The Impact of Heat Stress and Water Deficit on the Photosynthetic and Stomatal Physiology of Olive (Olea europaea L.)--A Case Study of the 2017 Heat Wave

Heat waves are predicted to increase in frequency and duration in many regions as globaltemperatures rise. These transient increases in temperature above normal average values will havepronounced impacts upon the photosynthetic and stomatal physiology of plants. During the summerof 2017, much of the Mediterranean experienced a severe heat wave. Here, we report photosyntheticleaf gas exchange and chlorophyll fluorescence parameters of olive (Olea europaea cv. Leccino) grownunder water deficit and full irrigation over the course of the heat wave as midday temperaturesrose over 40 C in Central Italy. Heat stress induced a decline in the photosynthetic capacity of theolives consistent with reduced ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity.Damage to photosystem II was more apparent in plants subject to water deficit. In contrast to previousstudies, higher temperatures induced reductions in stomatal conductance. Heat stress adverselyaffected the carbon efficiency of olive. The selection of olive varieties with enhanced tolerance toheat stress and/or strategies to mitigate the impact of higher temperatures will become increasinglyimportant in developing sustainable agriculture in the Mediterranean as global temperatures rise.