Effect of plant growth regulators on nitrate uptake and its reduction in radish cotyledons

Pretreatment of radish (Raphanus sativus L.) seedlings with exogenous hormones in the absence of external nitrate, resulted in a system having enough hormone levels to mediate the responses or activate the metabolic pathways which are necessary for nitrate (NO₃) uptake and reduction. Effects of pretreatment of radish seedlings with KN, GA, and ABA on the induction of NO₃ transport and corresponding NR activity, upon exposure to NO₃ were investigated. A low NO₃, uptake rate was observed with hormones when compared to DW‐control, while its induction pattern exhibited a sort of biphasic kinetics. It was observed that each hormone treatment affected NO₃ uptake and reduction specifically at different ambient concentrations of NO₃. On the basis of this, the operation of different constitutive and inducible (CHATS, LATS, HATS, and IHATS) transport systems was resolved for different hormonal treatments. Further, the hypothesis that nitrate uptake has direct role on nitrate reduction was supported by all treatments, except KN where highest NR activity despite lowest NO₃ uptake, was recorded. The results with KN points towards enhanced NR mRNA and de novo synthesis of enzyme.     

Effect of Plant Growth Regulators and Different Nitrogen Sources on Glutamate Dehydrogenase Activity

Radish (Raphanus sativus L.) seedlings, treated with various plant growth regulators (PGRs) [viz. kinetin (KiN), gibberellic acid (GA), and abscisic acid(ABA)] were exposed to different nitrogen (N) sources in light and dark condition, and aminative (NADH) and deaminative (NAD⁺) glutamate dehydrogenase (GDH) activities were measured in cotyledons. A differential effect of nitrogen sources, plant growth regulators, and light or dark condition was observed in all the treatments. The NAD‐GDH (deaminating) activity in radish seedlings was only about 10% of aminating activity (irrespective of the PGR treatment). Except with abscisic acid, in all other treatments, either NAD‐GDH or NADH‐GDH activities were more in dark than in light. The amination and deamination reactions also showed different ratios of activity under different N sources (KNO3, NH₄Cl and NH₄NO₃). These data suggest the presence of isoenzymes or conformers of GDH, specific for each tissue, whose activities vary depending on the physiological condition of the tissue. Different energy status of the seedlings during light or dark condition or with PGR treatments may affect the GDH activity differently.     

Barley growth,yield, antioxidant enzymes,and ion accumulation affected by PGRs under salinity stress conditions

Application of plant growth regulator (PGR) may alleviate some negative effects of environmental stresses such as salinity. A controlled environment experiment was conducted to study barley (Hordeum vulgare L. cv. Reyhane) growth, yield, antioxidant enzymes and ions accumulation affected by PGRs under salinity stress conditions at Shiraz University during 2012. The treatments were PGRs at four levels—water (as control), cycocel (CCC, 19 mM), salicylic acid (SA, 1 mM), and jasmonic acid (JA, 0.5 mM)—and four salinity levels—no stress (0.67 dS m^?1, as control), 5, 10, and 15 dS m^?1, which were arranged in a factorial experiment based on completely randomized design with four replicates. The results showed that salinity stress significantly decreased plant height, peduncle length, leaf area, ear length, grain number, dry weight, grain yield, harvest index, potassium (K⁺) accumulation, and potassium/sodium (K⁺/Na⁺) concentration ratio, which were closely associated with stress severity. However, PGRs compensated some of these negative effects, so that SA foliar application had the most ameliorative effect. Salt stress also increased Na⁺ accumulation as well as the activity of peroxidase, catalase, and superoxide dismutase (SOD). Since ion discrimination and enhanced antioxidant enzymes are associated with salt tolerance, in this experiment PGRs application might have enhanced K⁺ accumulation and antioxidant enzyme activity. The activity of SOD and K⁺/Na⁺ ratio were found to be useful in salt tolerance manipulation in barley plants.     

Do reactive oxygen species (ROS) induced by NaCl contribute to ammonium accumulation in Spartina alterniflora?

Growth, activity of antioxidant enzymes viz. glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX), and some metabolic processes related to ammonium metabolism were investigated in a salt‐tolerant Spatina alterniflora. In comparison to 0 mM–NaCl treatment, growth of S. alterniflora plant increased significantly at 200 mM NaCl, but was highly inhibited at 500 mM NaCl. Ammonium concentration in the leaves and roots increased 2.1–3.4 times when plants were treated with 500 mM NaCl. Under 200 mM NaCl, antioxidant‐enzyme activities increased, however, at 500 mM the antioxidant system was unable to compensate reactive oxygen species induced by NaCl. At this high level of salinity, ammonium production through nitrate reductase (NR) was inhibited, but no significant changes in the activities of glutamine synthetase (GS) or glutamate dehydrogenase (GDH) were found. We conclude that the accumulation of ammonium under high salt stress was not due to inhibition of the assimilatory activities of GS or GDH. Ammonia accumulation under high salinity may result from amino acid and protein catabolism activated by reactive oxygen species (ROS) and/or a lack of carbon skeletons to incorporate ammonium into organic molecules due to a decrease in photosynthetic activity in salt‐stressed plants.     

Intraspecific differences in nitrogen assimilating enzymes in spinach under contrasting forms of nitrogen supply 1

Intraspecific differences in the activities of nitrate reductase (NR), glutamine synthetase (GS), NADH dependent glutamate synthase (NADH‐GOGAT), and glutamate dehydrogenase (GDH) under contrasting forms of nitrogen (N) supply were studied in tissues of three spinach (Spinacia oleracea L.) cultivars. The varieties (Viroflay, Butterflay, and Giant) were smooth, curly and semicurly leaved, respectively. The plants were grown in nutrient solutions containing NO₃ as the sole source of N (100:0) and NO₃ plus NH₄ (80:20). Giant, the NH₄ tolerance of which had been evaluated in growth and on the basis of nutrient uptake, had much higher GS and GDH activities in the roots and higher NR and NADH‐GOGAT levels in the leaves of plants grown on NO₃ and NH₄ than that grown on NO₃ alone. On the level of N assimilating enzymes of Butterflay, mixed N nutrition caused an increase of GDH and NADH‐GOGAT in leaves and roots and at the same time a decrease of GS in the roots and NR in the leaves. An inverse relationship between GS and GDH activities was detected in the leaves and foots of Virofiay grown with both N sources. Finally, Viroflay gave the highest levels of GDH irrespective of the NO₃:NH₄ assayed, whereas the leaves of Giant were GDH deficient in comparison with the other cultivars. In addition, the GS activity approached zero in the roots of spinach cultivars characterized by hardly any NH₄ tolerance, whereas in those of Giant it increased remarkably with the supply of NO₃ plus NH₄.     

Forms of Nitrogen Alter Plant Phosphorus Uptake and Pathways in Rehabilitated Highly Alkaline Bauxite Processing Residue Sand

Understanding plant phosphorus (P) uptake and pathways is critical in the rehabilitation of degraded landscapes. This study investigated whether the uptake of P by Lolium rigidum was influenced by forms (inorganic and organic) of nitrogen (N) and whether the forms of N affected P loss by leaching in bauxite‐processing residue sand (BRS). Gypsum amended BRS was grown with L. rigidum and fertilized with P [calcium di‐hydrogen phosphate, Ca (H₂PO₄)₂], plus different forms of N [e.g. control (CK without N addition, glycine (P‐GL), ammonium (P‐AS) and nitrate (P‐KN))]. The experimental treatments were arranged in a complete randomized design. Aboveground biomass P under P‐KN accounted for 47.4% of applied P, but only 26.0% and 25.0% under P‐AS and P‐GL, respectively. However, root P contents showed a different trend where P‐AS (31.9%) was highest followed by P‐GLY (23.0%) and P‐KN (17.1%). Meanwhile, loss of P via leaching was minimal (<5% of applied P) regardless of treatment, which could be because of the high affinity of residue sand for P via specific adsorption sites. This was supported by high percentage recovery of applied P in BRS growth media under P‐GLY (48.1%), P‐AS (37.2%) and P‐KN (32.0%). It is concluded that loss of P via leaching may not be a problem in BRS; however, limited plant P availability may be of more concern. Further, uptake of P by L. rigidum in alkaline BRS was found to be more efficient under nitrate‐N fertilization. Understanding, however, the specific or associated mechanisms involved warrants further investigation. Copyright © 2016 John Wiley & Sons, Ltd.     

Responses of Batis maritima plants challenged with up to two‐fold seawater NaCl salinity

Batis maritima is a promising halophyte for sand‐dune stabilization and saline‐soil reclamation. This species has also applications in herbal medicine and as an oilseed crop. Here, we address the plant response to salinity reaching up to two‐fold seawater concentration (0–1000 mM NaCl), with a particular emphasis on growth, water status, mineral nutrition, proline content, and photosystem II integrity. Plant biomass production was maximal at 200 mM NaCl, and the plants survived even when challenged with 1000 mM NaCl. Plant water status was not impaired by the high accumulation of sodium in shoots, suggesting that Na⁺ compartmentalization efficiently took place in vacuoles. Concentrations of Mg²⁺ and K⁺ in shoots were markedly lower in salt‐treated plants, while that of Ca²⁺ was less affected. Soluble‐sugar and chlorophyll concentrations were hardly affected by salinity, whereas proline concentration increased significantly in shoots of salt‐treated plants. Maximum quantum efficiency (F_v/F_m), quantum yield of PSII (Φ_PSII), and electron‐transport rate (ETR) were maximal at 200–300 mM NaCl. Both nonphotochemical quenching (NPQ) and photochemical quenching (qP) were salt‐independent. Interestingly, transferring the plants previously challenged with supraoptimal salinities (400–1000 mM NaCl) to the optimal salinity (200 mM NaCl) substantially restored their growth activity. Altogether, our results indicate that B. maritima is an obligate halophyte, requiring high salt concentrations for optimal growth, and surviving long‐term extreme salinity. Such a performance could be ascribed to the plant capability to use sodium for osmotic adjustment, selective absorption of K⁺ over Na⁺ in concomitance with the stability of PSII functioning, and the absence of photosynthetic pigment degradation.     

Silicon‐induced cadmium resistance in rice (Oryza sativa)

Silicon (Si)‐induced cadmium (Cd) tolerance in rice (Oryza sativa L.) was investigated by analyzing Cd uptake, growth, and physiological parameters. Silicon treatments (0.0, 0.2, or 0.6 mM) were added to 6 d–old seedlings, and Cd treatments (0.0 or 5.0 μM) were added to 20 d–old seedlings. Parameters determined included: maximum net CO₂ assimilation (A_max), stomatal conductance (g_smax), and transpiration (E_max) rates at varying intercellular CO₂ concentrations (C_i). Also measured were chlorophyll fluorescence, growth, and Cd‐uptake parameters. Results showed a Si‐induced inhibition of Cd uptake. However, 0.2 mM or 0.6 mM Si treatment concentrations did not differentially inhibit Cd uptake or differentially alleviate Cd‐induced growth inhibition, despite a significant increase in tissue Si concentration due to 0.6 mM Si treatment compared to 0.2 mM Si treatment. Additionally, photosynthesis and chlorophyll‐fluorescence analysis showed that treatment with Cd significantly inhibited photosynthetic efficiency. Interestingly, the addition of 0.2 mM Si, more so than the addition of 0.6 mM Si, significantly alleviated the inhibitory effects of Cd toxicity on photosynthesis and chlorophyll‐fluorescence parameters. Our results suggest that 0.2 mM Si could be close to an optimum Si‐dose requirement for the alleviation of toxicity symptoms mediated by moderate (5 μM) Cd exposure.     

Isolation,distribution, and characterization of peach seedling nitrate reductase 1

Nitrate reductase (NR) was extracted from leaf, root, and stem tissue of ‘Lovell’ peach seedlings [Prunus persica (L.) Batsch] grown for 8 weeks in nutrient solution containing 15 mM nitrate. Enzyme activity of NR in leaf, stem, and root tissue was 10.20: 0.07: 0.04 nM N0₂/min/g tissue extracted, respectively. When seedlings wee transferred to nutrient solution containing 15 mM NH₄, NR activity was not detected after 72 hours. The enzyme was specific for NADH and had a pH optimum of 7.5. The K_m for NO₃ was 1.3 x 10–3 M and the rate of reaction remained linear for 45 min. Enzyme activity of leaf tissue was dependent on NO₃ concentration in the nutrient solution. At NO₃ concentrations of 15, 7.5, 1.5, and 0.15 mM, the NR activity was 22.8, 16.2, 13.8, and 2.2 nM NO₂/mg protein/hr.     

SOIL PROPERTY CHANGES FOLLOWING IRRIGATION WITH COALBED NATURAL GAS WATER: ROLE OF WATER TREATMENTS,SOIL AMENDMENTS AND LAND SUITABILITY

Saline‐sodic water is a by‐product of coalbed natural gas (CBNG) production in the Powder River Basin of Wyoming, USA and is being beneficially used in places as irrigation water. This study evaluated effects of 2 years of natural precipitation on soil properties of a hay field after the cessation of managed irrigation with CBNG water. The hay field had been irrigated with only CBNG water [CBNG(NT)], CBNG water amended with gypsum [CBNG(G)] or gypsum plus sulfur via a sulfur burner [CBNG(GSB)] in combination with soil amendments—gypsum ( +G ), elemental sulfur ( +S ), and both ( +GS ). Results indicated that infiltration rates were the lowest on fields irrigated with CBNG(NT), followed by CBNG(G) and CBNG(NT) +G treatments (12·2, 13·2, and 13·5 cm h⁻¹, respectively). The CBNG(GSB) +GS treatment had the highest infiltration rates (33·5 cm h⁻¹). By the second year, salinity and sodicity of treated soils had decreased in the A‐horizon of most CBNG‐water irrigated plots, whereas in Bt₁‐ and Bt₂‐horizons salinity generally decreased but sodicity increased; S and GS soil amended plots had higher profile salinities compared with NT and G soil treatments. Although Na⁺ leaching was observed in all fields that received soil and/or water amendments, CBNG(GSB) +GS plots had the lowest sodicity in the A‐ and Bt₁‐horizons. Effective managed irrigation requires knowledge of site‐specific soil properties, plant suitability, water chemistry, and amendments that would be needed to treat the CBNG waters and soils. This study indicates the greatest success was realized when using both soil and water amendments. Copyright © 2011 John Wiley & Sons, Ltd.     

Influence of the Modification of Nutritional Parameters in Aglaonema commutatum: K+, Ca2+, Mg2+ and Na+

Abstract

This trial was carried out to establish an appropriate nutrient solution for Aglaonema commutatum and to investigate the nutritional effects generated by modifications in the solution. Six treatments were tested: control (T₀; pH 6.5, E.C. 1.5 dS m^?1, 6 mmol L^?1 NO₃ ^?‐N, and 6 mmol L^?1 K⁺); high nitrogen (N) level (T₁; 9 mmol L^?1 6:3 NO₃ ^?–NH₄ ⁺); N form (T₂; 6 mmol L^?1 N‐NH₄ ⁺); high K⁺ level (T₃; 12 mmol L^?1 K⁺); high electrical conductivity (T₄; E.C. 4 dS m^?1, 25 mmol L^?1 NaCl), and basic pH (T₅; pH 8). At the end of the cultivation, leaf, shoot, and root dry weights and elemental concentrations were determined. Nutrient contents and total plant uptake were calculated from the dry weights and nutrient concentrations. Plant K⁺ uptake increased with application of K⁺ or basic nutrient solution. The uptake and transport of calcium (Ca) were enhanced by the use of NO₃ ^?‐N and inhibited by the presence of other cations in the medium (NH₄ ⁺, K⁺, Na⁺) and by basic pH. Magnesium (Mg) uptake increased with NO₃ ^?‐N application and with pH. Sodium (Na) uptake was the highest in the saline treatment (T₄), followed by the basic pH treatment. Sodium accumulation was detected in the roots (natrophobic plant), where the plant generated a physiological barrier to avoid damage. Dry weight did not differ significantly (p<0.05) among treatments except in the NaCl treatment. These results may help in the formulation of nutrient solutions that take into account the ionic composition of irrigation water and the physiological requirements of plants.     

In situ characterization of hydraulic conductivities of individual soil profile layers during infiltration over long time periods

Several studies have raised serious doubts about the suitability of small cores for measuring water‐movement attributes, due to their potential to provide unrealistic representation of macropore connectivity and abundance. This study explored the potential of lysimeter‐scale experiments to calculate the hydraulic conductivity, K(ψ_m), of undisturbed soil layers in a matric potential (ψ_m) range between 0 and −4 kPa. Four large lysimeters were collected from a Dystric Cambisol. For each lysimeter a tension infiltrometer supplied infiltrating water under suctions of 0, 0.5, 1 and 1.5 kPa. Soil water dynamics were measured in situ using arrays of tensiometers, at depths corresponding with layer boundaries. The results show clearly that infiltration and drainage rates are intimately linked to temporal ψ_m dynamics, which themselves are determined by preferential flow and soil‐layer interactions. A quasi‐steady state was identified as when infiltration matched drainage, and ψ_m measurements showed each layer had a stable hydraulic gradient, which then allowed in situ determination of the K(ψ_m) relationship of individual soil layers. For this soil K(ψ_m) is distinctly different for each soil layer, and these differences are consistent among the four lysimeters. A consistent feature is that all layers have a distinct change in the slope of the K(ψ_m) relationship, in the ψ_m range of −0.5 to −1.5 kPa, highlighting a dual‐porosity character. The whole‐column infiltration behaviour was strongly linked to the K(ψ_m) relationship of the surface layer (0–2 cm depth), and therefore hydraulic characterization of this layer should be a critical component of a soil survey.     

Effects of Nitrate and Potassium on Ammonium Toxicity in Cucumber Plants

ABSTRACT

Interactions between nitrate (NO₃ ^?), potassium (K⁺), and ammonium (NH₄ ⁺) were investigated using hydroponically grown cucumber (Cucumis sativus L.) plants. Ammonium as the sole nitrogen (N) source at 10 mM was toxic and led to overall growth suppression, chlorosis, and necrosis of leaves. After 20 days, 50% of the plants were dead. However, when NO₃ ^? was supplied at very low concentration together with high NH₄ ⁺ (only 1% of total 10 mM N) all seedlings survived and their growth was improved. High K⁺ concentration (5 mM) also alleviated NH₄ ⁺ toxicity and increased plant growth several fold compared to intermediate concentration of K⁺ (0.6 mM). Leaf total N and ¹⁵N derived from ¹⁵N-labelled NH₄ ⁺ increased in the presence of NO₃ ^?, but decreased at high K⁺ concentration. High K⁺ supply enhanced total carbon (C) and δ ¹³C and stimulated GS and PEPCase activities in leaves and roots. Nitrate supplementation had no effect on GS or PEPCase activities. It is concluded that K⁺ may alleviate NH₄ ⁺ toxicity, partly by inhibiting NH₄ ⁺ uptake, partly by stimulating C and N assimilation in the roots.     

Plant growth,leaf photosynthesis,and nutrient‐use efficiency of citrus rootstocks decrease with phosphite supply

Some formulations of phosphite (Phi) have been recommended as a source of P nutrition for several crops including citrus even though there are known negative effects of Phi on plant growth. Changes in plant growth and metabolism after Phi application should be reflected in altered nutrient‐use efficiency and leaf photosynthesis. We carried out a greenhouse study using seedlings of two contrasting citrus (Citrus spp.) rootstocks, Carrizo citrange (CC) and Smooth Flat Seville (SFS), growing in either aerated hydroponic culture or sterilized native sandy soil. Plants were subjected to four P treatments: No P (control, P₀); 0.5 mM P_i (PO₄‐P); 0.25 mM P_i + 0.25 mM Phi (P_i + Phi), or 0.5 mM Phi (Phi). Photosynthetic characteristics, concentrations of total P (P_t) and soluble PO₄‐P or PO₃‐P in leaves and roots, and plant growth were evaluated after 80–83 d P treatments. Overall, the P_i plants had the highest P_t (total P) and total plant dry weight while the P₀ plants had the lowest P_t but highest total root length and root‐to‐shoot ratio. Leaf chlorophyll (SPAD readings) and net assimilation of CO₂ (A_CO2) of the P₀ and Phi plants were similarly lower than those of P_i and P_i + Phi plants. Growth responses of the P_i + Phi treatment were intermediate between the P_i and Phi treatments. Although Phi increased P_t and soluble‐PO₄‐P concentration in leaves and roots above the P₀ treatment, this did not translate into increased plant growth. In fact, the Phi treatment had some phytotoxic symptoms, impaired P‐ and N‐utilization efficiency for biomass production as well as lower nutrient‐use efficiency in the photosynthetic process. Thus, these two rootstocks could not use Phi as a nutritional source of P.     

Fruit quality and partitioning of mineral elements in processing tomato in response to saline nutrients

A sand culture experiment was conducted to study the effect of saline water on the growth and fruit quality of processing tomato (Lycopersicon esculentum Mill.) Seedlings of five tomato cultivars were transplanted in quartz‐sand pots in a greenhouse at the Agricultural Experiment Station of Sultan Qaboos University. There were four saline nutrient solutions and a control consisting of half‐strength Hoagland solution. Salinity treatments were: 50 raM NaCl + 3 mM K₂SO₄ (EC 6.75), 50 mM NaCl + 1.5 mM orthophosphoric acid (EC = 7.18), 50 mM NaCl + 1.5 mM orthophosphoric acid + 3 mM R₂SO₄ (EC 7.29), and 50 mM NaCL (EC = 5.6). Treatments were applied daily commencing two weeks after transplanting. Data were collected on growth, and fruit yield and quality. Partitioning of mineral elements was determined in the vegetative tissue. The results obtained clearly show that concentrations of total soluble solids were increased in fruits treated with saline nutrients. Dry matter content of fruits exposed to salinity were higher than those from the control plants. Fruit acidity was increased with salinity, possibly due to a lower water content and increased organic acid accumulation. In the saline treatments, sodium (Na) content was decreased when potassium (K) was applied with NaCl but Na was higher in stems followed by root and leaf tissues. The partitioning of K followed a trend opposite to that for Na but with higher content in leaves. A similar situation was observed for calcium (Ca) and magnesium (Mg). Accumulation of phosphorus (P) was the lowest among all the ions. These results indicated that survival under saline conditions was accompanied by high ion accumulation. The study confirmed that saline nutrients are important for improving fruit quality of processing tomatoes.     

Differences in nitrogen‐assimilating enzyme activity in halophyte species are habitat‐related

The chemical form and content of available nitrogen (N) in salt marsh substrates varies considerably. On the western coast of Ireland, habitats designated as Ombrogenic Atlantic salt marshes were formed on ombrogenic peat substrate. The peat substrate in these systems has three times more ammonium than substrate from adjacent salt marsh habitats on sand and mud substrate. This study examined the extent to which the high concentration of ammonium in peat salt marsh substrate influences the N‐ assimilating enzyme activity of halophytes and the extent to which N metabolism differs between species. Specifically, this work investigated whether plants from peat salt marshes are more likely to assimilate ammonium than plants from non‐peat substrates. Four halophyte plant species—Armeria maritima, Aster tripolium, Plantago maritime, and Triglochin maritime—were sampled from various saltmarsh habitats including three sites on peat substrate and three on non‐peat substrate, comprising sand, mud and sand/mud. The activities of N‐metabolising enzymes—glutamine synthetase (GS), glutamate synthase, glutamate dehydrogenase (GDH), and nitrate reductase (NR)—were quantified in shoot and root parts. Root GS activity in Armeria maritima and shoot GS activity in Triglochin maritima were positively correlated with increasing soil ammonium levels. Root NR activity in Aster tripolium and shoot NR activity in Plantago maritima were significantly higher in plants grown on non‐peat substrates than peat substrates. The shoot : root GS activity ratio in Triglochin maritima on peat substrate was more than double the ratio on non‐peat substrates. It is concluded that all species tested displayed differences in N‐metabolising activities depending on the chemical form and/or concentration of N in the substrate, while three out of the four species were capable of taking advantage of the high levels of ammonium in peat substrates.     

Quantity‐intensity parameters of potassium in relation to uptake by guinea‐corn in representative soils of the ecological zones of Nigeria

Abstract

Quantity‐intensity (Q‐I) relation studies were often used to supplement information obtained from conventional soil tests for the estimation of potassium (K) needs of crops. With a view to ascertaining the reliability of the Q‐I relation parameters for comprehensive characterization of K dynamics in typical Nigerian soils, K values derived from Q‐I isotherms were related to neutral normal ammonium acetate (1 N NH₄OAc, pH 7.0) (exchangeable) K, other soil K forms [non‐exchangeable (K_ne), exchange (K_e), mineral K (K _m ), and solution K (K_s)] and the K uptake by Guinea‐corn (Sorghum bicolor, var. LS 187) subjected to weekly cuts in Neubauer cultivation vessels. Most of the soil K (about 98%) was in the form of soil minerals while less than 1% was plant available whereas about 1% was trapped within the interlattice layers of the clay minerals (as fixed K or K_ne). Mineral K (K_m) content was closely related to total K (K_t), but not to the other forms, K_ne, K_e, and K_s. A close relationship was noted between the two components of labile K (K_e and K_s). Except for % K saturation, the relationships between the K measurements with plant response were poor. The results of these investigations clearly demonstrate that the Q‐I relation could not adequately characterize the K dynamics of these tropical soils.     

Aluminum toxicity in maize: Biomass production and nutrient uptake and translocation

The effect of increasing aluminum (Al) concentrations on root nutrient contents along with the concurrent translocation to the shoot of C₄ plants prompted this study. Two‐week‐old maize (Zea mays cv XL‐72.3) plants were therefore submitted for 20 days to Al concentrations ranging from 0 to 3.00 mM in a medium with low ionic strength were used as a test system. Aluminum concentrations in root tissues showed a 3‐fold increase between 0 and 3.00 mM Al treatment, and was not detected in the shoot. Root plasma membrane‐H⁺ ATPase activity decreased after the 0.33 mg L^‐1 Al treatment, while membrane permeability increased up to 1.00 mM Al treatment. Root and shoot biomass decreased after the 0.33 mM Al treatment. All elements in the roots, except potassium (K), manganese (Mn), and zinc (Zn) were highest for plants treated with 0.33 mM Al. Potassium increased continuously between 0 and 3.00 mM Al treatments, and iron (Fe) decreased above 0.33 mM. Only a slight decrease in nitrogen (N) was observed. All the measured nutrients in shoots, except N, Mn, and Fe decreased above 0.33 mM, but calcium (Ca) and magnesium (Mg) had little variation as Al varied. Data indicated that maximum net uptake for mineral nutrients, except Mn, occurred up to 0.33 mM Al. Translocation of phosphorus (P), K, Mn, and Zn decreased above 0.33 mM Al, N, and Ca decreased when any Al was added, and no clear trend was observed for Mg and Fe. Between the 0 and the 3.00 mM Al treatments, electrolytic conductance did not increased significantly indicating that the observed inhibitions of translocation from roots to shoots were not directly related to increasing membrane degradation.     

Assessment of the Nitrogen and Potassium Fertilizer in Green Bean Irrigated with Disinfected Urban Wastewater

Green bean Helda in autumn cycle (118 days) was grown under greenhouse conditions in sand-mulched sandy loam soil. The crop was irrigated with disinfected urban wastewater (DUW) obtained from ozone from the Almería Purifying Plant. The average nutrient parameters of DUW were 0.4 mM of nitrate (NO₃ ^?), 2.1 mM of ammonium (NH₄ ⁺), 0.8 mM of potassium (K⁺), and electrical conductivity (EC) 1.6 dS m^?1. Three different treatments were established: DUW without additional fertilization (F_DUW), DUW with fertilization until the recommended rate was obtained (10.0 mM of N and 3.4 mM of K) (F_NK), and DUW with fertilization until 1.5 F_NK rate (15.0 mM of N and 5.1 mM of K) (F_1.5NK) was obtained. The dry-matter production was not conditioned by the fertilizer level. Treatments F_NK and F_1.5NK showed the greatest yield and uptake of N and K independent of the fertilizer level. The most nitrogen (N), calcium (Ca), and magnesium (Mg) were in the leaf, phosphorus (P) was high in fruit, and K was similar in leaf and fruit. With regard to the macronutrient absorption efficiency, the F_1.5NK treatment showed the least N and K efficiency and the greatest soil salinity.     

Iron and zinc absorption characteristics and copper inhibitions in cucurbitaceae

Iron and Zn absorption, interactions, and Cu inhibitions were characterized in cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thunb.), and pumpkin (Cucurbita moschata Poir.) by kinetic parameters V_max and K_m. Influx and V_max values for Fe and Zn absorption decreased in each species as plant age increased. For the Michaelis constant, K_m, Fe values in cucumber and watermelon and Zn values in watermelon and pumpkin were relatively unchanged with increased plant age. K_m values for Zn absorption in cucumber and Fe absorption in pumpkin decreased as plant age increased. Among species, watermelon appeared to have a particularly effective uptake mechanism for Zn at low solution concentrations. Non‐competitive inhibition of Zn absorption by Fe (20, 50 uM) was indicated in each species. Iron uptake in pumpkin was inhibited non‐competitively by Zn (5, 10 uM), however no significant effects of Zn on Fe absorption were evident in either watermelon or cucumber. Copper (0.5, 1, 5 uM) inhibited uptake of Fe non‐competitively and Zn competitively in each species.