The maternal environment of European beech (Fagus sylvatica L.) affects intrapopulation variability in seed traits and germination

Interpopulation variation was investigated using seed samples originating from twenty-six European beech (Fagus sylvatica L.) populations across the Balkan Peninsula, a part of the species’ distribution range characterized by high ecological heterogeneity in key climatic factors, such as temperature (5.8-10.6 °C), precipitation (648-1632 mm), and elevation (185-1410 m a.s.l.). The statistical significance of intrapopulation differences was confirmed by analysis of variance (ANOVA) for all seed traits analyzed: seed weight (g), length (mm), width (mm), thickness (mm), eccentricity and flatness indices, and germination capacity (%). Multivariate principal component analysis (PCA) was applied to examine seed traits in relation to environmental variables of the maternal site, such as mean temperature and precipitation in September and October (the seed maturation period), revealing distinct patterns of relationships among the variables studied. Seed traits were significantly positively correlated with mean temperatures of the maternal site in September and October, indicating that temperature during the seed-filling period affects seed mass. Germination capacity was associated with precipitation during the same period, though the correlation coefficient was not statistically significant; a shorter vector length in the PC biplot suggests a weaker contribution to population separation. Elevation of the site of origin showed a significant negative correlation with temperature, precipitation, and seed traits. Agglomerative hierarchical clustering analysis identified three distinct population clusters. Higher temperature and precipitation values did not necessarily result in higher seed trait values or higher germination percentages. The population with the highest seed mass exhibited the lowest germination capacity (32%) during seed maturation under the lowest precipitation. Conversely, the population characterized by the lowest seed mass showed a higher germination rate of 68% in environments with high precipitation. These results provide valuable insights into the reproductive ecology of European beech, suggesting that other factors beyond those analyzed here may have a more substantial influence on seed germination. The variation in seed traits across habitats that are either drier and hotter or colder and wetter, along the elevation gradient of the studied populations, paves the way for future research and breeding efforts to enhance the species’ survival and reproductive success amid anticipated climate change scenarios.