Water consumption of wine grapevines (Vitis vinifera 'Cabernet Sauvignon') was measured during three consecutive growing seasons (2012-2014) using 6 drainage lysimeters. The lysimeters (1.5 m3 each) were installed within a two-hectare commercial vineyard in a Mediterranean region in the central mountain region of Israel. Water consumption of the lysimeter-grown vines (ETc) was measured daily and reference evapotranspiration (ETo) was calculated from regional meteorological data according to the Penman Monteith equation. Seasonal curves of crop coefficient (Kc) were calculated as Kc = ETc/ETo. Maximum ETc values (weekly average) in different seasons ranged from 7.5 to 6.64 mm day-1 and seasonal ETc (from DOY 99 through DOY 288) ranged from 746 to 780 mm over the growing seasons. Leaf area index (LAI) was measured weekly using the SunScan Canopy Analysis System. Maximum LAI ranged from 1.36 to 1.16 m2 m-2 for the 2012-2013 seasons, the seasonal LAI pattern was quite similar to control vines grown in the surrounding vineyard. A linear curve relating Kc to LAI (R2 values ranged from 0.76 to 0.85) is proposed as the basis for efficient irrigation management. Some of the differences in ETc and Kc values that were observed are different from those obtained in table grapes (Williams et al., 2003; Netzer et al., 2009) and wine grapes (Picón-Toro et al., 2012) is explained by the different canopy size and architecture.

The olive tree is generally characterized by relatively low final fruit set consequential to a significant rate of undeveloped pistils, pistil abortion, and flower and fruitlet abscission. These processes are acknowledged to be governed by competition for resources between the developing vegetative and reproductive organs. To study the role of phosphorus (P) nutritional level on reproductive development, trees were grown under four levels of P for three years in large containers. Phosphorus nutritional level was positively related to rate of reproductive bud break, inflorescence weight, rate of hermaphrodite flowers, pistil weight, fruitlet persistence, fruit set and the consequential total number of fruits. The positive impact of P nutrition on the productivity parameters was not related to carbohydrate reserves or to carbohydrate transport to the developing inflorescence. Phosphorous deficient trees showed significant impairment of assimilation rate, and yet, carbohydrates were accumulated in inflorescences at levels comparable to or higher than trees receiving high P. In contrast to female reproductive organs, pollen viability was consistently higher in P deficient trees, possibly due to the enhanced carbohydrate availability. Overall, the positive effect of P on female reproductive development was found to be independent of the total carbohydrate availability. Hence, P is speculated to have a direct influence on reproductive processes. © 2016 Erel et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

PREMISE OF THE STUDY: Yield in sweetpotato is determined by the number of storage roots produced per plant. Storage roots develop from adventitious roots (ARs) present in stem cuttings that serve as propagation material. Data on the origin of sweetpotato ARs and the effect of nodal position on AR establishment and further development are limited. METHODS: We anatomically described root primordium initiation using stem sections and measured number of root primordia formed at different nodal positions using light microscopy and correlated nodal positions with AR number and length 14 d after planting (DAP). KEY RESULTS: Primordia for ARs initiate at the junction of the stem pith ray and the cambium, on both sides of the leaf gap, and they are well developed before emerging from the stem. The number of ARs that develop from isolated stem nodes 14 DAP corresponded to the number of AR primordia detected inside the stem. The total length of established roots at nodes 9-13 from the apex is about 2-fold longer than at nodes 5-8. CONCLUSIONS: Nodal position (age) has a significant effect on the developmental status and number of root primordia inside the stem, determining the number and length of ARs that have developed by 14 DAP. Adventitious roots originating from nodes 9-13 possess similar AR systems and develop better than those originating from younger nodes 3-8. The mechanism regulating AR initiation in nodes is discussed. This system can serve for studying the effect of environmental conditions on AR initiation, development, and capacity to form storage roots. © 2015 Botanical Society of America.

During the summer, evaporative demand at midday often exceeds the transport capacity of most desert plants. However, date palms maintain their ecological dominance with sustained and uniquely high rates of transpiration. This high rate of flow cannot be attributed to soil water supply alone. In order to quantify intra-plant water allocation in irrigated date palms, three water-sensing techniques have been incorporated: heat dissipation, gravimetric sampling, and time domain reflectrometry. Each of these methods has known limitations but their integration resulted in a quantitative in vivo accounting of the date palm diurnal and seasonal water mass balance. By incorporating these methods it was possible to determine that date palms substantially rely on the exploitation and recharge of the stem reservoir in their water budget. The stem of mature date palms can hold up to 1 m3 of water and supply 25% of daily transpiration (i.e. 5000 l of water in 100 d of summer). The internal stem water reservoir is consistently recharged by over 50 l per night which allows for successive daytime reuse throughout the entire growing season. More broadly, these findings suggest that internal water allocation and night-time soil-water availability could provide useful information for improving date palm irrigation practices. © The Author 2014.

Isohydric plants maintain constant water potential through rapid stomatal closure, whereas anisohydric plants only close their stomata at very low water potentials. However, distinctions between isohydric and anisohydric behaviors among different cultivars of the same species are unclear. This study compared the physiological response to prolonged drought stress in the isohydric Grenache and the anisohydric Shiraz cultivars of the Vitis vinifera species. Plants were exposed to 60-day periods of deficit irrigation (25% of plant water consumption under well-watered conditions) during the summers of 2011 and 2012. Physiological measurements, water potential, leaf gas exchange, canopy area, leaf senescence, stem characteristics, and morphological characteristics were analyzed. Stomatal conductance was consistently lower in Grenache than in Shiraz at all values of midday stem and predawn leaf water potentials, respectively. The Shiraz plants exhibited greater vegetative growth and less defoliation than the Grenache plants in response to water deficit. Anatomical architecture analyses revealed that Grenache plants had greater xylem vessel diameter, hydraulic conductivity, and stomatal density than the Shiraz plants. These results suggest isohydric and anisohydric behaviors may be well-defined, time-regulated responses rather than distinct mechanisms that plants use to cope with drought stress. The rapid response to water deficit exhibited by isohydric plants may be because they are more vulnerable to fatal xylem embolisms than anisohydric plants. Thus, the accelerated response allows isohydric plants to avoid drought stress and minimize risk of xylem cavitation, but may lower the plant’s ability to survive moderate stress of prolonged drought. © 2015 by the American Society for Enology and Viticulture. All rights reserved.

Potassium (K) is an essential macronutrient shown to play a fundamental role in photosynthetic processes and may facilitate photoinhibition resistance. In some plant species, sodium (Na) can partially substitute for K. Although photosynthetic enhancement has been well established, the mechanisms by which K or Na affects photosynthesis are not fully understood. Olive (Olea europaea L.) trees were previously shown to benefit from Na nutrition when K is limiting. In order to study the effect of K and Na on photosynthetic performance, we measured gas exchange and chlorophyll fluorescence in young olive trees supplied with either K, Na or no fertilizer, and subjected to manipulated levels of CO2, O2 and radiation. Light and CO2 response curves indicate substantially superior photosynthetic capacity of K-sufficient trees, while Na substitution generated intermediate results. The enhanced performance of K, and to a lesser extent, Na-supplied trees was found to be related mainly to modification of non-stomatal limitation. This indicates that K deficiency promotes inhibition of enzymatic-photochemical processes. Results indicate lower chlorophyll content and altered Rubisco activity as probable causes of photosynthetic impairment. Potassium deficiency was found to diminish photoprotection mechanisms due to reduced photosynthetic and photorespiratory capacity. The lower CO2 and O2 assimilation rate in K-deficient trees caused elevated levels of exited energy. Consequently, non-photochemical quenching, an alternative energy dispersion pathway, was increased. Nonetheless, K-deficient trees were shown to suffer from photodamage to photosystem-II. Sodium replacement considerably diminished the negative effect of K deficiency on photoprotection mechanisms. The overall impact of K and Na nutrition plays down any indirect effect on stomatal limitation and rather demonstrates the centrality of these elements in photochemical processes of photosynthesis and photoprotection. © 2015 Elsevier GmbH.

The use of screenhouses in protected cultivation is nowadays a common practice in many countries. When fine mesh screens are used in the screenhouse construction, the resistance of the screens to airflow is high and ventilation rate is strongly reduced in comparison to the open field. Thus, growers tend to move to higher screenhouses since they assume that in such structures accumulation of warm and humid air near the plants is diminished. The goal of this research was to investigate, in insect-proof screenhouses, the effect of screenhouse height on air temperature. Experiments were conducted in two flat top screenhouses each of an area of 745 m2; one with a roof height of 4 m (LSH) and the other with a roof height of 6 m (HSH) with 16 m of separation between them. The houses were covered with a '50-mesh' screen which is commonly used with tomato cultivation in Israel. The daily courses of air temperature were very similar in the two houses. The average air temperature in the HSH was nearly at all times higher than in the LSH. The largest differences in temperature between the houses, of about 1°C, were observed during day; slightly lower differences were observed during night. The most significant difference between the two houses was related to the vertical gradients of temperature. The results show that the microclimate in the vertical direction appears to be more homogenous in the HSH than in the LSH.

Date palms are widely cultivated in arid Mediterranean regions and require large quantities of water to produce commercial fruit yields. In these regions the plantations are commonly irrigated with low-quality water, which results in reduced growth and yields. To study the effect of using saline water for irrigation, date palm seedlings (cv. Medjool) were subjected to long-term irrigation treatments with water containing between 2 and 105mM NaCl. The effect of saline irrigation was determined according to leaf gas exchange, chlorophyll a fluorescence, growth parameters and the distribution of key minerals in different plant organs. High salinity decreased plant growth and increased Na+ accumulation in the roots and lower stem. However, Na+ ions were mostly excluded from the sensitive photosynthetic tissues of the leaf. Thus, the reduction in the CO2 assimilation rate was primarily attributed to a reduced stomatal conductance. Consistent with this finding, the photosynthetic response to variable intercellular CO2 concentrations (A/Ci curves) revealed no permanent damage to the photosynthetic apparatus and implicated developed photoprotective mechanisms. Independent of salinity treatment, 80% of the energy absorbed by the leaf was directed to non-photochemical quenching, as presented in electron-equivalent units. Functioning at full capacity, the non-photochemical mechanism could not compensate for all the excess irradiance. Thus, of the remaining absorbed energy, a significant portion was directed to photochemical O2 related processes, rather than CO2 prevented photoinhibition. The exclusion of toxic ions and O2-dependent energy dissipation maintained photosynthetic efficiency and supported survival under salt stress. © 2013 Elsevier B.V.

Irrigation of crops in arid regions with marginal water is expanding. Due to economic and environmental issues arising from use of low-quality water, irrigation should follow the actual crop water demands. However, direct measurements of transpiration are scant, and indirect methods are commonly applied; e.g., the Penman-Monteith (PM) equation that integrates physiological and meteorological parameters. In this study, the effects of environmental conditions on canopy resistance and water loss were experimentally characterized, and a model to calculate palm tree evapotranspiration ETc was developed. A novel addition was to integrate water salinity into the model, thus accounting for irrigation water quality as an additional factor. Palm tree ETc was affected by irrigation water salinity, and maximum values were reduced by 25 % in plants irrigated with 4 dS m-1 and by 50 % in the trees irrigated with 8 dS m-1. Results relating the responses of stomata to the environment exhibited an exponential relation between increased light intensities and stomatal conductance, a surprising positive response of stomata to high vapor pressure deficits and a decrease in conductance as water salinity increased. These findings were integrated into a modified 'Jarvis-PM' canopy conductance model using only meteorological and water quality inputs. The new approach produced weekly irrigation recommendations based on field water salinity (2.8 dS m-1) and climatic forecasts that led to a 20 % decrease in irrigation water use when compared with current irrigation recommendations. © 2014 Springer-Verlag Berlin Heidelberg.

Potassium (K) is a macro-nutrient understood to play a role in the physiological performance of plants under drought. In some plant species, sodium (Na) can partially substitute K. Although a beneficial role of Na is well established, information regarding its nutritional role in trees is scant and its function under conditions of drought is not fully understood. The objective of the present study was to evaluate the role of K and its possible replacement by Na in olive's (Olea europaea L.) response to drought. Young and bearing olive trees were grown in soilless culture and exposed to gradual drought. In the presence of Na, trees were tolerant of extremely low K concentrations. Depletion of K and Na resulted in ∼50% reduction in CO2 assimilation rate when compared with sufficiently fertilized control plants. Sodium was able to replace K and recover the assimilation rate to nearly optimum level. The inhibitory effect of K deficiency on photosynthesis was more pronounced under high stomatal conductance. Potassium was not found to facilitate drought tolerance mechanisms in olives. Moreover, stomatal control machinery was not significantly impaired by K deficiency, regardless of water availability. Under drought, leaf water potential was affected by K and Na. High environmental K and Na increased leaf starch content and affected the soluble carbohydrate profile in a similar manner. These results identify olive as a species capable of partly replacing K by Na. The nutritional effect of K and Na was shown to be independent of plant water status. The beneficial effect of Na on photosynthesis and carbohydrates under insufficient K indicates a positive role of Na in metabolism and photosynthetic reactions. © The Author 2014. Published by Oxford University Press. All rights reserved.

The effect of using treated wastewater for irrigation of table grapes (Vitis vinifera cv. Superior Seedless) was studied for six seasons. The experimental vineyard was grown on clay loam soil in a semi-arid area. Treated wastewater (5.83 meq L-1 Na+) with (TWW + F) and without (TWW) fertilizer, and fresh water with fertilizer (FW + F, 2.97 meq L-1 Na+), were each applied at three irrigation levels (80, 60 and 40 % of crop evapotranspiration before harvest). Root zone (0-60 cm soil depth) soil saturated paste extract Na+ concentrations and sodium adsorption ratio (SAR) values fluctuated over the years, but generally decreased in the order TWW > TWW + F > FW + F for each irrigation level. Both Na+ concentrations and SAR values developed faster and to a greater extent at higher irrigation. Adding fertilizer to TWW decreased Na+ and SAR only at the high irrigation level. Na+ concentrations in the trunk wood, bark and xylem sap of the TWW and TWW + F irrigated vines were significantly higher than those in the FW + F-irrigated vines. Leaf petiole Na+ content increased with time and its maximum value in TWW and TWW + F irrigated vines exceeded 6,500 mg kg-1, threefold higher than in FW + F irrigated vines. We conclude that in clay soils under relatively high irrigation, Na+ may pose a greater potential risk to plants and soil rather than Cl- or salinity per se. However, significant effects on yield were not recorded during this six-year study probably due to the high salinity tolerance of the 'Paulsen' rootstock used in the experiment. © 2014 Springer-Verlag Berlin Heidelberg.