Effect of lowering nutrient solution concentration at night on leaf calcium levels and the incidence of tipburn in lettuce (Var. Gloria)

Butterhead lettuce (var. Gloria) were grown in an evaporatively cooled glasshouse using the nutrient film technique (NFT). During the day all plants received a complete nutrient solution (EC 2 dS/m). Treatments were imposed at night and included: complete nutrient solution (control); tap water (EC 0.19 dS/m); and calcium nitrate solutions containing either 100 mg Ca/L (EC 0.80 dS/m), or 200 mg Ca/L (EC 1.45 dS/m).

Tipburn occurred in the control and its incidence was reduced by the other treatments. This effect was associated with an increase in the concentration of calcium in new leaves, except in the water treatment. The night treatments did not affect the fresh weight of mature lettuce.

Circulation of either water or calcium nitrate (100 mg Ca/L) at night may, therefore, be a commercially acceptable means of reducing tipburn losses in lettuce crops grown using hydroponics.     

Effect of NO3 and NH4 concentrations in nutrient solution on yield and nitrate concentration in seasonally grown leaf lettuce

The effect of suboptimal supply of nitrogen (N) and of replacing nitrate in the nutrient solution with ammonia on growth, yield, and nitrate concentration in green and red leaf lettuce was evaluated over two seasons (autumn and spring) using multiple regression analysis. The plants were grown in a greenhouse on a Nutrient Film Technique (NFT) system. Nitrogen concentrations in the nutrient solution were either 3?mM or 12?mM, and the form of N was varied as follows: 100% NO₃, 50% NO₃?+?50% NH₄, and 100% NH₄. In both seasons, the biomass (fresh weight) of lettuce heads increased with increasing NO₃ concentrations and in autumn, NO₃ even at 1.5?mM was sufficient for high yield. However, head dry weight was affected neither by the season nor by changes in the composition of the nutrient solution. The concentration of NO₃ had no effect on root dry weight, but it decreased at higher concentrations of NH₄. The number of leaves increased as the ratio of NO₃ to NH₄ in the nutrient solution increased and was higher in autumn because of the longer growth period. Increasing the concentration of NO₃ in nutrient solution increased both total N and nitrate concentration in lettuce heads (dry weight) but decreased the concentration of total C. Also, leaf nitrate concentration was lower in spring than in autumn and decreased with increasing NH₄ concentration. Nitrogen utilization efficiency was maximum when NH₄ levels in the nutrient solution were either 0% or 50% irrespective of the season. Our results thus show that suboptimal N supply in autumn will not affect lettuce yield, and that nitrate concentration in leaves is lower when NH₄ concentrations in nutrient solution are higher and also much lower in red lettuce than in green lettuce.     

Interactive effects of substrates and ectomycorrhizal colonization on growth of a poplar clone

A balsam poplar clone (Populus trichocarpa cv. Weser 6) was inoculated by two ectomycorrhizal strains (Laccaria bicolor MW 158 and Paxillus involutus 1444) in Kick‐Brauckmann‐pots. The substrates were two arable sandy soils (Cambisols) with different organic matter content and nutrient supply. One soil (WIL) was rich in organic matter (C_org = 1.6%) and total nitrogen (N_t = 0.14%), whereas the other soil (RIE) had low contents of C_org (0.8%) and N_t (0.08%). Leaf nutrient concentrations, shoot lengths, root and shoot biomass production and nitrogen accumulation in the biomass were determined to discover possible inoculation effects. Mycorrhization indices (% colonized fine roots) of 36% with Laccaria bicolor and 40% with Paxillus involutus were observed on the C_org rich soil (WIL) in contrast to 16% and 14% on the C_org poor soil (RIE), respectively. Inoculation of poplar on the soil WIL increased shoot length, biomass production, shoot:root ratio and total N uptake of the cuttings, whereas on the soil RIE only the shoot:root ratio increased and the N nutrition was improved. We conclude that interactions between soil and fungus should be tested when choosing ectomycorrhizal strains for inoculation.     

Adaptive attributes of tropical forage species to acid soils I. Differences in plant growth,nutrient acquisition and nutrient utilization among C4 grasses and C3 legumes

Low supply of nutrients is a major limitation of forage adaptation and production in acid soils of the tropics. A glasshouse study was conducted to find differences in plant growth, nutrient acquisition and use, among species of tropical forage grasses (with C₄ pathway of photosynthesis) and legumes (with C₃), when grown in two acid soils of contrasting texture and fertility. Twelve tropical forage legumes and seven tropical forage grasses were grown in sandy loam and clay loam Oxisols at low and high levels of soil fertility. After 83 days of growth, dry matter distribution among plant leaves, stems, and roots, leaf area production, shoot and root nutrient composition, shoot nutrient uptake, and nutrient use efficiency were measured. Soil type and fertility affected biomass production and dry matter partitioning between roots and shoots. The allocation of dry matter to root production was greater with low soil fertility, particularly in sandy loam. The grasses responded more than the legumes to increased soil fertility in both shoot and root biomass production. Leaf area production and the use of leaf biomass for leaf expansion (specific leaf area) were greater in legumes than in grasses, irrespective of soil type and fertility. But soil type affected shoot biomass production and nutrient uptake of the grasses more than those of the legumes. There were significant interspecific differences in terms of shoot nutrient uptake. The grasses were more efficient than legumes in nutrient use (grams of shoot biomass produced per gram of total nutrient uptake) particularly for nitrogen (N) and calcium (Ca).     

营养液浓度对水培生菜生长和硝酸盐积累的影响

该文研究了4种营养液浓度处理(山崎生菜配方的1/4(1/4s)、1/2(1/2s)、1(1s)和2(2s)单位)对水培生菜(品种为“弘农”和“绿领”)生长、硝酸盐积累和品质的影响。结果表明,1/2单位营养液浓度处理下生菜地上部和根的鲜重、叶长和叶宽最大,而2个单位营养液浓度处理下上述指标最小。不同营养液浓度处理下叶片硝酸盐积累的高低顺序为2s>1s>1/2s>1/4s,2个单位营养液浓度处理下生菜生长发育后期叶片中的SOD活性和M DA含量最高。对采收时生菜品质的分析表明,生菜体内的硝酸盐含量随着营养液浓度的增加而迅速上升,2个单位营养液浓度处理下生菜叶片中硝酸盐、可溶性糖和可溶性蛋白质R含量最高。综合考虑产量和品质,采用1/2单位的山崎生菜配方是适合生菜水培的营养液配方。     

Growth,water use efficiency,and sodium and potassium acquisition by tomato cultivars grown under salt stress

Three cultivars of tomato (Lycopersicon esculentum Mill., cvs. Sera, 898, Rohaba) were grown under different levels of NaCl in nutrient solution to determine effects of salt stress on shoot and root dry matter (DM), plant height, water use efficiency (WUE, g DM kg^‐1 water evapotranspired), shoot sodium (Na) and potassium (K) concentrations, and K versus Na selectivity (S_K,Na). Increasing NaCl concentration in nutrient solution adversely affected shoot and root DM, plant height, WUE, K concentration, and K/Na ratio of all cultivars. Shoot Na concentrations increased with increasing NaCl concentration in the nutrient solution. Although increasing salt concentration in the solution adversely affected growth of all cultivars, the cultivar Sera had the highest shoot and root DM than the other two cultivars (898 and Rohaba). Shoot and root DM of cultivar 898 was most affected by salt, while cultivar Rohaba had an intermediate salt sensitivity. The cultivar Sera generally had higher WUE values, shoot K concentrations, and S_K,Na, but had lower shoot Na concentrations than the other two cultivars when plants were grown under different salt levels. Greater Na exclusion, higher K uptake and shoot S_K,Na are suggested as being plant strategies for salt tolerance.     

Efficiency of h+‐atpase activity on cadmium uptake by four cultivars of lettuce

Cadmium (Cd) uptake by lettuce (Lactuca sativa L.) was studied in a hydroponic solution study at concentrations approaching the total concentration in contaminated soil solutions. Four cultivars of lettuce were tested (Divina, Reine de Mai, Melina, and J.44). Ten 12‐day old seedlings, pretreated in 0.5 μM CdCl₂ solution, were labelled with carrier free ¹⁰⁹CdCl₂ (from 0.05 μM to 5 μM Cd in nutrient solution) in the presence and absence of metabolic inhibitors, DNP and DCCD. Cadmium taken up by the roots was determined after a 30 min desorption in unlabelled CdCl₂ solution. In the absence of metabolic inhibitors and at 5 μM Cd, root absorbed from 2.5 to 8 mg Cd/g root dry weight. Exchangeable Cd measured after desorption represented less than 1% of the total Cd absorbed by the root. Cadmium absorption in presence of DNP showed that approximately 80% of the Cd enters the cell through an active process. This mechanism seems to be directly associated with H⁺‐ATPase as observed with DCCD inhibition. Varietal differences in shoot Cd uptake were only demonstrated at concentrations below 0.1 μM. Screening lettuce cultivars only by the Cd level in the tissue seems not to be possible for these cultivars except at concentrations close to that in the soil solution. But differences in relative contribution of uptake mechanisms in total Cd absorption were observed. High levels of Cd in roots were correlated with high contri‐ butions from H⁺‐ATPase in the active process of Cd uptake.     

Earthworm-Processed Organic Wastes as Components Of Horticultural Potting Media for Growing Marigold and Vegetable Seedlings

We germinated and grew tomato, pepper, lettuce, and marigold seedlings in a standard commercial soilless plant growth medium (Metro-Mix 360), and in coir/perlite and peat/perlite-based container media substituted with 10% or 20%, by volume, of vermicompost derived from pig manure or food wastes. Half of the treatments were watered with liquid inorganic fertilizer while the other half received only water. Germination rates of tomato, pepper, lettuce, and marigold seeds in the coir/perlite mixture did not differ significantly from that in Metro-Mix 360. However, the germination rate of tomato, pepper and lettuce seedlings was very low in the peat/perlite mixture. Substituting some of the peat/perlite mixtures with equal amounts of vermicomposts, particularly pig manure vermicompost, enhanced germination rates greatly, making it comparable to that in the commercial medium (Metro-Mix 360). Pepper, lettuce, and marigold seedlings grown in Metro-Mix 360, which already contains a starter nutrient fertilizer in its formulation, had greater root and shoot dry weights than those grown in the control media (coir/perlite mix and peat/perlite mix). Substituting coir/perlite and peat/perlite mixtures with 10% or 20% of either vermicompost enhanced the growth of seedlings significantly, resulting in an overall plant growth as good as and sometimes better than that in Metro-Mix 360. When the plants were provided daily with a complete fertilizer solution, marigold seedlings in peat-based substrate with 20% pig waste vermicompost, and lettuce seedlings in both coir and peat-based substrates, mixed with 20% food wastes vermicompost, produced greater shoot dry weights than those grown in the commercial potting medium. The growth enhancements tended to be greater in peat/perlite-based mixes than in coir/perlite-based mixes, more so with the addition of pig manure vermicompost than with food waste vermicompost. Earthworm-processed pig manure and food wastes would be suitable materials for inclusion into the formulation of soilless potting media, since substitution of these media with relatively low concentrations of vermicomposts can promote plant growth.     

营养液浓度对水培生菜生长和硝酸盐积累的影响

该文研究了4种营养液浓度处理(山崎生菜配方的1/4(1/4s)、1/2(1/2s)、1(1s)和2(2s)单位)对水培生菜(品种为“弘农”和“绿领”)生长、硝酸盐积累和品质的影响。结果表明，1/2单位营养液浓度处理下生菜地上部和根的鲜重、叶长和叶宽最大，而2个单位营养液浓度处理下上述指标最小。不同营养液浓度处理下叶片硝酸盐积累的高低顺序为2s>1s>1/2s>1/4s，2个单位营养液浓度处理下生菜生长发育后期叶片中的SOD活性和MDA含量最高。对采收时生菜品质的分析表明，生菜体内的硝酸盐含量随着营养液浓度的增加而迅速上升，2个单位营养液浓度处理下生菜叶片中硝酸盐、可溶性糖和可溶性蛋白质R 含量最高。综合考虑产量和品质，采用1/2单位的山崎生菜配方是适合生菜水培的营养液配方。     

土壤水分时间变异对油麦菜水分利用效率的影响机制

  【目的】  土壤水分根据其随时间的变异情况可分为稳定性和波动性土壤水分,稳定的土壤水分有利于提高作物的水分利用效率。我们研究了土壤水分的时间变异影响油麦菜水分、养分吸收利用效率的机制。  【方法】  以油麦菜(Lactuca sativa L. var. longifolia)为供试作物于遮阳网室内进行盆栽试验。设两个供水处理:传统浇灌(traditional irrigation, TI)和负压灌溉(negative pressure irrigation,NPI),其所提供的土壤水分分别为波动性土壤水分和稳定性土壤水分。供水处理于油麦菜4叶期开始运行,用土壤水分仪测定土壤含水量,每两天测定一次,处理28天后收获。于NPI开始运行的第1、11、21和28 天,测定油麦菜株高、叶片数、最大叶长和最大叶宽,同时用LI-6400便携式光合仪测定油麦菜叶片净光合速率(P_n)、胞间CO₂浓度(C_i)、蒸腾速率(T_r)和气孔导度(G_s),生化方法分析叶片抗旱生理指标游离脯氨酸(Pro)、丙二醛(MDA)、脱落酸(ABA)、水杨酸(SA)、可溶性蛋白(SP)和可溶性糖(SS)以及稳定碳同位素比值(δ13C)和分辨率(Δ13C)的变化。  【结果】  NPI和TI的累计灌水量和平均土壤体积含水量处于基本相同的水平,NPI土壤体积含水量的变异系数为5.0%,属于稳定性土壤水分,TI的变异系数为10.3%,属于波动性土壤水分。NPI处理油麦菜株高、最大叶长和最大叶宽分别显著高于TI 103.8%、155.4%和62.5%。NPI处理4次监测的各项光合参数值大多高于TI,第11 天的T_r和G_s值,以及收获时(处理第28天)的C_i均显著高于TI。收获时NPI处理油麦菜的产量、水分利用效率、叶片含磷量、氮磷钾养分吸收量和Δ13C明显高于TI,根冠比、脱落酸含量、可溶性糖含量和δ13C明显低于TI。Δ13C与水分利用效率呈正相关,与土壤水分变异系数呈显著负相关。  【结论】  相较于传统浇灌提供的波动性土壤水分,负压灌溉提供的稳定土壤水分降低或者避免了土壤水分胁迫,促进了油麦菜地上部的生长发育、光合作用、养分吸收和水分利用效率。     

基于蜣螂算法优化BP的冬夏生菜根区温度预测模型

为解决生菜应用营养液膜技术（nutrient film technique,NFT）在冬夏季根区温度控制的问题,该研究基于机器学习方法,结合温室内外历史环境数据,构建BP神经网络根区温度预测模型。为提高模型精度,采用蜣螂算法（dung beetle optimizer, DBO）优化BP神经网络模型的输入权重和阈值,构建了冬夏两个季节的基于DBO-BP神经网络的栽培槽内根区温度预测模型,并与GA-BP、BP神经网络模型进行对比。结果表明,根区温度预测值与真实值变化趋势较为一致,DBO-BP模型温度预测最大误差为2.21°C,决定系数为0.943,而GA-BP与BP模型决定系数分别为0.928、0.892;DBO-BP模型评价指标的均方根误差、平均绝对误差分别为0.707、0.549°C,均小于其他模型评价指标。DBO-BP神经网络可满足在NFT栽培中根区温度预测精度的需求,能够为生菜栽培根区快速控温提供有效方法。     

Composted Sewage Sludge as an Alternative Potting Media for Lettuce Cultivation

A study was conducted to evaluate the potential possibility of using composted sewage sludge (CSS) as an alternative potting media component to substitute for expensive peat (PE) in lettuce (Lactuca sativa L.) cultivation. Five different substrates were developed by changing the CSS and PE percentages in the growth medium. Percentages of CSS addition to PE were 0%, 15%, 30%, 50%, and 70% v/v, respectively. Growing media developed from CSS by substituting PE had plentiful physical and chemical properties and prominent contents of plant nutrients, mainly phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg). The greatest growth and yield increments were achieved from the medium with 30% CSS and 70% PE of the total volume, respectively. The shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight obtained from the medium with 30% CSS and 70% PE were increased by 56.53%, 43.93%, 29.46%, and 67.24%, respectively, compared to PE control.     

Fertilizer location modifies root zone salinity,root morphology,and water‐stress resistance of tree seedlings according to the watering regime in a dryland reforestation

There is a direct relationship between soil nutrient concentration in localized zones and root proliferation and elongation under well‐watered conditions. However, in field studies under semiarid conditions this relationship can change due to higher salt accumulation and soil dryness that affect root growth, water stress resistance, and seedling survival. We assessed the effect of different locations of fertilizer placement in the soil profile and water availability on root zone salinity, root development and ecophysiological responses of Quillaja saponaria Mol. after outplanting. A single dose (6 g L^?1) of controlled‐release nitrogen fertilizer (CRF_N) was placed at 0 cm (top layer), 15 cm (middle layer), or 30 cm (bottom layer) depth in the containers in a greenhouse, in addition to an unfertilized treatment (control). After 6 months, seedlings were transplanted to the field and subjected to weekly watering regimes (2 L plant^?1 and unwatered). Morphological and ecophysiological parameters were periodically measured on seedlings, as well as soil electrical conductivity (EC). After 1 year, the shoot : root ratio of unwatered seedlings decreased as a function of CRF_N placement depth, which was attributed to lower shoot growth and not to greater root growth. The root morphology of the bottom layer treatment was negatively affected by high EC in unwatered seedlings. Greater total root length and root volume of the middle layer treatment was found only when well‐watered; however, this did not contribute to improve physiological responses against water stress. The lowest EC and the highest photochemical efficiency, net photosynthesis, and stomatal conductance were shown by unfertilized seedlings, independent of water availability. Our findings suggest that varying depth of CRF_N placement does not contribute significantly to improve root growth under water restriction. Water supplements, independently of the CRF_N location in the substrate, contribute to decrease root zone salinity, and consequently, improve root volume growth.     

营养液供液高度对水培生菜生长及矿质元素吸收的影响

在密闭植物工厂条件内,设置5种营养液高度（2、3、4、5、6cm）水培种植生菜,以探究霍格兰（Hoagland）配方营养液不同供液高度对生菜十种矿质元素（K、P、Ca、Mg、Na、Fe、Mn、Zn、Cu、S）吸收及积累的影响。结果表明：生菜地上部生物量以及光合色素含量均在4cm供液高度处理下最大,而地下部生物量以及根长均随着营养液供液高度的增加而升高;生菜地上部十种矿质元素的含量均在供液高度6cm处理下最大,而矿质元素在生菜中的单株累积量则表现为Fe、Mn元素在6cm供液高度下最大,Ca、Mg、Na、Zn、Cu、S元素在4cm供液高度下最大,K、P元素在5cm供液高度下最大。因此,实际生产中可以通过调节水培生菜营养液的供液高度,以达到提高生菜产量或生产功能性蔬菜的目的。     

Chloride and carbonate salinity tolerance in Mimusops zeyheri seedlings during summer and winter shoot flushes

Shoot flushes alternate with root flushes and the evergreen red milkwood (Mimusops zeyheri Sond.) fruit tree has winter (May–July) and summer (October-December) shoot flushes in southern hemisphere. Fruit of this plant contain high vitamin C and the tree is being researched and bred for arid inland southern Africa regions. Climate change predictions suggested that by 2030 the regions would experience high temperatures (>45°C), recurrent floods and repeated droughts, which are associated with increased salinity challenges. The objective of this study was to determine the degree of salt tolerance in M. zeyheri seedlings to chloride and carbonate salinity during summer and winter shoot flushes under microplot conditions. Treatments, comprising untreated control, NaCl, KCl, CaCl₂ and Na₂CO₃ each at 1.0 molar (M) solutions, were applied weekly for eight weeks. During both seasons, CaCl₂ and Na₂CO₃ salinity had significant effects on soil pH and EC. During summer, salt types increased (106%–253%) dry shoot mass and reduced (53%–79%) root/shoot ratio. During winter, Na₂CO₃ salinity increased (114%) dry shoot mass, but the effects were not different to those induced by NaCl and CaCl₂ salinity. All other plant growth variables were not affected by salt type. Salt type had significant effects on assimilation of selected nutrient elements in leaf tissues of M. zeyheri seedlings during winter. Sodium chloride did not have significant effects on nutrient elements, whereas KCl, CaCl₂ and Na₂CO₃ significantly affected selected macronutrient elements and Zn. In conclusion, effects of chloride and carbonate salinity on M. zeyheri seedlings were both season- and salt type-specific, with seedlings displaying some degree of salt tolerance to chloride and carbonate salinity.     

Humus-Rich Compost Increases Lettuce Growth, Nutrient Uptake, Mycorrhizal Colonisation, and Soil Fertility

Sandy soils, typical of Australia's west, either have little or no habitat protection for microbes including arbuscular mycorrhizal (AM) fungi, which are essential for nutrient cycling. To minimize this problem, the application of organic matter, such as humus-rich composts, is necessary during vegetable crop production. This study aimed at determining the effects of humus-rich composts on either indigenous or inoculated AM fungal colonisation in roots, lettuce (Lactuca sativa L. var. Quechua) growth, and soil fertility improvement. Four different humus-rich composts with varying humus contents were applied at the same standard rate to lettuce grown under glasshouse conditions for 10 weeks after sowing and compared with two low-humus composts and non-amended soil (control). Humus-rich composts significantly increased lettuce shoot growth, root growth, and AM fungal colonisation in roots. Humus contents in the composts were also correlated with lettuce shoot and root growth. Soil dissolved organic carbon, microbial biomass carbon, and fertility were increased with the application of humus-rich composts. These humus-rich composts, especially the compost of higher humic acid with and without AM inoculation, might have a significant role in sustainable vegetable production, for example lettuce growth. Overall, the results indicate that supplementation with humus-rich compost is highly beneficial to enhance soil fertility and potentially maintain the sustainability of vegetable production.     

Nutrient supplementation increased growth and nitrate concentration of lettuce cultivated hydroponically with biogas slurry

Abstract

Recycling of biogas slurry via vegetable production is a multi-benefit and sustainable utilization strategy regarding agriculture and environment. A glasshouse experiment was conducted to investigate the effects of phosphorus (P) and iron (Fe) supplementation on growth and quality of lettuce cultivated hydroponically with diluted biogas slurry. The results showed that direct supplementation of P into diluted biogas slurry together with Fe improved the lettuce growth significantly, and decreased the root to shoot ratio. However, growth responses of lettuce to single addition of P or Fe into diluted biogas slurry were not significant. In addition, supplementation of P and Fe improved leaf chlorophyll content (determined as SPAD value), nitrate concentration significantly or slightly of the lettuces but not vitamin C content. However, addition of P and Fe or microelements through foliar spray is not effective in enhancement of growth and quality except for improving leaf SPAD. In conclusion, as a nutrient solution, the tested biogas slurry needs Fe and P supplementation, and P should be added together with Fe or post Fe supplementation in terms of lettuce yield. Also, direct addition of Fe into diluted biogas slurry was better than foliar spray.     

CO2浓度升高对不同水稻品种幼苗养分吸收和根系形态的影响

本文利用水培试验研究了CO2浓度升高对水稻幼苗生物量、养分含量和根形态的影响,探讨了CO2浓度升高下粤杂889(YZ)和荣优398 (RY)幼苗养分吸收和根系形态的差异性.结果表明,与CO2浓度正常水平(对照)相比,CO2浓度升高显著增加了2个水稻品种幼苗根系、茎叶和总生物量,YZ分别增加58.33％、27.96％、33.16％;RY分别增加45.87％、34.17％、36.07％.同时,CO2浓度升高增加了2个水稻品种的根冠比.CO2浓度升高显著降低了2个水稻品种茎叶中的N、P、K、Ca、Mg和Fe含量,这是“稀释效应”的结果;但YZ幼苗中S含量显著增加,2个品种幼苗Mn含量均显著增加.CO2浓度升高显著增加了2个水稻品种的幼苗根系根毛数、总根长、表面积,降低幼苗粗根比例,增加了细根比例.CO2浓度升高增加了细根在总根长中的比例,有利于水稻对养分的吸收,导致部分营养元素含量增加;但CO2浓度升高条件下水稻生物量的增加使大部分营养元素含量降低.同时,CO2浓度升高对水稻幼苗生物量、养分吸收和根形态的影响存在显著的品种差异.     

Effect of nutrient solution concentration on photosynthesis,growth, and content of the active substances of passionfruit 1

The objective of this study was to investigate the effects of exposure of passionfruit plants (Passiflora edulis Sims. var edulis) to five different electrical conductivity (EC) levels (1.2, 2.3, 4.5, 6.8, and 9.0 mS/cm) of the nutrient solution on net gas exchange (Pn), content of chlorophyll, the biologically active substances, vitexin and orientin, total biomass production, and morphological traits using plants grown in a greenhouse. Important traits, such as plant height, number of internodes, and leaf number per plant were significantly influenced and showed a linear relation to the increased EC levels of the solution. The highest biomass production, chlorophyll concentration, net carbon dioxide (CO₂) assimilation and leaf area were obtained at an EC of 6.8 mS/cm. At an EC level of 9.0 mS/cm, the growth of the plants was depressed and photosynthetic rate sharply declined. The highest photosynthetic rate (8.45 μmol/m²/s) was measured at an EC of 6.8 mS/cm and a photosynthetic photon flux of 1600 μmol/m²/s. The trend of photosynthesis was closely related to those of chlorophyll content, transpiration and mesophyll conductance. There was significant regression relating the shoot yield to increasing EC of the nutrient solution. The leaf chlorophyll content increased from 0.70 mg/g (75 mg/m²) at an EC of 0 to 1.74 mg/g at an EC of 6.8 mS/cm. The leaf water potential sharply declined with the increasing EC levels. The specific leaf area was high at EC of 2.3,4.5, and 6.8 mS/cm. The mean ratio of the root to the shoots decreased as EC was increased up to 6.8 mS/cm. Orientin content was the highest (168 mg %) at an EC of 9.0 mS/cm, having a linear effect, while the lowest vitexin content (36 mg %) was achieved at an EC of 6.8 mS/cm. The results suggest a positive role of increasing nutrient solution EC for orientin accumulation than to vitexin.     

INCIDENCE OF LETTUCE TIPBURN AS RELATED TO HYDROPONIC SYSTEM AND CULTIVAR

The incidence of tipburn was studied by growing late winter and spring lettuce cultivars in two consecutive experiments, in hydroponics, either with Deep Flow Technique (DFT) or on solid growth substrates, in Messinia, NW, Greece. Both experiments showed that the fresh marketable yield of lettuce in DFT was approximately twice as great compared to that of plants grown on solid substrates. Tipburn injury was not observed in the late winter experiment whereas it was severe in the spring one. In particular, lettuce grown with DFT in the spring presented significantly greater level of injury whereas when grown on perlite the least. Their shoot calcium concentration was significantly lowest whereas when grown on perlite the highest. Between the two spring cultivars included, ‘Merlin’, which presented the greatest injury, also had significantly higher shoot fresh weight, lower root/shoot ratio, higher tissue water content, and lower nitrogen, potassium, calcium, and magnesium concentrations compared to ‘Gramsi’.