Seedling traits from root to shoot exhibit genetic diversity and distinct responses to environmental heterogeneity within a tree population

Phenotypic diversity within plant species is crucial to shaping evolutionary responses of populations and interactions among species, yet intraspecific genetic variability notably in roots has attracted little attention. Further, evidence for the root−shoot trait synchronisation remains inconclusive, narrowing our understanding of the role that belowground traits play in local adaptation. We applied broad 'top-to-toe' phenotyping to a model system whose native environmental conditions were simulated in experimental settings. Fifteen maternal families of Norway spruce Picea abies from southern Finland grew in six combinations of two simulated growing seasons and three soil treatments. We scored variation in 25 functional traits, including size, architecture and morphology of intact root systems, and shoot growth and phenology. Careful phenotyping of roots uncovered five trait dimensions, with root size, architecture and morphology forming the three largest axes of variation. Dimensions v...