Divergent adaptive strategies in vascular and bryophyte species: Intraspecific trait variation in cold scree slope microrefugia versus adjacent forests

Microrefugia provide unique habitats where species can persist despite unfavourable regional conditions. Cold scree slope microrefugia, typically found in the montane and subalpine forest belts in the Alps, host mixed communities of cold-specialised and generalist species, reflecting long term adjustment of biotic interactions following abiotic forcing. The patterns and extent of intraspecific trait variation, underpinning how generalist species from surrounding forests may modify their traits to persist in these harsh conditions, remain poorly understood, especially for non-vascular plants. In this study, we analysed intraspecific variability in functional traits (height, SLA, LDMC, leaf N content, leaf C/N ratio, and leaf pH) for eight generalist species (five bryophytes and three vascular plants) across four cold scree slopes microrefugia and adjacent montane forests in the French Alps. All species exhibited intraspecific variability, but the magnitude and traits involved differed markedly between them. Maianthemum bifolium and Hylocomium splendens exhibited significantly lower SLA and higher LDMC on cold scree slopes. In contrast, Pleurozium schreberi showed a much lower leaf C/N ratio, while Ptilium crista-castrensis displayed a much higher ratio. Additionally, our observations for Rhododendron ferrugineum and Vaccinium myrtillus diverged from those reported in a previous study conducted in other alpine microrefugia. These findings demonstrate how phenotypic plasticity allows widespread generalist species to persist in harsh marginal environments such as cold scree slope microrefugia, through species-specific trait adjustments. Furthermore, we underscore the impact of distinct environmental conditions of each microrefugia, which coupled with its cold microclimate, shape biotic interactions and contrasting species adaptations.