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.

Jankowski et al. Data