Differentiation in phenological and physiological traits in European beech (Fagus sylvatica L.)

The knowledge of the extent of local adaptation is essential for forest reproductive material transfer, designing gene conservation programs and measures for mitigation of the ongoing climate change. A common methodology for assessing selection underlying local adaptation is the comparison of differentiation at neutral markers (measured by F (ST)) against quantitative traits (measured by Q (ST)). We investigated differentiation in phenology, height and diameter growth, and parameters of photosynthesis and water regime in a widespread European broadleaved tree, European beech (Fagus sylvatica L.). As the assessment of Q (ST) requires known pedigree structure of the tested populations, it was approximated by the coefficient of phenotypic differentiation P (ST). For all phenology traits, especially budburst timing, there is a strong and reliable evidence of local adaptation as indicated by P (ST) > F (ST). On the other hand, P (ST) was generally smaller than F (ST) for most growth and physiological traits, but the evidence for uniform selection or canalization acting at genes underlying these traits is generally absent or weak. Possible heritable basis of phenological differentiation is discussed, and implications for the current EU legislation on forest reproductive material are drawn.