In the Mediterranean evergreen oak woodlands of southern Portugal, the main tree species are Quercus ilex ssp. rotundifolia Lam. (holm oak) and Quercus suber L. (cork oak). We studied a savannah-type woodland where these species coexist, with the aim of better understanding the mechanisms of tree adaptation to seasonal drought. In both species, seasonal variations in transpiration and predawn leaf water potential showed a maximum in spring followed by a decline through the rainless summer and a recovery with autumn rainfall. Although the observed decrease in predawn leaf water potential in summer indicates soil water depletion, trees maintained transpiration rates above 0.7 mm day(-1) during the summer drought. By that time, more than 70% of the transpired water was being taken from groundwater sources. The daily fluctuations in soil water content suggest that some root uptake of groundwater was mediated through the upper soil layers by hydraulic lift. During the dry season, Q. ilex maintained higher predawn leaf water potentials, canopy conductances and transpiration rates than Q. suber. The higher water status of Q. ilex was likely associated with their deeper root systems compared with Q. suber. Whole-tree hydraulic conductance and minimum midday leaf water potential were lower in Q. ilex, indicating that Q. ilex was more tolerant to drought than Q. suber. Overall, Q. ilex seemed to have more effective drought avoidance and drought tolerance mechanisms than Q. suber.

b s t r a c tWater is now considered the most important but vulnerable resource in the Mediterranean region. Nevertheless, irrigation expanded fast in the region (e.g. South Portugal and Spain) to mitigate environmental stress and to guarantee stable grape yield and quality. Sustainable wine production depends on sustainable water use in the wine's supply chain, from the vine to the bottle. Better understanding of grapevine stress physiology (e.g. water relations, temperature regulation, water use efficiency), more robust crop monitoring/phenotyping and implementation of best water management practices will help to mitigate climate effects and will enable significant water savings in the vineyard and winery. In this paper, we focused on the major vulnerabilities and opportunities of South European Mediterranean viticulture (e.g. in Portugal and Spain) and present a multi-level strategy (from plant to the consumer) to overcome region's weaknesses and support strategies for adaptation to water scarcity, promote sustainable water use and minimize the environmental impact of the sector. © 2015 Published by Elsevier B.V. The wine grape industry in south Mediterranean EuropeWorld's wine production are located in a wide geographical Q2and climatic range, often in mid-latitude regions characterized by climate variability and stressful environments, such as the Mediterranean region (Fraga et al., 2013;Lionello et al., 2014). The European Union , is the world's leader in wine production with about 50% of world's vine-growing area and about 60% of total volume of production (USDA, 2014). France, Italy, Spain, Germany and Portugal are the five leading EU wine producers and altogether they represent 90% of EU production (USDA, 2014). Spain has the largest vineyard area in the world (950,541 ha in 2014) with an increasing irrigated area (36% of the total, in 2014) (MAGRAMA, 2014) (Fig. 1). Portugal is the EU's 5th largest wine producer with a total of 6.7 Mhl in 2013 and it has a cultivated area estimated to be about 224,000 ha (IVV, 2015). In 2010, the irrigated area was estimated in 15% of the total area of vineyards (INE, 2010). However, irrigation continued expanding in the recent years in Portugal, in particular in the Alentejo region, and presently, the percentage of irrigated vines should be slightly higher and around 20%. * Corresponding author.E-mail address: miguelc@itqb.unl.pt (J.M. Costa).Mediterranean fresh water resources are under high pressure due to fast-growing population, increased water scarcity, extreme climate variability and intensive water use in agriculture, industry and tourism activities (Lange et al., 2005;Costa et al., 2007; EEA, 2012a,b; Lereboullet et al., 2013a,b;Blum, 2014). Water is now considered by EU experts as the most important but vulnerable resource in the Mediterranean region (EU-ERANETMED, 2014). In addition, climate scenarios for South Mediterranean Europe are not favourable for agriculture. The predicted lower precipitation, higher air and soil temperatures, more frequent and l...

Responses of leaf water relations and photosynthesis to summer drought and autumn rewetting were studied in two evergreen Mediterranean oak species, Quercus ilex spp. rotundifolia and Quercus suber. The predawn leaf water potential (Ψ(lPD)), stomatal conductance (gs) and photosynthetic rate (A) at ambient conditions were measured seasonally over a 3-year period. We also measured the photosynthetic response to light and to intercellular CO₂ (A/PPFD and A/C(i) response curves) under water stress (summer) and after recovery due to autumn rainfall. Photosynthetic parameters, Vc(max), J(max) and triose phosphate utilization (TPU) rate, were estimated using the Farquhar model. RuBisCo activity, leaf chlorophyll, leaf nitrogen concentration and leaf carbohydrate concentration were also measured. All measurements were performed in the spring leaves of the current year. In both species, the predawn leaf water potential, stomatal conductance and photosynthetic rate peaked in spring, progressively declined throughout the summer and recovered upon autumn rainfall. During the drought period, Q. ilex maintained a higher predawn leaf water potential and stomatal conductance than Q. suber. During this period, we found that photosynthesis was not only limited by stomatal closure, but was also downregulated as a consequence of a decrease in the maximum carboxylation rate (Vc(max)) and the light-saturated rate of photosynthetic electron transport (J(max)) in both species. The Vc(max) and J(max) increased after the first autumnal rains and this increase was related to RuBisCo activity, leaf nitrogen concentration and chlorophyll concentration. In addition, an increase in the TPU rate and in soluble leaf sugar concentration was observed in this period. The results obtained indicate a high resilience of the photosynthetic apparatus to summer drought as well as good recovery in the following autumn rains of these evergreen oak species.

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We studied morphological, biochemical and physiological leaf acclimation to incident Photon Photosynthetic-Flux-Density (PPFD) in Quercus ilex (holm oak) and Quercus suber (cork oak) at Mediterranean evergreen oak woodlands of southern Portugal. Specific leaf area (SLA) decreased exponentially with increasing PPFD in both species. Q. ilex had lower SLA values than Q. suber. Leaf nitrogen, cellulose and lignin concentration (leaf area-based) scaled positively with PPFD. Maximum rate of carboxylation (Vcmax), capacity for maximum photosynthetic electron transport (Jmax), rate of triose-P utilization (VTPU) and the rate of nonphotorespiratory light respiration (Rd) were also positively correlated with PPFD in both Quercus species, when expressed in leaf area but not on leaf mass basis. Q suber showed to have higher photosynthetic potential (Vcmax, Jmaxmm and VTPUm ) and a higher nitrogen efficient nitrogen use than Q. ilex. Leaf chlorophyll concentration increased with decreasing PPFD, improving apparent quantum use efficiency (U) in both Quercus species. We concluded that, in Q. ilex and Q. suber, leaf structural plasticity is a stronger determinant for leaf acclimation to PPFD than biochemical and physiological plasticity.