Temperature effects on photosynthesis were studied in seedlings of evergreen Mediterranean cork oak (Quercus suber L.). Responses to changes in temperature and the temperature optima of maximal carboxylation rate (V(cmax)) and maximal light-driven electron flux (J(max)) were estimated from gas exchange measurements and a leaf-level photosynthesis model. The estimated temperature optima were approximately 34 and 33 degrees C for V(cmax) and J(max), respectively, which fall within the lower range of temperature optima previously observed in deciduous tree species. The thermostability of the photosynthetic apparatus was estimated according to the temperature at which basal chlorophyll a fluorescence begins to increase (T(c)). The T(c) was highly variable, increasing from 42 to 51 degrees C when ambient temperature rose from 10 to 40 degrees C, and increasing from 44 to 54 degrees C with decreasing soil water availability while net CO(2) assimilation rate dropped to almost zero. When a heat shock was imposed, an additional small increase in T(c) was observed in drought-stressed and control seedlings. Maximal T(c) values following heat shock were about 56 degrees C, which, to our knowledge, are the highest values that have been observed in tree species. In conclusion, the intrinsic temperature responses of cork oak did not differ from those of other species (similar T(c) under ambient temperature and water availability, and relatively low thermal optima for photosynthetic capacity in seedlings grown at cool temperatures). However, the large ability of cork oak to acclimate to drought and elevated temperature may be an important factor in the tolerance of this evergreen Mediterranean species to summer drought and high temperatures.

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Vetch species (Vicia narbonensis, V. sativa and V. villosa) are widely used for fodder production in Tunisia. This study aims to investigate vetch strategies involved in drought resistance through morphological and physiological criteria. Plants were sown in pots and subjected to four soil‐water levels: 100% (control), 80, 60 and 40% of field capacity (FC). After 133 d of water treatment, and under well‐watered conditions, V. narbonensis showed the largest plant height and shoot and root dry matter and the highest leaf relative water content and water potential (Ψw), whereas V. sativa had the greatest leaf area (LA). At the 40% FC treatment, V. narbonensis showed smaller decreases in plant height and LA, and the greatest reduction in Ψw (140%). Thus, it shows better adaptation and a more equilibrated water balance, despite having accumulated less proline than the two other species. Vicia sativa and V. villosa showed a similar behaviour under water stress with a superiority of the latter. Vicia sativa was the species most affected in terms of its growth and water‐status parameters. Vetch species mainly used avoidance mechanisms to withstand drought, with V. narbonensis showing the highest tolerance.

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