Large-scale genetic structure and drought-induced effects on European Scots pine (Pinus sylvestris L.) seedlings

Seedlings of ten provenances of Scots pine (Pinus sylvestris L.) from the southwestern to the central part of the species distribution range were investigated in a greenhouse experiment under dry conditions compared to a well-watered control. We conducted an isozyme study and recorded phenology as well as growth traits during the first year of growth. Genetic variability and genetic diversity increased from the westernmost provenances to those central to the distribution. Provenances from the Apennines and Spain revealed the strongest genetic differentiation compared to all others, whereas populations from Germany, Poland and Bulgaria were found to belong to the same gene pool. Seedling development and bud set were faster in northern populations. Shoot length was highest for Polish and German provenances within both regimes, populations from France and Spain had the longest roots. Reduced soil moisture slowed later development stages and delayed bud set for all provenances by about 5 days. Shoot growth decreased considerably under the dry regime for all provenances. German provenances were the most sensitive to drought, whereas Spanish provenances showed adaptation to drought conditions indicated by the lowest reduction in shoot growth relative to optimum conditions. The results of this pilot study show that under more pronounced drought conditions with repeated drought events, the so far established superiority of northeastern provenances compared to southwestern ones could diminish in the future.