Long-term acclimation to drought, salinity and temperature in the thermophilic tree Ziziphus spina-christi: Revealing different tradeoffs between mesophyll and stomatal conductance
. Tree Physiology 2019
, 701-716. Publisher's VersionAbstract
Photosynthesis is limited by three main factors: stomatal conductance (gs), mesophyll conductance (gm) and maximum capacity for Rubisco carboxylation (Vcmax). It is unclear how limiting factors vary under stress, particularly during long-term stress acclimation. In this work, we compared for the first time photosynthesis limitation resulting from long-term acclimation to three major abiotic stresses: drought, salinity and temperature. We used saplings of Ziziphus spina-christi, a thermophilic and drought-tolerant tree, which recently became more abundant in the Mediterranean, presumably due to increased winter temperatures. Stress acclimation was investigated by measuring growth, gas exchange, chlorophyll fluorescence and leaf structure. For each stress, photosynthesis-limiting factors were compared. We developed an integrative stress index that allowed us to precisely define stress level, enabling a comparison between stress types. Photosynthesis under all stresses was limited mostly by gs and gm (80–90%); whereas biochemistry (Vcmax) made a minor contribution (10–20%). The relative contribution of gs and gm on photosynthetic limitation was influenced by stress type. During acclimation to drought or salinity, photosynthesis was limited by a decline in gs, while intolerance to low temperatures was driven by decline in gm. In all the stresses, gm decreased only under progressive reduction in leaf physiological functionality and was associated with low turgor under drought, an increase in leaf Na+ under salinity and low leaf hydraulic conductance (Kleaf) at low temperatures. Mesophyll structure (mesophyll surface area exposed to the intercellular air spaces, leaf thickness, % intercellular air spaces) did not explain gm acclimation to stress. Current work gives methodology for stress studies, and defines the main factors underlying the plant response to climate change. The ability to minimize mesophyll-imposed limitations on photosynthesis was found as a strong indicator of progressive stress tolerance. Moreover, the results demonstrate how warming climate benefits the photosynthetic function in thermophilic species, such as Ziziphus spina-christi. © The Author(s) 2018.
Quantification of leaf-scale light energy allocation and photoprotection processes in a Mediterranean pine forest under extensive seasonal drought
. Tree Physiology 2019
, 1767-1782. Publisher's VersionAbstract
Photoprotection strategies in a Pinus halepensis Mill. forest at the dry timberline that shows sustained photosynthetic activity during 6-7 month summer drought were characterized and quantified under field conditions. Measurements of chlorophyll fluorescence, leaf-level gas exchange and pigment concentrations were made in both control and summer-irrigated plots, providing the opportunity to separate the effects of atmospheric from soil water stress on the photoprotection responses. The proportion of light energy incident on the leaf surface ultimately being used for carbon assimilation was 18% under stress-free conditions (irrigated, winter), declining to 4% under maximal stress (control, summer). Allocation of absorbed light energy to photochemistry decreased from 25 to 15% (control) and from 50% to 30% (irrigated) between winter and summer, highlighting the important role of pigment-mediated energy dissipation processes. Photorespiration or other non-assimilatory electron flow accounted for 15-20% and 10% of incident light energy during periods of high and low carbon fixation, respectively, representing a proportional increase in photochemical energy going to photorespiration in summer but a decrease in the absolute amount of photorespiratory CO loss. Resilience of the leaf photochemical apparatus was expressed in the complete recovery of photosystem II (PSII) efficiency (φPSII) and relaxation of the xanthophyll de-epoxidation state on the diurnal cycle throughout the year, and no seasonal decrease in pre-dawn maximal PSII efficiency (Fv/Fm). The response of CO assimilation and photoprotection strategies to stomatal conductance and leaf water potential appeared independent of whether stress was due to atmospheric or soil water deficits across seasons and treatments. The range of protection characteristics identified provides insights into the relatively high carbon economy under these dry conditions, conditions that are predicted for extended areas in the Mediterranean and other regions due to global climate change. © 2019 The Author(s). Published by Oxford University Press. All rights reserved.
Structural memory in grapevines: Early season water availability affects late season drought stress severity
. European Journal of Agronomy 2019
, 96-103. Publisher's VersionAbstract
In the future drought events are expected to occur more frequently, with unpredictable rain and heat events. In current research we investigated how different water availability patterns influenced late season plant water status in Vitis vinifera. ‘Cabernet Sauvignon’ grapevines were grown for three consecutive years. We compared the response to five water availability regimes: High, Intermediate, Low (along all season) and High-to-Low (High during the beginning of vegetative seasons switched to low during the rest of season) and Low-to-High (opposite treatment). Midday stem water potential (SWP) was measured weekly to determine the seasonal pattern of drought stress. Xylem anatomy was investigated by trunk vessel diameter measurements, and specific axial xylem conductivity was calculated according to Hagen-Poiseuille's law. Vines exposed to high water availability treatment showed improved seasonal water status along the season, compared to vines in the low treatment. Vines exposed to High-to-Low water regime showed a markedly improved water status at the beginning of the season, but became the most severely stressed toward the end of season. The SWP values were more negative in the High-to-Low regime even when compared to the Low water regime. Water availability at the beginning of the season (during main period of cambial activity) determined the vessel characteristics: high water availability during cambial activity increased vessel diameter and thus specific hydraulic conductivity. Our data strongly indicates that regulated drought stress can be induced by manipulating xylem structural parameters via controlling water availability during the period of stem cambial activity. © 2019 Elsevier B.V.
Water consumption, crop coefficient and leaf area relations of a Vitis vinifera cv. 'Cabernet Sauvignon' vineyard
. Agricultural Water Management 2019
, 86-94. Publisher's VersionAbstract
Most cultivated vineyards worldwide are located in semi-arid and arid regions with a limited water supply. Skilled vineyard water management is considered the main tool for controlling vegetative growth and grape quality and for ensuring vineyard sustainability. Imposing an appropriate drought stress at a suitable phenological stage can improve wine quality with almost no yield reduction. A comprehensive irrigation model enabling precise vineyard irrigation should be based on changes in vine water consumption as a function of climate conditions and canopy area. In 2011, six drainage lysimeters were constructed within a commercial 'Cabernet Sauvignon' vineyard located in the central mountains of Israel. Data were collected during six successive years from 2012 – 2017. The daily vine water consumption, ETc (L day−1), was calculated by subtracting the amount of collected drainage (over a 24 h period) from the amount of applied irrigation during the same time period. Seasonal water consumption (ETc) was 715 mm season−1 on average, while seasonal calculated reference evapotranspiration (ETo) was 1237 mm season−1 on average. Maximal crop coefficient (Kc) was 0.8 – 0.9, meaning that actual water consumption was lower than the calculated reference evapotranspiration. Maximal leaf area index (LAI) was 0.9 to 1.7 m2 m-2. The multi-seasonal linear correlation between LAI and Kc was strongly positive and significant. The robust multiyear relationship between LAI & Kc proves that measuring canopy area of wine grapevines is a reliable approach for estimating their Kc. The LAI to Kc relationship that we have established can be used as a basis for developing a comprehensive irrigation model for wine grapevines that integrates both climatic conditions and canopy area. © 2019 Elsevier B.V.
The effect of irrigation level in the kernel dry matter accumulation period on almond yield, kernel dry weight, fruit count, and canopy size
. Irrigation Science 2018
. Publisher's VersionAbstract
The effect of irrigation regime in the kernel filling stage of almond was examined in a field experiment. The experiment was conducted on 9-year-old local variety (Um-El-Fahem) grafted on GF677 rootstock in Israel. Five irrigation treatments were applied during the main kernel dry matter accumulation. Irrigation rates in June varied from 1 to 8 mm/day and midday stem water potentials varied from −2.6 to −1.3 MPa. Seasonal irrigation varied from 394 to 801 mm. Kernel yield increased in the high irrigation treatments in the first four seasons where it decreased in the three lower irrigation treatments. Similarly, the four-season trunk cross-sectional area accumulation increased with increasing irrigation. Kernel yield increased with both midday stem water potential and irrigation rate. Kernel dry weight decreased with increasing fruit count where higher kernel weights were found in the higher irrigation treatments at similar fruit count. Kernel relative growth rates of all treatments were similar along the dry matter accumulation stage except for around 1 June where the lowest irrigation rate had significantly lower growth rate. Spurs survival analysis showed that the number of fruits per spur, fruiting spurs, and alive spurs increased with increasing irrigation. © 2017, Springer-Verlag GmbH Germany.
Water availability dynamics have long-term effects on mature stem structure in Vitis vinifera
. American Journal of Botany 2018
, 1443-1452. Publisher's VersionAbstract
Premise of the Study: The stem of Vitis vinifera, a climbing vine of global economic importance, is characterized by both wide and narrow vessels and high specific hydraulic conductivity. While the effect of drought stress has been studied in 1- and 2-yr-old stems, there are few data documenting effects of drought stress on the anatomical structure of the mature, woody stem near the base of the vine. Here we describe mature wood anatomical responses to two irrigation regimes on wood anatomy and specific hydraulic conductivity in Vitis vinifera Merlot vines. Methods: For 4 years, irrigation was applied constantly at low, medium, or high levels, or at alternating levels at two different periods during the growing season, either early spring or late summer, resulting in late season or early spring deficits, respectively. The following variables were measured: trunk diameter, annual ring width and area, vessel diameter, specific hydraulic conductivity and stem water potential. Key Results: High water availability early in the season (late deficit) resulted in vigorous vegetative growth (greater trunk diameter, ring width and area), wider vessels and increased specific hydraulic conductivity. High water availability early in the season caused a shift of the vessel population towards the wider frequency classes. These late deficit vines showed more negative water potential values late in the season than vines that received low but relatively constant irrigation. Conclusions: We concluded that high water availability during vegetative growth period of Vitis increases vessels diameter and hydraulic conductivity and causes the vines to be more vulnerable to drought stress late in the season. © 2018 Botanical Society of America
Long-term acclimation to drought, salinity and temperature in the thermophilic tree Ziziphus spina-christi: revealing different tradeoffs between mesophyll and stomatal conductance. Tree Physiol 2018
Photosynthesis is limited by three main factors: stomatal conductance (gs), mesophyll conductance (gm) and maximum capacity for Rubisco carboxylation (Vcmax). It is unclear how limiting factors vary under stress, particularly during long-term stress acclimation. In this work, we compared for the first time photosynthesis limitation resulting from long-term acclimation to three major abiotic stresses: drought, salinity and temperature. We used saplings of Ziziphus spina-christi, a thermophilic and drought-tolerant tree, which recently became more abundant in the Mediterranean, presumably due to increased winter temperatures. Stress acclimation was investigated by measuring growth, gas exchange, chlorophyll fluorescence and leaf structure. For each stress, photosynthesis-limiting factors were compared. We developed an integrative stress index that allowed us to precisely define stress level, enabling a comparison between stress types. Photosynthesis under all stresses was limited mostly by gs and gm (80-90%); whereas biochemistry (Vcmax) made a minor contribution (10-20%). The relative contribution of gs and gm on photosynthetic limitation was influenced by stress type. During acclimation to drought or salinity, photosynthesis was limited by a decline in gs, while intolerance to low temperatures was driven by decline in gm. In all the stresses, gm decreased only under progressive reduction in leaf physiological functionality and was associated with low turgor under drought, an increase in leaf Na+ under salinity and low leaf hydraulic conductance (Kleaf) at low temperatures. Mesophyll structure (mesophyll surface area exposed to the intercellular air spaces, leaf thickness, % intercellular air spaces) did not explain gm acclimation to stress. Current work gives methodology for stress studies, and defines the main factors underlying the plant response to climate change. The ability to minimize mesophyll-imposed limitations on photosynthesis was found as a strong indicator of progressive stress tolerance. Moreover, the results demonstrate how warming climate benefits the photosynthetic function in thermophilic species, such as Ziziphus spina-christi.
The effect of blue light on stomatal oscillations and leaf turgor pressure in banana leaves
. Plant Cell and Environment 2017
, 1143-1152. Publisher's VersionAbstract
Stomatal oscillations are cyclic opening and closing of stomata, presumed to initiate from hydraulic mismatch between leaf water supply and transpiration rate. To test this assumption, mismatches between water supply and transpiration were induced using manipulations of vapour pressure deficit (VPD) and light spectrum in banana (Musa acuminata). Simultaneous measurements of gas exchange with changes in leaf turgor pressure were used to describe the hydraulic mismatches. An increase of VPD above a certain threshold caused stomatal oscillations with variable amplitudes. Oscillations in leaf turgor pressure were synchronized with stomatal oscillations and balanced only when transpiration equaled water supply. Surprisingly, changing the light spectrum from red and blue to red alone at constant VPD also induced stomatal oscillations – while the addition of blue (10%) to red light only ended oscillations. Blue light is known to induce stomatal opening and thus should increase the hydraulic mismatch, reduce the VPD threshold for oscillations and increase the oscillation amplitude. Unexpectedly, blue light reduced oscillation amplitude, increased VPD threshold and reduced turgor pressure loss. These results suggest that additionally, to the known effect of blue light on the hydroactive opening response of stomata, it can also effect stomatal movement by increased xylem–epidermis water supply. © 2017 John Wiley & Sons Ltd
From structural constraints to hydraulic function in three Vitis rootstocks
. Trees - Structure and Function 2017
, 851-861. Publisher's VersionAbstract
Key message: Narrow stem size in limitingVitisrootstocks imposes a morphological constraint on the scion via reduced annual ring size, and thus reduces hydraulic conductivity and subsequently physiological performance and yield. Abstract: Graft is a union between two separate species or cultivars, which produces a chimera plant with new qualities—as rootstock affects scion growth, yield, and adaptability to different environmental conditions. In Vitis, it is possible to generate rootstock/scion combinations that produce a desired drought stress effect crucial for high-quality wine production, though the mechanisms for such interactions are complex and poorly understood. The current study was done on vines with an identical scion (Vitis vinifera ‘Cabernet Sauvignon’) grafted on three different rootstocks—either Riparia Gloire, Paulsen 1103 or 420A—in attempt to explain the differences in water status by examining the underlying anatomical constraints and calculated theoretical hydraulic conductivity. There was a significant difference in physiological responses and yield between the grafts. Riparia Gloire grafts had the lowest water potentials and the highest quality grapes, together with low root, scion stem, and branch theoretical hydraulic conductivity. In scions grafted on Riparia Gloire, the annual growth rings were significantly narrower than in the other two grafts, causing a significantly lower theoretical hydraulic conductivity per annual ring. The narrow annual ring size in scion stem was imposed by the morphological constraint of the stem size. In hydraulically inferior Riparia Gloire grafts, the difference was disproportionally large, with a wide scion grafted on a very narrow rootstock, and Paulsen 1103 had the smoothest graft union. Our results indicate that the ability to develop stronger drought stress in Vitis grafts depends on rootstock-imposed morphological restriction of hydraulic conductivity. © 2016, Springer-Verlag Berlin Heidelberg.
Insights from "the Hidden Half": The impact of root-zone oxygen and redox dynamics on the response of avocado to long-term irrigation with treated wastewater in clayey soil
. Israel Journal of Plant Sciences 2017
, 92-109. Publisher's VersionAbstract
Treated wastewater (TWW) is a major source of water for agriculture in Israel; however, recent reports indicate a marked yield loss in TWW-irrigated avocado and citrus orchards planted in clayey soils. The association of the yield loss with clayey soils rather than sandy soils suggests that it is associated with conditions in the root zone, and specifically poor aeration. A three-year study (2012-2015) was conducted in an avocado orchard planted in clayey soil, comparing the oxygen and redox conditions in the root zone of TWW-irrigated plots with fresh water (FW)-irrigated plots, together with the physiological status of the trees. Soil parameters included: continuous in-situ measurement of soil-water tension (SWT), soil oxygen, and soil redox potential, and periodic measurements of soil solution composition. Physiological parameters included: mineral composition of plant tissue from the leaves, trunk xylem and roots, root growth, yield, fruit setting, plant volume, and yield. TWW-irrigated plots were found to endure longer periods of low SWT indicating higher water content, accompanied by lower oxygen levels and more reduced conditions in comparison to FW-irrigated plots. The differences in these soil parameters between treatments were greater during the irrigation season than during the rainy period. The more reduced conditions in the TWW plots did not lead to significant differences in Fe or Mn concentrations in the soil solution or in plant leaves. TWW soil solution had significantly higher Na levels compared with FW. This did not affect the leaf Na content, but was expressed in substantially higher Na content in the root and trunk xylem, with up to seven times more trunk xylem Na in TWW-irrigated plants compared with FW-irrigated plants. Root growth was significantly hindered in TWW-irrigated plots compared with FW-irrigated plots. A negative correlation was found between root growth and the duration of hypoxic conditions, and similarly between root growth and the Na levels in the roots. TWW-irrigated plants had greater fruitlet numbers at the initial fruit-setting stage, but had a smaller number of fruit and a lower yield at harvest. The yield (kg/tree) negatively correlated with the duration of hypoxic conditions in the root zone but not with the Na levels in the roots or xylem. Our findings point towards a substantial role of oxygen deprivation as a major factor leading to the damage to TWW-irrigated orchards in clayey soils. Based on the assimilation of data, we suggest that a downward cascade is instigated in the TWW-irrigated orchards by increased input of Na into the soil, leading to degradation of soil hydraulic properties and reduced aeration. Impaired physiological functioning of the roots due to limited oxygen supply results in less roots growth, lower water uptake and impaired selectivity against Na uptake, thus imposing a negative feedback to increase soil water content, reduce aeration and root-zone oxygen availability for the roots, and further impair plant resistance to the high Na levels. © 2017 by Koninklijke Brill NV, Leiden, The Netherlands.
Optimization of calcium and magnesium concentrations for fertigation of tomato with desalinated water
. Israel Journal of Plant Sciences 2017
, 80-91. Publisher's VersionAbstract
Desalinated water has become a legitimate alternative water resource for the irrigation of intensive crops in semiarid regions. The concentrations of calcium (Ca) and magnesium (Mg) in water (CCa and CMg, respectively) supplied from desalinated plants are much lower than the values typically found in irrigation water resources in semiarid regions. blossom-end rot (BER), a physiological disorder at the blossom-end part of the fruit resulting in tissue disintegration and dehydration, is considered a Ca-related disorder and therefore the optimization of CCa has to consider not only total fruit production but also the occurrence of BER. There is a lack of information regarding the optimal CCa and CMg and Ca/Mg ratio in low-salinity water under Mediterranean conditions for high-quality yield of tomato fruits.The main objective of the research was to optimize CCa and CMg for the production of high tomato fruit yield with minimal occurrence of BER. A secondary objective was to determine critical levels of Ca, Mg and Ca/Mg ratio in leaves in relation to yield and the occurrence of BER.Tomato plants were grown in an inert media and fed with a wide range of CCa and CMg. Fruit yield was shown to decrease significantly when CCa was at or below 0.40 mmol l-1. In moderate CMg (1.4 mmol l-1) treatment, BER was negatively correlated to Ca level up to and including 1.4 mmol l-1 and was not manifested above that level under the prevailing conditions. Elevating CMg above 0.25 mmol l-1 enhanced BER occurrence. Concentrations of Ca and Mg in tomato organs increased with the respective mineral concentration in irrigation solution, whereas each element was reduced in organs as a function of the increased solution concentration of the other. The Ca concentration in diagnostic leaves (the diagnostic leaf is the fully developed youngest leaf) for optimal fruit yield with minimum BER was found to be 1.6%. The optimum CCa for high fruit yield with minimal BER occurrence was found to be in the range of 1.5-2.5 mmol l-1 combined with CMg at 0.25 mmol l-1. © 2017 by Koninklijke Brill NV, Leiden, The Netherlands.
Stomatal cell wall composition: Distinctive structural patterns associated with different phylogenetic groups
. Annals of Botany 2017
, 1021-1033. Publisher's VersionAbstract
Background and Aims Stomatal morphology and function have remained largely conserved throughout ∼400 million years of plant evolution. However, plant cell wall composition has evolved and changed. Here stomatal cell wall composition was investigated in different vascular plant groups in attempt to understand their possible effect on stomatal function. Methods A renewed look at stomatal cell walls was attempted utilizing digitalized polar microscopy, confocal microscopy, histology and a numerical finite-elements simulation. The six species of vascular plants chosen for this study cover a broad structural, ecophysiological and evolutionary spectrum: ferns (Asplenium nidus and Platycerium bifurcatum) and angiosperms (Arabidopsis thaliana and Commelina erecta) with kidney-shaped stomata, and grasses (angiosperms, family Poaceae) with dumbbell-shaped stomata (Sorghum bicolor and Triticum aestivum). Key Results Three distinct patterns of cellulose crystallinity in stomatal cell walls were observed: Type I (kidney-shaped stomata, ferns), Type II (kidney-shaped stomata, angiosperms) and Type III (dumbbell-shaped stomata, grasses). The different stomatal cell wall attributes investigated (cellulose crystallinity, pectins, lignin, phenolics) exhibited taxon-specific patterns, with reciprocal substitution of structural elements in the end-walls of kidneyshaped stomata. According to a numerical bio-mechanical model, the end walls of kidney-shaped stomata develop the highest stresses during opening. Conclusions The data presented demonstrate for the first time the existence of distinct spatial patterns of varying cellulose crystallinity in guard cell walls. It is also highly intriguing that in angiosperms crystalline cellulose appears to have replaced lignin that occurs in the stomatal end-walls of ferns serving a similar wall strengthening function. Such taxon-specific spatial patterns of cell wall components could imply different biomechanical functions, which in turn could be a consequence of differences in environmental selection along the course of plant evolution. © The Author 2017.
Sustained and regulated deficit irrigation of field-grown Merlot grapevines
. Australian Journal of Grape and Wine Research 2017
, 87-94. Publisher's VersionAbstract
Background and Aims: The aim of this research was to examine the effect of sustained and regulated deficit irrigation regimes on vegetative growth, physiological aspects and yield parameters of field-grown Merlot grapevines. Methods and Results: The 4-year trial (2009–2012) in a 13-year-old commercial vineyard of Vitis vinifera cv. Merlot compared the following irrigation treatments: three sustained deficit irrigation treatments and two regulated deficit irrigation treatments. We measured leaf area index and pruning mass to assess vegetative growth, and we recorded stem water potential and gas exchange parameters to examine vine water status. At harvest, we measured yield parameters, crushed berries and analysed must. High water availability during early berry development enhanced vegetative growth and increased berry size and yield. Reducing water supply in order to create a certain level of drought stress during late berry development did not damage yield or berry maturation. Conclusions: Regulated deficit irrigation treatment combining higher irrigation from flowering to bunch closure and lower irrigation from bunch closure to harvest has the potential to generate the best balance between vegetative growth, high yield and wine with enhanced colour and aroma compounds. Significance of the Study: This study demonstrates the implications of skilled irrigation, in particular the specific effect of irrigation alternation at different phenological stages. © 2016 Australian Society of Viticulture and Oenology Inc.
Stomatal cell wall composition: distinctive structural patterns associated with different phylogenetic groups. Ann Bot 2017
Background and Aims: Stomatal morphology and function have remained largely conserved throughout ∼400 million years of plant evolution. However, plant cell wall composition has evolved and changed. Here stomatal cell wall composition was investigated in different vascular plant groups in attempt to understand their possible effect on stomatal function.
Methods: A renewed look at stomatal cell walls was attempted utilizing digitalized polar microscopy, confocal microscopy, histology and a numerical finite-elements simulation. The six species of vascular plants chosen for this study cover a broad structural, ecophysiological and evolutionary spectrum: ferns ( Asplenium nidus and Platycerium bifurcatum ) and angiosperms ( Arabidopsis thaliana and Commelina erecta ) with kidney-shaped stomata, and grasses (angiosperms, family Poaceae) with dumbbell-shaped stomata ( Sorghum bicolor and Triticum aestivum ).
Key Results: Three distinct patterns of cellulose crystallinity in stomatal cell walls were observed: Type I (kidney-shaped stomata, ferns), Type II (kidney-shaped stomata, angiosperms) and Type III (dumbbell-shaped stomata, grasses). The different stomatal cell wall attributes investigated (cellulose crystallinity, pectins, lignin, phenolics) exhibited taxon-specific patterns, with reciprocal substitution of structural elements in the end-walls of kidney-shaped stomata. According to a numerical bio-mechanical model, the end walls of kidney-shaped stomata develop the highest stresses during opening.
Conclusions: The data presented demonstrate for the first time the existence of distinct spatial patterns of varying cellulose crystallinity in guard cell walls. It is also highly intriguing that in angiosperms crystalline cellulose appears to have replaced lignin that occurs in the stomatal end-walls of ferns serving a similar wall strengthening function. Such taxon-specific spatial patterns of cell wall components could imply different biomechanical functions, which in turn could be a consequence of differences in environmental selection along the course of plant evolution.
Evaluation of seasonal water use and crop coefficients for 'Cabernet Sauvignon' grapevines as the base for skilled regulated deficit irrigation
. Acta Horticulturae 2016
, 33-39. Publisher's VersionAbstract
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.
Phosphorous nutritional level, carbohydrate reserves and flower quality in olives
. PLoS ONE 2016
. Publisher's VersionAbstract
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.
Adventitious root primordia formation and development in stem nodes of ‘Georgia jet’ sweetpotato, Ipomoea batatas
. American Journal of Botany 2015
, 1040-1049. Publisher's VersionAbstract
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.
Direct in vivo evidence of immense stem water exploitation in irrigated date palms
. Journal of Experimental Botany 2015
, 333-338. Publisher's VersionAbstract
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.
Grapevine anatomy as a possible determinant of isohydric or anisohydric behavior
. American Journal of Enology and Viticulture 2015
, 340-347. Publisher's VersionAbstract
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.