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Information about the availability of soil mineral nitrogen (N) in organic greenhouse tomatoes after the application of mobile green manure (MGM), and its impact on plant nutrient status and yield is scarce. Considering this knowledge gap, the effects of legume biomass from faba beans that are cultivated outdoors (FAB), or from feed-grade alfalfa pellets at two different doses (AAL = 330 g m−2, AAH = 660 g m−2) that were applied as MGM on the nutrition and yield of an organic greenhouse crop of tomatoes were evaluated. All of the MGM treatments increased the mineral N concentrations in the soil throughout the cropping period, and the total N concentration in tomato leaves when compared to the untreated control. FAB and AAH treatments had a stronger impact than AAL in all of the measured parameters. In addition, AAL, AAH, and FAB treatments increased the yield compared to the control by 19%, 33%, and 36%, respectively. The application of MGM, either as faba bean fresh biomass or as alfalfa dry pellets, in organic greenhouse tomatoes significantly increased the plant available soil N, improved N nutrition, and enhanced the fruit yield. However, the N mineralization rates after the MGM application were excessive during the initial cropping stages, followed by a marked decrease thereafter. This may impose an N deficiency during the late cropping period.

In this study, we investigated the impact of phosphorus (P) supply levels (0.8, 1.3 and 1.8 mM) in two green leaf lettuce (Lactuca sativa L.) types, namely ‘Romaine’ (cv. Nader), and ‘Lollo’ (cv. Bionda) grown in a recirculating nutrient solution. The biomass yield of the Romaine type was reduced by 15% at the lowest P supply (0.8 mM) and plants showed reduced photosynthetic function (i.e., net photosynthesis, stomatal conductance, quantum yield and electron flow) and increased root/shoot ratio. On the other hand, the Lollo type maintained photosynthetic rates and biomass accumulation in all cases and proved less sensitive to low P levels in the NS. At the lowest P supply, the P concentration in the recirculating solution declined to 0.1 mM and showed a decline in leaf P and Ca concentrations and an increase in total sugar and nitrate content, depending on the cultivar. Also, lowering P supply boosted P-use efficiency (kg biomass kg−1 P supply) in both types of lettuce. Nutrient to water uptake ratios of macro nutrients N, P, K, Ca and Mg were determined as follows: (i) 16.0, 1.3, 9.1, 3.1 and 0.9 mmol L−1, respectively for Romaine, and (ii) 16.4, 1.3, 9.1, 3.3 and 0.9 mmol L−1, respectively for Lollo. The current experimental results suggest that, reducing the P supply to lower levels than those currently recommended for lettuce crops grown in closed hydroponics considerably improves the P use efficiency in Mediterranean greenhouses without compromising yield.

Background The use of water containing calcium bicarbonate (Ca(HCO3 )2 ) at excessively high concentrations in closed hydroponic crops can cause calcium ion (Ca2+ ) accumulation in the recycled nutrient solution (NS) and concomitantly negatively affect yield and product quality. The aim of the study was to determine maximum Ca2+ concentrations that do not harm the crop and to simulate the pattern of Ca2+ accumulation when the Ca2+ concentration in the irrigation water, and concomitantly in the replenishment nutrient solution (RNS), is excessive. In the current study, irrigation water containing 1.5, 3.0, 4.5 and 6.0 mmol L-1 Ca2+ was used to prepare the RNS supplied to pepper cultivated in a closed hydroponic system. Results At 1.5 mmol L-1 Ca2+ , no Ca2+ accumulation was observed in the recirculating NS. However, at 3.0, 4.5 and 6.0 mmol L-1 in the irrigation water, the Ca2+ concentration in the recirculating NS, increased by the latter cropping stages to 17, 28 and 37 mmol L-1 , corresponding to 6.4, 9.0 and 10.8 dS m-1 . The accumulation of Ca2+ in the recirculating NS affected both tissue nutrient concentrations and uptake concentrations of Ca2+ , sulphate ion (SO4 2- ) and magnesium ion (Mg2+ ), but this was not the case for nitrogen (N) or potassium ion (K+ ). Growth, yield and plant water uptake were restricted at moderate (3.0 and 4.5 mmol L-1 ) and high (6.0 mmol L-1 ) external Ca2+ levels. Conclusion In soilless pepper crops with zero discharge of fertigation effluents, the Ca2+ concentration in the irrigation water and the RNS should be lower than 3.0 mmol L-1 to avoid yield restrictions due to salinity. © 2021 Society of Chemical Industry.

Cichorium spinosum L. is considered a health-promoting vegetable that has been recently introduced in cultivation, and thus information on the responses of its different ecotypes to N supply level and source is largely fragmented. To cover this gap of knowledge, seeds of two different local ecotypes of C. spinosum L. originating from a coastal and a montane habitat of the island of Crete were propagated, and the obtained seedlings were grown hydroponically. The supplied nutrient solution differed in the total-N level (4 or 16 mmol L&ndash, 1) and N source (NH4-N/-N/total-N: 0.05, 0.25, or 0.50). The impact of N supply level and N source ratio on the metabolism of the two ecotypes was assessed by gas chromatography&ndash, electron impact&ndash, mass spectrometry (GC/EI/MS) metabolomics combined with bioinformatics analyses. A general disturbance of the plants&rsquo, metabolism was recorded, with results revealing that the genotypic composition was the predominant factor for the observed discriminations. The montane ecotype exhibited substantially lower levels of metabolites such as fructose and &alpha, &alpha, trehalose, and higher levels of glucose, myo-inositol, and fatty acids compared to the coastal ecotype when both were treated with low N. Carboxylic acids and metabolites of the tricarboxylic acid cycle (TCA) were also substantially affected by the N supply level and the NH4-N/total-N ratio. The obtained information could be further exploited in the breeding of cultivars with improved nutritional value and resilience to variations in N supply levels and sources.

In this study, we investigated the effect of individual and combined applications of manganese (Mn) and zinc (Zn) chelates on common bean grown in hydroponics (nutrient film technique&mdash, NFT) on physiological and agronomical responses. Inorganic sulphate forms of Mn and Zn were compared to their synthetic chelate forms, in the replenishment nutrient solution (RNS). Nutrient (N, P, K, Ca, Mg, Fe, Mn, Zn and Cu) to water uptake ratios (termed uptake concentrations, UCs), growth, pods yield and quality, photosynthetic parameters and tissue nutrient status were evaluated in different cropping seasons (spring-summer and autumn-winter crops). Mean UCs of nutrients ranged as follows: 10.1&ndash, 12.4 (N), 0.8&ndash, 1.0 (P), 5.2&ndash, 5.6 (K), 1.8&ndash, 2.2 (Ca), 0.9&ndash, 1.0 (Mg) mmol L&minus, 1, 12.2&ndash, 13.4 (Fe), 5.2&ndash, 5.6 (Mn), 4.4&ndash, 4.9 (Zn), 0.9&ndash, 1.0 (Cu) &mu, mol L&minus, 1. Tissue macronutrient status remained unaffected in both seasons, however, Mn chelates in the RNS affected Fe within plants. Pod yield and quality, growth, photosynthesis and water uptake did not differ among treatments, however, seasonal variations are presented. Results suggest that the chelate forms of Mn and/or Zn in the refill solution for NFT-grown beans do not lead to any changes, adding superiority in the yield, photosynthesis, and nutritional status of the crops compared to their mineral forms.

One of the strategies that contributes to more sustainable crop production in greenhouses is the reduction of nitrogen input without compromising yield. In legume crops, this goal can be achieved by using efficient rhizobial strains capable of biologically fixing atmospheric nitrogen to inoculate the seeds or the young seedlings. In soilless culture, inoculation of legumes with rhizobia can considerably reduce the input of inorganic nitrogen when preparing nutrient solutions. However, the practical application of this approach faces some difficulties. On the one hand, the supply of plant-available nitrogen is important at the early growth stage, when the rhizobia are still not functional in terms of N(2) fixation. On the other hand, inorganic nitrogen and especially nitrate N inhibits rhizobium colonization. To cope with these two contrasting needs, fine tuning of the nitrogen supply is needed, whereby legumes grown in soilless culture are inoculated with relevant rhizobial strains. In the present study, two different indigenous rhizobia, Bradyrhizobium sp. VULI1.1 and Ensifer sp. VUKA2, and a mixture of them were used to inoculate cowpea [Vigna unguiculata (L.) Walp.] grown in Perlite and supplied with different nitrogen levels to test their inoculation and nitrogen-fixation ability. Plants were supplied with either full-N (total-N 11.2 mM) or 60% of full-N until the flowering stage. Afterwards, the nitrogen supply was reduced to either 30 or 0% until the end of the cultivation period. Nodule number and weight per plant were also estimated. The reduction of nitrogen supply to 60% of the full requirements during the vegetative stage and 0% during the reproductive stage led to increased nodule weight but decreased number of nodules per plant, which resulted in reduced growth and yield. However, supplying 60% of the full nitrogen requirements up to the flowering stage and 30% thereafter increased both nodulation and yield in rhizobium-inoculated cowpea plants in comparison with 100% nitrogen supply without rhizobium inoculation throughout the cropping period. These results indicate that applying different rates of inorganic nitrogen before and after the formation of N(2)-fixing nodules could be considered an effective strategy to reduce nitrogen fertilizer supply in hydroponic cowpea crops without compromising yield.

Soilless zucchini (Cucurbita pepo L.) crops were grown in two distinct cropping periods (spring-summer; SS and autumn-winter; AW) using irrigation water with different Ca2+ concentrations (1.5, 3, 4.5 and 6 mM). The objectives of this study were to: (i) mathematically correlate the accumulation of Ca2+ in the root environment with the respective Ca2+/water uptake ratio (namely uptake concentration; UC), and (ii) determine the UC of macronutrients (i.e., N, P, K, Ca and Mg) under these conditions. Equations of the literature, initially developed to predict NaCl accumulation in a closed hydroponic system, were further extended to fit experimental results. The evolution of Ca2+ accumulation in the drainage exhibited a sigmoid pattern with time and the relationship between the concentration of Ca2+ in the root zone and the corresponding uptake ratio Ca2+/water was better described by curvilinear functions. Validation of the model showed a very good agreement between simulated and measured values. Increasing Ca2+ levels affected both tissue concentrations and UC of Ca and N, but this was not the case for P, K, and Mg. Photosynthesis, growth, yield and plant water uptake were restricted (avg. 15% decrease) at high external Ca2+ levels, due to high total salt concentration (EC) in the recycled solution (4.2–5.5 dS m−1). Fruit quality attributes, however, remained unaffected by treatments with the exception of fruit nitrate content. The empirical model parameterized and tested in this work may serve as a tool to predict Ca2+ ion concentrations in the root environment of zucchini crops as relationships of the water absorbed by the crop. Finally, the results showed that in soilless zucchini crops with zero discharge of fertigation effluents, there is no compelling reason not to use irrigation water resources with Ca2+ concentration up to 3 mM.

The cultivation of most legumes, aims to the production of either dry seeds consumed by humans, also known as pulses, or animal fodder. However, some legumes are cultivated for fresh consumption either as pods or as immature seeds. The economically most important legumes consumed as vegetables are green pods of common bean, cowpea, faba bean, snow pea (mangetout) and green pea seeds. As a rule, the legume vegetables are consumed after cooking and in many countries, they may be used to cover primary nutritional needs, because their protein content is high in comparison with most other vegetables. Furthermore, the legume vegetables, which have distinct organoleptic properties when compared to pulses, are also considered important sources of carbohydrates, essential minerals, vitamins, several other antioxidants and health promoting compounds, and dietary fiber. On the other hand, legume vegetables constitute a low-fat foodstuff. Legume vegetables may contain some antinutritional factors, particularly lectins, phytic acid, saponins, oligosaccharides belonging to the raffinose-family, and vicin and convicin in faba bean, but the levels of most of them are lower than in dry pulses and generally do not constitute a constraint to their consumption. Breeding is one of the most efficient tools to reduce the concentrations of antinutritional factors and increase the levels of health promotic compounds and the taste in legume vegetables. Among the legume species frequently consumed as vegetables, a relatively large number of local accessions and landraces are available, which constitute a valuable genetic material for breeding programs aiming at improving their quality. Breeding of more resilient cultivars to combined stress conditions characterized by a higher nutritional value entails also a better understanding of the physiological mechanisms underlying the biosynthesis of health promoting and antinutritional compounds, as well as the plant adaptation to adverse environmental conditions. Last but not least, agronomical practices, such as crop establishment and plant density, fertilization, irrigation, weed control, and harvesting time and practices play a crucial role for the quality of legume vegetables and deserve special attention.

Partial substitution of nitrate (NO3-) with chloride (Cl-) in the nutrient solution supplied to tomato crops (beefsteak and cherry types), grown in a closed hydroponic system, maintained nitrogen (N)- and carbon (C)- assimilation status in plants despite N-supply limitations. Lowering NO3- ions (90% of total N) supply to 2/3 of the standard recommendations, which was electrochemically compensated for by an equivalent increase of the Cl- concentration in the replenishment nutrient solution (RNS), increased N use efficiency (kg produce kg−1 N supply) and decreased NO3- in the drainage without compromising growth, yield and nutritional quality. Tomato plants supplied with Cl--amended RNS increased leaf Cl- content to macronutrient level (35 mg g−1 dry weight), retaining photosynthetic rates and crop yield potential at lower stomatal conductivity and transpiration. Nutrient to water uptake ratios (mass of nutrient per water volume absorbed), which are commonly termed ‘uptake concentrations’, were defined in different cropping seasons and ranged as follows: 12.1–13.5 (Nitrogen- NO3-+NH4+), 1.25–1.35 (Phosphorus-P), 6.1–6.3 (Potassium-K), 3.6–4.0 (Calcium-Ca), 1.0–1.3 (Magnesium-Mg, mmol L−1), 13.0–14.3 (Iron-Fe), 7.6–8.4 (Manganese-Mn), 5.1–5.2 (Zinc-Zn) and 0.7–0.9 (Copper-Cu, μmol L−1). The levels of N and Cl- supply had no impact on the uptake concentrations. This study suggests that replacing 1/3 of the standard NO3- supply by Cl- in closed hydroponic tomato crops enhances N use by two-fold and eliminates NO3- losses to one-half, with no significant effects on assimilation processes and fruit biomass production, suggesting that Cl- at appropriate concentrations is not only an essential micronutrient but also a beneficial macronutrient. The obtained uptake concentrations may be used through on-line operating decision support systems to optimize nutrient supply in hydroponic cultivations in Mediterranean greenhouses.

Wild edible mushroom species are appreciated for consumption due to their high nutritional value. The aim of the present study was to examine in vitro beneficial bioactivity of mushroom extracts and to investigate the molecular identity of the active ingredients. In this regard, methanol extracts of 29 different wild edible mushroom species, that are traditionally consumed by residents in the National Park of North Pindos in North-Western Greece, were examined for antioxidant, antiproliferative, cytotoxic, and pro-apoptotic activities towards a human lung adenocarcinoma cell line A549 by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and by flow cytometry. Certain mushroom species exhibited high antioxidant activity, which was related to their high content in total phenols and flavonoids. Methanol extracts of Cantharellus cibarius, Cantharellus cinereus, Craterellus cornucopioides and Hydnum repandum, which belong to the order Cantharellales, exhibited high cytotoxicity and induced apoptosis–necrosis to A549 cells. High Performance Liquid Chromatography (HPLC) coupled with Mass Spectrometry analysis revealed as an active ingredient piceatannol ((E)-4-[2-(3,5-dihydroxyphenyl)ethenyl]1,2-benzenediol-3,3′,4,5′-tetrahydroxy-trans-stilbene). Piceatannol, according to our best knowledge, is identified for the first time in wild edible mushrooms. Experiments with authentic piceatannol confirmed the potent antiproliferative activity of this compound. Tested mushrooms are promising sources of bioactive compounds.

In the present study, two contrasting stamnagathi (Cichorium spinosum L.) ecotypes originating either from a mountainous or from a seaside habitat were grown hydroponically and supplied with a nutrient solution differing in the total-N level (4 or 16 mmol L-1 ) and the N source (NH4+ -N/total-N: 0.05, 0.25 or 0.50). The aim was to search for genotypic differences in nitrogen nutrition.; Results: At commercial maturity, the dry weight of mountainous plants was higher than that of seaside plants. The shoot mineral concentrations were higher in seaside plants than in mountainous plants in both harvests. The leaf nitrate concentration was influenced by the levels of both total-N and NH4+ -N/total-N at both harvests, whereas plants with a seaside origin exhibited higher nitrate concentrations than those originating from a mountainous site in all total-N and NH4+ -N/total-N treatments.; Conclusion: The two stamnagathi ecotypes differed considerably in their responses to nitrogen nutrition and tissue nitrate content. The mountainous ecotype was superior in terms of growth, tissue nitrate concentration and antioxidant capacity, whereas the seaside ecotype accumulated more nutrient microcations in leaves. A low total-N concentration (up to 4 mmol L-1 ) combined with a high NH4+ -N/total-N ratio (up to 0.05) could minimize tissue NO3- concentrations without compromising yield. © 2017 Society of Chemical Industry.; © 2017 Society of Chemical Industry.

Spiny chicory ( Cichorium spinosum L.) is used as a health promoting vegetable in Crete, where it is known as stamnagathi . In this paper, the effects of different isosmotic salt solutions on growth, mineral composition and metabolism of hydroponically-grown C. spinosum were investigated. Nine nutrient solutions (NS) were compared, particularly a basic NS used as control, and eight saline NS obtained by adding to the basic NS either NaCl, or KCl, or Na 2 SO 4 , or CaCl 2 at two rates each, corresponding to two isosmotic salt levels. The osmotic potential at 20 °C was −0.286 MPa and −0.480 MPa at the low and the high isosmotic salt level, respectively. C. spinosum proved to be highly tolerant to salinity, suffering only about 20% growth reduction at the high salinity level (53.6 mmol L −1 CaCl 2 or Na 2 SO 4 , and 80 mmol L −1 NaCl or KCl), regardless of the salinity source. At the low salinity level (26.8 mmol L −1 CaCl 2 or Na 2 SO 4 , and 40 mmol L −1 NaCl or KCl), only the bivalent ions reduced slightly the fresh shoot biomass, while only CaCl 2 restricted the dry shoot biomass. Application of 1 H NMR metabolomics to monitor fluctuations in plant metabolism caused by salinity revealed that γ -aminobutyric acid (GABA), glutamate, pyroglutamate, l -proline, and sucrose were the key osmoprotectants in salt-stressed C. spinosum . The levels of glutamine and asparagine, as well as organic acids were reduced by salinity while aromatic compounds had a minor leverage on the observed discriminations, regardless of the salt source, indicating lack of osmoprotection by these metabolites in salt-stressed C. spinosum . Salt-induced changes in tissue mineral levels did not seem to be associated with salinity stress. The present study showed that the osmotic potential level is the dominant factor for the impact of salinity on stamnagathi, but the salt source may also play a minor role, especially at lower salinity levels.

Minimizing salinity impacts on yield in melon crops cultivated in closed-loop hydroponic systems requires better understanding of the physiological impact of gradual salt accumulation in the recycled solution. To attain this objective, different sodium chloride (NaCl) concentrations in the irrigation water, i.e. 0.7, 2.5, and 5 mM, were applied in two cropping seasons (winter-spring;WS and spring-summer;SS). In both seasons plant biomass and yield were negatively affected only in high NaCl-treated plants, due to stomatal limitations, which restricted carbon dioxide (CO2) diffusion into the leaf, osmotic and salt-specific effects. However, a progressive NaCl built-up to maximum concentrations in the root zone solution of 15 (WS) and 20 mM (SS), enabled plants to preserve several physiological mechanisms, thereby adjusting growth and yield without impairing fruit quality. Our results suggest that the use of irrigation water, containing up to 2.5 mM NaCl, is feasible in melon crops grown in closed-lo...

Cowpea is traditionally cultivated in some regions of southern Europe for its dried seeds; however, there is a scarcity of information on the quality and dietary characteristics of fresh pods, which are occasionally used in folk diets. This paper aims at covering this gap in knowledge, thereby contributing to the dissemination of fresh cowpea pods as a novel product for the market. The quality and dietary characteristics of pods from 37 accessions (Vigna unguiculata ssp. unguiculata and ssp. sesquipedalis) grown in southern Europe were assessed in an attempt to provide information on pod quality and nutritional properties and to identify relationships between quality traits and accession origin.; Results: Pods from the sesquipedalis accessions were heavier and larger, and reached commercial maturity 2 days later, than those from the unguiculata accessions. There were also large differences in the quality and dietary characteristics of the accessions. The pods of most accessions were rich in proteins, chlorophylls, carotenoids and phenolics, and showed high antioxidant activity and low concentrations of nitrates and raffinose-family oligosaccharides. Cluster analysis based on quality, dietary or antinutritional traits did not reveal any apparent grouping among the accessions. All the quality characteristics were independent of accession origin and subspecies.; Conclusion: Most of the accessions produced fresh pods of good quality and high dietary value, suitable for introduction in the market and/or for use as valuable genetic material for the development of new improved varieties. © 2017 Society of Chemical Industry.; © 2017 Society of Chemical Industry.

Zucchini squash (Cucurbita pepo L.) plants were grown in a closed-loop hydroponic system and supplied with nutrient solution (NS) containing NaCl at different concentrations (0.7, 3, 5, and 7 mM). The primary aim of the study was to define the relationship between the concentration of Na+ and Cl− in the root zone solution and the respective Na+/water or Cl−/water uptake ratios (uptake concentrations, UC). A second objective was to determine the UC of macronutrients (i.e., N, P, K, Ca, and Mg) and to test whether they are influenced by the gradual increase of the root zone salinity due to progressive NaCl accumulation. Two experiments were conducted, of which one (spring crop) was used to parameterize an existing empirical model, while the second one (autumn-winter crop) was commissioned to test the validity of the determined model parameters. Both Cl− and Na+ ions accumulated progressively in the root zone solution over time, showing a tendency to stabilize at final concentrations according to the corresponding NaCl treatment. The relationship between the Na+ and Cl− concentrations in the root zone and the Na+/water or Cl−/water uptake ratios was exponential and the model parameters successfully fitted to data from crops cultivated in different growth seasons. This model may be used to monitor Na+ and Cl− concentrations in the root environment of zucchini crops as relationships of the plant water consumption. The exposure of plants to NaCl affected the UC of N, K, Ca, and Mg, but the results for some nutrients were not consistent in both growth seasons. The measurements of plant growth characteristics (i.e., biomass, yield, fruit quality, and photosynthesis) revealed that water resources containing up to 3 mM NaCl do not cause unacceptable yield losses in zucchini crops grown in completely closed hydroponic systems.

Testing rhizobial inoculation of common bean (Phaseolus vulgaris L.) in hydroponics enables accurate quantification of biological N2 fixation (BNF) and provides information about the potential of reducing inorganic N fertilizer use. In view of this background, common bean grown on pumice was inoculated with Rhizobium tropici CIAT899 (Rt) and supplied with either full-N (total nitrogen 11.2 mmol L-1 ), 1/3 of full-N or N-free nutrient solution (NS). BNF was quantified at the early pod-filling stage using the 15 N natural abundance method.; Results: Full-N supply to Rt-inoculated plants resulted in markedly smaller nodules than less- or zero-N supply, and no BNF. Rt inoculation of full-N-treated plants did not increase biomass and pod yield compared with non-inoculation. Restriction (1/3 of full-N) or omission of inorganic N resulted in successful nodulation and BNF (54.3 and 49.2 kg N ha-1 , corresponding to 58 and 100% of total plant N content respectively) but suppressed dry shoot biomass from 191.7 (full-N, +Rt) to 107.4 and 43.2 g per plant respectively. Nutrient cation uptake was reduced when inorganic N supply was less or omitted.; Conclusion: Rt inoculation of hydroponic bean provides no advantage when full-N NS is supplied, while 1/3 of full-N or N-free NS suppresses plant biomass and yield, partly because the restricted NO3- supply impairs cation uptake. © 2017 Society of Chemical Industry.; © 2017 Society of Chemical Industry.

Tomato plants (cv. Primadonna F1), non-grafted, self-grafted, or grafted onto the commercial rootstocks ‘He-man’ and ‘Maxifort’, were grown in recirculating nutrient solution. The uptake concentrations (UCs), i.e. mean nutrient-to-water uptake ratios of N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, and B, were estimated based either on depletion from the nutrient solution or on accumulation in the plant biomass. Grafting onto both commercial rootstocks increased the total plant biomass. Hetero-grafting also increased the leaf N, Ca, and Cu concentrations but decreased those of Mg and Fe in comparison with self- and non-grafted plants. The mean UCs of N, Ca, and Cu were higher in plants grafted onto both commercial rootstocks in comparison with self- and non-grafted plants. However, hetero-grafting also raised the UCs of P, Fe, Mn, and B, because of an increased deposition of these nutrients to the roots in comparison with self-rooted plants. The method used to estimate the UCs, i.e. nutrient removal from the r...

The hydroponic cultivation of spiny chicory (Cichorium spinosum L.), also known as stamnagathi, allows the development of year-round production. In the current study, two contrasting stamnagathi ecotypes originating from a montane and a coastal-marine habitat were supplied with nutrient solution containing 4 or 16 mM total-N in combination with 0.3, 20, or 40 mM NaCl. The primary aim of the experiment was to provide insight into salinity tolerance and nutrient needs in the two ecotypes, thereby contributing to breeding of more resilient cultivars to salinity and nutrient stress. Nutritional qualities of the stamnagathi genotypes were also tested. The coastal-marine ecotype was more salt tolerant in terms of fresh shoot biomass production and contained significantly more water and macro- and micro-nutrients in the shoot per dry weight unit. The root Na+ concentration was markedly lower in the coastal-marine compared to the montane ecotype. The leaf Na+ concentration was similar in both ecotypes at external NaCl concentrations up to 20 mM, but significantly higher in the montane compared to the coastal-marine ecotype at 40 mM NaCl. However, the leaf Cl- concentration was consistently higher in the coastal-marine than in the montane ecotype within each salinity level. The marine ecotype also exhibited significantly less total phenols, carotenoids, flavonoids, and chlorophyll compared to the montane ecotype across all treatments. Integrating all findings, it appears that at moderate salinity levels (20 mM), the higher salt tolerance of the coastal-marine ecotype is associated with mechanisms mitigating Na+ and Cl- toxicity within the leaf tissues, such as salt dilution imposed through increased leaf succulence. Nevertheless, at high external NaCl levels, Na+ exclusion may also contribute to enhanced salt tolerance of stamnagathi. Both ecotypes exhibited a high N-use efficiency, as their shoot biomass was not restricted when the total-N supply varied from 16 to 4 mM. The leaf organic-N was not influenced by salinity, while the interaction ecotype × N-supply-level was insignificant, indicating that the mechanisms involved in the salt tolerance difference between the two ecotypes was not linked with N-acquisition or -assimilation within the plant. The current results indicate that both ecotypes are promising germplasm resources for future breeding programs.

In areas characterized by mild winter climate, pepper is frequently cultivated in unheated greenhouses in which the temperature during the winter may drop to suboptimal levels. Under low temperature (LT) conditions, the uptake of nutrients may be altered in a different manner than that of the water and thus their uptake ratio, known as uptake concentration, may be different than in greenhouses with standard temperature (ST) conditions. In the present study, pepper plants of the cultivars &ldquo, Sammy&rdquo, and &ldquo, Orangery&rdquo, self-grafted or grafted onto two commercial rootstocks (&ldquo, Robusto&rdquo, Terrano&rdquo, ), were cultivated in a greenhouse under either ST or LT temperature conditions. The aim of the study was to test the impact of grafting and greenhouse temperature on total yield, water use efficiency, and nutrient uptake. The LT regime reduced the yield by about 50% in &ldquo, and 33% in &ldquo, irrespective of the grafting combination. Grafting of &ldquo, onto both &ldquo, increased the total fruit yield by 39% and 34% compared with the self-grafted control, while grafting of &ldquo, increased the yield only when the rootstock was &ldquo, The yield increase resulted exclusively from enhancement of the fruit number per plant. Both the water consumption and the water use efficiency were negatively affected by the LT regime, however the temperature effect interacted with the rootstock/scion combination. The LT increased the uptake concentrations (UC) of K, Ca, Mg, N, and Mn, while it decreased strongly that of P and slightly the UC of Fe and Zn. The UC of K and Mg were influenced by the rootstock/scion combination, however this effect interacted with the temperature regime. In contrast, the Ca, N, and P concentrations were not influenced by the grafting combination. The results of the present study show that the impact of grafting on yield and nutrient uptake in pepper depend not merely on the rootstock genotype, however on the rootstock/scion combination.

To optimize nutrient supply in melon (Cucumis melo L.) cultivated in closed-loop hydroponic systems under Mediterranean climatic conditions, the process of salinity build-up has to be better understood. To attain this objective, two experiments were conducted in two cropping seasons (winter–spring and spring–summer) in order to: (i) establish relationships between Na+ and Cl− concentrations in the root zone and uptake concentrations (UC) of Na+ and Cl−, respectively, i.e., Na+/water and Cl−/water uptake ratios, and (ii) test whether macronutrient UC in melon grown in closed hydroponic systems are influenced by the gradual salinity build-up. Three different NaCl concentrations in the irrigation water used to prepare nutrient solutions, i.e., 0.7, 2.5, and 5 mM, were applied. The UC of Na+ and Cl− increased over time but at a certain time point in the cropping cycle they converged to a plateau corresponding to the salinity treatment. Exponential relationships between the Na+ and Cl− concentrations in the root zone and the UC of Na+ and Cl−, respectively, were fitted to experimental results in both experiments. However, parameterization of the model with data from the high-transpiration season revealed superiority. The established model parameters corresponded well over the whole melon cultivation cycle and a wide range of climatic conditions. The NaCl-salinity up to the tested level had no significant effect on the UC of macronutrients (i.e., N, P, K, Ca and Mg). The mean UC of Ca and N were higher than those reported under northern-European climatic conditions. The obtained results may be used through on-line operating decision support systems to optimize nutrient supply and minimize salinity impacts in melon grown in closed hydroponic systems when the quality of the irrigation water is sub-optimal.

The data presented here were derived by 1H NMR metabolic profiling of stamnagathi (Cichorium spinosum L.) plants following treatments with different isosmotic salt solutions; eight saline nutrient solutions with two different levels of total molar concentrations, which were obtained by adding different amounts of NaCl, KCl, Na2SO4 or CaCl2 to the replenishment nutrient solution, were applied. The 1H NMR metabolite profiles of stamnagathi plants’, which are included in this article, were recorded 56 days after transplanting. Since stamnagathi is a niche product combining unique taste and superior phytonutrient content (e.g. vitamins C and K1, lutein, β-carotene, tocopherols, phenolic acids, fatty acids, minerals, and glutathione), the dataset could serve as a reference for future metabolomics studies related to the investigation of the effects of the four salinity sources on the plant's metabolism. Also, the dataset could be a valuable resource for the discovery of validated biomarkers of the plant's tolerance to salinity stress and responses to new plant protection products (e.g. bioelicitors). The dataset support the research article “Salinity source alters mineral composition and metabolism of Cichorium spinosum” authored by Ntatsi et al., (2017) [1].

In closed-cycle hydroponic systems (CHS), nutrients and water should be delivered to the plants at identical ratios to those they are removed via plant uptake, to avoid their depletion or accumulation in the root zone. For a particular plant species and developmental stage, the nutrient to water uptake ratios, henceforth termed "uptake concentrations" (UC), remain relatively constant over time under similar climatic conditions. Thus, the nutrient to water uptake ratios can be used as nutrient concentrations in the nutrient solution (NS) supplied to CHS to compensate for nutrient and water uptake by plants. In the present study, mean UC of macro- and micronutrients were determined during five developmental stages in different pepper cultivars grown in a closed hydroponic system by measuring the water uptake and the nutrient removal from the recirculating NS. The experiment was conducted in a heated glasshouse located in Athens Mediterranean environment and the tested cultivars were 'Orangery,' 'Bellisa,' 'Sondela,' 'Sammy,' self-grafted and 'Sammy' grafted onto the commercial rootstock 'RS10' (Capsicum annuum). 'Sondela' exhibited significantly higher NO3-, Mg2+, Ca2+ and B UC, while Bellisa exhibited higher K UC in comparison with all other cultivars. The UC of all nutrients were similar in the grafted and the non-grafted 'Sammy' plants, which indicates that this Capsicum annum rootstock does not modify the uptake of nutrients and water by the scion. The UC of macronutrients estimated in the present study (mmol L-1) ranged from 2.4 to 3.7 for Ca, 1.0 to 1.5 for Mg, 6.2 to 9.0 for K, 11.7 to 13.7 for N, and 0.7 to 1.1 for P. The UC of N, K, Ca, and Mg were appreciably higher than the corresponding values found in Dutch tomato glasshouse, while that of P was similar in both locations during the vegetative stage and higher in the present study thereafter. The UC of Fe, Zn and B tended to decrease with time, while that of Mn increased initially and subsequently decreased slightly during the reproductive developmental stage.

Although silicon (Si) is the second most abundant element in the earth’s crust, it is not considered an essential element for plant nutrition. However, both research results and practical experience advocate for a beneficial impact of Si on growth and development of many plant species, especially when exposed to abiotic or biotic stress. In this review, only the biostimulating effects of Si on plants exposed to abiotic stress are considered. In the soil solution, Si occurs mainly as monomeric silicic acid (H4SiO4) at concentrations ranging from 0.01 to 2.0 mM. H4SiO4 does not dissociate at pH lower than 9 and thus plants take up Si in this non-ionic form, actively or passively, depending on the external Si concentration and their inherent requirements. The latter vary considerably as indicated by the large variation in tissue Si concentrations between species, which range from 0.1% to 10% in dry weight. After uptake, Si accumulates in various tissues mainly as a polymer of hydrated amorphous silica. Currently, Si is applied in some commercial crops aiming at inducing resistance to abiotic stresses, diseases, and pathogens but the use of this element as a biostimulant in horticulture can be further extended. Si alleviates salt, drought, and nutrient stress, as well as stress associated with climatic conditions, minimizes metal and metalloid toxicities, and may delay plant senescence processes. However, the mechanisms underlying Si-mediated alleviation of abiotic stresses remain poorly understood. The key mechanisms involved in Si-mediated alleviation of abiotic stresses in higher plants include: (1) silica deposition inside the plant tissues which provides mechanical strength and erectness to leaves and modulates nutrient and water mobility inside the plants, (2) stimulation of antioxidant systems in plants, (3) complexation or co-precipitation of toxic metals with Si both in plant tissues and in soil, (4) modulation of gene expression and signaling through phytohormones, although evidence for a direct Si involvement in plant metabolic functions is currently lacking.

To date, few attempts have been made to assess the impact of Rhizobium inoculation on N2 fixation and plant yield in soilless cultivations of common bean. In the present study, common bean (P. vulgaris L.) grown on an inert medium (pumice) was inoculated with either Rhizobium tropici CIAT899 or a commercial product containing a mix of N2-fixing bacteria, specifically rhizobia, and Azotobacter sp. The plants treated with both inoculants were supplied with nitrogen (N)-free (0% N) nutrient solution (NS) throughout the cropping period. A third treatment with non-inoculated plants, which were supplied with a standard (100% N) NS was applied as a control. Inoculation with R. tropici significantly increased the total number of root nodules (80 nodules per plant on average) in comparison with the other two treatments (nine nodules per plant on average). The supply of N-free NS restricted markedly both total plant biomass and pod yield, whereas the inoculation with R. tropici mitigated this effect. The aboveground tissues of plants fed with N-free NS contained appreciably less N than those fed with standard solution when they were inoculated with the commercial inoculant (1.7 vs. 29 mg·g−1 dry weight, respectively). The shoot total N concentration 45, 65, and 90 days after transplanting (32, 31, and 29 mg·g−1 dry weight, respectively) was not reduced by the supply of N-free NS when the plants were inoculated with R. tropici. This finding indicates that, at least from the first sampling date onward, the tissue N level was not a limiting factor for growth and yield in plants inoculated with R. tropici. The supply of N-free NS restricted appreciably the potassium (K), magnesium (Mg), and zinc (Zn) levels in the aboveground plant biomass, regardless of inoculation treatment. The impaired growth and yield in plants fed with N-free NS and inoculated with R. tropici is ascribed to both a N shortage at early growth stages and a reduced K+ uptake aimed at electrochemically balancing the anion-to-cation uptake ratio under conditions of no external NO3– supply.

The aim of the present study was to determine uptake ratios between macronutrients and water for melon (Cucumis melo L. cv. Dikti) grown in a closed soilless cropping system. The obtained data can be used to establish standard nutrient solution compositions for melon crops grown in closed hydroponic systems under Mediterranean climatic conditions. Nutrient and water uptake by plants in the closed hydroponic system was compensated for by supplying replenishment nutrient solutions (RNS) differing either in the concentrations of K+, Ca2+, and Mg2+ or in their mutual ratio. The RNS, used as control treatment, had an electrical conductivity (EC) of 1.74 dS m−1 and contained 6.5 mM K+, 2.8 mM Ca2+, and 1.0 mM Mg2+ (K+ : Ca2+ : Mg2+ = 0.63 : 0.27 : 0.10). Control RNS was compared with two other RNS, both with a high Ca2+ level (4.2 mM). The K+ and Mg2+ levels in these two RNSs were: (1) not altered (corresponding to a ratio of K+ : Ca2+ : Mg2+ = 0.55 : 0.36 : 0.09; EC = 2.0 dS m−1) or (2) increased to maintain the same K+ : Ca2+ : Mg2+ ratio as in the control RNS (EC = 2.45 dS m−1). Nutrient to water uptake ratios, commonly termed uptake concentrations (UCs), were assessed by two alternative methods, i.e., (1) estimating the ratio between nutrient and water removal from the system or (2) estimating the ratio between the mass of the nutrient that was recovered from plant biomass and the water consumption. Over the two methods, mean UCs for N, P, K, Ca and Mg were 15.4, 1.31, 5.47, 3.78, and 1.02 mmol L−1, respectively, and tissue analysis resulted in a K : Ca : Mg molar ratio of = 0.55 : 0.34 : 0.11 in the whole plant. Moreover, the UCs tended to decrease as the crop aged although, in absolute values, the mass of nutrients absorbed increased following dry-weight accumulation. Based on the obtained results, adapting the composition of the nutrient solution at least three times during the cropping period of melon is recommended. Further, the results revealed that the damage caused by the increase of the EC when attempting to maintain a target K+ : Ca2+ : Mg2+ ratio in the replenishment NS is higher than the benefits from the optimal cation ratio. Increasing K+ and Mg2+ concentration in addition to that of Ca2+ to maintain a standard K+ : Ca2+ : Mg2+ ratio raises the EC in the root zone (4.62 dS m−1), due to increased accumulation of nutrients, thereby reducing the mean fruit weight and concomitantly the total fruit yield (20% decrease). Leaf gas exchange, chlorophyll parameters and fruit taste quality were not influenced by the differences in macronutrient cation concentrations or ratios in the RNS, whereas phenolics and antioxidant capacity in melon fruit were enhanced by the increased root-zone EC.

To elucidate the role of abscisic acid (ABA) in tomato (Solanum lycopersicum L.) responses to suboptimal root temperature (T), a near-isogenic line carrying the notabilis null mutation in the ABA biosynthesis gene LeNCED1 was reciprocally grafted with its parental cultivar Ailsa Craig. Exposure of tomato to suboptimal root T (15 °C) decreased leaf area expansion, shoot elongation and plant biomass in comparison with optimal root T (25 °C). Both suboptimal root T and null mutation of the LeNCED1 gene in root and shoot reduced leaf area and total plant biomass, but these two factors did not interact. Transpiration rates and stomatal conductances decreased, while net CO2 assimilation was not influenced by root exposure to suboptimal T. However, notabilis scions exhibited higher net assimilation rates, stomatal conductances and transpiration rates than Ailsa Craig scions. Moreover, notabilis plants invested much more biomass into the root than Ailsa Craig self-grafts, thereby improving their water uptake capacity. Lipid peroxidation as well as polyamines and guaiacol-peroxidase (G-POD), which are considered to possess antioxidant properties, increased in the leaves of all grafting combinations of tomato when exposed to suboptimal root T. All grafting combinations showed an increase in shoot ABA levels when exposed to suboptimal root T. However, the levels of ABA in the shoot of notabilis did not differ significantly from those found in Ailsa Craig, indicating that inactivation of LeNCED1 did not impair ABA accumulation in the leaves at low root-zone T. The genes LeNCED2 and LeNCED6 were not up-regulated at low root-zone T and therefore not responsible for ABA biosynthesis in notabilis. Increased ABA levels in tomato exposed to suboptimal root T were associated with elevated levels of the polyamine putrescine which contributes to ABA biosynthesis. In conclusion, the introgression in Ailsa Craig that contains the mutation resulting from inactivation of the LeNCED1 gene includes further genetic differences that influence responses to suboptimal root-zone T, such as plant growth restriction and ROS scavenging modification.

Increased tomato tolerance to sub-optimal temperature (T) through grafting onto wild tomato species that are cold-tolerant could extend the growing period in the field and unheated greenhouses and reduce energy costs in heated greenhouses. Phytohormones seem to be involved in the tolerance of tomato to sub-optimal T stress. Hence, the selection of rootstock/scion combinations with enhanced tolerance to sub-optimal T requires a better understanding of the root-to-shoot interactions with respect to hormonal transport and signalling. To attain this goal, six trials were conducted employing reciprocal grafting of standard tomato cultivars and mutants that are deficient in the biosynthesis/catabolism of abscisic acid (ABA), cytokinin (CK) or salicylic acid (SA) or low-sensitive to ethylene (ET) or auxin (IAA). The exposure of tomato to sub-optimal day/night T (17/14 °C) decreased drastically the rates of shoot elongation and leaf area expansion in all trials in comparison with optimal day/night T levels (22/18 °C). With respect to the genetic combination of rootstock and scion genotypes, it was found that ABA produced in both plant parts exerts a protective role to tomato shoot growth under sub-optimal T stress, while the contribution of ABA was only partially reflected by leaf ABA levels. The use of an ET-insensitive genotype either as rootstock or as scion improved also sub-optimal T tolerance. Sufficient IAA sensitivity in tomato shoot seems to be positively related to shoot elongation rates under sub-optimal T conditions. The use of a mutant with enhanced CK catabolism either as rootstock or as scion restricted leaf expansion at optimal T but had no impact on leaf expansion under sub-optimal T conditions. Impaired SA biosynthesis in the shoot was associated with a higher susceptibility to sub-optimal T in terms of shoot elongation whereas leaf expansion was similarly affected by SA biosynthesis at both T regimes. In conclusion, ABA seems to contribute to enhanced tomato tolerance to sub-optimal T and to indirect control of endogenous ET level while IAA and SA in the shoot promote shoot elongation in tomato plants grown under sub-optimal T conditions.

SummaryExcessive Ca2+ ion concentrations in hydroponic nutrient solutions (NS) are inevitable if the Ca2+ ion concentration of the irrigation water exceeds standard recommendations. The aim of the present study was to compare three different strategies to adjust the K+ and Mg2+ ion supply and the K+: Ca2+: Mg2+ ratio in the NS supplied to hydroponically-grown strawberry (Fragaria × ananassa Duch. cv. Camarosa) plants when the Ca2+ ion concentration in the irrigation water exceeded recommended levels.The standard NS (SNS) for strawberry that was used as a control treatment had an electrical conductivity (EC) of 1.8 dS m–1 and contained 6 mM K+, 3 mM Ca2+, and 1.4 mM Mg2+ ions. SNS was compared with three NS, all with an excessively high Ca2+ ion level (5 mM), while their K+ and Mg2+ ion levels were: (i) either not altered (“High Ca”); (ii) increased to maintain the same K+:Ca2+:Mg2+ ratio as in SNS (“High all”); (iii) or decreased to maintain the same EC as SNS (“Compensation”). The EC values of these thre...

Previous research has indicated that grafting fruit vegetables onto some rootstocks may restrict heavy metal uptake while improving the uptake of some nutrients. In the present study, the ability of four commercial C. maxima × C. moschata rootstocks to restrict Cd and Ni uptake and enhance nutrient uptake by cucumber ( Cucumis sativus L. cv. ‘Creta’) under Cd or Ni stress was tested. In an experiment conducted at the Agricultural University of Athens from 04/11/2009 to 06/06/2009, non-grafted and grafted cucumber plants were exposed to excessively high external Cd and Ni concentrations (10 and 50 μmol L −1 , respectively). The rootstocks used for grafting were ‘Creta’ (self-grafting treatment), ‘Power’, ‘TZ-148’, ‘Ferro’, and ‘Strong Tosa’. Of the tested rootstocks, ‘Power’ could efficiently restrict the Cd levels in all of the tested plant parts by 12–50% in comparison with all other grafting treatments. The levels of Ni in old leaves and fruit were significantly reduced in all grafted plants including the self-grafted ones by 22–32%, in comparison with non-grafted plants, with the exception of ‘Power’ in fruit. With respect to the root, the plants grafted onto‘TZ-148’, ‘Ferro’, and ‘Strong Tosa’ exhibited significantly lower Ni levels than both self-grafted and non-grafted ‘Creta’ plants, as well as plants grafted onto ‘Power’. Grafting onto the tested rootstocks did not improve nutrient uptake by cucumber, with the exception of ‘Power’ which enhanced the levels of K, Zn, and Mn in fruit, but this difference disappeared under Cd stress. Cadmium had little effect on Ca, Mg and K uptake by cucumber. Nickel enhanced Mg levels in stem, old leaves and fruit, Ca in fruit, and K in root and young leaves, while reducing the levels of Ca in stem and old leaves, and K in fruit. Both Cd and Ni imposed a deposition of Fe and Cu to the roots while restricting the Fe and Cu translocation to the aerial plant parts. The levels of Mn were reduced by both Cd and Ni in some plant parts, while those of Zn were reduced only by Ni stress in stem, fruit and young leaves. In conclusion, Cd and nutrient uptake by grafted cucumber depends on the rootstock genotype, while Ni uptake and translocation to different plant tissues depends on both, root genotype and grafting incision. Furthermore, Cd affects mainly the uptake of micronutrient cations by cucumber, while Ni results in a redistribution of all nutrient cations between some plant parts.

The residues of the aquatic plant Posidonia oceanica that are washed ashore, thereby causing environmental problems in coastal areas, can be used as growing media in horticulture. In the present study, the hydraulic characteristics of raw or composted Posidonia residues, coir, and their 1:1 blends (v/v) with pumice were determined, and their agronomic performance was evaluated in a lettuce crop. The mixture of all three substrates with pumice reduced their effective pore space and increased their bulk density. Furthermore, the water and air capacity (determined at a suction of 10 cm) and the easily available water were also reduced by mixing the three tested media with pumice. The relative hydraulic conductivity (Kr) decreased with increasing suction (ψ) in all of the tested media. The highest and the lowest rates of Kr decrease with increasing ψ were observed in the mix of non-composted Posidonia with pumice and in 100% composted Posidonia, respectively. Blending composted or non-composted Posidonia with pumice at a 1:1 ratio raised the rate of Kr decrease with increasing ψ in comparison with 100% composted or 100% non-composted Posidonia, respectively. In contrast, blending coir with pumice reduced the rate of Kr decrease with increasing ψ in comparison with 100% coir. The differences in the mean fresh weight between lettuce plants grown on the six growing media were similar with those in the rate of Kr decrease with increasing ψ. These results indicate that the crucial factor for the yield performance of lettuce grown on the tested growing media was not the air but the water availability. Furthermore, the present results indicate that the actual water availability to plants grown on the tested substrates depends much more on water flux toward roots and concomitantly on their hydraulic conductivity than on the easily available water (i.e., the difference in water content between 10 and 50 cm suction).

A standard and a high manganese (Mn) level (10 and 160 μM) were combined with a standard and a high zinc (Zn) level (4 and 64 μM) in the nutrient solution supplied to cucumber in closed-cycle hydroponic units to compensate for nutrient uptake. The concentrations of all nutrients except Mn and Zn were identical in all treatments. The objectives of the experiment were to establish critical Zn and Mn levels in both nutrient solutions and leaves of cucumber grown hydroponically, to assess the impact of gradual Zn and/or Mn accumulation in the external solution on nutrient uptake and gas exchange, and to find whether Mn and Zn have additive effects when the levels of both ions are excessively high in the root zone. The first symptoms of Mn and Zn toxicity appeared when the concentrations of Mn and Zn in the leaves of cucumber reached 900 and 450 mg kg–1 in the dry weight, respectively. Excessively high Mn or/and Zn concentrations in the leaves reduced the fruit biomass production due to decreases in the number of fruits per plant, as well as the net assimilation rate, stomatal conductance, and transpiration rate, but increased the intercellular CO2 levels. Initially, the Mn or Zn concentrations in the recirculating nutrient solution increased rapidly but gradually stabilized to maximal levels, while the corresponding concentrations in the leaves constantly increased until the end of the experiment. The uptake of Mg, Ca, Fe, and Cu was negatively affected, while that of K and P remained unaffected by the external Mn and Zn levels. The combination of high Mn and Zn seems to have no additive effects on the parameters investigated.

Tomato (Solanum lycopersicum Mill. cv. Belladona F1) plants were either self-rooted, self-grafted, or grafted onto the commercial rootstocks “Beaufort”, “He-Man”, and “Resistar” and grown in a recirculating hydroponic system. Three nutrient solutions differing in NaCl-salinity level (2.5, 5.0, and 7.5 dS m–1, corresponding to 0.3, 22, and 45 mM NaCl) were combined with the five grafting treatments in a two-factorial (3 × 5) experimental design. At the control NaCl level (0.3 mM), fruit yield was not influenced by any of the grafting treatments. However, at low (22 mM NaCl) and moderate (45 mM NaCl) salinity levels, the nongrafted and the self-grafted plants gave significantly lower yields than the plants grafted onto He-Man. The plants grafted onto the other two rootstocks gave higher yields only in comparison with the nongrafted plants, and the differences were significant only at low (Beaufort) or moderate (Resistar) salinity. Yield differences between grafting treatments at low and moderate salinity arose from differences in fruit number per plant, while mean fruit weight was not influenced by grafting or the rootstock. NaCl salinity had no effect on the yield of plants grafted onto He-Man but restricted the yield in all other grafting treatments due to reduction of the mean fruit weight. With respect to fruit quality, salinity enhanced the titratable acidity, the total soluble solids, and the ascorbic acid concentrations, while grafting and rootstocks had no effect on any quality characteristics. The leaf Na concentrations were significantly lower in plants grafted onto the three commercial rootstocks, while those of Cl were increased by grafting onto He-Man but not altered by grafting onto Beaufort or Resistar in comparison with self-grafted or nongrafted plants. Grafting onto the three tested commercial rootstocks significantly reduced the leaf Mg concentrations, resulting in clear Mg-deficiency symptoms 19 weeks after planting.

The response of grafted vegetables to stress conditions owing to the nutrient status, and the presence of heavy metals in the root environment may be different than that of self-rooted plants, depending mainly on the rootstock genotype. Several studies have indicated that some rootstocks are capable of restricting the uptake and/or the transport of heavy metals (e.g. Cd, Ni, Cr) and micronutrients (e.g. Cu, B and Mn) to the shoot, thereby mitigating the stress caused by excessive external concentrations of them. However, other mechanisms driven by the root system, such as detoxification of harmful elements or hormonal signals modifying gene expression in the scion, seem to be involved in the mitigation of stress caused by excessive external nutrient or heavy metal concentrations. On the other hand, the uptake and/or utilization efficiency of macronutrients (N, P, K, Ca and Mg) by plants may be enhanced by grafting onto some rootstocks. This is ascribed mainly to the root characteristics of these rootstocks, which are more vigorous than those of highly productive cultivated varieties. However, other mechanisms implicated in the efficiency of active nutrient absorption by the roots, as well as signals arising from the scion, which are mainly governed by sink demand, may also enhance nutrient uptake and utilization. The higher efficiency of some graft combinations of fruit vegetables to take up and utilize nutrients may mitigate yield losses owing to shortages of these nutrients in the root environment of plants and restrict nutrient losses due to leaching. Nevertheless, it is important to specifically test each grafting combination and not merely each rootstock for its ability to ameliorate nutrient or heavy metal stress because in many instances the responses depend on the rootstock/scion combination. This report gives an overview on the prospects and restrictions of grafting as a means to minimize the negative effects of heavy metals, excessive nutrient availability, nutrient deficiency, and alkalinity stress on vegetable crop performance taking into consideration agronomical, physiological and biochemical aspects.

The aim of the present investigation was to simulate the uptake concentrations (weights of ion per volume of water absorbed) of Na+ and Cl− in hydroponic tomato crops as a function of the NaCl concentration in the root zone. An empirical model was calibrated and validated, which can be incorporated into on-line operating decision support systems aimed at optimizing the nutrient supply and minimizing the discharge of drainage solution in tomato crops grown in closed-cycle hydroponic systems. Three experiments were conducted, of which one was carried out to calibrate the model using irrigation water with NaCl concentration ranging from 0 to 14.7 mol m−3 while the other two experiments were commissioned to validate the model within either a low (0.5–2 mol m−3) or a high (1.2–12 mol m−3) concentration range. The model could successfully predict the uptake concentration of Na+, but Cl− could not be simulated by this model at external Cl− concentrations lower than 10 mol m−3. The results indicate that Na+ is excluded actively and effectively by the tested tomato cultivar even at low external Na+ concentrations, while Cl− is readily taken up at low concentrations, particularly during the initial growing stages. Due to the efficient exclusion of Na+ by tomato, the Na+ concentration in the root environment increased rapidly to extremely high levels even when the Na+ concentration in the irrigation water was relatively low. These results indicate that tomato genotypes characterized by high salt-exclusion efficiency, require irrigation water with a very low NaCl concentration, if they are grown in closed hydroponic systems and the drainage water is not flushed periodically. To maintain Na+ at levels lower than 19 mol m−3 in the root zone of the tomato hybrid ‘Formula’ in closed hydroponics, a maximum acceptable Na+ concentration of 0.53 mol m−3 was estimated for the irrigation water.

SummaryEggplants (Solanum melongena L.) grown on rockwool in a glasshouse were supplied with a nutrient solution (NS) containing 1.0 mM NH4+-N, or three NS containing 4.0 mM NH4+-N. In one of the high NH4+-N treatments, the K, Ca, Mg, and NO3–-N concentrations were reduced to maintain the same electrical conductivity (EC; 2.0 dS m–1), total-N (14.25 mM), and K:Ca:Mg ratio as in the low NH4+-N treatment. In the other two high NH4+-N treatments, the K, Ca and Mg levels were not altered, thus the extra NH4+-N elevated the EC to 2.3 dS m–1, while the NO3–-N was either reduced to maintain the same total-N as in the low NH4+-N treatment, or not altered, in which case the total-N rose to 17.25 mM. The concentrations of P, Fe, Mn, Zn, Cu, B, and Mo were identical in all four treatments, while in the high NH4+-N treatments, ion balance was achieved by adjusting the concentration of SO42–. The increase in NH4+-N from 1.0 mM to 4.0 mM in the NS resulted in similar increases in NH4+-N in the root zone, as indicated b...

SummaryZucchini squash (Cucurbita pepo L., cv. Rival) plants were grown in perlite and supplied with a nutrient solution to which NaCl (0.8 or 35 mM) and silicon (0.2 or 1 mM) were added in four combinations. Fruit quality was assessed on the basis of weight loss, external and internal fruit firmness (FF) after storage at 5°C or 10°C for 2 weeks in air, or enclosed in a polyethylene film. The higher salinity level increased the total soluble solids content (TSSC) of the fruit and improved the storage ability of uncovered fruit, as indicated by their lower weight loss and higher internal FF, but the marketable fruit yield decreased due to a reduced fruit size. Furthermore, at the higher salinity level, the concentrations of K and Mg within the fruit declined. Enclosing fruit in polyethylene reduced weight loss during storage and increased internal FF, irrespective of salinity. Weight loss was also lower, and internal FF was higher, in fruit stored at 5°C than in fruit stored at 10°C, irrespective of salini...

A mass balance model relating the concentrations of Na or Cl in the recycled nutrient solution to the cumulative uptake of water by the plants was calibrated and validated in greenhouse sweet pepper crops grown in closed-cycle cultivation systems. The results indicated that the model allows for simulation of the courses of Na and Cl accumulation in closed-cycle cultivations of pepper, provided that the fluctuations in the volume of drainage solution and the moisture status of the substrate during the cropping period are small. Furthermore, the model predicts a delay in the process of salt accumulation in closed-cycle hydroponic systems when the drainage percentage is relatively high due to enhanced irrigation frequency, in compassion with standard irrigation frequency. The proposed model may be incorporated into intelligent automation systems to automatically adjust the target total salt concentration in the outgoing irrigation solution to levels allowing for a constant nutrient supply, despite the Na and Cl accumulation in the recycled leachate. As a result, the entire amount of drainage solution can be recycled without risking depletion of essential nutrients in the root zone.

Cyromazine was applied at two doses (375 and 750 mg l(-1)) via the nutrient solution in a winter crop of gerbera (Gerbera jamesonii) grown on pumice in a closed-loop system. The persistence of cyromazine in the system and its uptake and distribution within the plant were studied for a period of 121 days by regularly collecting and analysing samples of nutrient solution, drainage solution, substrate, roots, leaves, and flowers. The residues of cyromazine in leaf were further studied in a summer experiment which lasted 50 days. The concentration of cyromazine fluctuated within a relatively high range in both the drainage solution and the nutrient solution supplied to the plants during the first day after its application but declined progressively thereafter. Nevertheless, 37 days after application, mean concentrations of 6.2 and 10.9 mg l(-1) cyromazine were found in the drainage solution at low and high doses, respectively. The corresponding cyromazine concentrations 121 days after its application were 0.02 and 0.03 mg l(-1). Similar values were measured also in the nutrient solution. The adsorption of cyromazine by the pumice was lower than 0.02 mg kg(-1). The half-life time of cyromazine in the closed system was 9.65 days. In the winter experiment, the highest cyromazine concentrations were determined 17 days after application in root and 56 days in leaf and flower, regardless of the dose, while on day 121 the leaf concentrations were 52 and 62 mg kg(-1) fresh weight (f. wt) at the low and the high dose, respectively. In the summer experiment, the leaf concentration of cyromazine reached a maximum (232 mg kg(-1) f. wt) 14 days after its application and decreased only slightly on day 24, but dropped rapidly to 66 mg kg(-1) f. wt on day 50. The above results indicate that cyromazine applied via the nutrient solution may persist for more than 120 days in closed hydroponic systems, while its maximum concentration in the plant tissues occurs several days after application. (c) 2006 Elsevier Ltd. All rights reserved. Crop Protection

Four different NaCl concentrations in the irrigation water, 0.8, 3, 6 and 9 mol m −3 , were applied as experimental treatments to beans ( Phaseolus vulgaris L.) grown in completely closed hydroponic systems in a greenhouse. Initially, the Na and Cl concentrations increased rapidly in the root zone, as indicated by the values measured in the drainage water, and this resulted in corresponding increases in the Na/water and Cl/water uptake ratios. However, as these ratios approached equilibrium with the NaCl/water ratios in the irrigation water, the Na and Cl concentrations in the root zone converged to maximal levels, which depended on the treatment. The highest Na and Cl concentrations in the root zone and the corresponding NaCl concentrations in each treatment were used to establish relationships between the external NaCl concentration and the Na/water or Cl/water uptake ratios, which proved to be exponential for Na but linear for Cl. These relationships were then used in a previously established model [Savvas, D., Kotsiras, A., Meletiou, G., Margariti, S., Tsirogiannis, I., 2005a. Modeling the relationship between water uptake by cucumber and NaCl accumulation in a closed hydroponic system. HortScience 40, 802–807] to enable the prediction of the Na and Cl concentrations in the root zone in relation to the cumulative water uptake. The curves predicted by the model followed a convex pattern, with an initially rapid increase in Na and Cl concentrations in the root zone followed by a gradual levelling out as the cumulative water consumption rose. The measured Na and Cl concentrations in the drainage water were more accurately predicted at the higher NaCl concentrations in the irrigation water, although those predicted at 0.8 mol m −3 of NaCl were considered acceptable for use in commercial practice. Bean showed a high efficiency of Na exclusion from the upper leaves, while Cl was readily translocated to the young leaves as the external Cl concentration rose. Plant growth decreased with increasing salinity in a way similar to that reported for beans constantly exposed to comparable salinity levels.

A field experiment was carried out to determine the effects of cultural system and pea varieties on weed flora, under Mediterranean conditions. The experiment was laid out in a split-plot design with four replicates having two main plots (conventional and organic farming system) and four sub-plots (pea varieties: Onward (commercial variety), Amorgos, Andros and Schinousa (local varieties). Our results indicate that the pea varieties varied in their ability to compete with weeds. The commercial variety Onward showed significantly lower competitive ability against weeds in both cultural systems. Finally, pendimethalin provided 66% and 70% control of Sinapis arvensis and Papaver rhoeas , respectively.

To evaluate the effects of organic and conventional fertlization on root and soil quality of four different pea varieties ( Pisum sativum L.), a spilt-plot experiment with four replications was conducted in 2014-15 in central Greece. The experimental factors were organic manure 1000 kg ha - 1 and NPK fertilizer 600 kg ha - 1 , in the main plots and four pea varieties: Onward (commercial variety), Amorgos, Andros and Schinousa (local varieties) as subplots. The soil and root parameters that were determined are the following: mean weight diameter, macroporosity, penetration resistance, total nitrogen, organic matter, root density and arbuscular mycorrhizal (AMF) root colonization. The results indicated that the soil and root properties were influenced by organic fertilization but this effect is in direct correlation with the different pea varieties. The soil parameters of organic matter and penetration resistance influenced by the type of fertilization regardless of pea variety, with the values of organic matter to be significantly higher by using of organic fertilization compare to conventional and the values of penetration resistance to be significantly higher by conventional fertilization. While regarding the parameters of mean weight diameter of soil aggregates (MWD), soil macroporosity and soil total nitrogen were observed differences between the varieties, but independent of the type of fertilization. As concerns the root properties, the values of root density were different in all four pea varieties, but only for the variety Schinousa there were an increase of the root density derived from the type of fertilization and specifically from organic fertilization. As concerns the percentage of abscular muccorhizal fungi (AMF) colonization the highest percentace were recorded, in all four pea varieties, in organic fertilization compared to conventional, and in all traditional varieties.

The effects of four different NaCl concentrations in the irrigation water used to replenish the transpiration losses in a cucumber (Cucumis sativus L.) crop grown in a closed hydroponic system were investigated for 4 months in a glasshouse experiment. Four different NaCl concentrations in the irrigation water, particularly 0.8, 5, 10 and 15 mM, were compared. These were obtained by automatically injecting the required amounts of NaCl to irrigation water containing 0.8 mM NaCl. During the experiment, no drainage solution was discharged. Initially, the electrical conductivity (EC) increased rapidly in the root environment, as indicated by the values measured in the drainage solution. However, 6-7 weeks after recycling initiation the EC of the drainage water approached asymptomatically a maximal level depending on the treatment. The concentration of some macronutrients showed also an increasing tendency with time, but this increase was relatively small and could not account for the observed rise of EC. Hence, this pattern of EC increase was ascribed to accumulation of Na and Cl, which was initially rapid but tended to be minimized as uptake concentrations of Na and Cl were approaching the corresponding concentrations in the irrigation water used to compensate for the transpiration losses. The yield was suppressed by the progressive increase of EC at a rate of 12.3% per unit of EC increase above 3.02 dS m. The yield suppression was due to decrease of both the mean fruit weight and the number of fruits per plant. The mean length of the cucumber fruit was also affected by the progressively increasing salinity. INTRODUCTION A major problem in closed hydroponic systems is the accumulation of salt ions occurring in the irrigation water at concentrations exceeding the corresponding ratios of ion to water uptake by the plants (Sonneveld, 2000; Savvas, 2002a). Sodium chloride is the most frequently accumulating salt in closed hydroponic systems. Lately, some models have been proposed to predict the rate of salt accumulation in closed hydroponic systems (Silberbush and Ben-Asher, 2001; Pardossi et al., 2004; Savvas et al., 2004a). The accumulation of NaCl originating from the irrigation water in closed hydroponic systems may force the growers to regularly discharge a part of the drainage solution (Raviv et al., 1998). This practice restrict the efficiency of closed hydroponic systems to prevent groundwater contamination with nitrates and phosphates. An efficient management of drainage solution discharge may effectively restrict groundwater pollution while minimizing or even avoiding yield losses. However, to efficiently manage the drainage solution in closed hydroponic systems, a good understanding of the responses of the plants to increasing and not to constant salinity levels is required. The effects of progressively increasing salinity in closed hydroponic systems on plant growth and yield have been studied for some crop species (Bar-Yosef et al., 1999, 2000; Raviv et al., 1998). However, there is no information on the effects of a progressively increase of salinity in the root zone due to recycling of the drainage solution on the yield of cucumber. Therefore, in the present paper we address also the impact of NaCl accumulation in a closed system on the yield of cucumber. Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilan Acta Hort. 697 ISHS 2005 94 MATERIALS AND METHODS Cucumber (Cucumis sativus L. cv. ‘Camaron’) plants were grown in a glasshouse for 4 months in a closed hydroponic system. The experiment was conducted in a glasshouse located in Arta (lat. 397 N, long. 2056 E), Greece. There were four different treatments corresponding to four different NaCl concentrations in the irrigation water used to compensate for transpiration losses, particularly 0.8, 5, 10 and 15 mM. These concentrations were obtained by automatically injecting the required amounts of NaCl to irrigation water containing 0.8 mM NaCl when it was mixed with drainage solution and nutrients to prepare fresh nutrient solution. At each watering cycle, the entire volume of drainage solution selected after the previous watering application was recycled. Hence, the recycled drainage fraction (a) was a variable at each irrigation application. As a result, the volume of the replenished water, and thus the amount of NaCl required to establish each treatment, were also variables, which were automatically calculated in real time as functions of a. The required amounts of NaCl stock solution were dispensed by means of a peristaltic pump having a constant injection rate. The injection time (T in s) was automatically calculated in each irrigation cycle, using equation DJ C C a MV T w i ) )( 1 ( − − = where Μ denotes the molecular weight of NaCl, V the volume (m) of the prepared fresh nutrient solution, Ci the concentration of NaCl in the irrigation water of each treatment (mM), Cw the natural concentration of NaCl in the irrigation water (0.8 mM), D the concentration of NaCl in the NaCl stock solution (kg.m) and J injection rate of the peristaltic pump (L.s). Recycling was based on a previously developed model, which ensured adequate supply of all nutrients, despite the increasing concentrations of Na and Cl in the closed system (Savvas, 2002b). The electrical conductivity (EC) and the concentrations of Na, Cl and major nutrients in both the irrigation solution and the drainage water were measured at 8 sampling dates. At three sampling dates, the micronutrient status in the root zone was also checked to confirm that their supply was adequate (data not shown). The experiment was established by transplanting cucumber seedlings grown in peat cubes (4×4×4 cm) at the stage of the third true leaf into channels connected to 12 fully automated hydroponic installations, which constituted the experimental units. Each experimental unit consisted of two channels, 5 m in length, and accommodated 20 plants (10 plants/channel). Porous polyurethane slabs (100×20×6 cm) were used as growing media. A crop density of 1.6 plants per m was employed. The plants were automatically supplied with nutrient solution via a trickle irrigation system at intervals depending on solar radiation intensity. All channels were covered with polyethylene sheets to prevent water evaporation. The cucumber seedlings were planted on 13 June, the recycling of the drainage solution was initiated five days later, and the experiment was terminated on 15 October. The electrical conductivity in the nutrient solution samples was measured automatically by means of a GLMU-020 instrument. The concentrations of Ca, Mg and K in the same samples were measured by atomic absorption spectrophotometry (GBC 932 A/A), while that of NH4 was determined colorimetrically at 640 nm by the phenate method using a "Continuous Flow Analyzer", type San++ of SKALAR (Eaton et al., 1996). RESULTS AND DISCUSSION In Figure 1, the best fit curves illustrating the changes in the electrical conductivity (EC) of both the irrigation solution and the drainage water with time are presented. Initially, the EC increased rapidly in the root environment, as indicated by the values measured in the drainage water. However, after some time, the rate of EC increase showed a constantly declining course and gradually approached asymptomatically a maximal level depending on the treatment. In particular, the presence of 0.8, 5, 10 and 15 mM NaCl in the irrigation water raised the EC of the drainage solution up to 3.25, 5.80, 6.96 and 8.62 dS m, respectively. The maximal values were approached nearly 50 days after treatment initiation. The course of the Na and Cl concentrations with time in both the irrigation solution and the drainage water have been presented in a previous paper (Savvas et al., 2004b). As shown in Figure 2, the concentration of some macronutrient cations, particularly Ca and Mg, showed an increasing tendency with time, but this increase was relatively small and could not