Microorganisms perform essential functions in Arctic terrestrial ecosystems. Yet, their ecology and biogeography are poorly understood, despite being necessary to predict microbial responses to future climate change. Here, we provide the first large‐scale floristic and biogeographic study of the moss diatom flora in the tundra regions of the North Atlantic sector of the Arctic. Diatom communities in 284 terrestrial moss samples from herbarium and recent collections (1962–2023) were analysed by light and scanning electron microscopy. Moss diatoms show clear regionalisation across the Arctic, with strong compositional differences between the three biogeographic regions (High Arctic, Low Arctic and Subarctic), reflecting contemporary microclimatic conditions and historical processes. We identified an inverse latitudinal diversity gradient with species richness increasing towards the High Arctic, likely driven by a temperature–moisture gradient. Nearly half of all taxa in our study are currently only observed in and known from the Arctic, and 44% were confined to a single biogeographic region, indicating a high degree of potential endemism. Our results serve as a foundation for future studies on polar diatoms and highlight their potential use as bioindicators for reconstructing and monitoring past, present, and future climate change.
Goeyers et al. (Wed,) studied this question.