Genetic variation for needle traits in Scots pine (Pinus sylvestris L.)

The remnants of the Caledonian Native Pinewood are distributed across a relatively narrow geographic area in the Scottish Highlands yet inhabit a steep environmental gradient in terms of rainfall, temperature and altitude. Previous work based on common garden trials has demonstrated that native pine populations (Pinus sylvestris (L.)) exhibit differentiation in terms of growth, phenology and frost resistance. However, despite their important role in plant fitness, no such information is available on leaf traits, which have shown both plastic and adaptive genetic responses to environmental variation in other species. We analysed a subset of 11 needle characters in 192 saplings grown in a population-progeny common garden trial based on seedlots from eight native pinewoods. Narrow-sense heritability (h²) was estimated for each trait and found to be particularly high (1.30 ± 0.33) for resin canal density. The majority of the phenotypic variation found was within populations, although interpopulation differentiation was detected for needle length (ΔAICc = 2.55). Resin canal density was positively correlated with longitude (β = 0.45, ΔAICc = 4.23), whereas stomatal row density was negatively correlated (β =−0.12, ΔAICc = 2.55). These trends may reflect adaptation for differences in moisture availability and altitude between eastern and western populations in Scotland.