Timing of autumnal leaf senescence in a common shrub species depends on the level of preceding summer drought symptoms

More severe water limitations will challenge forest ecosystems in Europe. To gain more insight into the putative consequences for forests, we studied how the common shrub Cornus sanguinea L. responds to a period of water withholding in summer, followed by rewatering. We grew potted saplings of a local Belgian and a Pyrenean provenance in a common garden experiment. We quantified the impact on growth and several phenological traits, with a specific focus on autumnal leaf senescence. We showed that the timing of autumnal leaf senescence was earlier in plants that displayed no to little leaf desiccation due to the experienced drought, compared to the controls. On the contrary, plants that suffered heavy to total leaf desiccation resprouted after the drought period and displayed delayed leaf senescence. No shift in the timing of autumnal leaf senescence was observed for plants with intermediate leaf desiccation. Our results suggest two different post-drought recovery strategies acting in the same experiment. Which strategy was activated depended on the severity of the drought stress, and the two strategies cancelled each other for the group of plants with intermediate drought symptoms. The earlier leaf senescence is likely an acclimation response whereas the delayed leaf senescence enables plants to repair damaged tissues. Our results also suggest provenance-dependent responses as the earlier leaf senescence was activated earlier in the Pyrenean provenance (no difference in timing for the delayed leaf senescence).