil microbial communities play a crucial role in the functioning of terrestrial ecosystems. Rapid changes in climate and land-use will likely cause major changes in belowground biodiversity with unknown consequences on ecosystem functioning. The functional traits, taxonomic and functional diversities of soil microorganisms are known to vary in relation to soil type and climate, but few studies have compared these patterns and explored assembly community mechanisms systematically in contrasted ecological conditions. Here we address this gap and focus on testate amoebae, a key group of shell-producing microbial predators known to play significant roles in C and N cycling in terrestrial ecosystem. We used morphological approach to assess and compare their taxonomic and functional diversity in organic (Histosols) and mineral soils in six regions (320 samples) spanning a wide range of latitudes (52–67°N, ∼2126 km) and longitudes (46–107°E, ∼3927 km) in Central-North Eurasia. Our study revealed significant differences in testate amoeba community composition, diversity, functional traits and assembly mechanisms among ecoregions and soil type. In the ecoregions with drier soils, testate amoeba taxonomic and functional diversities were higher in organic soils compared to mineral soils, while the opposite was observed in ecoregions with wetter soils. With respect to morphological traits, in drier-soil ecoregions such as forest-steppes, testate amoebae were longer and had a relatively smaller aperture in organic soils, while the opposite is true in wetter-soil ecoregions such as taiga and tundra. Habitat filtering was identified as the leading assembly process in mineral soils, while biotic factors were more influential in organic soils. This study provides a comprehensive comparative analysis of testate amoeba communities, enhancing our understanding of how abiotic and biotic factors shape microbial communities in ecosystems, highlighting the role of soil moisture regime, and offering valuable insights for predicting ecological responses to environmental changes.