"Global climate change, combined with the further increase of atmospheric CO2, is expected to affect plant growth and performance and, as a consequence, the spatial distribution of species in terrestrial ecosystems within the next 50 to 100 years. In the Mediterranean region, the combined impact of current aridity with climate change will particularly threaten forest ecosystems. In addition, global change is likely to impact carbon sequestration in the forest sector, and trade-offs between mitigation and adaptation measures may arise in the future. Thus, a proper use of genetic material for reforestation (one of the main mitigation options in European forestry) is crucial to face new climate circumstances at an early stage through anticipatory adaptation. In this regard, there is a need to understand long-term plant responses to climate changes in order to define the most appropriate adaptation measures. Tree rings provide an easily datable archive that can be explored for physiologically relevant signals. In particular, the analysis of carbon and oxygen stable isotopes in tree-rings combines the ability to integrate physiological information over different time scales, which allows validating the results over a great number of sites. However, although the basic principles for carbon and oxygen isotopes in plants are well known, there are still some unsolved questions. The general objective of the proposal is to explore and further develop the application of stable isotopes in Mediterranean pines as ecophysiological tools. This will involve 1) basic research to better understand the underlying mechanisms determining stable isotope composition in trees and their relationship with physiological processes, and 2) applied research to develop the use of stable isotopes as tools to characterise genetic material for reforestation and to monitor long-term response to global changes in Mediterranean pines."