Contrasted tolerance to low and high temperatures of three tree taxa co-occurring on coastal dune forests under Mediterranean climate

This work compares the tolerance to low and high temperatures of the photosynthetic apparatus of the tree species Pinus pinea, Juniperus oxycedrus subsp. macrocarpa and Juniperus phoenicea subsp. turbinata, which co-occur on coastal dunes under Mediterranean climate on SW Iberian Peninsula. Chlorophyll (Chl) fluorescence, gas exchange and water potential (W) measurements were recorded for over two years in the field and in a controlled-temperature study. P. pinea showed a high sensitivity to the combined effects of drought and high temperatures at the end of the drier and warmer summers. In addition, its net photosynthetic rate decreased with warmer temperatures. The lower thermotolerance of R pinea to higher temperatures was supported by the laboratory results. J. oxycedrus showed the lowest tolerance to chilling stress with its highest chronic photoinhibition levels during wetter and colder periods and its lower net photosynthetic rates at lower temperatures. The photosynthetic apparatus of J. phoenicea showed a suboptimal state during summertime denoted as high chronic photoinhibition levels that increased with lower W. These results show that air temperature, with its synergic effects in combination with drought and solar radiation, is a key climatic factor conditioning stress levels of tree species growing on coastal sand dunes under Mediterranean climate. (C) 2009 Elsevier Ltd. All rights reserved.