P.1.04.12 The CLIMOOR project. Effects of an experimental increase of temperature and drought on the ecophysiology of shrub species at four sites in Europe

L. Llorens*, CREAF SPAIN, J. Penuelas, CREAF SPAIN, B. Emmet, CEH UNITED KINGDOM, A. Tietema, University of Amsterdam NETHERLANDS, C. Beier, RIS National Laboratory DENMARK

CLIMOOR manipulations started in March 1999 and were carried out at four shrubland ecosystems in Spain, The Netherlands, Wales and Denmark. The Mediterranean site is an Erica shrubland, whereas the three northerly sites are Calluna heathlands. The four European sites span a gradient in the factors we study: temperature and precipitation. Temperature manipulations were designed to obtain night-time warming of the ecosystem by reducing the loss of IR radiation at night, resulting in an increase of 0.5-1.5 #C in relation to untreated plots. Precipitation manipulations were designed to extend drought periods by reducing water input, excluding rain for 2 months during the growing season. At each of the four sites, 9 plots (20 m2 per plot) were established: 3 untreated controls, 3 heating and 3 drought plots. Measurements of transpiration, net photosynthetic rates and Chla fluorescence of Calluna vulgaris in Denmark, Wales and The Netherlands, and Erica multiflora and Globularia alypum in Spain were conducted in June-July 1999 and 2000. We expected warming effect to be greatest at northern countries, where temperature is more limiting for plants. Conversely, we expected drought effect to be greatest in the Spanish site, where plants are more limited by water availability. Results showed a decrease of net photosynthetic and transpiration rates from northern to southern countries, in agreement with the natural geographical gradient in water availability. No general response to the warming treatment was found. Whereas warming reduced net photosynthetic rate in Wales, it increased potential photochemical efficiency in The Netherlands. In general, drought treatment reduced rates of photosynthesis and transpiration, although the decrease was only significant in The Netherlands. In Spanish site, we performed gas exchange and Chla fluorescence measurements of plants seasonally during two years. Warming treatment decreased photosynthetic rates for Erica multiflora in Autumn 1999, but not for Globularia alypum. These results suggest that susceptibility to warming differ among species, which could have long-term implications on community composition. On the other hand, drought treatment reduced values of the ecophysiological parameters studied for both species (Erica multiflora and Globularia alypum) in Autumn-Winter 1999, whereas no clear effect was found in 2000. These results suggest a possible acclimation of these species during the second year.