ORIGINAL PAPER Effects of long-term experimental night-time warming and drought on photosynthesis, Fv/Fm and stomatal conductance in the dominant species of a Mediterranean shrubland Patricia Prieto Æ Josep Pen ˜ uelas Æ Joan Llusia ` Æ Dolores Asensio Æ Marc Estiarte Received: 28 October 2008 / Revised: 8 January 2009 / Accepted: 2 February 2009 / Published online: 26 February 2009 Ó Franciszek Go ´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´w 2009 Abstract We conducted a night-time warming and drought field experiment for 7 years (1999–2005) in a Mediterranean shrubland. We focused on the two dominant shrub species, Erica multiflora L. and Globularia alypum L. and the tree Pinus halepensis L. and the final years to study the effects of the experimental night-time warming and drought on Fv/Fm, photosynthesis, and stomatal conductance. Warming treatment increased mean air tem- perature and mean soil temperature through the years by an average of 0.7 and 0.9°C respectively, and drought treat- ment reduced soil moisture through the years by an average of 19%. Warming tended to increase photosynthetic rates in E. multiflora, G. alypum and P. halepensis mostly in the cold seasons, when plants were more limited by tempera- ture, as shown by the lowest values of Fv/Fm being detected in winter in the three studied species. A negative effect of warming was only detected for E. multiflora in summer 2003. Drought treatment generated different responses of net photosynthetic rates depending on the species, season and year. Stomatal conductance showed the same pattern as photosynthesis for the three studied spe- cies, displaying seasonal and inter-annual variability, although with an overall negative effect of drought for P. halepensis. Photosynthetic rates decreased significantly in the dry winter 2005 and spring 2005 in comparison to the same seasons of 2003 and 2004. There were positive correlations between the photosynthetic rates in different seasons for E. multiflora, G. alypum and P. halepensis and the soil moisture of the week prior to measurements. The great variation in the photosynthetic rates was thus explained in a significant part by soil moisture levels. The lowest Fv/Fm values usually corresponded with lowest stomatal conductances suggesting that drought stress could be associated to stress by low temperatures in winter. Keywords Erica multiflora Á Globularia alypum Á Pinus halepensis Á Mediterranean shrubland Á Fluorescence Á Photosynthesis Á Stomatal conductance Á Global warming Á Drought Introduction The main conclusions of most General Circulation Models (GCMs) indicate that over this century, the mean global surface temperature will increase by 1.1–6.4°C depending on the socio-economic scenario and the resulting emissions of greenhouse gases (IPCC 2007). Although there is no general agreement regarding future rainfall regimes, most GCM and ecophysiological models such as GOTILWA project drier conditions in the Mediterranean ecosystems (IPCC 2007; Sabate ´ et al. 2002; Pen ˜uelas et al. 2005), as has already occurred in the last decades (Le Houe ´rou 1996; Pin ˜ol et al. 1998; De Luis et al. 2001; Pen ˜uelas et al. 2002, 2005; Pen ˜uelas and Boada 2003). The predicted temperature rise could affect plant growth due to changes in photosynthetic rate, CO 2 losses by res- piration, enhanced photorespiration and VOC production which present different responses depending on the tem- perature range (Long 1991; Huntingford et al. 2000; Communicated by J. Zwiazek. P. Prieto Á J. Pen ˜uelas Á J. Llusia `(&) Á D. Asensio Á M. Estiarte Ecophysiology and Global Change Unit CREAF-CEAB-CSIC, Centre for Ecological Research and Forestry Applications, Universitat Auto `noma de Barcelona, Edifici C, 08193 Bellaterra, Barcelona, Spain e-mail: j.llusia@creaf.uab.cat J. Pen ˜uelas e-mail: josep.penuelas@uab.cat 123 Acta Physiol Plant (2009) 31:729–739 DOI 10.1007/s11738-009-0285-4