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 du...