Data from: Cold adaptation drives variability in needle structure and anatomy in Pinus sylvestris L. along a 1,900 km temperate–boreal transect

1. Occupancy of cold habitats by evergreen species requires structural
modification of photosynthetic organs for stress resistance and longevity.
Such modifications have been described at inter-specific level while
intra-specific variation has been underexplored. 2. To identify structural
and anatomical traits that may be adaptive in cold environments, we
studied intra-specific variability of needles of Scots pine (Pinus
sylvestris L.), a wide-ranging tree, along a 1900 km temperate-boreal
transect in Europe. 3. Needles from 20 sites representing mean minimum
winter temperatures between -4.0°C and -19.9°C and mean annual
temperatures between 8.3°C and -1.7°C were sampled for measurements of
leaf mass per area (LMA, g m-2), leaf density (LD, g cm-3) and 30 other
morpho-anatomical traits. 4. Needles from cold sites lived longer, were
shorter, showed higher LMA and LD, had narrower and more
collapse-resistant tracheids, thicker epidermal cells with thicker cell
walls, and wider resin ducts occupying larger fraction of needle volume in
comparison to needles from warmer sites. 5. Along the steep climatic
gradient, needles presented a coordinated phenotypic spectrum of external
and internal traits that are largely interpretable in functional, adaptive
terms. This intra-specific pattern of co-varying traits provides insight
into the adaptive syndrome associated with stress tolerance and extended
needle longevity under cold conditions of high latitudes.