SummaryIn plants with sclerophyll leaves, the response of stomatal and mesophyll conductance to CO2 to water stress and recovery is correlated with the expression of aquaporins and carbonic anhydrase.

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Regulated deficit irrigation (RDI) has been proposed as one of the most promising irrigation strategies for hedgerow fruit orchards with high plant densities. Scheduling a RDI strategy, however, is highly demanding, since the targeted water savings must be achieved at the same time that episodes of excessive water stress are avoided when the crop is most sensitive to drought. Here we tested an approach to schedule a RDI strategy supplying 45% of the crop irrigation needs, specially designed for hedgerow olive orchards. Our approach is based on the use of a water stress indicator derived from the shape of the daily curves recorded with ZIM sensors, which are related to the leaf turgor pressure. We worked in a mature, fully productive 'Arbequina' olive orchard with 1667 trees ha-1 , under both a daily irrigated (FI) treatment and the mentioned RDI strategy. We found that the relation between the shape of the curves and the tree water stress levels holds for olive trees of different age under a wide range of growing conditions. We were able to schedule irrigation just from the visual analysis of the curves derived from the ZIM outputs, without any further data processing. A comparison with the crop coefficient approach showed that, with our approach, we achieved greater water savings without affecting neither the trees water status nor the crop performance. Still, further studies are required to confirm whether empirical aspects of our approach are limiting and, if so, to derive suitable alternatives.

The control of plant transpiration by stomata under water stress and recovery conditions is of paramount importance for plant performance and survival. Although both chemical and hydraulic signals emitted within a plant are considered to play a major role in controlling stomatal dynamics, they have rarely been assessed together. The aims of this study were to evaluate (i) the dynamics of chemical and hydraulic signals at leaf, stem and root level, and (ii) their effect on the regulation of stomatal conductance (gs) during water stress and recovery. Measurements of gs, water potential, abscisic acid (ABA) content and loss of hydraulic functioning at leaf, stem and root level were conducted during a water stress and recovery period imposed on 1-year-old olive plants (Olea europaea L.). Results showed a strong hydraulic segmentation in olive plants, with higher hydraulic functioning losses in roots and leaves than in stems. The dynamics of hydraulic conductance of roots and leaves observed as water stress developed could explain both a protection of the hydraulic functionality of larger organs of the plant (i.e., branches, etc.) and a role in the down-regulation of gs. On the other hand, ABA also increased, showing a similar pattern to gs dynamics, and thus its effect on gs in response to water stress cannot be ruled out. However, neither hydraulic nor non-hydraulic factors were able to explain the delay in the full recovery of gs after soil water availability was restored.

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24 25The research on species with capacity to tolerate and accumulate zinc is of 26 paramount importance for phytoremediation purposes. An experiment was designed to 27 investigate the effect of Zn from 0 to 100 mmol l -1 on the growth, photosynthetic 28 apparatus and nutrient uptake of the halophytic species Juncus acutus. Gas exchange, 29 chlorophyll fluorescence and photosynthetic pigments concentration were measured. 30We also determined total zinc, magnesium, potassium, phosphorus and sodium 31 concentrations, as well as C/N ratio. J. acutus showed high tolerance to Zn-induced 32 stress, since all plants survived and none of them showed any toxicity symptoms, such 33 as chlorosis, necrosis or growth reduction at concentrations up to 100 mmol l -1 Zn. The 34 integrity and functionality of the photosynthetic apparatus were unaffected even at zinc 35 concentrations greater than 500 mg Kg -1 on tillers. Likewise, nutrient absorption was 36 relatively unaffected. Zn tolerance was associated with the capacity to accumulate Zn in 37 roots (with values up to 2500 mg Kg -1 41) and largely avoid its transport to tillers. These 38 characteristics, along with its ability to establish in a wide variety of ecosystems, render 39 this species a useful phytostabilizer for revegetation of Zn-contaminated lands. 40 42 43