Uncover the link between functional trait diversity and thermal insulation effects of bryophytes and lichens in permafrost regions: Insights from a processed-based model

Bryophytes and lichens in permafrost regions act as a natural insulation cover and thus cool underlying soil layers due to their porous, air-filled structure. The retained water content varies in response to evapotranspiration and freeze-thaw transitions, thereby modulating the insulation effects. Climate change is driving alterations in functional diversity of these highly sensitive non-vascular vegetation communities. Shifts in functional traits are closely linked to height and water retention capacity, thus the insulating properties, of the bryophyte and lichen layer. However, it is largely unclear how changes in functional diversity of non-vascular vegetation will affect soil temperature. Yet this gap may be addressed by trait-based models that simulate the mutual interaction between biodiversity and soil state.

This study focuses on bryophyte and lichen vegetation in high-latitude permafrost ecosystems, aiming to: (1) quantify their insulation effects on soil temperature under long-term climate change, and (2) clarify the underlying mechanisms by which functional diversity modulates the insulation effects. To this end, we refine the permafrost processes within the trait- and process- based LiBry model to accurately capture the coupled states of soil and diversity. Model experiments to isolate effects of bryophyte and lichen vegetation are implemented to determine their contribution to soil temperature variations. We further drive the model with a gradient of climate and diversity scenarios to reveal the relationships between distribution of functional traits and insulation effects. Our findings contribute to a more comprehensive understanding of the impacts of functional diversity on key permafrost processes in data-scarce contexts.