Combined drought resistance strategies and the hydraulic limit in co-existing Mediterranean woody species

Abstract

SummaryWoody species employ various strategies to cope with drought stress. We investigated similarities and differences in response to chronic drought to understand resistance strategies in co-occurring Mediterranean species.We studied five predominant Mediterranean species; Quercus calliprinos, Pistacia palaestina, Pistacia lentiscus, Rhamnus lycioides, and Phillyrea latifolia over two summers at three sites with different aridities. We measured key hydraulic and osmotic traits related to drought resistance, including resistance to embolism (Ψ50), carbon isotope signature (δ13C), pre-dawn (ΨPD) and mid-day (ΨMD) water potentials, and native (Ψs) and full turgor (П0) osmotic potentials.Significant differences among species appeared in resistance to embolism. The species also showed differences in the water potential plastic response over the dry season. This interspecific variation increased at the end of the dry season and resulted in very narrow hydraulic safety margins (HSM). Consequently, predicted loss of hydraulic conductivity revealed species with significant native embolism. Two of the species also had seasonal changes in osmotic adjustment.Our detailed analysis indicates that co-existing Mediterranean woody species combine various drought resistance strategies to minimize mortality risk. However, all of them risk mortality as they approach their hydraulic limit near the dry margin of their distribution.