Differential response of citrus rootstocks to aluminum levels in nutrient solutions: II. Plant mineral concentrations 2

The objective of this study was to determine relations between Al effects and mineral concentrations in citrus seedlings. Six‐month‐old seedlings of five citrus rootstocks were grown for 60 days in supernatant nutrient solutions of Al, P, and other nutrients. The solutions contained seven levels of Al ranging from 4 to 1655 μM. Al and similar P concentrations of 28 μM P. Aluminum concentrations in roots and shoots increased with increasing Al concentration in the nutrient solution. Aluminum concentrations in roots of Al‐tolerant rootstocks were higher than those of Al‐sensitive rootstocks. When Al concentrations in nutrient solution increased from 4 to 178 μM, the K, Mg, and P concentrations in roots and the K and P levels in shoots increased. Conversely, Ca, Zn, Cu, Mn, and Fe in the roots and Ca, Mg, Cu, and Fe in the shoots decreased. The more tolerant rootstocks contained higher Fe concentrations in their roots than did the less tolerant ones when Al concentrations in solution were lower than 308 μM. Concentrations of other elements (Ca, K, P, Mg, Zn, and Mn) in roots or shoots exhibited no apparent relationship to the Al tolerance for root or shoot growth of the rootstocks. Calcium, K, Zn, Mn, and Fe concentrations in roots and Mg and K concentrations in shoots of all five rootstocks seedlings had significant negative correlations with Al concentrations in corresponding roots or shoots.     

Differential response of citrus rootstocks to aluminum levels in nutrient solutions: I. plant growth 2

The objectives of this study were to determine and compare the Al tolerance of selected citrus rootstocks. Six‐month‐old seedlings of five citrus rootstocks were grown for 60 days in nutrient solutions. The solutions contained 7 levels of Al ranging from 4 to 1655 μM and similar P concentration of 28 μM. The nutrient solution pH was maintained at 4.0±0.1 and the temperature at 25±1°C. At high Al treatment levels, plants had thickened root tips and root caps covered with black gelatinous material. At high levels of Al treatments, seedlings of some rootstocks had yellow, mottled, and withered new leaves near end of experiment. New‐growth root lengths and shoot height responded differently to Al concentrations in the nutrient solution. New‐growth fresh weight of whole plants appeared to be the most sensitive indicator of Al tolerance. Based on response of fresh weight of whole plants to Al concentrations, relative Al tolerances of the rootstocks were Cleopatra mandarin > rough lemon > sour orange > Swingle citramelo > Carrizo citrange. The neutral or dividing Al concentrations in solution between beneficial and toxic effects were 371, 193, 189, 178, and < 100 μM Al, respectively, for the above rootstocks. Concentrations below or above the neutral Al levels caused either beneficial or toxic effects, respectively. The apparent optimum Al concentrations for the growth of whole plants were 163, 93, 89, 85, and <50 μM, respectively.     

Differential aluminum tolerance in some tropical rice cultivars. II. mechanism of aluminum tolerance

Ten‐day‐old seedlings of 22 rice (Oryza sativa L.) cultivars were subjected to aluminum (Al) stress in nutrient solutions with an initial pH of 4.0±0.1. The rice cultivars exhibited a wide range of response by changing the rhizosphere pH, and the uptake and efficiency ratio (ER) of utilization of nutrients both in the presence (222 μM Al) and absence of Al. In the presence of Al, the cultivars Co 37 and Basmati 370 recorded maximum uptake and highest ER's for calcium (Ca), potassium (K), magnesium (Mg), manganese (Mn), phosphorus (P), and iron (Fe). The cultivars Damodar and ADT 36 performed very poorly in terms of nutrient uptake. The tolerant cultivars (Al‐insensitive) efficiently took up and utilized Ca and P in the presence of Al. The susceptible (Al‐sensitive) and intermediate cultivars exhibited less Ca and P uptake and utilization. There was no apparent relationship between foliar Al content and the efficiency ratios. However, the Al‐tolerant cultivars, Co 37 and Basmati 370, accumulated less Al in their foliage which was the reverse in case for the Al‐susceptible cultivars. Among the 22 rice cultivars tested, Co 37 and Basmati 370 emerged as the most Al‐tolerant. Hence, they would be recommended for cultivation in acidic, infertile soils of the tropics. The results of this study are discussed in terms of identifying the mechanism of Al tolerance or sensitivity among the studied rice cultivars as related to their nutrient metabolism.     

Effects of aluminum on nutrient solution pH and nitrate/ammonium uptake by triticale

Aluminum (Al) plant tolerance has been frequently associated with a pH increase in the rhizosphere. The changes in pH are dependent on plant genotypes and ionic composition and strength of nutrient solutions. This work was performed in order to study in triticale (Triticosecale Wittm.) the association of pH change with nitrogen (N) uptake and growth performance in acid conditions. Three‐day‐old seedlings were treated with Al (185 μM) in solutions having different proportion nitrate/ammonium (NO₃/NH₄), 15/1 and 8/1, but the same total N content. Along the period with Al treatment, several measurements have been made: pH, every day; NO₃ and NH₄ uptake from the solution as well as shoot and root biomass production every two days (five and seven days of plant age). The maximum growth inhibition (30%) of fresh weight was found in roots of plants in the 15/1 (NO/NH,) nutrient solution. The presence of a higher proportion of NH₄ (8/1 solution) had a protective effect on Al damage as shown by less growth inhibition and less reduction in NO₃ uptake. Changes in pH apparently were not relevant for the tolerance. The results suggest that NH₄ fertilization may be useful for alleviating Al toxicity in triticale.     

Aluminum tolerance in maize: Minimizing pH changes in screening solutions 1

Preliminary screening of maize (Zea mays L.) genotypes for aluminum (Al) tolerance in nutrient solutions over a 12‐day growth period showed greater plant‐induced pH changes in solutions without Al than in solutions containing Al. Such pH changes may alter the specific effect of Al on relative root length (length in Al‐containing solution/length in 0 Al solution) commonly used as an index to rank genotypes with respect to Al tolerance. The objective of this study was to examine several screening methods for identifying Al‐tolerant maize genotypes, and to identify those procedures which resulted in minimal pH fluctuations during the course of screening. The following methods of controlling pH in nutrient solutions were compared: (i) 12‐day exposure to 0 or 5 mg Al/L in nutrient solutions (a) with or (b) without daily pH adjustment or (c) with different NO₃ ^‐/NH₄ ⁺ ratios, and (ii) 2‐day exposure to 0, 5, 10, 25 or 40 mg Al/L treatment solutions followed by a 3‐day recovery period in solutions with an initial pH at (a) 4.6 or (b) 4.0. In the 12‐day experiments, daily pH adjustment to 4.6 did not eliminate large pH fluctuations in the control (0 Al) solutions, and it substantially decreased the soluble Al concentration in the Al‐treatment solution. Varying the ratio of NO₃ ^‐ to NH₄ ⁺ did not eliminate large pH fluctuations. Exposing the seedlings for 2 days to Al solutions at pH 4.6 resulted in large pH differences between 0 Al and Al‐containing solutions and in precipitation of large amounts of Al. In contrast, the 2‐day procedure using solutions with an initial pH at 4.0 was more satisfactory in that the pH was maintained between 4.0 and 3.7 in all solutions, and Al precipitation was minimized. When the 2‐day method at pH 4.0 was used to screen the genotypes, PDMR3 had consistently higher relative root lengths in Al‐containing solutions than did Kalimpos, IPB Varl, UPCA Varl and Trinidad Grp1&2.     

Identification of an aluminum tolerant tropical cowpea cultivar by growth and biomass accumulation parameters

Ten‐day‐old seedlings of four cowpea (Vigna unguiculata Walp) genotypes were subjected to six levels of aluminum (Al) (0, 74, 148, 222, 296, and 370 μM/L) to test their tolerance to Al toxicity in a nutrient solution at pH 4.0±0.1. Seedlings were grown in the presence of Al under controlled environmental conditions in a growth chamber. The nutrient solutions were replenished once a week. After 20 days, treatments were terminated and the differences in their growth patterns were compared. Standard growth parameters, such as plant growth, dry matter production, relative growth reduction in roots (RGRS) and shoots (RGRS), and root and shoot tolerance indices (RTI and STI) have been used as markers of Al toxicity. The cowpea genotypes studied exhibited a wide range of responses in their tolerance to Al. Though the genotypes were subjected to six levels of Al, a good degree of separation in their responses was observed only at the 222 μM Al/L treatment level. Therefore, this concentration was chosen to treat and compare the performances of the genotypes. The genotype Co 3 showed an increase in growth, while Paiyur 1 and other genotypes showed severe inhibitions in the presence of Al. Furthermore, for RTI and STI, Co 3 also registered its tolerance to Al by showing increased ratios in the presence of Al. Whereas, Paiyur 1 recorded severe reductions. The RGRR and RGRS data also substantiates this finding. Based on the growth parameters, the four cowpea genotypes were ranked based on their tolerance to Al: Co 3 > Co 4 > KM > Paiyur 1. Co 3 was the most Al‐tolerant genotype which performed extremely well in the presence of Al, while Paiyur 1was the most Al‐susceptible genotype. Therefore, the Al‐tolerant genotype can be used for future breeding programmes to produce Al‐tolerant genotypes, subsequently, can be recommended for acidic infertile soils in the tropics.     

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.     

Effects of aluminum source and level,nutrient solution ph and tissue age on elemental concentrations in ryegrass

Abstract

Recent studies have indicated that A1 concentrations in excess of 1000 μg/g have occurred in grass species susceptible to Al toxicity, although other studies have suggested that high Al concentrations were the result of soil contamination. Our objectives were to determine the effect of Al source, Al level, nutrient solution pH, and tissue age on elemental concentrations in ryegrass.

An experiment was conducted in which ryegrass (Lolium multiflorum Lam.) cv ‘Gulf grown in nutrient solution at pH 5 and 6 received 0 Al or 100 and 500 μg Al/ml as Al‐sulfate and as NaAl‐citrate. Plant shoots were harvested 35 and 42 days after planting. Where nutrient solution pH was adjusted daily to pH 5 or 6, highest forage Al concentrations averaged only 295 μg/g. Where pH was not adjusted, highest Al concentrations averaged over 2000 μg/g. Plants having Al concentrations above 500 μg/g showed visible signs of Al toxicity. Source and level of Al in the nutrient solution, initial nutrient solution pH, and age of tissue at harvest had little effect on other elemental concentrations in the ryegrass.     

Factors contributing to the development of aluminum resistance in the Madeiran maize germplasm

Forty genotypes representing maize genetic diversity from the Island of Madeira were screened for resistance to aluminum (Al) in nutrient solution. Seeds of maize were obtained from local farmers from field plots spread around the island in a range of altitudes from 99 to 1000 m above sea level. The content of ionic aluminum and the pH of soils cultivated with maize were determined. The mean pH value of all examined soils was 4.9, while the mean ionic Al content was 0.76 cmol kg^–1. Seventy‐two hours (h) exposure to 100 and 200 μM Al followed by a 48 h recovery period of 4‐day old seedlings revealed significant differences in Al resistance in the Madeiran maize germplasm. Root survival and regrowth exceeding 80 % of the seedlings were observed in 22 and 8 of the tested genotypes screened at 100 and 200 μM Al in nutrient solution. High Al resistance among Madeiran maize genotypes appeared not to be associated with the lower pH of soil, and did not correlate with the amount of soil Al³⁺ or the altitude at the site of collection. The high level of Al resistance of the maize cultivars indicates an initial genetic trait enhanced by open pollination of maize.     

Assessing the relative effects of hydrogen and aluminum ions on primary root growth of white clover seedlings

White clover (Trifolium repens L., cultivar Huia), a dominant forage legume in Appalachia, usually grows poorly on acidic soils common to the region. The effects of bulk solution concentrations of calcium (Ca), hydrogen (H), and aluminum (Al) on the relative root growth (RRG) of white clover were determined using one‐ to three‐day‐old seedlings to assess the relative toxicity of H⁺ and Al. The RRG was affected by bulk solution concentrations of Ca, Al, and pH, in a manner indicative of significant interactions among these parameters. The RRG was directly related to the activities of Al³⁺ or H⁺ at the surface of the root as calculated by the Gouy‐Chapman‐Stern model. Fifty percent inhibition of RRG occurred at activities of 5 and 200 μM Al³⁺ and H⁺, respectively. A large part of the interaction between bulk solution concentrations of Ca, Al, and H could be explained by how these parameters affected the activities of these ions at the root surface.     

Differential tolerances of two old world bluestem genotypes to excess aluminum in acid soil and nutrient solution

Two genotypes of Old world bluestems from the species Bothriochloa intermedia (R. Br.), A. Camus, shown earlier to differ in tolerance to acid, Al‐toxic Tatum subsoil at pH 4.1, were characterized further with respect to growth in pots of Tatum soil over a wider pH range and tolerance to Al in nutrient solutions. The two genotypes studied were acid‐soil tolerant P. I. 300860 (860) and acid soil sensitive P. I. 300822 (822).

The soil experiment confirmed earlier rankings of acid soil tolerance in these two genotypes. For example, with 0, 375 or 750 ug CaCO₃ g^‐1 soil (final pH 4.0, 4.3 and 4.6), the 860 genotype produced significantly more dry top weight than 822, but these differences were precluded with 1500 or 3000 ug g^‐1 CaCO₃ added (pH 4.7 and 5.4). At pH 4.3 and 4.6, the root dry weights of the two genotypes were also significantly different and weights were equalized at pH 4.7 and 5.4. The 860 genotype made fairly good top growth (67% of maximum) at pH 4.3 and a soil Al saturation of 63%; this situation was lethal for 822. When grown in greenhouse pots, the acid‐soil tolerant 860 genotype required only about one fourth as much CaCO₃ as 822 to produce good growth of forage on acid Tatum subsoil. If confirmed under field conditions, such a difference could be economically significant in reclaiming acidic marginal land and in producing forage at low cost.

Differential Al tolerance in the two genotypes was confirmed in nutrient solutions. For example, with 8 mg Al L^‐1 added, both top and root dry weights of 860 were significantly higher than those of 822, but with no Al added, these growth differences disappeared.

Mineral analyses of plants did not shed much light on mechanisms of differential acid soil or Al tolerance. For example, Al concentrations in plant tops associated with toxicity varied from 33–43 ug g^‐1 in nutrient solutions containing Al to 119–283 ug g^‐1 in acid soil It appears that elucidation of Al‐adaptive mechanisms will require physiological and biochemical studies at the cellular level.     

Differential aluminum tolerance in some tropical rice cultivars: I. Growth performance

Ten‐day‐old seedlings of 22 rice (Oryza sativa.L) cultivars originated from various tropical countries were subjected to six levels of aluminum (Al) [0, 74, 148, 222, 296, and 370 μM] to test their tolerance to Al toxicity in nutrient solutions at pH 4.0±0.l. Seedlings were grown in the presence of Al under controlled environmental conditions in growth chambers. The nutrient solutions were replenished once a week. After 30 days, treatments were terminated and the differences in their growth patterns were compared. Standard growth parameters such as plant growth, dry matter production, relative growth reduction in roots (RGRS) and shoots (RGRS), root tolerance index (RTI) and shoot tolerance index (STI) have been used as markers of Al toxicity.

Rice cultivars studied exhibited wide range of responses in their tolerance to Al. Though, the rice cultivars were subjected to six levels of Al, a good degree of separation in their responses was observed only at 222 μM Al. Therefore, this concentration was chosen to analyze and compare the performances of the cultivars. Further, only six cultivars showed significant changes in their expression in the presence of Al compared to control, and so data have been presented only for those cultivars for clarity. The cultivars BW 196, Bhura Rata, Basmati 370 and Co 37 recorded increases in growth, while Damodar and ADT 36 showed severe inhibitions in the presence of Al. Furthermore, in RTI and STI also Co 37 and Basmati 370 registered their tolerance to Al by showing increased growth in the presence of Al. Whereas, Damodar and ADT 36 recorded severe reductions. The RGRR and RGRS data also substantiates this finding. Based on the growth parameters, the six rice cultivars were ranked based on their tolerance to Al: Co 37 > Basmati 370 > BW 196 > Bhura Rata > Damodar > ADT 36. Co 37 and Basmati 370 are the two most tolerant cultivars which performed extremely well in the presence of Al, and Damodar and ADT 36 are the most susceptible cultivars. Therefore, the Al‐tolerant cultivars can be used for future breeding programes to develop Al‐tolerant, cultivars that subsequendy can be recommended for planting in acidic, infertile soils of the tropics.     

Responses of Kentucky bluegrass cultivars to excess aluminum in nutrient solutions

Kentucky bluegrass, Poa pratensis L., is generally regarded as an acid‐soil‐sensitive species. However, previous studies in our laboratory showed that cultivars within the species differed widely in tolerance to acid Tatum subsoil (pH 4.6) which is used routinely to screen plants for aluminum (Al) tolerance. In the early studies, specific differential Al tolerance was not demonstrated. The objective of the current study was to test the hypothesis of differential Al tolerance more precisely in nutrient solutions. In one experiment, acid‐soil‐tolerant Victa and Fylking and acid‐soil‐sensitive Windsor and Kenblue cultivars were grown for 35 days in nutrient solutions containing 0, 2, 4, 6, 12, and 24 mg Al L^‐1, at initial pH 4.5, with no subsequent adjustment. In a second experiment, Victa and Windsor were grown for 30 days in solutions containing 0, 4, and 6 mg Al L^‐1, at initial pH 4.5, with no further adjustment. For Victa and Windsor, tolerance to Al in nutrient solution corresponded with tolerance to acid Tatum subsoil, however, the cultivar difference in tolerance, based on relative root dry weight, was only about 2‐fold, compared with 20‐fold in acid Tatum subsoil. Fylking and Kenblue cultivars, which showed a wide difference in tolerance to acid Tatum subsoil, did not show distinct differences in tolerance to Al in nutrient solutions. Possible reasons for this discrepancy are discussed. Superior Al tolerance of Victa (compared with Windsor) was associated with a greater plant‐induced increase in the pH of its nutrient solutions and a corresponding decrease in concentrations of soluble Al in the filtered solutions at the end of the experiments. Greater Al sensitivity in Windsor (compared with Victa) was not related to reduced uptake of phosphorus (P) or excessive uptake of Al; neither cultivar accumulated appreciable Al concentrations in its shoots. The observed differential acid soil and Al tolerance among bluegrass cultivars appears worthy of further study. Improved understanding of Al tolerance mechanisms would contribute to fundamental knowledge of plant mineral nutrition and could aid plant breeders in tailoring plants for greater tolerance to acid subsoils.     

Effect of calcium and magnesium on 65zinc absorption and translocation in rice seedlings

Effect of calcium and magnesium on zinc absorption by 21‐day‐old rice seedlings and its translocation within the plants was studied in the nutrient solution culture using radioactive zinc. The concentrations of the elements in the nutrient solution were 0.5, 1.0 and 2.0 μM zinc and 0, 10 and 20 mM calcium and magnesium. Absorption of ⁶⁵zinc was studied for 30, 60 and 90 minutes and translocation for 24 hours. Zinc absorption increased with time and increased zinc concentration in the nutrient solutions. Addition of calcium and magnesium reduced zinc absorption by rice seedlings by about 60 and 90% respectively at a concentration of 20 mM. The nature of inhibition of both calcium and magnesium on zinc was non‐competitive as indicated by Michaelis constants. A large fraction of zinc absorbed remained in roots and only 5.3% was translocated to shoots even at 2.0 #GMM zinc concentrations in solution. The effect of cations on translocation of ⁶⁵zinc within rice seedlings was more at lower( 0.5 μM zinc) than at higher (2.0 μM zinc) concentrations.     

Suitability of the aluminon technique for measuring phytotoxic aluminum in solutions with varying sulfate concentrations

Abstract

Considerable uncertainty prevails concerning a suitable measure that can adequately describe Al phytotoxicity in nutrient and soil solutions. A study was conducted to evaluate the ability of a modified aluminon technique to discriminate between phytotoxic and non‐phytotoxic Al in solutions containing 80 μM Al with varying levels of CaSO₄(625 to 10000 μM), at two pH levels (4.2 and 4.8). The concentration of Al measured by the modified aluminon technique ranged from 18.3 to 77.7 μM,thereby indicating substantial polymerization in some of the solutions. The greatest amount of polymerization occurred at pH 4.8 in the presence of 625 μM CaSO₄. Increasing additions of CaSO₄resulted in an increase in predicted activity of AlSO₄ ⁺at both pH levels. However, with increasing addition of CaSO₄, the predicted activity of Al³⁺decreased at pH 4.2 or remained relatively constant at pH 4.8. The relationship between the sum of predicted activities of monomeric Al (Sa_{Al mono.}) in solution and tap root length of soybean [Glvcine max(L.) Merr.] cv. Lee was extremely poor, thereby indicating the inability of the modified aluminon technique to measure phytotoxic Al in solutions employed in the current study. This difficulty was due to failure of the modified aluminon technique to exclude lesser phytotoxic AlSO₄ ⁺species. The activity of Al³⁺was closely related to tap root length (R²= 0.865). The prediction of root length response to Al was further improved (R²= 0.899) by considering the solution Al index as: S[3a_A13+ + 2a_Al(OH)2+ + a_A1(OH)+]. There was a poor relationship between tap root length and the concentration of polymeric Al, thus suggesting the lower phytotoxicity of this component under the prevailing solution conditions.     

Phytotoxicity of organic acids as influenced by montmorillonite,hydroxy‐Al montmorillonite and phosphate fertilization

Abstract

The germination and growth of wheat seedlings were studied at pH 5.5 in liquid growth media with organic acids in concentrations ranging from 800 to 1200 ppm, before and after interaction of the organic acids with montmorillonite and hydroxy‐Al montmorillonite. Germination was not affected by the organic acids, but subsequent growth was dependent on the kind and concentration of organic acid in the growth medium. Acetic acid was more inhibitory than citric acid. Gallic acid polymerized at pH 5.5 and was phytotoxic at 1200 ppm. Interaction of organic acids with montmorillonite and hydroxy‐Al montmorillonite reduced the concentration of organic acids in solution by adsorption. Despite this reduction in concentration the phytotoxicity of the growth media was enhanced after the interaction. This was caused by the dissolution of surface Al and the effect was more pronounced in cases where hydroxy‐Al interlayered montmorillonite was the adsorbent. Additions of P as KH₂PO₄ alleviated the phytotoxicity of organic acids but not the associated Al toxicity. The amount of P lost by adsorption or precipitation was dependent on the form of Al in the growth media.     

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.     

Calcium alleviation of hydrogen and aluminum inhibition of soybean root extension from limed soil into acid subsurface solutions

Alleviation by calcium (Ca) of inhibition of soybean [Glycine max (L.) Merr. cv. ‘Ransom'] root elongation by hydrogen (H) and aluminum (Al) was evaluated in a vertical split‐root system. Roots extending from a limed and fertilized soil compartment grew for 12 days into a subsurface compartment containing nutrient solution with treatments consisting of factorial combinations of either pH (4.0, 4.6, and 5.5) and Ca (0.2, 2.0, 10, and 20 mM), Al (7.5, 15, and 30 μM) and Ca (2.0,10, and 20 mM) at pH 4.6, or Ca (2, 7, and 12 mM) levels and counter ions (SO₄ and Cl) at pH 4.6 and 15 μM Al. Length of tap roots and their laterals increased with solution Ca concentration and pH value, but decreased with increasing Al level. Length of both tap and lateral roots were greater when Ca was supplied as CaSO₄ than as CaCl₂, but increasing Ca concentration from 2 to 12 mM had a greater effect on alleviating Al toxicity than Ca source. In the absence of Al, relative root length (RRL) of tap and lateral roots among pH and Ca treatments was related to the Ca:H molar activity ratio of solutions (R²≥0.82). Tap and lateral RRL among solutions with variable concentrations of Al and Ca at pH 4.6 were related to both the sum of the predicted activities of monomeric Al (R²≥0.92) and a log‐transformed and valence‐weighted balance between activities of Ca and selected monomeric Al species (R²≥0.95). In solutions with 15 μM Al at pH 4.6, response of tap and lateral RRL to variable concentrations of CaSO₄ and CaCl₂ were related to predicted molar activity ratios of both Ca:Al³⁺ (R²≥0.89) and Ca:3 monomeric Al (R²≥0.90), provided that AISO₄ and AI(SO₄)₂ species were excluded from the latter index. In all experiments H and Al inhibited length of lateral roots more than tap roots, and a greater Ca:H or Ca:Al concentration ratio was required in solutions to achieve similar RRL values as tap roots.     

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

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% reduction in root elongation being 12.2 μM Ce and 4.8 μM La at pH 5.5, or 7.1 μM La at pH 4.5.     

Effect of nitrogen source on aluminum toxicity in nonmycorrhizal and ectomycorrhizal pitch pine seedling

The effect of elevated nitrate [(NO₃‐nitrogen (N)] or ammonium (NH₄)‐N on the response of nonmycorrhizal (NM) and ectomycorrhizal (ECM) pitch pine (Pintis rigida Mill.) seedlings to aluminum (Al) was determined in experiments in which N was increased three times above ambient levels. Seedlings with and without the mycorrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch were grown in sand irrigated with nutrient solution (pH 3.8) containing 0, 10, or 20 mg Al L^‐1 (0, 370, or 740 μM Al). The nutrient solution simulated that for the sandy, nutrient‐poor soil of the New Jersey Pine Barrens. Elevated NO₃‐N had no significant effect on Al toxicity in NM seedlings, but Al toxicity at ambient NH₄‐N was ameliorated by elevated NH₄‐N. Symptoms of Al toxicity in roots (thick and stunted) of ECM seedlings at ambient N levels were reduced by elevated NH₄‐N and absent at elevated NO₃‐N. When N was elevated by an increase in NO₃‐N or NH₄‐N, uptake of N and relative increases in total biomass were greater in ECM than in NM seedlings.