Plant Mineral Composition Research Articles

Foliar application of zinc and its effect on greenhouse grown cucumber

The experiment was conducted to examine the effect of the foliar application of zinc on yield and crop quality and on fruit mineral composition of cucumber plants (Cucumis sativus cv. Mustang) which were grown in peat in containers under unheated conditions and were not showing visible signs of zinc deficiency.
 In the trial the following 3 treatments were set up in 4 replications: Znl = 0.35 g/litre Zn, as foliar fertilizer; Zn2 = 0.7 g/litre Zn, as foliar fertilizer, control = no foliar fertilization. Foliar fertilization was applied 5 times with 10 day intervals. After their planting out the plants were fertigated daily with water soluble complex fertilisers. Fruits were harvested twice a week, 16 times in all, and were divided into three quality classes (class I, class II and substandard). Shoot length of the plants (plant height) was measured on 3 occasions. Zinc content of the fruits and leaves was analysed at two times.
 From the results of the trials it can be concluded that the 0.35 g/litre Zn (0.35 mg/ml) foliar fertilisation had beneficial effect on cucumber both in terms of yield and quality. Under the conditions of the experiment (daily fertigation through drip irrigation) the effect of a more concentrated foliar application of zinc seemed less beneficial.
 The zinc content of the fruits showed no evident increase in response to foliar fertilization, while a significant increase was seen in the leaves, particularly with the more concentrated Zn treatment. This indicates that in the case of cucumber zinc, through its assimilation in vegetative parts, has an indirect effect on fruit development.

Concentração de macronutrientes em crisântemo de vaso, cultivado sob diferentes relações NO3-/NH4+

In order to study the effects of different ratios of NO3-/NH+4 on the development and mineral composition of chrysanthemum plants, an experiment was carried out in a greenhouse. Five plants in each vase containing 0.75 dm3 of substrate (soil: sand: coffee bean skin: manure at volumetric proportion of 2:0.5:1:1) were used. The treatments were arranged in complete randomized blocks in a factorial scheme (5x5) with three replications. There were five varieties (Puritan, Indianápolis, Coral Charm, Festival Time, Fine Time) and five ratios of NO3-/NH+4 (100/0, 75/25; 50/50; 25/75, 0/100) totalizing 75 vases. The ratios NO3-/NH+4 affected the dry weight accumulation in the aerial portion of the plants. There were differences among the varieties regarding the tolerance to presence of NH4+ in the irrigation solution. The Fine Time was the most sensitive, supporting only 25% of NH4+ in the solution. When 50/50 ratio was used the concentrations of N, P, K, Ca, Mg and S were adequate for the development of the plants.

Soil and plant mineral composition and productivity of Acacia nilotica (L.) under irrigation with municipal effluent in an arid environment

Municipal effluent is becoming an increasing environmental threat and needs appropriate disposal measures to safeguard soil and environmental quality. As an important source of water and nutrients, municipal effluent could be used to increase productivity in nutrient deficient dry areas. Acacia nilotica L. (Babool) seedlings were grown using municipal effluent. Five treatments comprised: irrigation of soil (without seedlings) with municipal effluent at potential evapotranspiration (PET) (treatment T1), irrigation of seedlings at 0.5 PET (T2), PET (T3), and 2 PET (T4), and canal water irrigation of seedlings at PET (T5). Seedlings in the T3 and T4 treatments attained greater height and collar diameter, and produced 22% and 54% more biomass than those in T5. After 24 months, biomass production was 7.43–12.96 t ha−1 as compared to 5.73 t ha−1 in T5. Nutrient concentrations in the seedlings were positively correlated with effluent quantity (r = 0.82, p < 0.01), being greater in foliage than in stems and roots. Uptake of nitrogen (N) was 2.70%, and of iron (Fe) 0.11%, of seedling biomass. Relative increase in metal concentration was greater than that in nutrients. The availability of potassium (K), copper (Cu), Fe, manganese (Mn) and zinc (Zn) in the soil increased twofold and that of NH4-N and PO4-P by 4.5- and 7.9-fold, respectively, in T4 relative to T5. Available NH4-N, PO4-P, Mg and K were highest in the 0–15 cm depth soil, whereas NO3-N, Na, Cu, Fe, Mn and Zn availability were highest in deeper soil layers. Relatively low soil nutrients in T3 compared to T1 indicated withdrawal and accumulation of these nutrients in the seedlings. In several respects municipal effluent benefited A. nilotica seedlings and soil properties, and produced 5.59–12.96 t ha−1 dry biomass. Municipal effluent could help to meet the fuel need of suburban areas, although long-term application of effluent would lead to metal accumulation in soil and plants.

Growth of Dalbergia sissoo in desert regions of western India using municipal effluent and the subsequent changes in soil and plant chemistry

Increasing demand for fodder and fuelwood and the scarcity of a good quality water in arid areas has resulted in a search for an alternative source of water for biomass production. An experiment utilizing municipal effluent in growing Dalbergia sissoo was conducted. Five treatments included T 1, municipal effluent at 1 PET (Potential evapo-transpiration) (without plant); T 2, municipal effluent at 1/2 PET; T 3, municipal effluent at 1PET; T 4, municipal effluent at 2 PET; and T 5, canal water at 1 PET. Observations included plant height, collar diameter at one-month intervals and plant mineral composition, mineral uptake and changes in soil properties at 24 months of plant age. Application of municipal effluent produced better growth in D. sissoo seedlings. Concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) were greater in seedlings irrigated with municipal effluent than those of the seedlings irrigated by the treatment T 5, and positively related with the quantity of irrigation. The concentrations were greatest in foliage compared to the other parts of seedling, with the exception of Cu concentration. Application of municipal effluents resulted in a 2- to 3-fold increase in the concentrations of soil K, Cu, Fe, Mn and Zn, whereas NH 4-N and PO 4-P availability increased by 8.1- and 4.5-fold, respectively. The increase in soil organic carbon was only observed in treatments T 3 and T 4. The accumulations of soil NO 3-N, Na, Cu, Fe, Mn and Zn were more in lower soil layers but the other soil parameters showed their greatest values in the upper soil layer. Irrigation using municipal effluent did not result in toxicity to the seedlings before the age of 24 months. The results suggest that municipal effluent could be utilized, as an important source of water and nutrients in growing D. sissoo to increase biomass production in the needs of suburban dwellers. However, a preliminary treatment to reduce excess NH 4-N and PO 4-P will be required before application to the plantation.

Mineral Composition and Dry Mass Production of Corn Plants Affected by Different Phosphate Sources and Different Soil Aluminum Saturation Levels

The effects of different commercial phosphate fertilizers [Triple superphosphate (TSP), Tricalcium phosphate (TCP), and ARAD rock phosphate) and soil aluminum (Al) saturation (86, 29, and 0%) on the mineral composition and dry mass production of corn (Zea mays) plants were studied. As soil Al saturation values decreased, pH, calcium (Ca), and magnesium (Mg) levels in the soil increased. High Ca values in the shoot resulted in the reduction in potassium (K) concentrations. The high values of P availability in the soil for the ARAD source of P did not correspond to the high values of dry mass production of corn plants. The high values of corn mass production were noticed for the TSP phosphate source, and the mass productions values were reduced as the soil Al saturation values increased.

Tolerance and bioaccumulation of heavy metals in five populations of Cistus ladanifer L. subsp. ladanifer

The effects of heavy metals on the growth, mineral composition (P, K, Fe and Mn) and metal accumulation of five populations of Cistus ladanifer subsp. ladanifer from NE Portugal were investigated in hydroponic experiments. Plants were exposed to increasing concentrations (0–2000 μM) of one of eight heavy metals: Cd, Co, Cr, Cu, Mn, Ni, Pb or Zn. Populations of C. ladanifer, whose origin was ultramafic soils (S and UB) or soils developed on basic rocks (B), showed a higher tolerance to the metals Cd, Co, Cr, and Mn, and a considerable degree of tolerance to Ni. In contrast, populations originating on acid-rock soils (M and SC) showed higher tolerance to the metals Cu and Zn. Populations showed different patterns of metal accumulation and distribution in the plant parts, suggesting different mechanisms of metal tolerance are used. The more Cd-, Co- and Mn-tolerant populations (S, UB, B and SC (Cd)) showed accumulation of these three metals in the shoots (shoot:root metal concentration ratios (S:R) > 1). Shoot concentrations of up to 309 μg Cd g−1, 2667 μg Co g−1 and 6214 μg Mn g−1 were found in these populations. The populations, UB and M, showed considerable tolerance to Ni and Zn, respectively. These populations accumulated up to 4164 μg Ni g−1 and 7695 μg Zn g−1 in their shoot tissues, and these metals were efficiently transported from the roots to aerial parts (S:R > 3 (Ni), S:R > 1 (Zn)). In contrast, the S and SC populations maintained higher growth rates in the presence of Ni and Zn, respectively, but showed exclusion mechanisms of metal tolerance: reduced Ni and Zn transport to shoots (S:R < 1). Cistus ladanifer was not able to efficiently transport Cr, Cu or Pb from its roots to its aerial parts (S:R ranged from 0–0.4). The more Cu-tolerant populations, M and SC, showed a greater restriction of Cu transport to the shoots than the ultramafic- or basic-rock populations. Significant changes in the plant mineral composition were found, however, concentrations were generally above mineral deficiency levels. Based on these preliminary results the possible usefulness of this plant for phytoremediation technologies is discussed. However, further investigations are necessary to evaluate its growth and metal accumulation under soil and field conditions.

Yield, water requirement, nutrient uptake and fruit quality of zucchini squash grown in soil and closed soilless culture

SummaryThe effects of soil and closed soilless systems (cocofibre, perlite and pumice culture) on precocity, productivity, water use, plant mineral composition and fruit quality were studied on zucchini plants (Cucurbita pepo L. ‘Afrodite’ grown in a greenhouse at Viterbo, central Italy. The plants grown in a soilless system exhibited higher yield (total, marketable and fruit number), harvest index, and water-use efficiency compared with those grown in soil. Among soilless treatments, pumice had the lowest water requirement and hence the highest water use efficiency. Use of cocofibre led to the earliest yield compared with the other substrates due probably to the higher minimal temperatures recorded on the organic substrate. Plants grown in soilless culture had a higher uptake of N, Mg, Na, Fe, Cu, Mn, Zn than those grown in soil. After 73 d of solution recycling in soilless treatments, N-NO3, K, P, Fe and Mn were depleted by 26, 16, 40, 92, and 25% respectively, while Ca, Mg, Na, Cu and Zn increased by 6, 69, 113, 360, and 981 % respectively. Carbohydrate concentration (glucose, fructose, sucrose and starch) increased in soilless over soil culture. No significant differences were observed in dry matter or total protein content. Nitrate concentration of fruits was lower in soil than in soilless treatments. The results demonstrated that the growers may improve water and nutrient control, yield and fruit quality by switching from soil to closed soilless culture.

Mineral Composition and Dry Mass Production of Corn Plants Affected by Different Phosphate Sources and Different Soil Aluminum Saturation Levels

Abstract The effects of different commercial phosphate fertilizers [Triple superphosphate (TSP), Tricalcium phosphate (TCP), and ARAD rock phosphate) and soil aluminum (Al) saturation (86, 29, and 0%) on the mineral composition and dry mass production of corn (Zea mays) plants were studied. As soil Al saturation values decreased, pH, calcium (Ca), and magnesium (Mg) levels in the soil increased. High Ca values in the shoot resulted in the reduction in potassium (K) concentrations. The high values of P availability in the soil for the ARAD source of P did not correspond to the high values of dry mass production of corn plants. The high values of corn mass production were noticed for the TSP phosphate source, and the mass productions values were reduced as the soil Al saturation values increased.

EFFECTS OF SUBSTRATES ON YIELD, QUALITY AND MINERAL COMPOSITION OF SOILLESS-GROWN CUCUMBERS

Cucumber plants (Cucumis sativus L.) were grown in soilless culture under greenhouse conditions at the Experimental farm of University of Tuscia, Central Italy to evaluate the effects of four substrates (rockwool, pumice, perlite, and coir) on growth, yield, fruit quality, and plant mineral composition. Plants grown in coir, perlite and pumice yielded more than those grown in rockwool. Similar results were obtained for dry weight of leaves, stems, and fruits. Fruit quality in term of dry matter, soluble solid content, titratable acidity, and pH was not significant affected by treatments. Concentrations of K and Na were highest in nutrient solution, and fruits of coir treatment while perlite and pumice treatments had highest Ca concentration in nutrient solution, leaves and fruits. Phosphorus and Mg were highest in nutrient solution and plant organs of coir treatment, respectively. The above findings may be explain by the different chemical and physical properties of substrates and their interaction with nutrient solution composition and plant nutrient uptake.

Relationships between soil cations and plant characteristics based on spatial variability in a forage field

Spatial variability within a forage field can be used to assess how soil properties relate to forage characteristics of yield, mineral composition, and nutritive value. The relationship between the dietary cation-anion difference (DCAD) of the forage and soil cations is of particular interest to dairy farmers because of problems related to hypocalcemia. An experiment was conducted on a dairy farm in southern Québec (Canada) to determine the variability in soil cations (K, Mg, Ca) and forage characteristics (yield, mineral composition, and nutritive value) and to establish relationships between them, primarily with respect to DCAD. A 10-ha field with a tile-drained silty loam soil was seeded in 1998 with a mixture of timothy (Phleum pratense L.) and red clover (Trifolium pratense L.). Soil samples were collected on a systematic grid in spring (n = 151) and fall (n = 38) 1999. Forage samples were collected at these sampling points at the first harvest in June 1999 and 2000. Soil K and K-related properties (K/CEC, Mg/K, Ca/K) displayed the largest variability among selected soil cation properties in both samplings, with coefficients of variation (CV) ranging from 35 to 58%. Dry matter (DM) yield, plant mineral composition, and forage nutritive value had low to moderate variabilities (8 &lt; CV &lt; 38%). Dry matter yield was not closely related to soil cations. High correlation coefficients were found between plant K and soil K (0.62 &lt; r &lt; 0.67), and between DCAD and soil K (0.67 &lt; r &lt; 0.72). Other plant mineral composition (P, Mg, Ca, S, Cl, and Na), CP, K/(Ca + Mg) and relative feed value showed low correlations and inconsistent trends with soil cations. Considering the importance of DCAD in predisposing dry cows to milk fever, the spatial variability of soil K should be considered to reduce the incidence of this metabolic disorder. Key words: Dietary cation-anion difference, forage, milk fever, spatial variability, soil K

Soil enzymatic activity and growth of rice and barley as influenced by organic manure in an anthropogenic soil

Pot experiments were conducted with rice and barley to investigate the influence of incorporated organic manure in an anthropogenic (paddy) soil on the enzymatic and biological activities and on the growth and mineral composition of plants. The soil used for the experiments was sampled in the coastal zone of eastern Jiangsu Province, China. The soil was an anthropogenic derived from alluvial and marine deposits. Four treatments, consisting of 20 g kg −1 rice straw alone (RS), 20 g kg −1 pig manure alone (PM), 20 g kg −1 rice straw plus 20 g kg −1 pig manure (RS+PM), and a control (no manure added) were investigated with rice as the first and barley as the second crop. The results showed that urease activity for RS+PM, PM and RS treatments increased by 163%, 96% and 21%, respectively, compared to the control at tillering stage of rice. Similar results were obtained at jointing stage. During the barley season, the urease activity of RS, PM and RS+PM treatments at tillering stage increased by 57.4%, 93.1% and 152.5%, respectively, compared to the control. The incorporation of organic manure into the soil significantly ( P<0.01) increased soil alkaline phosphatase activity and soil respiration rate regardless of crop species and growth stage. The addition of organic manure increased K ion but decreased Na ion uptake and transport to shoots from roots, thus enhancing K/Na selectivity ratio and salt tolerance of rice and barley plants. As a result, the dry weight of rice and barley for the treatments with organic manure significantly increased compared to the control. The incorporation of organic manure into salinised anthropogenic soil seems to be a practical and effective way to improve soil fertility, and enhance the salt tolerance and growth of crops. However, organic manure incorporated at excess dosage should be avoided, especially in a soil under long-term flooded condition, to reduce the risk of toxic effects of reduced metabolic intermediates.

Accumulating behaviour of Lupinus albus L. growing in a normal and a decalcified calcic luvisol polluted with Zn

Lupinus albus L. is a leguminous plant that is starting to generate interest for the phytoremediation soils showing intermediate metal pollution. Among these metals, Zn causes major phytotoxicity problems and is common in polluted soils of central Spain. The purpose of this study was to explore the nutritional behaviour of this plant species towards increasing Zn concentrations in two calcic luvisol soils: a normal basic soil and a decalcified acid soil. For this purpose the effects of different Zn concentrations on mineral nutrition, growth, nodulation and nitrogenase activity of nodulated Lupinus albus cv. Multolupa plants has been investigated. A 12-week trial was performed in pots under greenhouse conditions. In each soil, four replicate pots were set up per treatment (100, 150, 300, 500 and 700 ppm Zn). Seeds were inoculated with a Bradyrhizobium sp. (Lupinus) strain ISLU-16. Statistical analysis of data revealed significant effects of soil Zn on grown, plant mineral composition and nodulation. Lupin growth was better in acid soil than in basic soil with the low dose of Zn applied, although plant growth in acid soil was severely affected from 300 ppm Zn, where the pH of the soil was 4.7. Zn application produce nutritional imbalances, especially with the higher dose added. Most of Zn accumulation occurred in the roots in both types of soils. In acid soil, lupin absorbs high amounts of Zn in both root (4650 ppm) and aerial part (3605 ppm), when the doses of Zn applied was 300 ppm. This feature permits Lupinus albus cv. Multolupa to be considered as potential phytoremediator and also for the revegetation of degraded landfill areas with slightly acid or neutral soils polluted with Zn.

EFFECTS OF ROOT-ZONE TEMPERATURE ON THE ROOT DEVELOPMENT AND NUTRIENT UPTAKE OF LACTUCA SATIVA L. “PANAMA” GROWN IN AN AEROPONIC SYSTEM IN THE TROPICS

Lactuca sativa L. cv. Panama is a temperate plant, but can be grown in the tropics by only subjecting its roots to 20°C while its aerial portions are exposed to the hot, fluctuating temperatures in the greenhouse. This study showed that in Lactuca sativa L. cv. Panama grown at 20°C root-zone temperature (RZT) in the tropics, the roots were longer with a greater number of root tips and total root surface area, and smaller average root diameter as compared with those of ambient RZT (A-RZT) plants. In plants transferred from 20°C to A-RZT (20°C ⇒ A-RZT) when they were 3 weeks old, rate of increase in root length was decreased as was root tip number and surface area; root thickening was increased. The reverse was observed for plants transferred from A-RZT to 20°C-RZT (A ⇒ 20°C-RZT). Mineral nutrients such as NO3 −, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), and zinc (Zn) present in the plant shoot and root tissues were also determined. Generally, it was found that 20°C-RZT plants had higher leaf N and P concentrations on the basis of per unit dry weight compared with plants grown at A-RZT. Results also showed that total shoot and root NO3 −, K, Ca, Cu, Fe, Mg, Mn, and Zn accumulation of 20°C-RZT plants were more than A-RZT plants. 20°C ⇒ A-RZT plants suffered from a reduction of total mineral accumulation, and Ar ⇒ 20°C-RZT plants increased in total mineral accumulation. Relationships between RZT, root growth, and mineral composition of the experimental plants are discussed.

Nitrogen Nutrition of Greenhouse Pepper. I. Effects of Nitrogen Concentration and NO3: NH4 Ratio on Yield, Fruit Shape, and the Incidence of Blossom-end Rot in Relation to Plant Mineral Composition

Blossom-end rot (BER) is one of the major physiological disorders of green-house bell pepper (Capsicum annuum L.). The objective of the present work was to study the effects of the solution N concentration and N-NO3: N-NH4 ratio on fruit yield and the incidence of BER and other fruit-quality traits of greenhouse-grown bell pepper in a Mediterranean climate. Three experiments were conducted: Expt. 1 included five total N concentrations (0.25 to 14 mmol·L-1, with a constant N-NO3: N-NH4 ratio of 4); Expt. 2 included five treatments of different NO3: NH4 molar ratios (0.25 to 4, with a constant N concentration of 7 mmol·L-1); and Expt. 3 included three treatments of different NO3: NH4 molar ratios (1.0, 3.0 and 9.0, with a constant N concentration of 7 mmol·L-1). Plants were grown in an aero-hydroponics system in Expts. 1 and 2 and in tuff medium in Expt. 3, in greenhouses in Israel. The optimal values of N concentration for total fruit yield and for high fruit quality (marketable) were 9.3 and 8.3 mmol·L-1, respectively. The total and high-quality fruit yields both increased with increasing N-NO3: N-NH4 ratio in the range studied. The total and high-quality fruit yields both decreased sharply as the NH4 concentration in the solution increased above 2 mmol·L-1. The increase in the NH4 concentration in the solution is the main cause of the suppression of Ca concentration in the leaves and fruits and the increased incidence of BER. The occurrence of flat fruits also increased with increasing NH4 concentration in the solution.

MINERAL COMPOSITION OF FORAGE LEGUMES AS INFLUENCED BY ALUMINUM

The nutritional quality of plants is primarily controlled by concentrations of essential nutrients and potentially detrimental substances, and these are influenced to a great extent by phytotoxic aluminum (Al). Alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and birdsfoot trefoil (Lotus corniculatus L.), cultivars were grown in nutrient solution culture under controlled conditions and the effects of Al on growth and mineral composition of plants were evaluated. With a few exceptions, Al significantly reduced shoot and root dry weights, and generally increased the concentrations of elements in shoots. Further increases in Al tended to reduce mineral concentrations in each species and cultivar. This was probably related to root injury, reduced dry matter accumulation at higher Al, and reduced nutrient demand at higher Al levels. In alfalfa and red clover cultivars, elemental equivalency ratios for K/Mg and K/(Ca + Mg) increased, and ratios for Ca/P decreased in plants grown with Al. Forage with low Ca/P indicates poor quality, and high K/Mg and K/(Ca + Mg) ratios indicates higher grass tetany hazard to animals. Most of the elemental concentrations and nutrient ratios were similar for Al-sensitive and Al-tolerant cultivars of alfalfa and red clover. The species and cultivars used in this study had inter- and intraspecific differences in growth and nutrient concentrations, both in the presence and absence of phytotoxic levels of Al.

Interactive effects of boron and salinity stress on the growth, membrane permeability and mineral composition of tomato and cucumber plants

A greenhouse study was conducted in order to determine interactive effects of NaCl salinity and B on the growth, sodium (Na), chloride (Cl), boron (B), potassium (K) concentrations and membrane permeability of salt resistant Tomato (Lycopersicon esculentum L. cv. Lale F1) and salt sensitive cucumber (Cucumis sativus L. cv. Santana F1) plants. Plants were grown in a factorial combination of NaCl (0 and 30 mM for cucumber and 0 and 40 mM for tomato) and B (0, 5, 10 and 20 mg kg−1 soil). Boron toxicity symptoms appeared at 5 mg kg−1 B treatments in both plants. Salinity caused an increase in leaf injury due to B toxicity, but it was more severe in cucumber. Dry weights of the plants decreased with the increasing levels of applied B in nonsaline conditions, but the decrease in dry weights due to B toxicity was more pronounced in saline conditions especially in cucumber. Salinity × B interaction on the concentration of B in both plants was found significant. However, increase in B concentrations of tomato decreased under saline conditions when compared to nonsaline conditions. Contrary to this, B concentration of cucumber increased as a result of increasing levels of applied B and salinity. Salinity increased Na and Cl concentrations of both plants. Potassium concentration of tomato was not affected by salinity and B treatments, but K concentration of cucumber was decreased by salinity. Membrane permeability of the plants was increased by salinity while toxic levels of B had no effect on membrane permeability in nonsaline conditions. Membrane permeability was significantly increased in the presence of salinity by the increasing levels of applied B.

Cd/Fe Interaction in Higher Plants - Its Consequences for the Photosynthetic Apparatus

Cadmium is one of the most dangerous environmental pollutants, affecting, among other things, plant mineral composition. It easily interacts with iron, one of the most important elements for plant growth and metabolism. This interaction, including modifying effects of lowered or excessive Fe supply on Cd-exposed plants and its consequences for the photosynthetic apparatus is reviewed. The influence of modified Fe and Cd supply on the uptake of both metals, their distribution, plant growth, and photosynthesis is also explained. Moderate Fe excess has a beneficial influence on Cd-treated plants, resulting in more intensive growth, photosynthetic pigments accumulation, and more efficient light phase of photosynthesis. Nutrient-medium Fe deficiency increases plant susceptibility to Cd. The main open questions of Cd/Fe interaction are: (1) the strong Fe-dependency of Cd mobility within the plant, and (2) photosynthetic dark phase adaptation to Cd stress.

IMPROVING THE NUTRIENT COMPOSITION OF PLANTS TO ENHANCE HUMAN NUTRITION AND HEALTH

Plant foods contain almost all of the mineral and organic nutrients established as essential for human nutrition, as well as a number of unique organic phytochemicals that have been linked to the promotion of good health. Because the concentrations of many of these dietary constituents are often low in edible plant sources, research is under way to understand the physiological, biochemical, and molecular mechanisms that contribute to their transport, synthesis and accumulation in plants. This knowledge can be used to develop strategies with which to manipulate crop plants, and thereby improve their nutritional quality. Improvement strategies will differ between various nutrients, but generalizations can be made for mineral or organic nutrients. This review focuses on the plant nutritional physiology and biochemistry of two essential human nutrients, iron and vitamin E, to provide examples of the type of information that is needed, and the strategies that can be used, to improve the mineral or organic nutrient composition of plants.

Effect of night humidity on the vegetative growth and the mineral composition of tomato and strawberry plants

Conditions of low night humidity (50–55%) and high night humidity (90–95%) were imposed on tomato plants ( Lycopersicon esculentum Mill. cv. Young-Kwang) for 30 days, and on strawberry plants ( Fragaria grandiflora Ehrh. cv. Bogyo) for 40 days. Shoot dry weight and leaf area in tomato plants increased with high night humidity whereas the strawberry plants did not show any such increases. The concentrations of five major nutrients (N, P, K, Ca and Mg) were reduced in tomato plants under high night humidity, with the calcium content in younger leaves being the most severely affected. For the strawberry plants, however, high night humidity tended to increase the concentrations of major nutrients, including calcium in the younger leaves. Possible reasons for the differences in response of these two species to night humidity are discussed.

Relationship between chloride and nitrate and its effect on growth and mineral composition of avocado and citrus plants

Two rootstocks of avocado (Persea americana Mill.), the salt‐tolerant ‘Degania‐113’ and the salt‐sensitive ‘Smith’, and two rootstocks of citrus, the salt‐tolerant ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tan) and the salt‐sensitive ‘Troyer’ citrange (Poncirus trifoliata x Citrus sinensis [L.] Osbeck), were grown in a sandy soil and irrigated daily with nutrient solutions containing various chloride concentrations. Increasing the concentration of chloride resulted in elevated chloride levels in all avocado plant parts, and toxic symptoms that were more pronounced in the ‘Smith’ than in the ‘Degania‐113’ avocado rootstock. When leaves of both rootstocks had accumulated similar chloride levels and showed scorching damage, the leaves of ‘Degania‐113’ abscised, while those of ‘Smith’ did not. High chloride reduced the total dry matter yield of the root more than that of the shoot, decreasing the “root: shoot”; dry weight ratio in both rootstocks. Addition of nitrate to the irrigation water reduced chloride accumulation in the plant and alleviated its adverse effects. Accumulation of nitrogen in the plant exceeded that of chloride in all cases. High nitrate reduced phosphorus levels in the plant and caused chlorosis in young leaves. High chloride partially reversed this effect. Citrus rootstocks responded similarly, but leaves of the chloride‐sensitive ‘Troyer’ accumulated more chloride than ‘Cleopatra’. High chloride resulted in scorching damage in the leaves and branches of ‘Troyer’, but not in ‘Cleopatra’. Nitrate reduced chloride accumulation and toxic symptoms as well as boron levels in the leaves. The results of this study suggests that water containing high chloride levels may be used to irrigate avocado and citrus orchards, provided that nitrate is supplied continuously at a molar concentration equivalent to half that of chloride. Our results also suggest that a nitrate supplement applied to citrus will reduce the undesirable uptake of boron. The difference in mode of resistance to chloride between avocado and citrus rootstocks is discussed.