Leafy season length is reduced by a prolonged soil water deficit but not by repeated defoliation in beech trees (Fagus sylvatica L.): comparison of response among regional populations grown in a common garden

Bud-burst and leaf-senescence determine the length of growing season for deciduous trees therefore duration potential carbon assimilation with consequences on biomass production. In Fagus sylvatica L., leaf phenology depends both photoperiod temperature. The future climate is expected to induce more frequent soil water deficits biotic attacks (possibly resulting in severe defoliation). aim study assess whether these constrains may alter phenology. a common garden, we sowed seeds collected from six beech forests along small latitudinal gradient (140 km) North-Eastern France. 2014, after seven years growth, rain exclusion was installed above test how recurrent impacted bud-burst (BB) leaf-yellowing (LY) over three years. We also analyzed response annual defoliation, aiming at affecting nitrogen availability trees. Delayed BB early LY were observed, reducing (GS) until 14 days deficit whereas no influence defoliation detected. These time lags not relation content. control treatment, occurred earlier later northernmost populations than southernmost without clear relationships local climate. A significant treatment x population interaction observed revealing plasticity among populations. results suggest that present genetic differentiation even within but differentiations could be disrupted by predicted increase future.