Dilute Nutrient Solution Research Articles

Hydrophilic Gel Amendments to Sand Soil Can Increase Growth and Nitrogen Uptake Efficiency of Citrus Seedlings

We tested the hypothesis that amendments of two hydrophilic gels to a sand soil would reduce N leaching losses and increase growth of citrus seedlings. Three-month-old seedlings of `Swingle' citrumelo [Citrus paradisi Macf. × Poncirus trifoliata (L.) Raf.] were transplanted into containers of steam-sterilized Candler sand, amended with a linear acrylamide/acrylate copolymer (PAM), and/or a cross-linked copolymer agronomic gel (AGRO). Two rates of each amendment were applied either alone or together and were either mixed into dry sand prior to seedling transplant, used as a root-dip slurry at transplant or applied to the soil surface in a solution after transplant. Seedlings were grown in the greenhouse for 5 months and irrigated to container capacity with a dilute nutrient solution without leaching. Pots were leached every 2 weeks and total N losses from the soil were measured in the leachate. PAM amendments increased N retention in soil slightly but PAM had no effect on plant growth, water use, N uptake, or N leaching relative to unamended control plants. The AGRO amendments increased seedling growth, plant water use and uptake of N from 11% to 45% above that of the unamended control plants depending on application method. AGRO decreased N concentrations in the leachate to as low as 1 to 6 mg·L-1. Only 6% of the total applied N was leached from the AGRO treatments, which was about half that from the untreated control plants. There was no additional benefit of using both amendments together or of an additional AGRO root dip treatment. The largest plants used the most water, required the most N and had the greatest N uptake efficiency. AGRO amendments clearly enhanced seedling growth, increased their N uptake efficiency, and reduced N losses from this sand soil.

A gnotobiotic system for studying root carbon release using lettuce ( Lactuca sativa L.)

A cultivation system was developed for studies of root exudation and plant–microbial interactions under gnotobiotic, hydroponic conditions. The system was tested by determining root carbon release from lettuce ( Lactuca sativa L. cv. Grand Rapids) grown axenically at different ionic strengths for 3 weeks. Growth of the axenic plants was similar at 25, 50 or 100% of the full strength nutrient solution (NS) during the first 2 weeks. After 3 weeks, however, plant dry weights and total uptake of K, Ca, P, S, Mn, Fe, Zn and Cu were highest when the full strength NS was supplied. Also, the concentration of dissolved organic carbon (DOC) in the NS was higher in the 100% compared with the more dilute NSs. Estimated net root release of DOC after 3 weeks varied from 6 to 14 mg g −1 root dry weight. The DOC relative release rate (RRR) was lower than the relative plant growth rate (RGR), indicating a reduction of the amount of DOC released per gram root dry weight with increasing plant growth. We conclude that the cultivation system allows axenic studies of root carbon release during 3 weeks with a high number of experimental units and a low incidence of contamination.

Efeito do alumínio sobre o crescimento de duas espécies florestais

Para estudar o efeito do Al no crescimento inicial de duas espécies florestais, foi instalado um experimento em novembro de 1998, em solução nutritiva, em casa de vegetação do Departamento de Ciência do Solo da Universidade Federal de Lavras. Após duas semanas em solução nutritiva diluída a 1/3 e sem Al, duas plantas de Moringa (Moringa oleifera) e duas de Angico (Anandenantha peregrina) foram transplantadas para vasos de 1,5 L e crescidas em solução nutritiva. Os teores de Al utilizados foram de 0,0; 2,5; 5,0; 7,5; e 10,0 mg L-1, com pH 4,0 ± 0,2, ajustado diariamente durante 70 dias. Após este período, foi determinada a altura das plantas, as quais, posteriormente, foram divididas em parte aérea e raiz, para determinação da matéria seca e dos teores de N e P. Os teores crescentes de Al reduziram progressivamente a altura das plantas e a produção de matéria seca das raízes nas duas espécies e da parte aérea no Angico. O teor de nitrogênio na Moringa diminuiu com o incremento nos teores de Al. O teor de fósforo na parte aérea da Moringa e do Angico diminui a partir de 5 mg L-1 de Al na solução nutritiva.

Effect of aluminium on bananas (Musaspp.) cultivated in acid solutions. II. Water and nutrient uptake

Introduction. A previous paper showed that Al in the nutrient solution affected the growth, biomass production and chemical composition of bananas (Musa spp.). This paper aims at providing complementary results on the effect of Al on water and nutrient uptake by young banana plants. Materials and methods . Vitroplants of five cultivars (Grande Naine, Agbagba, Obino l'Ewai, Igitsiri and Kayinja) were grown for 40 d in a phytotron with a temperature close to that of their cropping areas. Dilute nutrient solutions without Al and with 78.5 μ M Al were supplied continuously with peristaltic pumps. Measurements of daily water and nutrient uptake were carried out twice a week. Rhizosphere acidification or alcalinisation were also monitored. Results and discussion . Aluminium reduced plant water uptake and cumulative detrimental effects were observed. After 40 d, water uptake was only 30-40% of the control. Without Al, nutrient uptake (Ca, Mg, K, P, NO3 -N, NH4 -N) increased with time, whereas Al inhibited the uptake of all elements, particularly Mg. As for water absorption, cumulative effects were observed: after 40 d, most nutrient uptake rates were reduced by more than 50% relatively to the control. The plantain bananas, Agbagba and Obino l'Ewai, were more resistant to Al than the others. Changes of temperature are likely to modify Al sensitivity as one cultivar, Kayinja, showed greater Al sensitivity at 28/25°C than at 24/20°C.

Suitability of hydroxyapatite and iron phosphate as P sources for Lupinus albus grown in nutrient solution

Most solution cultures require maintenance of relatively constant concentrations of nutrients in the root environment. This requirement is most relevant for the macronutrient phosphorus (P), the plant demand for which is high but whose concentration in nutrient solution should be kept low to mimic the concentration in soil solution. This study examined suitability of iron phosphate (FePO4) and hydroxyapatite (HAP) to supply P to N2-fixing plants of Lupinus albus (cv. Kiev Mutant) grown in nutrient solution. Five plants were grown in each 5-L pot containing dilute nutrient solution, with five dialysis pouches containing either HAP or FePO4 at rates of 0.02, 0.1, 0.5 or 2 g L−1. Solution pH was maintained at 5.6 using 2 mM MES. The solutions and pouches were renewed weekly.

Toxicity of copper and zinc in seedlings of Mung bean and inducing accumulation of polyamine

A solution culture was conducted to investigate the effects of copper (Cu) and zinc (Zn) toxicity on growth of mung bean (Phaseolus aures Roxb. cv VC‐3762) and accumulation of polyamine. Eight‐day‐old seedlings were grown in diluted nutrient solution with different concentrations of Cu and Zn for 6 days. Results showed that elongation of epicotyl and fresh weight of plants were decreased by 10 μM Cu and 100 μM Zn significantly compared to control (0.03 μMCu and 0.1 μMZn). Accumulation of polyamine, especially putrescine (Put) was found in the epicotyl of mung bean seedlings. Addition of 5 mM calcium (Ca) into nutrient solution improved the growth of 10 μM Cu‐treated seedling, and decreased the concentration of Put and increased concentrations of spermine and spermidine in epicotyl of plants. Moreover, supplying Put did not increase tolerance of plant to Cu or Zn. It was suggested that Put accumulation resulting from toxicity of Cu and Zn might merely be a symptom of stress injury.

Phytotoxicity of hydrogen fluoride and fluoroborate and their uptake from solution culture by Lycopersicon esculentum and Avena sativa

The aims of this paper were to determine the phytoavailability and phytotoxicity of hydrogen fluoride (HF) and fluoroborate (BF 4 - ) in solution when exposed to the root of the plant. As fluoroborate undergoes a slow hydrolysis to F and borate ions, the stability of BF 4 - under solution culture conditions was determined. Fluoroborate was found to have a zero order rate constant of 0.0136 and took approximately 72 days to hydrolyse completely. Tomato (Lycopersicon esculentum) and oat (Avena sativa) plants were grown in dilute nutrient solutions which contained a range of activities of HF and BF 4 - . Dry matter production of both tomato and oat plants grown in nutrient solutions were found to be restricted by increased activity of HF and BF 4 - in solution. Tomatoes were more sensitive to HF and BF 4 - than oats. Limitations to dry matter production coincided with increased uptake of F for F concentrations in tissue of both tomatoes and oats. Fluoride uptake of both HF and BF by tomatoes and oats was orders of magnitude higher compared to similar activities of other ionic species of F reported in previous studies. Possible mechanisms of uptake are discussed.

Phytotoxicity of the fluoride ion and its uptake from solution culture by Avena sativa and Lycopersicon esculentum

Avena sativa (oats) and Lycopersicon esculentum (tomatoes) were grown in dilute nutrient solutions containing varying concentrations of fluoride (F). Shoot and root growth of tomatoes were limited when calculated F ion activities (F-) were greater than 1473 μM in solution. However, F- activities up to 5130 μm had no effect on the dry weights of oat shoots or roots, suggesting that tomatoes are more sensitive to F toxicity. At low F activities in solution (<1684 μM) F concentrations in plant shoots increased almost linearly with activity, but then increased rapidly before reaching an upper asymptote. These findings are discussed in relation to plant uptake and toxicity of F. The complexation of Ca with F has been proposed as the mechanism of selectively altering membrane permeability to F, but further studies are required to confirm the role of Ca. Data recalculated from the literature and from this paper also suggest that growth solution ionic strength is positively related to uptake of F- by plants.

Effects of humic and fulvic acids on the rhizotoxicity of lanthanum and aluminium to corn

Effects of varying lanthanum (La) or aluminium (Al) concentrations (0-30 µM) on corn (Zea mays L.) root elongation were examined in the presence and absence of (i) humic acid (HA) at 35 mg carbon (C)/L, or (ii) fulvic acid (FA) at 15 mg C/L, using dilute nutrient solutions. The organic acids were extracted from a mixture of decomposed grass (Sorghum halepense) and lucerne (Medicago sativa) hay. In the absence of added HA or FA, the addition of La at ≥5 µM and Al at 30 µM was toxic to the root growth of corn. The rhizotoxic effects of La at 5 and 10 µM were negated by HA. The ability of FA to overcome La rhizotoxicity was much less, significantly ameliorating the toxic effects of 5 µM La but not those of 10 or 30 µM La. HA and FA did not precipitate La from solution. Both organic acids ameliorated Al toxicity by complexing Al and reducing monomeric Al in solution. It is concluded that concentrations of HA and FA, commonly present in soil solutions, are capable of forming non-rhizotoxic complexes with La, hence plant tolerance to La in the soil solution may be appreciably higher than would be indicated by results of solution culture experiments in which these ligands are not present.

Effects of Intermittent Desiccation on Nutrient Economy and Growth of Two Ecologically Contrasted Mosses

The mossesBrachythecium rutabulum(Hedw.) B., S. & G. andPseudoscleropodium purum(Hedw.) Fleisch. were cultivated for more than 50 d in a growth cabinet with or without weekly drying interludes of 24 h. Some plants also received applications of a dilute NPK nutrient solution at weekly intervals. The continuously hydrated plants showed appreciably more biomass production than those receiving intermittent desiccation. Desiccation led to some bleaching of the green tissues inB. rutabulumbut not inP. purumwhich appeared more desiccation-tolerant. NPK addition caused a further significant growth stimulation in continuously hydrated plants, but not in intermittently desiccatedB. rutabulum. Pseudoscleropodium purumshowed NPK-induced growth stimulation even when intermittently desiccated. Net uptake of N was similar in desiccated and hydrated plants in both species. Considerable net uptake of P and K+occurred in continuously wetB. rutabulum, but uptake was much reduced in intermittently desiccated plants. Net uptake of P and K+byP. purumwas similar in desiccated and hydrated samples. Intracellular K+, leaked from the cells during the desiccation treatment, was retained by cation exchange on the negatively charged cell walls in both species. Levels of intracellular K+and Mg2+in the new growth were maintained at the expense of the pool of exchangeable cations. The growth stimulation and the net uptake of nutrients under intermittent desiccation was greatest when the NPK application was made at the start of rehydration, possibly because of accentuated uptake in the early stages of recovery. The results support the hypothesis thatP. purumhas a lower nutrient requirement thanB. rutabulumand highlight the importance of continuous hydration for the latter's more productive plant life strategy. The data also show that considerable new growth of bryophyte tissues is possible without additional nutrient absorption.

環境制御装置を利用した培養器外直接発根法におけるイチゴ植物体の生長

The growth of the strawberry (Fragaria×ananassa Duch. cv. Houkouwase) explants/plantlets rooted by the direct ex-vitro rooting method (DM) was compared with that of those rooted by the conventional method (CM). In DM, explants taken from micropropagated shoots were inserted into rockwool plugs and cultured in the environmental control unit by hydroponics using a diluted nutrient solution. In CM, the explants were cultured and grown in vitro to the plantlets on a sugar-added medium. After rooting, they were acclimatized in the same environmental control unit. Fresh and dry weights, leaf area, number of leaves, and plant height of the plantlets were larger by the DM than CM.

Phytotoxicity of aluminium-fluoride complexes and their uptake from solution culture by Avena sativa and Lycopersicon esculentum

Avena sativa (oats) and Lycopersiconesculentum (tomatoes) were grown in dilute nutrientsolutions supplemented with Al only, F only or acombination of both. In solutions containing Al andF, shoot growth was limited when predicted Alr(Al3+, AlOH2+ and Al(OH)\(_2^ + \))activities were < 0.1 μM, activities three orders ofmagnitude lower than the critical value determinedwith Al only. The data suggest that at the activitiesused in these experiments, Alr is most toxic,AlF2+ and AlF\(_2^ + \) are toxic to a lesserextent, and AlF3, AlF\(_4^ - \) and F-are least toxic. Fluoride concentrations in shootsgrown in solutions correlated best with positivelycharged AlF\(_x^{3 - x} \) species (i.e.AlF2+, AlF\(_2^ + \)) and the molar ratio ofF:Al in most plants shoots was about 3:2. However,when activities of positively chargedAlF\(_x^{3 - x} \) species were low (< 50 μM)and theactivity of AlF3 species high (500 μM) the molarratio of F:Al in plant shoots suggested AlF3 wastaken up. These findings are discussed in relation toplant uptake and toxicity. Measured concentrations of Alr and F- insolutions containing Al and F were compared withconcentrations predicted by a computer model(GEOCHEM-PC). The method for measuring F-concentrations, using a non-complexing buffer and Fion-selective electrode, gave good agreement withpredicted F- concentrations. The8-hydroxyquinoline method for measuring Alrconcentrations did not agree with predictedconcentrations, highlighting the limitations of thismethod when measuring Alr in the presence of F ina multi-ligand system with high concentrations of Fand Al.

Flowering and fruiting rootless cuttings of kiwifruit

Abstract Fully‐functional flowers and young fruit were produced in vitro on rootless, one‐bud kiwifruit (Actinidia deliciosa) cuttings. The cuttings were made from dormant canes with diameters ofbetween 7 and 10 mm, lengths of at least 150 mm, and weights of more than 12 g. Cuttings made from nodes 5, 10, and 15 on canes were more successful for flower production than cuttings made from nodes 20 and 25. The cuttings were grown in water or dilute nutrient solution and the new shoots bore flower buds. Anthesis only occurred on shoots which were modified by removing the shoot tip and all but one leaf and its subtended flower bud. Earlier shoot modification resulted in more flower buds reaching anthesis. Competition between reproductive and vegetative structures appeared to be a major factor determining the degree of flower development. The use of this system as a tool in different areas of research is discussed.

Changes in the expression of photosynthetic genes precede loss of photosynthetic activities and chlorophyll when glucose is supplied to mature spinach leaves

To study the molecular mechanism of ‘sink’ regulation on photosynthesis, thylakoid protein synthesis and content of photosynthetic proteins were compared with changes in photosynthetic activities and in leaf chlorophyll (chl) content in detached leaves kept on a diluted nutrient solution in the presence or absence of 50 mM glucose for 4 days at 60 μmol m −2 s −1. During the experiment, leaf chl content decreased in glucose-supplied leaves about 50%, in detached control leaves about 20%. The degradation of the photosynthetic apparatus was not connected with any substantial changes in photosynthetic parameters, when determined by pulse-modulated chl fluorescence at growth light conditions. However, at saturating light intensities of 1000 μmol m −2 s −1, leaf oxygen production was inhibited about 43% in leaves supplied with glucose, leading to a substantial increase in membrane energetization, as indicated by the increase of the non-photochemical quench, q n, and a down-regulation of photosystem (PS) II activity in the light, as determined by ΔF F′ m (yield of variable fluorescence under steady state conditions/fluorescence yield when all reaction centres are closed (after a saturating flash) under steady-state conditions). No substantial changes were observed in the detached control leaves. The reduction of leaf oxygen production under external glucose supply was probably caused by a 60% loss of ribulose-1,5-bisphosphat-carboxylase, as revealed by Western blotting. In the detached control leaves, the content of Rubisco stayed stable. The content of D1 protein of the PS II reaction centre was reduced by 43% in the glucose-supplied leaves, when related to chl. However, a substantial loss of D1 protein of 30% was observed in the detached control leaves. As in other systems, the specific loss of D1 protein initiated the degradation of PS II and via the breakdown of light harvesting complex (LHC) II the loss of leaf chl. By measuring thylakoid protein synthesis, it could be shown that the changes in D1 protein content were caused by an inhibition of its synthesis, together with an increase in its degradation. In the glucose-supplied leaves, the expression of the 25 kDa polypeptide of the LHC II was also inhibited.

Effect of aluminium and 6‐benzylaminopurine on the growth of the epicotyl in mungbean seedlings

Abstbact Aluminium (Al) toxicity was studied for mungbean (Phaseolus aureus Roxb.) seedlings under controlled environmental conditions in a growth chamber. Ten‐day‐old seedlings or cuttings (root removed) grew in dilute nutrient solution (pH 4.1) with Al levels and 6‐benzylaminopurine (6‐BA) concentrations for six days. Results showed that Al concentrations less than 2 mM had no significant effect on the length of the epicotyl in mungbean seedlings. Elongation of the epicotyl of intact seedlings was inhibited by 5 mM Al. The decrease in dry weight of the epicotyl was more evident than that in dry weight of hypocotyl, root, and primary leaves, indicating that epicotyl damage was greater than other organs by Al toxicity. No significant difference was found in the length of epicotyl between seedlings with and without 6–3A treatment. But there was a marked decrease in length of the epicotyl when cuttings were treated with 1 mM and 5 mM Al. Addition of 6‐BA to the nutrient solution significantly increased the ...

Rare earth elements and plant growth: II. Responses of corn and mungbean to low concentrations of lanthanum in dilute, continuously flowing nutrient solutions.

Abstract Corn (Zea mays cv. Hycorn 82) and mungbean (Vigna radiata cv. Berken) plants were grown for 16 d in dilute nutrient solutions containing constant cerium (Ce) concentrations from 0 to 1.31 μM. Corn root growth was increased approx. 2 fold at Ce concentrations 0.63 μM. However, the total dry matter production of corn was not significantly increased by Ce addition. With mungbean, the addition of as little as 0.19 μM Ce to the nutrient solution caused significant reductions in the dry weight of root (26%), shoot (48%) and total plant (44%). The youngest leaves of mungbean plants in the treatments containing 0.63 μM Ce displayed symptoms of manganese (Mn) deficiency. These leaves contained deficient Mn concentrations (5 mg/kg). Tissue concentrations of other nutrients in mungbean and all essential elements in corn were within ranges where healthy growth would be expected. The concentrations of Ce measured in the roots and shoots of mungbean were higher than in corn. Roots of both species accumulated m...

Rare earth elements and plant growth: III. Responses of corn and mungbean to low concentrations of cerium in dilute, continuously flowing nutrient solutions.

Abstract Corn (Zea mays cv. Hycorn 82) and mungbean (Vigna radiata cv. Berken) plants were grown for 16 d in dilute nutrient solutions containing constant cerium (Ce) concentrations from 0 to 1.31 μM. Corn root growth was increased approx. 2 fold at Ce concentrations 0.63 μM. However, the total dry matter production of corn was not significantly increased by Ce addition. With mungbean, the addition of as little as 0.19 μM Ce to the nutrient solution caused significant reductions in the dry weight of root (26%), shoot (48%) and total plant (44%). The youngest leaves of mungbean plants in the treatments containing 0.63 μM Ce displayed symptoms of manganese (Mn) deficiency. These leaves contained deficient Mn concentrations (5 mg/kg). Tissue concentrations of other nutrients in mungbean and all essential elements in corn were within ranges where healthy growth would be expected. The concentrations of Ce measured in the roots and shoots of mungbean were higher than in corn. Roots of both species accumulated much higher concentrations of Ce than the shoots. Cerium accumulated in the oldest leaves of both plant species. These patterns of distribution were similar to those reported previously for lanthanum.

Rare earth elements and plant growth: I. Effects of lanthanum and cerium on root elongation of corn and mungbean.

Abstract Root elongation of corn (Zea mays cv. Hycorn 82) and mungbean (Vigna radiata cv. Berken) seedlings was measured in dilute complete nutrient solutions to which varying amounts of lanthanum (La) or cerium (Ce) had been added. The nutrient solutions were aged for 9 d prior to conducting the root elongation experiments and solution samples ultra‐filtered to 0.025 μm before chemical analyses for La or Ce, and phosphorus (P). Concentrations of La up to 10 μM and concentrations of Ce up to 8 μM remained in solution in the presence of 5 μM P at pH 4.5, but substantial losses of these elements and P occurred at pH 5.5. The relative root elongation of both plant species decreased with increasing concentrations of La or Ce in solution. Mungbean was much more sensitive than corn. Cerium was more toxic than La to mungbean, the concentrations associated with a 50% reduction in root elongation being 0.9 μM Ce and 3.1 μM La. Lanthanum was more toxic to corn than Ce, the concentrations corresponding to a 50% redu...

Using small tubes to measure root elongation of newly germinated alfalfa seedlings in relation to moisture

A method of growing newly germinated seedlings in small tubes was developed to enable the study of early root elongation. Three newly germinated alfalfa (Medicago sativa L.) seeds were placed in tubes of various diameters and volumes filled with sand at several moisture tensions, and the tubes were sealed to prevent moisture loss. For the first 4 d, roots elongated at approximately 8 mm d−1 in polyvinyl chloride plastic tubes holding 60 mL of sand with a moisture tension of 100 kPa or less. After the initial 4 d, root elongation continued at a slower rate, and branch roots developed before termination of the experiments at 12 d after germination. At a moisture tension of 300 kPa, root elongation was markedly less than at 100 kPa, and was zero at moisture tensions of 500 kPa or greater. In round-bottom glass tubes, root elongation rate was significantly slower in a sand volume of 23 mL than in 65 mL, and there was evidence of slower seedling development as the diameter of the tubes was reduced from 20 to 15 mm. Wax plus masking tape or nylon tape were equally effective in sealing the sides of tubes formed from the two halves of a plastic pipe previously cut lengthwise. A plastic cap plus wax was significantly better than plastic film for sealing the bottom ends of plastic tubes. Neither aeration nor replacement of water with a dilute nutrient solution had an effect on root elongation of young seedlings. Key words: Alfalfa, seedling, root elongation, moisture stress, Medicago sativa

Aluminum toxicity in tomato. Part 2. leaf gas exchange, chlorophyll content, and invertase activity

Abstract The effect of aluminum (Al) toxicity on leaf gas exchange, leaf chlorophyll content, and sucrose metabolizing enzyme activity of two tomato cultivars (Lycopersicon esculentum Mill. ‘Mountain Pride’ and ‘Floramerica') was studied to determine the mechanism of growth reduction observed in a related study (Simon et al., 1994, Part 1). Plants were grown in diluted nutrient solution (pH 4.0) with 0, 10, 25, or 50 μM. Al for 16 days. Leaf gas exchange was reduced 2–3 fold in both cultivars as Al concentration increased. Gas exchange of ‘Mountain Pride’ was more sensitive to Al toxicity than ‘Floramerica’, agreeing with growth responses observed. Reductions in carbon dioxide (CO2) assimilation rate appeared to be due to nonstomatal factors in ‘Floramerica’, but stomatal and non‐stomatal limitations in ‘Mountain Pride’. Chlorophyll content of leaves was not affected by Al. Acid invertase (AI) and neutral invertase (NI) activity of roots responded consistently to Al concentration in both cultivars. Root A...