Bryophyte sedimentary ancient DNA as a proxy for environmental change in northern Fennoscandia

Broad geographic distribution yet narrow habitat tolerances of bryophytes make them sensitive indicators of disturbance and climate change in northern ecosystems. However, long-term, high-resolution palaeoecological records are rare because bryophyte macrofossils are often sparse and fragmentary. Sedimentary ancient DNA ( sed aDNA) provides a powerful alternative, offering improved taxonomic resolution and more continuous occurrence data. We analysed sed aDNA records from ten lake sediment cores spanning the period from the deglaciation of the Fennoscandian Ice Sheet approximately 16 thousand years before present to the present to reconstruct bryophyte diversity and assess regional dispersal dynamics in relation to ecological and functional traits. In total, 77 taxa were detected, of which 42% were identified to species and 14% to genus level, exceeding the resolution typically achievable by conventional paleoproxies. Bryophyte richness increased progressively through the Holocene in most lakes. Early colonizers were species adapted to acidic substrates and cool to relatively warm climates. Taxa possessing traits linked to enhanced dispersal generally appeared earlier than those lacking such attributes, and first occurrence was negatively correlated with spore size, underscoring the importance of wind dispersal in postglacial expansion. Overall, our results demonstrate that sed aDNA enables high-resolution reconstruction of bryophyte colonization dynamics since deglaciation and reveals trait-mediated patterns of dispersal and establishment through the Holocene. As bryophyte-targeted genetic markers and reference databases improve, bryophyte sed aDNA will become an increasingly powerful tool for reconstructing long-term environmental change, further strengthening the role of bryophytes as ecological indicators.