Structural and physiological mechanisms underlying abiotic stress tolerance in the Mediterranean shrub Cistus albudus L.

Mediterranean species have to be in constant acclimation to seasonal environmental changes, including variations in water availability, air temperature and solar radiation. Due to global warming, these environmental changes are predicted to increase in frequency and intensity. Shrubs have a crucial role in plant communities such as avoiding soil erosion and, therefore, the study of shrub responses to abiotic stresses is essential to predict future changes in populations. Here, we evaluated the performance of the Mediterranean shrub, Cistus albidus, under several abiotic stresses in natural and controlled conditions. It was found that C. albidus plants have to face several combinations of abiotic stressors, with drought and cold being the main environmental cues that threaten their performance during winter. As a first line of defence, C. albidus diurnally changed the angle of their most apical leaves together with a decussate leaf disposition to avoid photoinhibition. Structural mechanisms were not always effective for the whole plant, and carotenoids had a primordial role during the day, dissipating excess energy as a second line of defence. They also had an important function under sustained winter stress, but α-tocopherol was the crucial antioxidant responding to stress, as a third line of defence. Jasmonates seemed to be involved in many abiotic stress responses, including cold stress and drought. High jasmonates contents, especially those of 12-oxo-phytodienoic acid, jasmonic acid and jasmonoyl-isoleucine, were found in natural conditions during a particularly cold day and after a winter drought event in C. albidus seedlings. Furthermore, it is shown that α-tocopherol and jasmonates have an important role in drought tolerance and survival of seedlings in natural field conditions. Even though seedlings have evolved numerous mechanisms to tolerate stress, there was a 30% decrease in survival after summer drought. It is concluded, given the variability in stress responses and the number of mechanisms to withstand abiotic stress, that C. albidus is a highly tolerant and resilient plant to abiotic stress. However, there are still tipping points that could become more frequent in the wake of global change that could cause shifts in C. albidus populations