BackgroundCavitation resistance to water stress-induced embolism determines plant survival during drought. This adaptive trait has been described as highly variable in a wide range of tree species, but little is known about the extent of genetic and phenotypic variability within species. This information is essential to our understanding of the evolutionary forces that have shaped this trait, and for evaluation of its inclusion in breeding programs.MethodologyWe assessed cavitation resistance (P
50), growth and carbon isotope composition in six Pinus pinaster populations in a provenance and progeny trial. We estimated the heritability of cavitation resistance and compared the distribution of neutral markers (F
ST) and quantitative genetic differentiation (Q
ST), for retrospective identification of the evolutionary forces acting on these traits.Results/DiscussionIn contrast to growth and carbon isotope composition, no population differentiation was found for cavitation resistance. Heritability was higher than for the other traits, with a low additive genetic variance (h2
ns = 0.43±0.18, CVA = 4.4%). Q
ST was significantly lower than F
ST, indicating uniform selection for P
50, rather than genetic drift. Putative mechanisms underlying QST
We assessed the adaptive potential of seed and leaf phenology in 10 natural populations of sessile oak (Quercus petraea) sampled along two altitudinal transects using common garden experiments. Population differentiation for both phenological traits was observed with high‐altitude populations germinating and flushing later than low altitude ones. However, high genetic variation and heritability values were also maintained within populations, despite slightly decreasing for dates of leaf unfolding with increasing altitude. We suggest that biotic and abiotic fluctuating selection pressures within populations and high gene flow are the main mechanisms maintaining high genetic variation for these fitness related traits. Moreover, changes in selection intensity and/or selection pressures along the altitudinal gradient can explain the reduction in genetic variation observed for leaf phenology. We anticipate that the maintenance of high genetic variation will be a valuable resource for future adaptation of sessile oak populations undergoing an upslope shift caused by climate change.
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