Tree-ring carbon and oxygen isotopes indicate different water use strategies in three Mediterranean shrubs at Capo Caccia (Sardinia, Italy)

Key message: Variations in stable carbon and oxygen isotope compositions of co-occurring plant species reflect their different water use strategies and indicate the importance of screening species’ WUE<inf>i</inf>to plan climate change adaptation strategies. Abstract: The different abilities of plant species to cope with drought have been associated with structural and ecophysiological constraints. In this paper, we evaluate interspecific differences in intrinsic water use efficiency (WUE<inf>i</inf>) and the ratio of photosynthesis (A) to stomatal conductance (g<inf>s</inf>) in three co-occurring Mediterranean shrubs: two broad-leaved evergreen (Pistacia lentiscus and Phillyrea angustifolia) and one needle-like-leaved evergreen (Juniperus phoenicea). We used δ¹³C in rings to assess inter-annual changes in WUE<inf>i</inf> while the influence of the stomatal conductance was explored through δ¹⁸O. Our results indicate consistent differences in WUE<inf>i</inf> in the three species, largely determined by leaf traits and differences in stomatal conductance control. Juniperus phoenicea could be the most threatened by the current trend of increasing temperature and summers drought. Phillyrea angustifolia and P. lentiscus seem to be less affected by drought stress because of their tighter stomatal control and high survival rate under field conditions. Our study shows that shrubs with different leaf traits employ different plant ecophysiological strategies under drought stress.