Das Projekt "Recovery from drought stress: Are the processes of plant's capacity to adapt and survive under climate-driven environmental extremes underestimated?" wird vom Umweltbundesamt gefördert und von Departament de Qimica Universitat de les Illes Balears durchgeführt. With regard to climate-driven environmental changes in Europe during the next decades (heatwaves and extended drought periods) the understanding of how plants may adapt to these environmental constraints and ensure their survival awaits further attention. Moreover, besides well studied responses of plants to various drought intensities, the capacity of recovery from drought and its velocity and rate will become an important issue for plant species across Europe. As there is a scarcity of studies in the field of recovery from drought, this project is designed to unravel its underlying physiological processes by a systematic analysis of photosynthetic and respiratory traits of several Mediterranean species during recovery from various drought intensities. The time frame of drought within a vegetation period may additionally affect the capacity of drought tolerance and rate of recovery, as well as growth and survival. Main Results and Conclusions The rate of photosynthetic restoration after drought-induced suppression depends on the intensity of drought, as recovery of all examined plant species has always been more rapid after mild or moderate drought (one to three days) than after severe drought (more than three days). Differences appeared among species, as annual species (Nicotiana sylvestris, Glycine max) recovered more rapidly from severe drought than perennial ones (Vitis vinifery, Cistus albidus, Quercus ilex). However, perennials followed a more conservative strategy during drought progression by loosing less water than the annual plants (which reached severe stress more rapidly but recovered also quicker after the short drought period). Limitation of photosynthetic recovery during the re-watering phase was driven by a delayed stomatal opening and impaired internal CO2 diffusion, namely the mesophyll conductance (gm). The gm has been found to be an important factor in limiting photosynthesis during drought and after subsequent re-watering, which further supports the idea of an important role of gm in photosynthetic regulation during stress and the necessity of further studies on its regulation under climatic variables. The impact of other climatic variables than water stress on gm could be assumed by comparing tobacco plants under different growth conditions. Besides the role of gm, the interaction of photosynthesis and respiration during drought and recovery has been shown to be important and highly flexible, as impaired respiratory chain was overcome by enhanced cytochrome pathway activity and hence higher total respiration. This adjustment might help to match the cellular ATP demand and maintain the cell redox balance, thus resulting in a similar response of photosynthesis to drought and re-watering.