Method for the quantification of acid production by plants in gel

Abstract

Hydrogen (H⁺) and hydroxyl ion (OH^‐) production by the tropical grass, Brachiaria humidicola, is quantified using a method in which the plants are grown in soil then transferred to agar gel for 24 h. The amount of H⁺ and OH^‐produced was calculated from the pH of the melted gel and the gels’ buffer curve. Values were obtained for plants of different ages and with nitrogen (N) supplied in the gel as nitrate (NC₃ ^‐), ammonium (NH₄ ⁺), or ammonium nitrate (NH₄NO₃) and compared with data calculated using the sum of H⁺ changes in differently colored zones of the gel. Daily H⁺ and OH^‐ production increased with plant age and total dry matter for the NH₄ ⁺‐ and NO₃ ^‐‐fed plants, respectively. By integrating the data over time, a value of 0.33 mmol H⁺ plant^‐1 was obtained for the total H⁺ production over 62 d. The proposed method was sufficiently rapid and versatile to allow the comparison between plant species or genotypes, which were grown using a variety of nutrient supplies. This procedure may indicate how acid production affects plant nutrient acquisition and aid the prediction of soil acidification by different plant species or cultivars.     

Evaluation of Extractants and Quantity–Intensity Relationship for Estimation of Available Potassium in Some Calcareous Soils of Western Iran

Accurate estimation of the available potassium (K⁺) supplied by calcareous soils in arid and semi‐arid regions is becoming more important. Exchangeable K⁺, determined by ammonium acetate (NH₄OAc), might not be the best predictor of the soil K⁺ available to crops in soils containing micaceous minerals. The effectiveness of different extraction methods for the prediction of K‐supplying capacities and quantity–intensity relationships was studied in 10 calcareous soils in western Iran. Total K⁺ uptake by wheat grown in the greenhouse was used to measure plant‐available soil K⁺. The following methods extracted increasingly higher average amounts of soil K⁺: 0.025 M H₂SO₄ (45 mg K⁺ kg^?1), 1 M NaCl (92 mg K⁺ kg^?1), 0.01 M CaCl₂ (104 mg K⁺ kg^?1), 0.1 M BaCl₂ (126 mg K⁺ kg^?1), and 1 M NH₄OAc (312 mg K⁺ kg^?1). Potassium extracted by 0.01 M CaCl₂, 1 M NaCl, 0.1 M BaCl₂, and 0.025 M H₂SO₄ showed higher correlation with K⁺ uptake by the crop (P < 0.01) than did NH₄OAc (P < 0.05), which is used to extract K⁺ in the soils of the studied area. There were significant correlations among exchangeable K⁺ adsorbed on the planar surfaces of soils (labile K⁺) and K⁺ plant uptake and K⁺ extracted by all extractants. It would appear that both 0.01 M CaCl₂ and 1 M NaCl extractants and labile K⁺ may provide the most useful prediction of K⁺ uptake by plants in these calcareous soils containing micaceous minerals.     

Fixed ammonium and potassium release from two soils

Abstract

Release of native and added K⁺ and NH⁺ ₄ from two soils was monitored during a 166 day incubation/leaching experiment. One soil (Brookston) represented a major soil series In Ontario whereas the other (Harriston) was suspected having a relatively large fixation capacity. Treatments were imposed involving addition of 50 μM g^‐1 soil of K⁺(KCl) or NH⁺ ₄ (NH₄Cl) only or one added after the other on successive days. The addition of either K⁺ or NH⁺ ₄ on day 2 tended to inhibit the release of the other added on day I. Also the addition of either K⁺ or NH⁺ ₄ on day 1 tended to inhibit the sorption or fixation of the other on day 2. The release rate of K⁺ during the 10 to 166 day period was almost constant and not affected by the addition of NH⁺ ₄. Alternatively, the addition of K⁺ on day 2 slowed the release rate of NH⁺ ₄ measured by NO^? ₃ appearance from day 10 to 40 but had no effect thereafter. At the end of the experiment considerably more K⁺ than NH⁺ ₄ was retained suggesting that K⁺ was more firmly fixed. However, the continuing nitrification of NH⁺ ₄ must be contrasted with periodic removal of K⁺ by leaching with 0.01 M CaCl₂ solution since the equilibrium between exchangeable and fixed ions was affected. There were no notable differences between the two soils inspite of a considerable difference in clay content.     

不同铵钾比对高铵下拟南芥地上部和根系生长的影响

钾在缓解植物铵毒害的过程中起着重要的作用。本文研究了高铵(30 mmol/L)条件下,不同铵钾比(7.5︰1和150︰1)对拟南芥(Col-0)主根、侧根以及地上部生长的影响。结果表明:30 mmol/L NH4+条件下,高铵钾比(150)处理显著加重了拟南芥铵毒害现象,地上部和根系生长所受的抑制作用更为明显并导致更严重的氧化胁迫。相比低铵钾比水平,在高铵处理下,高铵钾比使得拟南芥主根伸长量降低57.4%,侧根数量减少33.3%,而地上部鲜重减轻69.9%。DAB(3,3￠-二氨基联苯胺,3,3￠-diaminobenzidine)叶片染色结果表明,不加铵处理下,外源不同钾水平(0.2和4.0 mmol/L)对拟南芥叶片的氧化胁迫作用没有显著差异;而高铵处理下,相比低铵钾比处理,高铵钾比显著增加了叶片中过氧化氢的含量,加重了其氧化胁迫。伊文思蓝(Evans blue,EB)染色结果表明,不加铵处理下,外源不同钾水平对拟南芥地上部和根部的膜透性没有显著差异,而高铵处理下,高铵钾比显著增强了拟南芥地上部和根部的膜透性,表明其对细胞的伤害程度加重。可见,高铵抑制拟南芥根系和地上部生长,高铵钾比则会加重这种抑制,其原因除了高浓度钾能减少植物对铵的吸收外,可能与高铵钾比条件加剧了植物的氧化胁迫有关。因此,适宜的铵钾比在植物应对铵毒害的过程中发挥重要作用。     

Indications for passive rather than active release of natural nitrification inhibitors in Brachiaria humidicola root exudates

Plants have the ability to suppress microbial nitrification process through secondary metabolites released from their root exudates or/and leaf litter. For decades, grasses were suggested to control nitrification process, and recently, Brachiaria humidicola accession 26159 (BH) as a tropical and subtropical grass has been shown to reduce nitrification rates under laboratory and soil conditions. In this study, experiments were conducted under controlled conditions in nutrient solution culture to investigate whether the reported release of natural nitrification inhibitors from root exudates of BH is an active or passive phenomenon. So different variables such as N-form (nitrate vs. ammonium), collecting medium (distilled water vs. 1 mM NH₄Cl) and collecting period (6 vs. 24 hrs) were included to study the hypothesis. Results showed when root exudates were collected in distilled water there was no nitrification inhibition activity for all ammonium and nitrate grown plants. However, when collection was done in a medium containing 1 mM NH₄Cl, root exudates showed significant nitrification inhibition activity similar to results obtained by Subbarao et al. The observed nitrification inhibition activity had a positive correlation to ammonium treatment particularly in collection medium, probably due to root cells damage induced by low pH and membrane depolarization under ammonium nutrition. This was more supported by application of shoot homogenates of NH₄⁺, NO₃^? or NH₄NO₃ grown plants that showed significant nitrification inhibition activity compared to distilled water and DMPP controls in a bioassay test, independent of N-form. Potassium concentrations in root exudates (as a result of potassium leakage) were found to increase in root washings of plants, which were grown with ammonium, particularly when root exudates were collected in 1 mM NH₄Cl solution. In addition, higher electric conductivity of root washings after collection of root exudates in ammonium containing medium (low pH) and also in nitrate containing medium which adjusted to pH 3 by applying H₂SO₄, strongly suggest that release of natural nitrification inhibitors from root exudates of B. humidicola may not be an active process, but instead it is rather a passive phenomenon by ammonium induced root physicochemical damages.     

Importance of plasmalemma ATPase in the retention and exclusion of inorganic ions

The experiments were focused on the question whether the plasmalemma ATPase activity (proton pump) has an influence on the efflux of major inorganic ion species. Efflux from roots of intact Trifolium pratense, Hordeum vulgare, Glycine max, and Zea mays was examined into a solution containing 100 μM CaCl₂ and 500 μM NH₄⁺ as sulfate in the control solution and 100 μM CaCl₂ and 500 μM NH₄⁺ as vanadate in the test solution. Vanadate being an inhibitor of the plasmalemma ATPase depressed significantly the H⁺ secretion of roots into the outer solution but had no major impact on the efflux of cation species. In the presence of vanadate significantly higher amounts of sulfate, phosphate, and nitrate were released into the outer solution by roots of soya and maize as compared with the control treatment (no vanadate). In the absence of vanadate, virtually no nitrate was released by all species examined whereas in the vanadate treatment significant amounts of NO₃^? were released. Vanadate inhibited the uptake of Cl^? in barley and maize and increased the uptake of Ca²⁺ in soya. It is concluded that the plasmalemma ATPase activity plays a major rule in the “ionic stat” of cells in providing protons to the apoplast for the reabsorption of sulfate, phosphate, and particularly nitrate which have leaked out of the cytosol.     

Blocking the release of potassium from clay interlayers by small concentrations of NH4+ and Cs+

To understand the process and the kinetics of potassium release from the clay interlayer in natural and arable soils in more detail, I tested the hypotheses that large, monovalent cations, especially NH₄⁺ and Cs⁺, can reduce the release rates of K⁺ which is exchanged by Ca²⁺, even if these monovalent cations are present in concentrations of only a few μm . Percolation experiments were carried out with different illitic soil materials, some containing vermiculite, with 5 m m CaCl₂ at pH 5.8 and 20°C, in some cases for over 7000 h. NH₄⁺ and Cs⁺ both caused a large decrease in the rate at which K⁺ was released, Cs⁺ especially. Suppression began at 5 μm NH₄⁺ Blocking by 20 μm NH₄⁺ was easily reversible: the release rates readily increased when NH₄⁺ was omitted from the exchange solution. Blocking by 2 μm Cs⁺ was equal to approximately 90% of that at 10 μm Cs^+. Larger concentrations of Cs⁺ than 10 μm did not further reduce release but rather caused a slight increase, probably because of enhanced exchange of K⁺ by Cs⁺ without exfoliation of the interlayer space. Blocking by Cs⁺ was not reversible within > 7000 h of percolation by 5 m m CaCl₂. The blocking effect was reproduced in several different soil materials using 10 μm Cs⁺ but was most pronounced in vermiculite-rich samples. As NH₄⁺ is present in most arable soils, at least in concentrations of a few μm , I conclude that the observed effects are of significance in the K dynamics processes in soils, for example near the roots of plants. Further, very small concentrations of Cs⁺ in exchange solutions containing a large background of Ca²⁺ appear to be useful for suppressing K⁺ release from the interlayer in laboratory studies, probably without significantly altering the exchange at outer mineral surfaces.     

Evaluation of Chemical Extraction Methods for Determining Plant-Available Potassium in Some Soils of West Bengal,India

The effectiveness of eight chemical extraction methods was evaluated on 15 Indian soils for the prediction of plant-available potassium (K⁺) to Sudan grass (Sorghum vulgare var. sudanensis) grown in modified Neubauer technique. Average amounts of soil K⁺ extracted were in descending order: Morgan’s reagent > 0.5 M sodium bicarbonate (NaHCO₃) > neutral 1N ammonium acetate (NH₄OAc) > 1N nitric acid (HNO₃) > 0.02 M calcium chloride (CaCl₂) > 0.1N HNO₃ > Bray and Kurtz No.1> distilled water. The highest simple correlation with plant K⁺ uptake was obtained with NH₄OAc-K⁺ (r = 0.866**) and the lowest with CaCl₂-K⁺ (r = 0.45*). To develop the predictive models using stepwise regression, plant K⁺ uptake was used as the dependent variable and the extractable soil K⁺, pH, sand, silt and organic carbon (C) contents as the independent variables. Based on the final R², the NH₄OAc model was found to be the best predictor of plant-available K⁺ in the soils when used along with sand and organic C.     

GROWTH AND NUTRITION OF YOUNG BEAN PLANTS UNDER HIGH ALKALINITY AS AFFECTED BY MIXTURES OF AMMONIUM,POTASSIUM, AND SODIUM

High concentrations of bicarbonate (HCO^? ₃) cause alkalinity of irrigation water and are associated with suppression in plant growth and micronutrient deficiencies, such as iron (Fe) and zinc (Zn). Because reports indicate that the deleterious effects of alkalinity may be counteracted partially by supplementary potassium (K⁺) or ammonium (NH₄ ⁺) an experiment was designed to evaluate the response of bean plants (Phaseolus vulgaris L.) grown in high alkalinity conditions to varying proportions of NH₄ ⁺, K⁺, or sodium (Na⁺) (as a potential substitute for K⁺). Plants established in a growth chamber were grown in hydroponics for 21 days in solutions containing 5 mM HCO^? ₃ and a total of 5 mM of a mixture of NH₄ ⁺, K⁺, and Na⁺. The proportions of NH₄ ⁺, K⁺, and Na⁺ were designed according to mixture experiment methodology. Total N in all the mixture treatments was maintained at 10 mM by using nitrate (NO^? ₃)-N, thus the NH₄ ⁺:NO^? ₃ ratio varied according to the proportion of NH₄ ⁺ in the mixtures. Alkalinity caused suppression in plant growth and chlorophyll concentration in the younger leaves, whereas excessive NH₄ ⁺ was associated with leaf scorching and decreased leaf expansion. High proportions of K⁺ alleviated alkalinity symptoms and produced higher shoot and root dry mass provided that NH₄ ⁺ was included in the mixture. However, a proportion of NH₄ ⁺ higher than 0.333 in the mixture (>1.66 mM NH₄ ⁺) induced toxicity. The highest shoot dry mass occurred if the NH₄ ⁺:NO^? ₃ ratio was 0.19:0.81 and the NH₄ ⁺:K⁺:Na⁺ proportion was 0.38:0.38:0.24 (1.9 mM NH₄ ⁺ + 1.9 mM K⁺ + 1.2 mM Na⁺). Thus, an improvement in plant growth is achieved when NH₄ ⁺, K⁺, and Na⁺ are blended together, in spite of the high alkalinity treatment imposed. Optimum NH₄ ⁺ was associated with a decrease in solution pH and an increase in shoot Fe and Zn concentration.     

Leaching behaviour of a sandy soil amended with natural and NH4+ and K+ saturated clinoptilolite and chabazite

Using saturated or enriched zeolites as slow release fertilizers (SRFs) is considered as an environmental-friendly strategy to enhance use of macronutrients in sandy soils. In this paper, two natural zeolites, clinoptilolite (CLI) and chabazite (CHA) were used as mineral precursors to prepare NH₄⁺/K⁺ saturated clinoptilolite (NH₄⁺/K⁺-CLI) and chabazite (NH₄⁺/K⁺-CHA) as zeolitic nutrient sources (ZNSs). Comparison between the nutrient retention capabilities of these ZNSs was one of the main objectives of this study. The NH₄⁺/K⁺-CLI and NH₄⁺/K⁺-CHA were prepared by soaking the zeolites in NH₄Cl and KCl solutions, respectively. Leaching tests were performed on a sandy soil amended with chemical fertilizers (CFs), NH₄⁺/K⁺-CLI and NH₄⁺/K⁺-CHA to evaluate the leaching properties of them. The results indicated that approximately 84% and 88% of the NH₄⁺ and K⁺ of soils fertilized with CFs were lost during the experiment, respectively. While, the NH₄⁺ and K⁺ losses from soils amended with NH₄⁺/K⁺-CLI and NH₄⁺/K⁺-CHA were 29%, 23%, and 14%, 24%, respectively. Despite of drastic changes in leaching behavior of CFs, nutrient losses from ZNSs were more uniform during the experiments. No significant difference was found between the two studied zeolites on reduction of K⁺ loss. However, CHA was more effective in preventing NH₄⁺ loss during leaching.     

Potassium→ammonium exchange of two benchmark soils from Botswana and its implication for nitrogen economy of the soils

Ion exchange preferences for NH₄⁺ and K⁺ by soil exchanger surface can greatly affect the NO₃^? leaching into groundwater and nitrogen-use efficiency in agricultural production. Since NH₄⁺ and K⁺ salts are usually applied together as fertilizers, the binary K→NH₄ exchange of two benchmark Botswana soils, Pellustert and a Haplustalf, was studied to determine the selectivity coefficients and the thermodynamic exchange constant with special reference to N economy. The Vanselow and the Gaines and Thomas coefficients indicated preference for NH₄⁺ by the Pellustert and K by the Haplustalf across the exchanger phase composition. The equilibrium constant (K_ex) was 1.807 for the Pellustert and 0.174 for the Haplustalf. The exchange free energy (ΔG_ex⁰) was ?1.467 kJ mol^?1 for the Pellustert and 4.334 kJ mol^?1 for the Haplustalf. Negative ΔG_ex⁰ for the Pellustert is consistent with preference for NH₄⁺ to K⁺ in contrast to positive ΔG_ex⁰ for the Haplustalf. The greater stability of NH₄X than KX complex in the Pellustert, and KX than NH₄X in the Haplustalf, would mean increased residence time of NH₄⁺ in the Pellustert than the Haplustalf. The implication of short residence time of NH₄⁺ in soil is rapid nitrification, thereby leading to NO₃^??N leaching losses and possible groundwater contamination.     

Kinetics of nonexchangeable‐potassium release and plant response in some calcareous soils

Nonexchangeable K⁺ constitutes a slowly available reserve that may significantly influence K⁺ fertility of soils. Laboratory and greenhouse experiments were conducted to characterize the K⁺ supply and nonexchangeable K⁺–release kinetics in 10 calcareous soils using 0.01 M CaCl₂ and 0.01 M oxalic acid extractions. Total K⁺ uptake by wheat (Triticum aestivum L.) grown in the greenhouse was used to measure plant‐available K⁺. The release of K⁺ was characterized by an initial fast rate followed by a slower rate. The nonlinear relationship in the early stages of the K⁺ release may be attributed to the edge sites, and release of K⁺ from interlayer exchange sites may be responsible for the second part of the K⁺ release. Kinetics of K⁺ release was described best with power function, which showed the best fit of the four models tested. Parameters of kinetics models in 0.01 M CaCl₂ were significantly related to K⁺ uptake by wheat. Potassium release was also correlated to initial NH₄OAc‐extratable K⁺ and to HNO₃‐extractable K⁺.     

Effects of phosphate fertilizer on biomass production and N2(C2H2) fixation by pot-grown Ulex gallii Planchon in a forest soil

Summary N₂(C₂H₂) fixation by Ulex gallii Planchon (dwarf or autumn flowering gorse/furze) seedlings was determined following 8 months of growth (December-August) in the glasshouse in a very acid, N- and P-deficient forest soil. Application of Na₂HPO₄·12H₂O or North African ground rock phosphate fertilizer was essential for growth, nodulation and C₂H₂ reduction activity. Overall, both the sodium phosphate and the rock phosphate were equally effective P sources and the maximum acetylene reduction by intact roots was measured as 4.09 and 4.69 mol C₂H₄g^-1 fresh weight nodule h^-1, respectively. Applied NH₄Cl severely inhibited nodulation and restricted acetylene reduction activity but not seedling growth. The results are discussed in relation to the spread of U. gallii in the south of Ireland and its potential as a leguminous nurse crop for Sitka spruce on the very impoverished forest soils of the region.     

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.     

Characteristics of ammonium and nitrate fluxes along the roots of Picea asperata

Nitrogen (N), ammonium (NH₄⁺) and nitrate (NO₃^?), is one of the key determinants for plant growth. The interaction of both ions displays a significant effect on their uptake in some species. In the current study, net fluxes of NH₄⁺ and NO₃^? along the roots of Picea asperata were determined using a Non-invasive Micro-test Technology (NMT). Besides, we examined the interaction of NH₄⁺ and NO₃^? on the fluxes of both ions, and the plasma membrane (PM) H⁺-ATPases and nitrate reductase (NR) were taken into account as well. The results demonstrated that the maximal net NH₄⁺ and NO₃^? influxes were detected at 13–15?mm and 8–10.5?mm from the root apex, respectively. Net NH₄⁺ influx was significantly stimulated with the presence of NO₃^?, whereas NH₄⁺ exhibited a markedly negative effect on NO₃^? uptake in the roots of P. asperata. Also, our results indicated that PM H⁺-ATPases and NR play a key role in the control of N uptake.     

Nitrogen budget in a soil-plant system after brachiaria grass desiccation

Abstract

Brachiaria spp. have been grown in a variety of cropping systems and are often terminated with herbicides, which may cause nitrogen (N) loss from the soil-plant system. In this study ammonia (NH₃-N) loss by shoots and N balance in a soil-plant system were determined after desiccation of palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf, cv. Marandu), signalgrass (Brachiaria decumbens Stapf), humidicola (Brachiaria humidicola (Rendle) Schweick) and Congo grass (Brachiaria ruziziensis Germain et Evrard). The grasses were grown in pots filled with an Oxisol in a greenhouse. Sixty days after planting, the plants were desiccated with glyphosate. Analyses were performed on plant and soil at desiccation and then at 7, 14, 21 and 28 days after desiccation in order to assess NH₃-N losses by shoots and to estimate the N balance in the system. Total nitrogen (Total-N) concentration in shoots and roots of brachiarias decreased after desiccation, thereby reducing the amount of N in plants of the four brachiaria species. However, as most of the N lost by plants was released into the soil, N losses from the soil-plant system were small compared with the total N in the system: 1.2, 0.5, 0.4 and 1.4% for palisade grass, signalgrass, humidicola and Congo grass, respectively. N losses as NH₃ from the soil-plant system after desiccation with glyphosate varied among brachiaria species, ranging from 0.8 to 2.0 g m^?2 kg^?1, and accounted for 30–80% of total loss.     

Impact of nitrogen and phosphorus additions on soil gross nitrogen transformations in a temperate desert steppe

Nutrient addition has a significant impact on plant growth and nutrient cycling. Yet, the understanding of how the addition of nitrogen (N) or phosphorus (P) significantly affects soil gross N transformations and N availability in temperate desert steppes is still limited. Therefore, a ¹⁵N tracing experiment was conducted to study these processes and their underlying mechanism in a desert steppe soil that had been supplemented with N and P for 4 years in northwestern China. Soil N mineralization was increased significantly by P addition, and N and P additions significantly promoted soil autotrophic nitrification, rather than NH₄⁺-N immobilization. The addition of N promoted dissimilatory NO₃⁻ reduction to NH₄⁺, while that of P inhibited it. Soil NO₃⁻-N production was greatly increased by N added alone and by that of N and P combined, while net NH₄⁺-N production was decreased by these treatments. Soil N mineralization was primarily mediated by pH, P content or organic carbon, while soil NH₄⁺-N content regulated autotrophic nitrification mainly, and this process was mainly controlled by ammonia-oxidizing bacteria rather than archaea and comammox. NH₄⁺-N immobilization was mainly affected by functional microorganisms, the abundance of narG gene and comammox Ntsp-amoA. In conclusion, gross N transformations in the temperate desert steppe largely depended on soil inorganic N, P contents and related functional microorganisms. Soil acidification plays a more key role in N mineralization than other environmental factors or functional microorganisms.     

Synthesis of a Novel Ambipolar Resin Membrane for Ion Adsorption

ABSTRACT

We have synthesized a novel composite ambipolar resin membrane with a high water absorption capacity (150?200%) and superior ion adsorption properties. The ambipolar membrane was capable of adsorbing nitrate, ammonium, potassium and phosphorus simultaneously from aqueous solutions. The adsorption capacity of the membrane varied with ionic concentration and composition. Thus, from a mixed solution of 30 mmol…L^{? 1}NH₄ ⁺ and 10 mmol…L^{? 1} each of NO₃ ^?, K⁺, and H₂PO₄ ^?, the synthetic membrane was able to take up 0.241 mmol NH₄ ⁺, 0.151 mmol NO₃ ^?, 0.120 mmol K⁺, and 0.046 mmol H₂PO₄ ^? per g membrane. A large proportion (73.9?92.5%) of the adsorbed ions could be desorbed with dilute (5%) HCl. The rate of desorption is inversely related to the cross-linking density of the membrane. The competition between NO₃ ^?and H₂PO₄ ^? as well as between K⁺ and NH₄ ⁺ was also investigated.     

Comparison of the early response to aluminum stress between tolerant and sensitive wheat cultivars: Root growth,aluminum content and efflux of K+

In order to characterize the mechanism of Al tolerance (Atlas 66) and Al sensitivity (Scout 66) in two cultivars of wheat (Triticum aestivum L.), the early responses to Al stress under acidic conditions were investigated. Marked inhibition of root elongation of Scout was observed upon treatment with 10 μM AlCl₃ for less than 3 h. The inhibition of root elongation of Scout was reversed within 3 days when the treated samples were transferred to a solution without Al. However, treatment for 6 h with AlCl₃ repressed root elongation almost completely and irreversibly. Root elongation of Atlas was only partially inhibited by the treatment with 10 μM AlCl₃ for more than 6 h. Levels of Al in two portions of roots, namely, portions 0–5 mm and 5–10 mm from the tip, were lower in Atlas than those in Scout. In Atlas the levels of Al on a fresh weight basis in both portions were very similar, while the level of Al in the portion 0–5 mm from the tip was almost double than that in the 5–10 mm portion in Scout. A distinct increase in levels of Al in the 0–5 mm portion over that in the 5–10 mm portion of Scout was observed even after 3 h of treatment with AlCl₃.

Both Atlas and Scout were preloaded with K⁺ at pH 5.5 and transferred to distilled water at various pH values to monitor the efflux of K⁺. A reduction in the pH induced increases in the efflux of K⁺ in both cultivars, and the rate of efflux in Scout was twice that in Atlas at pH 4.2. AlCl₃ at concentrations as low as 5 μM markedly repressed K⁺efflux at pH 4.2 and this effect was more pronounced in Scout. Ca²⁺ also had a repressive effect on K⁺ efflux, while EGTA increased K⁺ efflux. Vanadate increased K⁺ efflux, a result that suggests the involvement of a H⁺ pump in K⁺ efflux. Ca²+ failed to repress the increased efflux of K⁺ caused by vanadate while Al repressed the K⁺ efflux even in the presence of vanadate. These results suggest that a low extracellular pH may cause an increase in the cytoplasmic concentration of H⁺ that is followed by depolarization of the plasma membrane, which may be modified by the efflux of K⁺ and H⁺. The characteristic difference in terms of K⁺ efflux between Atlas and Scout at low pH may be caused by differences associated with plasma membrane potentials, as follows. The net influx of H+ at low pH, which causes depolarization of the plasma membrane, is higher in Scout than in Atlas. The difference in the net influx of H⁺ may be regulated in part by Ca2⁺, that either repress the influx of H⁺ or the activate of the H⁺ pump. Inhibition of K⁺ efflux by Al, which tends to depolarize the plasma membrane at low pH, may be an important factor in determining sensitivity and/or tolerance to Al.     

Herstellung und Verwendung 33P-markierter Carbonatfluorapatite zur Untersuchung der Wirkung rohphosphathaltiger Düngemittel

Preparation and use of ³³P labelled carbonate fluorapatite in studies on the effect of phosphate rock containing fertilizers For a precise evaluation of the effectiveness of the different phosphate fractions in partially acidulated phosphate rocks these fractions were alternatively labelled. For this purpose a technique was developed to prepare synthetic, ³³P labelled carbonate fluorapatite (francolite type). A labelled (NH₄)₂HPO₄ solution (+ Na₂CO₃, NH₄F) was poured into a Ca(NO₃)₂ × 4H₂O solution (pH 12) and the washed precipitate heated until the aimed solubility was reached (e.g. 2 h 400°C + 1.5 h 600°C). After grinding this mother phosphate rock was acidulated with sulphuric acid to fully acidulated superphosphate and partially acidulated phosphate rock. The nonacidulated rock residue was extracted from the partially acidulated phosphate rock. In an identical procedure phosphate rock was prepared without addition of ³³P and in part acidulated to superphosphate. Mixing of labelled phosphate rock and not labelled superphosphate (and vice versa) gave two fertilizer mixtures with alternate labelled fractions equivalent to the fully labelled partially acidulated phosphate rock. Mineralogical properties of the synthetic phosphate fertilizers and their turnover in pot experiments with rye grass were corresponding to that of commercial products. The reactivity of the nonacidulated rock residue was inferior to that of the original phosphate rock after the process of partial acidulation. Fertilizer utilization was determined by use of isotopes (³³P) and total P uptake method. P utilization as determined by total P uptake method was significantly higher compared to the real fertilizer effectiveness measured by ³³P labelling.