Influence of the ionic strength of nutrient solutions and tropical acid soil solutions on aluminum activity

Aluminum (Al) activity was determined in nutrient solutions and in acid soil solutions. Aluminum concentrations in the solutions ranged from 7.4 μM to 370.3 μM giving values of ionic strength of nutrient solutions higher than the values of acid soil solutions. The increase of ionic strength values was due to the increase of Al concentrations. The values of Al activities of 20 uM in the acid soil solutions were noticed when Al concentrations were lower than 70 μM. On the other hand, these values of Al activities in nutrient solutions were noticed only when the Al concentrations were higher than 70 μM. This study demonstrates why it is important to use higher Al concentrations in nutrient solutions to obtain Al toxic effects.     

The Effect of the Ionic Strength of Nutrient Solution on Gas Exchange,Ionic Concentration and Leaf Biomass of Annona emarginata (Schltdl.) H. Rainer Variety ‘Terra-Fria’ Seedlings

The present study aimed to test the hypothesis that different levels of the availability of mineral nutrients from Hoagland and Arnon's nutrient solution no. 2 affect the photosynthesis, ionic concentration and biomass production in seedlings of Annona emarginata (Schltdl.) H. Rainer variety ‘terra-fria’. Seedlings were grown in a hydroponic setting with 100% ionic strength and with ionic strength reduced to 75%, 50%, and 25%. Ionic strengths intermediate resulted in higher rates of carbon net assimilation and plants grown under these conditions increased biomass as well ionic concentrations of calcium, magnesium and sulfur. The ‘terra-fria’ plants with nutrient solutions of 50% and 75% ionic strength exhibited higher ionic concentrations, instantaneous carboxylation efficiency and biomass production. It can be concluded that the ‘terra-fria’ does not require the maximum mineral nutrients availability from Hoagland and Arnon's nutrient solution to achieve high primary productivity and intermediate ionic strengths can even reduce the time required for rootstock formation.     

Ionic Activity in Soil Solution as Affected by Application Of Newsprint and Nitrogen Sources

The influence of noncomposted ground newsprint (GNP) and nitrogen (N) source on corn (Zea Mays L.) dry matter production, grain yield, and soil chemical properties has been previously reported (Lu et al. 1995). The effects of GNP and N source on soil solution ionic activities at 40 days after planting in a field study; seed germination and extractable aluminum (Al) in GNP in laboratory studies were evaluated to determine their effects on corn seedling stunting and nutrient imbalances during early growth stages. Ammonium nitrate (NH₄NO₃), urea, anhydrous ammonia (NH₃), or poultry litter (PL) were the N sources used in the field study to adjust the C:N ratio of the GNP to ≤ 30:1. In laboratory experiments, cotton, soybean, and corn germination at seven days was not affected by N source or GNP applied at a rate of 2.44 kg C/m² soil; but N source did influence the dry weight of corn root/shoot ratio at 21 days. The Al extracted from GNP increased as the NH₄OH concentration in the extracting solution increased and followed a quadratic relationship with an r² of 0.90. The σα_ca/σα_cation ratio in soil solution for all N sources was greater than the 0.15 reported by Bennett and Adams (1970a), where incipient NH₃ phytotoxicity can occur. At 40 days after planting, a two-fold increase in soil monomeric Al (σAlα_mon.) ionic activity and a five-fold increase in soil P (σPα) ionic activity were measured in GNP treatments as compared to no N GNP treatments. When NH₃ was the N source used to adjust the C:N ratio of GNP, the σAlα_mon. ionic activities were increased by a factor of five as compared to NH₃ applied alone. When PL was the N source, the Al_T (σAlα_species) ionic activity was 119 mmol L^?1 compared to the σAlα_mon. ionic activity of 0.53 mmol L^?1. It appears that σAlα_mon. ionic activity induced nutrient disorder and caused severe stunting of corn seedlings during early season growth. The relatively high water-soluble organic carbon in PL (18 percent) may have acted as a chelating agent to reduce the σAlα_mon. ionic activities in the GNP, or as a soluble carbon source for increasing microbial utilization of all the N, thus slowing the formation and accumulation of phytotoxic levels of by-products.     

Effect of water stress on aluminum toxicity in pitch pine seedlings

A decrease in soil water content during droughts may increase aluminum (Al) to concentrations that are toxic to the growth of trees. The effects of water stress (WS) on the response of ectomycorrhizal pitch pine (Pinus rigida Mill.) seedlings to aluminum was determined by growing seedlings in sand irrigated with nutrient solution (pH 3.8) containing 0, 5, or 10 mg L^‐1 Al. Water stress was imposed for 41 days by withholding nutrient solution for five consecutive days each week. At harvest time, seedlings at high WS had 72% of mean gravimetric water contents of seedlings at low WS. Aluminum decreased growth of seedlings at high WS, but had no effect on growth of seedlings at low WS. Aluminum toxicity symptoms in roots (e.g., dark thickened tips) were observed at lower Al levels at high WS than at low WS. Stem dry weight was the only plant part decreased by water stress alone. Across Al levels, Al concentration in roots was higher at low WS than at high WS. Water stress alone reduced root [phosphorus (P), potassium (K), and calcium (Ca)] and foliar [P, K, and magnesium (Mg)] concentrations of mineral nutrients. Decreases of nutrients in roots with increasing Al was greater at low than at high WS. Calcium was the only foliar nutrient decreased by Al treatment.     

Supernatant solutions containing various levels of aluminum and similar concentrations of phosphorus for aluminum phytotoxicity studies

Abstract

Precipitation of Al(OH)₃ and aluminum phosphate may occur in nutrient solution if a large amount of Al and P have been added to a relatively high pH. The objective of this study was to develop and test a supernatant‐solution method for Al phytotoxicity studies with large and/or old plant seedlings. Effects of pH and additions of Al and P on ionic strength and concentrations of Al and P in supernatant nutrient solutions were investigated. Two sets of supernatant nutrient solutions at two pH levels were prepared. The pH 4.0 set and 4.5 set contained seven levels of Al (maximum Al concentration of 6355 and 378 μM) and similar P concentration about 32 and 6 μM P, respectively. The Al concentrations in supernatant solutions were dependent on preparation procedure. The pH 4.0 set was tested in the greenhouse study with 6‐month‐old citrus seedlings and found to be successful as culture solutions for Al phytotoxicity studies. These two sets are suitable for growth of large (about 0.3 m) and/or old (about 6 mon.) seedlings. This supernatant‐solution method makes it possible to study Al phytotoxicity of large and/or old seedlings, to avoid the confounding effects of P on Al with respect to plant growth, and to report the actual concentrations of Al and P in growth solutions.     

Sorption and fate of perchlorate in arid soils

The mobility of perchlorate in soils depends on several factors, including soil mineralogy and the presence of other oxyanions that compete with perchlorate for the retention sites. Currently, there are no studies that evaluate the mobility of perchlorate in arid soils. The present study evaluated the mobility of ClO₄^– in three arid soils, Canchones, Humberstone and Pica, exposed to two ClO₄^– concentration ranges and different ionic strengths. In Humberstone (non-agricultural) and Pica (agricultural) soils, the sorption processes were not important for both concentration ranges, while Canchones soil (agricultural) showed a decrease in perchlorate concentration associated with microbial degradation processes. The increase of medium ionic strength by addition of Ca(NO₃)₂ only had an important effect on Humberstone soil, associated with the presence of kaolinite and muscovite (variable charge). A competition effect was observed between perchlorate, nitrate and other anions presents in solution by absorption sites generated from variable charge mineral and calcium. Considering the quite low sorption capacity of the soils and the high solubility, perchlorate can be absorbed by fruit and vegetables of export in concentrations over the healthy levels established by international organization.     

Phosphorus uptake by mycorrhizal and nonmycorrhizal roots of soybean

Kinetics of phosphorus absorption were investigated with mycorrhizal and nonmycorrhizal soybean (Glycine max Merr.) plants which were grown in a greenhouse and growth chamber and with nutrient solutions. Mycorrhizal plants depleted phosphorus from a dilute (<30uM) nutrient solution three times faster and had lower apparent efflux of phosphorus than the uninfected plants. The affinity (K_m) of roots for phosphorus from the solution was not increased by mycorrhizal infection. The results indicate that enhanced phosphorus absorption by mycorrhizal roots of soybean is due to an increase in the number of uptake sites per unit area of root (^v max).     

营养液对鸭儿芹幼苗生长、抗氧化酶活性及叶绿素荧光参数的影响

为了探索适合鸭儿芹幼苗生长的营养液浓度,分别研究了6种山崎营养液浓度（1/12s、1/10s、1/8s、1/4s、1/2s和1s)对鸭儿芹幼苗生长及叶绿素荧光参数的影响。结果表明,在1/8s浓度下,鸭儿芹幼苗的各生长因子（株高、单株叶面积、茎粗、地上部鲜重、干重,地下部鲜重、干重,株鲜重、干重）均达到最大。壮苗指标随着营养液浓度的增大出现先上升后降低的趋势,在1/8s浓度下亦达到最大,且显著高于其它处理(P 0. 05)。在1/12s～1/8s的浓度变化下,随着营养液浓度的增大,POD、CAT以及SOD活性在逐渐上升,MDA含量在逐渐降低,而在1/8s~1s的浓度变化下,随着营养液浓度的增大,POD、CAT以及SOD活性在逐渐降低,MDA含量在逐渐上升,在1/8s浓度下POD、CAT以及SOD活性达到最大,MDA含量达到最小。叶绿素a、叶绿素b及叶绿素总量出现先上升后下降的趋势,在1/8s浓度下均达到最大。1/4s～1s浓度,初始荧光（Fo）值均高于1/12s～1/10s处理,而最大荧光（Fm）、PSⅡ的潜在活性（Fv/Fo）、PSⅡ最大光化学效率（Fv/Fm）值分别低于1/12s～1/10s处理;1/8s浓度的Fo值达到最小,而Fm、Fv/Fo、Fv/Fm值达到最大。实验表明了营养液浓度对鸭儿芹幼苗具有双重作用,即低浓度下随浓度的升高,营养胁迫逐渐减低,促进幼苗生长;高浓度下随浓度的升高,营养胁迫逐渐增强,抑制幼苗生长。结果得出,采用1/8浓度的山崎配方是鸭儿芹幼苗生长的最适营养液浓度。     

CO2与养分交互作用对番茄幼苗叶片碳、氮积累及碳、氮比动态的影响

营养液栽培条件下,以番茄(品种,合作906)为材料,研究CO2施肥与4种不同养分供应强度的交互作用对番茄幼苗生长及其叶片中的碳、氮浓度与碳、氮比动态变化的影响。结果表明,在不同营养液养分浓度下,CO2施肥能增加番茄幼苗生物量的积累,提高生长速度;增加番茄幼苗叶片中氮、碳积累量与吸收速率;而且对CO2作用效果的响应随营养液养分浓度的提高而增加。在所有处理中碳、氮积累量与吸收速率随生育期的延长呈上升趋势。说明在番茄育苗后期要增加施肥量,而且在CO2施肥的情况下施肥量增加的量要大。CO2施肥对生长在不同营养液中番茄叶片中的碳、氮比在不同生长阶段的影响是不同的,但在同一CO2浓度条件下,番茄幼苗各个取样阶段均表现为碳、氮比随营养液浓度的降低而增加。对番茄幼苗碳、氮积累量、总干生物量与生长时间的关系研究表明,氮积累量、总干生物量与生长时间均符合二次曲线变化。     

Nutrient status of rhizosphere and phosphorus response of radish

Radish (Raphanus sativus L.) exhibits a high efficiency in the utilization of sparingly‐soluble phosphates. A greenhouse experiment was designed to investigate the growth response of radish to different phosphorus (P) sources and the nutrient status of the rhizosphere associated with radish growth and nutrient absorption. Radish plants were grown in pots with the roots confined in rhizobags, in such a manner that the concentration of roots was very high within the rhizobag. The rhizosphere soils and non‐rhizosphere soils were analyzed separately for active silicon (Si), aluminum (Al), iron (Fe), and manganese (Mn) using Tamm's solution and for “available”; P using the Bray P1 extraction reagent. The radish growth response was mostly attributable to phosphate amount and availability, and the lime level used in the experiment. Concentrations of active Fe, Si, Al, and Mn were reduced in the rhizosphere, especially when lime and rock phosphate (Ps) were added. Available soil P was accumulated in the rhizosphere under lime and Ps addition, whereas its concentration was reduced with the zero lime treatment. Phosphorus utilization, characterized by P accumulation in shoots, was in accordance with the concentration pattern for “available”; P in the rhizosphere, but not with the growth response of radish itself. The calcium (Ca) concentration of the shoot followed the same trend as the radish growth. There was an antagonism between potassium (K) and Ca absorption as well as between Ca and magnesium (Mg) absorption. With the addition of P, shoot Mn concentration increased, while shoot Fe and Al concentrations increased with no lime addition but decreased with lime addition. The high P efficiency of radish is discussed from the view of rhizosphere chemistry. The high Mn efficiency of radish may be influenced by the same rhizosphere processes that are involved in its high P efficiency. It was concluded that rhizosphere processes and the status of nutrients determined the nutrient efficiency of radish and thus influenced its growth response and nutrient uptake.     

K和Al对水稻生长和养分吸收的影响

The effects of K and Al in K-deficient and complete nutrient solutions on the growth and nutrient uptake of rice were studied in the work.The effect of Al on the growth of roots and above-ground part of rice was associated with the concentration of Al in solution .A low level(0.1 mmol L^-1) of Al promtoed but a high level(1 mmol L^-1)of Al inhibited the growth of both the root and the aerial part of rice,and the magnitude of K concentration in the nutrient solution also had an appreciable impact on this,Thus ,in the low-Al solution,the plant treated with K2(80 mg K L^-1)produced much longer roots,showing the presence of interaction between Al and K; in the high-Al solution the K-reated plant had more and longe roots and a considerably greater dry weigh of the above-ground part compared with the plant deficient in K, showing the alleviating effect of K^ on Al toxicity.The mechanism of the Al-K interaction affecting the rice aerial part growth is not yet known,but part of the reason might be that the excessive amount of Al inhibited the uptake of some nutrients such as Ca and Mg and reduced their transfer to the plant aerial organs,whereas K showed its compensating effect on this;therefore,K could relieve Al toxicity at a high level of Al and promoted rice growth at a low level of Al.     

Effect of aluminium on onions,asparagus and squash

The effect of Al on the growth and chemical composition of onions (Allium cepa L. cv Pukekohe longkeeper), asparagus (Asparagus officinalis L. cv Lucullus) and squash (Cucurbita maxima L. cv Delica) was investigated using a low ionic strength solution‐culture technique. Onions and asparagus were sensitive to Al while squash was relatively tolerant. The dry matter yields of onion, asparagus and squash tops were reduced 50% by 5, 3, and 26 μM Al in the solution, respectively. Similarly, root dry matter yields were reduced 50% by 1, 5, and 26 μM Al, respectivley. Aluminium reduced the concentration of macro nutrients in both asparagus and onion tops but had no consistent effect on squash tops. Plant analysis and visible symptoms indicated that Al affected magnesium nutrition more than that of any other nutrient.

The roots of squash showed an ability to recover from Al stress by modifying their morphology. However, this effect was insufficient to totally alleviate Al toxicity. Squash also became more sensitive to Al as the growing period progressed. These observations suggest that care is needed in using short term experiments to assess Al tolerance for some species.     

Effects of root-zone temperature and N,P, and K supplies on nutrient uptake of cucumber (Cucumis sativus L.) seedlings in hydroponics

The nutrient uptake and allocation of cucumber (Cucumis sativus L.) seedlings at different root-zone temperatures (RZT) and different concentrations of nitrogen (N), phosphorus (P), and potassium (K) nutrients were examined. Plants were grown in a nutrient solution for 30?d at two root-zone temperatures (a diurnally ?uctuating ambient 10°C-RZT and a constant 20°C-RZT) with the aerial parts of the plants maintained at ambient temperature (10°C–30°C). Based on a Hoagland nutrient solution, seven N, P, and K nutrient concentrations were supplied to the plants at each RZT. Results showed that total plant and shoot dry weights under each nutrient treatment were significantly lower at low root-zone temperature (10°C-RZT) than at elevated root-zone temperature (20°C-RZT). But higher root dry weights were obtained at 10°C-RZT than those at 20°C-RZT. Total plant dry weights at both 10°C-RZT and 20°C-RZT were increased with increased solution N concentration, but showed different responses under P and K treatments. All estimated nutrient concentrations (N, P, and K) and uptake by the plant were obviously influenced by RZT. Low root temperature (10°C-RZT) caused a remarkable reduction in total N, P, and K uptake of shoots in all nutrient treatments, and more nutrients were accumulated in roots at 10°C-RZT than those at 20°C-RZT. N, P, and K uptakes and distribution ratios in shoots were both improved at elevated root-zone temperature (20°C-RZT). N supplies were favorable to P and K uptake at both 10°C-RZT and 20°C-RZT, with no significantly positive correlation between N and P, or N and K uptake. In conclusion, higher RZT was more beneficial to increase of plant biomass and mineral nutrient absorption than was increase of nutrient concentration. Among the three element nutrients, increasing N nutrient concentration in solution promoted better tolerance to low RZT in cucumber seedlings than increasing P and K. In addition, appropriately decreased P concentration favors plant growth.     

The solution chemistry of podzolic soils from the eastern Canadian shield: a thermodynamic interpretation of the mineral phases controlling soluble Al3+andH4SiO4

Thirty-one soil solutions were extracted by immiscible displacement with CCl₄ under high speed centrifugation from sub-horizons of three podzolic soils from north-eastern Ontario, Canada. The solutions were analysed for major cations and anions and a speciation of dissolved Fe and Al was attempted to distinguish 'free', 'organically bound' and 'inorganically bound' species. Results indicated that the Ae (E) horizon solutions were of low pH and contained mainly organically bound Fe and Al. With depth, _pHs increased, ionic strengths decreased and the relative proportion of inorganically bound Fe and Al increased. Although application of phase diagrams permitted only a semi-quantitative interpretation of the data, all horizon solutions, with the exception of some Ae solutions, appeared supersaturated with respect to likely occurring crystalline and amorphous aluminosilicates [kaolinite, halloysite, allophane (Al:Si=l) and imogolite]. Of the phases considered, reactions involving imogolite-allophane, gibbsite-halloysite, gibbsite-allophane and gibbsite-imogolite all appeared reasonable in controlling the content of Al³⁺ and H₄SiO₄ in solution, although the presence of gibbsite and imogolite could not be definitely confirmed in these soils.     

Effect of Glomus etunicatum inoculation on aluminum,phosphorus, calcium,and magnesium uptake of two barley genotypes with different aluminum tolerance

Abstract

This study was conducted to evaluate the effect of vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus etunicatum on growth, absorption, and distribution of calcium (Ca), magnesium (Mg), phosphorus (P), and aluminum (Al) in one Al‐tolerant and one Al‐sensitive barley cultivar. The plants were grown in sand daily irrigated with nutrient solution containing 0 or 600 μM Al at pH 4.8. Significant interaction (P=0.05) among variety, mycorrhiza, and aluminum (VxMxAl) were noted for both shoot and root dry matter (DM); shoot concentration and content of Al, P, Ca, and Mg; root concentration of Al, P, and Mg; and root content of Al, P, Ca, and Mg. With VAM inoculation: i) root colonization degree was about 50% in all treatment, ii) shoot DM yield increased between 30 and 70%, iii) Al concentration and content decrease down to a half both in shoots and roots of sensitive barley, iv) Ca concentration in shoots of sensitive barley showed a high increase at 600 μM Al, and v) P concentration and content in shoots of both varieties increased significantly.     

Mineral element concentration of two barley cultivars in relation to water deficit and aluminum toxicity

The separate and combined effects of water and Al stress on concentrations of P, K, Ca, Mg, Fe, Mn, Zn, Cu, B, Al, Sr, and Ba were determined in tops of ‘Dayton’ (Al‐tolerant) and ‘Kearney’ (Al‐sensitive) barley (Hordeum vulgäre L.) grown in an acid, Al‐toxic, Tatum subsoil (clayey, mixed, thermic, Typic Hapludult). Plants were grown 4 weeks in a plant growth chamber at high (pH 4.7) or low (pH 6.6) Al stress. During the last 2 weeks they were also subjected to low (‐20 to ‐40 kPa), moderate (‐40 to ‐60 kPa), or high (‐60 to ‐80 kPa) water stress. In general, Al stress had a greater overall effect on mineral element concentration of tops than water stress. Aluminum stress significantly decreased concentrations of P, Ca, and Mg and increased concentrations of Zn, Sr, and Ba, irrespective of the cultivar or water stress treatment. Cultivar differences in Mn concentration were observed with Al stress under all water stress conditions. In each case, Mn concentration was lower in ‘Kearney’ than in ‘Dayton’. Potassium, Ca, and Mg were lower in ‘Kearney’ than in ‘Dayton’ only at low and moderate water stress, under low Al stress, ‘Kearney’ had significantly higher concentrations of K and Ca than did ‘Dayton’ under all water stress conditions. The effects of water stress on mineral element concentration varied greatly with cultivar, Al stress treatment, and severity of water stress. Under high Al stress, increasing drought conditions from low water stress (‐20 to ‐40 kPa) to high water stress (‐60 to ‐80 kPa) significantly increased the concentrations of Ca, K, Zn, Sr, and Ba in Al‐sensitive ‘Kearney’ and reduced the concentrations of Zn, Sr, and Ba in Al‐tolerant ‘Dayton'; P and Mg concentration were unaffected by water stress. In contrast, under low Al stress, a corresponding increase in water stress significantly increased the concentrations of Ca and reduced that of P in ‘Kearney’ and increased Ca and B concentration in ‘Dayton'; Mg concentrations were unaffected in either cultivar. Thus, it appears that Al stress and water stress had opposite effects on Ca accumulation in barley tissue.     

Comparison of aluminum tolerance and phosphate absorption between rape (Brassica napus L.) and Tomato (Lycopersicum esculentum Mill.) in relation to organic acid exudation

Aluminum (Al) tolerance and phosphate absorption in rape and tomato were compared under water culture and field conditions. The relative growth rate in the Al treatment compared with -A1 treatment was similar in the two crops under water culture conditions, while under field conditions, the growth rate was 2- to 3-fold higher in rape than in tomato in spite of the higher Al concentration in the soil solution than in the culture solution. The relative amount of phosphate absorbed in the Al treatment compared with - Al was not appreciably different between rape and tomato under water culture conditions, while under field conditions, it was 3- to 6-fold larger in rape than in tomato. The exudation rate of citric acid by roots was much higher in rape than in tomato. The plant growth, root elongation, and amount of phosphate absorbed in rape were inhibited in the 150 µM Al in the culture solution. However, the inhibition was alleviated by the addition of 200 µM citric acid or 500 µM malic acid. The P concentration in the culture solution decreased by the presence of Al as aluminum phosphate. However, addition of citric and malic acids increased the amount of phosphate released from the precipitated aluminum phosphate. In conclusion, one of the mechanisms for the higher Al tolerance and larger phosphate absorption in rape than in tomato under field conditions was ascribed to the higher concentration of exuded citric acid by Al in the rhizosphere. It was suggested that the exudation of citric acid might contribute to the detoxification of Al and to the increase phosphate availability in the rhizosphere in rape.     

Impact of foliar-applied Hoagland’s nutrient solution on growth and yield of mash bean (Vigna mungo L.) under different growth stages

In a field experiment, various strengths of Hoagland’s nutrient solutions were sprayed to mitigate the deleterious effects of nutrient stresses at different growth stages on mash bean cultivars. Hoagland’s nutrient solution strengths of 0, 25, 50, and 75% were applied at 7, 14, and 21?days after emergence on mash bean cultivars namely Mash-2 and Mash-88. Hoagland’s nutrient solution of 75% strength markedly increased the growth and yield of mash bean cultivars if applied at 21?days after crop emergence. The Mash-88 showed superiority in terms of growth and yield traits as compared to Mash-2. The results suggested that growth and yield was not enhanced effectively by a low strength of Hoagland’s nutrient solution applied at initial growth stages. It is concluded that foliar-applied Hoagland’s nutrient solution of 75% strength can be used as an efficient tool when applied at appropriate growth stage (21?days after emergence) to get optimal yield.     

Light-scattering study of the structure of aggregates and gels formed by heat-denatured whey protein isolate and beta-lactoglobulin at neutral pH

The structure of aggregates and gels formed by heat-denatured whey protein isolate (WPI) has been studied at pH 7 and different ionic strengths using light scattering and turbidimetry. The results were compared with those obtained for pure beta-lactoglobulin (beta-Lg). WPI aggregates were found to have the same self-similar structure as pure beta-Lg aggregates. WPI formed gels above a critical concentration that varied from close to 100 g/L in the absence of added salt to about 10 g/L at 0.2 M NaCl. At low ionic strength (<0.05 M NaCl) homogeneous transparent gels were formed, while at higher ionic strength the gels became turbid but had the same self-similar structure as reported earlier for pure beta-Lg. The length scale characterizing the heterogeneity of the gels increased exponentially with increasing NaCl concentration for both WPI and pure beta-Lg, but the increase was steeper for the former.     

Short‐term effects of pH and aluminium on mineral nutrition in maize varieties differing in proton and aluminium tolerance

In short‐term (24 h) nutrient solution experiments, the influence of different proton (pH 6.0 and pH 4.3) and aluminium (Al) (0, 20, and 50 μM) concentrations on root and coleoptile elongation, dry weight, and the uptake of selected mineral nutrients was studied in maize (Zea mays L.) varieties that differ in acid soil tolerance under field conditions. The acid‐soil‐tolerant maize varieties, Adour 250 and C525M, proved to be hydrogen (H⁺) ion sensitive, but Al tolerant, while the acid soil tolerant variety BR201F was H⁺ tolerant but Al sensitive. The acid soil sensitive variety HS 7777 was affected by both H⁺ and Al toxicity. The proton‐induced inhibition of root elongation was closely related to the proton‐induced decrease of the specific absorption rates (SAR) of boron (B), iron (Fe), magnesium (Mg), calcium (Ca), and phosphorus (P). In contrast, only the specific absorption rate of B (SARB) was significantly correlated to the Al‐induced inhibition of root elongation. It is concluded, that alterations of nutrient uptake may play an important role in H⁺ toxicity, while at least after short‐term exposure to Al, alterations of Ca, Fe, Mg, or P uptake do not seem to be responsible for Al‐induced inhibition of root elongation. Further attention deserves the Al‐B interaction, moreover taking into account that a highly significant correlation between Al‐induced increase of callose concentration in root tips and Al‐induced decrease of SAR_B could be established.