Adaptation of resource acquisition and investment in resource acquiring tissues of Betula nana in response to climatic constraints

Several plant species have moved further north in their range in response to climatic shifts. This study aimed to investigate how leaf and root functional traits of B. nana vary across a 2000 km latitudinal gradient from Arctic to temperate Europe, with a focus on comparing continuous and relict populations along the gradient to identify the climatic and edaphic factors limiting the occurrence of B. nana and shaping resource acquisition traits. We evaluated morphological, biochemical, isotopic, and anatomical features of leaves and roots in relation to environmental variables using ecological niche modeling (MaxEnt) and trait-based analyses across the latitudinal transect. Results revealed that soil organic carbon was the dominant limiting factor for the occurrence of relict populations, while temperature seasonality constrained northern populations. Compared to northern sites, relict populations exhibited shorter specific root length (SRL), high intrinsic water use efficiency (iWUE), and greater nitrogen concentrations in leaves and roots, suggesting adaptations to warmer and drier conditions. In contrast, northern populations displayed more negative δ¹ ³C values and less iWUE, indicating increased stomatal opening and water loss per unit of carbon assimilated. Nitrogen concentration was weakly associated with temperature but more closely linked to precipitation seasonality. Our findings demonstrate that relict populations of B. nana maintain distinct trait configurations shaped by local environmental constraints, particularly soil carbon availability and water stress. These results underscore the importance of integrating multiple environmental variables when assessing functional trait responses and suggest that relict populations may harbor adaptive potential critical for species resilience under future climate scenarios.