Spring dynamics and regional variation in two different root developmental types in seedlings of a boreal evergreen conifer species

Premise of researchIn boreal forests with various snow cover conditions, local adaptation can be expected in spring root exploration due to soil freezing or competition for the fundamental niche. However, few studies have investigated the adaptive strategies for acquiring soil space and resources after snow thawing. To get insights for the eco-evolutional significance of root growth dynamics in boreal regions, this study evaluated the intraspecific variation of morphology and structures in pioneer roots and fibrous roots. MethodologyValidation model specie was Abies sachalinensis, a representative boreal conifer species with local adaptation. Five-year-old seedlings derived from an eastern provenance with low snow cover and a northern provenance with high snow cover were grown for two years in a common garden of high snow cover region. To predict spring growth patterns of roots, seedlings were dug up in early spring just after snow thawing and late spring after one month has passed. Pioneer roots exploring soil space and fibrous roots acquiring soil resource were respectively collected, and their functions were evaluated by morphology and structures indicating its construction costs and maturity. Pivotal resultsIn pioneer roots, morphological and structural difference between sampling months were significant only in northern provenance, and high construction cost and well-developed structure were observed in early spring. This represents the intraspecific variation in reaction norms of pioneer roots to spring soil environment, indicating the soil space exploration in northern provenance may start in early spring or earlier. In fibrous roots, differences of specific root length and area between sampling months were significant only in eastern provenance, and low construction cost were observed in early spring. This may reflect the plastic responses of fibrous roots to the condition of high snow cover region. ConclusionsThis study indicated that local adaptation to contrasting snow cover condition may lead to the differentiation of spring root growth dynamics for the competitive or conservative strategies. Our results address better understandings of the mechanisms of niche acquisition in evergreen conifer.