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1.
Common bean (Phaseolus vulgaris L.) proved to be very sensitive of low pH (4.3), with large genotypic differences in proton sensitivity. Therefore, proton toxicity did not allow the screening of common bean genotypes for aluminium (Al) resistance using the established protocol for maize (0.5 mM CaCl2, 8 μM H3BO3, pH 4.3). Increasing the pH to 4.5, the Ca2+ concentration to 5 mM, and addition of 0.5 mM KCl fully prevented proton toxicity in 28 tested genotypes and allowed to identify differences in Al resistance using the inhibition of root elongation by 20 μM Al supply for 36 h as parameter of Al injury. As in maize, Al treatment induced callose formation in root apices of common bean. Aluminium‐induced callose formation well reflected the effect of Ca supply on Al sensitivity as revealed by root‐growth inhibition. Aluminum‐induced callose formation in root apices of 28 bean genotypes differing in Al resistance after 36 h Al treatment was positively correlated to Al‐induced inhibition of root elongation and Al contents in the root apices. However, the relationship was less close than previously reported for maize. Also, after 12 h Al treatment, callose formation and Al contents in root apices did not reflect differences in Al resistance between two contrasting genotypes, indicating a different mode of the expression of Al toxicity and regulation of Al resistance in common bean than in maize.  相似文献   

2.
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.  相似文献   

3.
Rhizobium trifolii were isolated from soils along a transect covering a range of soil pH (3.6–5.6) using two varieties of white clover by either growing seedlings directly in soil or in nutrient solution in tubes inoculated with soil. Rhizobia were present at pH 4.5 but absent at pH 3.9. Neither nodule number nor effectiveness were influenced by the method of isolation and the clover variety on which the strain was isolated. There was no relationship between the pH of the soils and either the number of nodules or the effectiveness of the isolates from those soils. Screening the isolates for tolerance of acidity and Al showed that multiplication was unaffected at pH 5.0 but was slowed for all strains at pH 4.5. Multiplication at pH 5.5 was unaffected by 10 μM Al but was inhibited by 50 μM Al. At pH 4.5 all but 16% of the isolates were inhibited by 10 μM Al; none multiplied with 50 μM Al. The strains which multiplied at pH 4.5 with and without Al were isolated equally from soils in the range pH 4.5–5.6. They were also isolated in almost equal proportions from the two varieties of clover and by the two isolation methods. Overall there was little variation in the effectiveness and acid- and Al-tolerance of isolates from these soils of different pH.  相似文献   

4.
Aluminum (Al) and cadmium (Cd) are two elements that contaminate soil in different ways as waste products of some industrial processes and that can be tolerated by some plant species in different concentrations. In this study, growth parameters of leaves and stems (fresh and dry weights, stem lengths, leaf surface area, and lamina thickness), anatomical changes in leaves (lower and upper epidermis, stomata and mesophyll tissue), and photosynthetic pigment contents (chlorophyll a and b, total chlorophyll, and carotenoids) were investigated in cotton (Gossypium hirsutum L. cv. Nazilli 84S), which was treated with Al and Cd for 3 months. Cotton seedlings were grown in greenhouse conditions and watered with Hoagland nutrient solutions, which contained 0, 100, and 200 μM aluminum chloride (AlCl3) and cadmium chloride (CdCl2). It was observed that reduced soil pH positively affected many parameters in cotton plants. Aluminum accumulation was greater in leaves than stems while the opposite was true for Cd accumulation. Leaves and stems of cotton plants treated with 100 and 200 μM Al and Cd showed slight growth changes; however, high concentrations of Al (200 μM) caused significant reductions in leaf area and leaf fresh weight, whereas stem fresh weight decreased with 200 μM Cd treatment. Anatomical parameters were mostly affected significantly under both concentrations of Al and Cd solutions (100 and 200 μM). The results revealed that the anatomical changes in the leaves varied in both treatments, and the long-term effect of the tested metals did not include harmful effects on anatomical structures. Moreover, the variations could be signals of tolerance or adaptive mechanisms of the leaves under the determined concentrations.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
Purpose

The purpose of this study is to determine the critical soil pH, exchangeable aluminum (Al), and Al saturation of the soils derived from different parent materials for maize.

Materials and methods

An Alfisol derived from loess deposit and three Ultisols derived from Quaternary red earth, granite, and Tertiary red sandstone were used for pot experiment in greenhouse. Ca(OH)2 and Al2(SO4)3 were used to adjust soil pH to target values. The critical soil pH was obtained by two intersected linear lines of maize height, chlorophyll content, and yield of shoot and root dry matter changing with soil pH.

Results and discussion

In low soil pH, Al toxicity significantly decreased plant height, chlorophyll content, and shoot and root dry matter yields of maize crops. The critical values of soil pH, exchangeable Al, and Al saturation varied with soil types. Critical soil pH was 4.46, 4.73, 4.77, and 5.07 for the Alfisol derived from loess deposit and the Ultisol derived from Quaternary red earth, granite, and Tertiary red sandstone, respectively. Critical soil exchangeable Al was 2.74, 1.99, 1.93, and 1.04 cmolckg?1 for the corresponding soils, respectively. Critical Al saturation was 5.63, 12.51, 14.84, and 15.16% for the corresponding soils.

Conclusions

Greater soil cation exchange capacity and exchangeable base cations led to lower critical soil pH and higher critical soil exchangeable Al and Al saturation for maize.

  相似文献   

8.
Screening cultivars for aluminum (Al) tolerance is often conducted in acid soils or in complete nutrient solutions. The former method lacks precise measurements of Al, and the second requires high Al concentrations because of precipitation and chelation of the Al and is less representative of the actual environmental stresses to which plants must adapt. These experiments were designed to determine Al tolerance of wheat (Triticum aestivum L. em Thell) and sorghum (Sorghum bicolor L. Moench) using incomplete solutions with very low Al concentrations. Six wheat and five sorghum cultivars were screened for Al tolerance in solution culture with 0 to 10 μM Al and only Ca, K, Mg, NO3, and Cl in the solutions. Plants were subjected to the solutions for 4 d, and the change in relative root length was measured. Solution Al levels and pH were measured after the termination of the experiments. ‘Atlas’ 66 and ‘Stacy’ were the most tolerant wheat cultivars ('Atlas 66’ = ‘Stacy’ ≥ ‘Monon’ ≥ ‘Scout 66’ ≥ ‘Arthur 71’ = ‘Oasis'). The wheat cultivars were effectively separated on a genetic response basis at 2 μM Al. Sorghum cultivars were uniform in their Al tolerance, but did show some separation at 1 μM Al (SC56 > Tx430 > ‘Funk GS22DR’ > SC283 = SC599). The pH and Al variations did not account for any of the differences observed, indicating that root length differences were caused by genetic control of response to high Al.  相似文献   

9.
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.  相似文献   

10.
The impacts of simulated acid rain on leachability of major plant nutrients, toxic element [aluminum (Al)], and acidity development in highly weathered tropical soils of Thailand were studied. Leaching experiments were conducted on soil columns with acidic solutions of pH 5.0, 4.0, 3.0, 2.0, and with water of pH 7.0 as a control treatment. Leaching losses of base cations from all soils increased with the decrease in pH associated with simulated acid rain (SAR) additions, and were found to be quite high under SAR with pH 2.0. The leaching removal of these cations was lesser at pH 3.0, 4.0, and 5.0 but greater than that in pH 7.0. The leaching of base cation from the soils depended not only on acid rain pH but also on soil properties, especially cation exchange capacity, soil texture, and initial base content. The significant losses of major plant nutrients [such as potassium (K+), calcium (Ca2+), and magnesium (Mg2+)] from the plant root zone over extended periods could cause nutrient imbalance and lower soil productivity.  相似文献   

11.
Abstract

Aluminum concentrations in soil solutions are not only controlled by inorganic clay minerals but also by organically bound aluminum. The objective of this study was to determine which pools contribute to Al dissolution. Soil samples were taken at various distances from tree trunks and at various depths at the Rolling Land Laboratory (RLL), Hachioji, Tokyo. Selective dissolution techniques were used to analyze the changes in pools of solid-phase aluminum. Soil pH values around Hinoki cypresses were in the aluminum buffer range. Exchangeable aluminum contents in soils under Hinoki cypresses were 104 mmolc kg-?1 on the average. This value was similar to that of the cation exchange capacity (CEC) of Andisols at RLL at a soil pH of 4. The relationship between the soil pH and exchangeable, organically bound, and amorphous aluminum pools showed that dissolved aluminum ions in the soil solution were primarily derived from the amorphous Al pool. Dissolved aluminum ions were substituted with base cations of soils, resulting in the increase of the content of exchangeable Al and/or the formation of complexes with organic matter which increased the proportion of organically bound Al pools. Increase in the proportion of organically bound Al pools indicated the importance of complexation with soil organic matter for controlling the aluminum concentration in the soil solution.  相似文献   

12.
Maize cultivars (Zea mays L.) were evaluated for their aluminum (Al) sensitivity using intact plants and excised root tips exposed to 25 μM Al in nutrient solution of low ionic strength and pH 4.3. Aluminum supply increased callose formation and Al concentrations in root tips of intact plants as well as in excised root tips. Using intact plants, differences in Al sensitivity among cultivars could be characterized by Al‐induced callose formation, Al‐induced inhibition of root elongation, as well as Al contents in root tips as parameters. Significant correlations between Al‐induced callose formation and Al contents in root tips (r2 = 0.64**) and inhibition of root elongation (r2 = 0.80***) were found. Excised root tips did not show a significant Al‐induced inhibition of root elongation. While average Al‐induced callose formation was similar for root tips of intact plants and excised root tips, mean Al contents in excised root tips were up to 1.5‐fold higher than in root tips of intact plants after 24 h of Al treatment. Aluminum‐induced callose formation as found in excised root tips did neither correspond to Al‐induced callose formation nor to inhibition of root elongation of intact plants. The addition of 10 mM glucose to the incubation medium led to a significant increase in the elongation of excised root tips and a 2‐3‐fold increase in Al‐induced callose formation. Staining with triphenyl‐tetrazolium‐chloride (TTC) revealed increased viability of these root segments. However, these effects of glucose supply did not improve the characterization of the cultivars for Al resistance. The results presented suggest that Al exclusion mechanisms expressed in root tips of intact plants might be non‐operational in excised root tips. Therefore, the characterization of maize germplasm for Al resistance using excised root tips appears not to be reliable.  相似文献   

13.
In view of restrictions in the application of antibiotics in animal production, Lanthanum (La) is intended to be introduced as a new growth promoter for pigs. Because most of the supplied La is subsequently excreted, it will be found in organic fertilizers which are applied to agricultural land. Thus, we examined the effect of lanthanum on the growth and La contents of plants in nutrient solution and in soils as well as its extractability from different soils. In nutrient solutions with concentrations of available La of up to 20 μmol L–1, shoot growth of bush bean was markedly reduced by up to 60% of the control at 20 μM La. By contrast, growth was not affected in maize. Lanthanum was mainly accumulated in the roots, but maize shoot contained considerable amounts of La as well. In contrast to nutrient solution, shoot growth of bush bean and spinach in soils supplemented with La up to 360 μmol kg–1 (50 mg kg–1) was not decreased. In contrast to spinach, bush bean shoots showed an increased La content at the highest La level. Extractability of La with 0.1 mol L–1 acetic acid from 12 different soils previously spiked with La was related mainly to soil pH, CEC, and Corg. We therefore conclude that except of strongly acidic conditions, the application of La‐containing organic fertilizers does not represent a risk for plant growth for the next over 100 years, provided that the recommended doses of feed supplementation is not increased.  相似文献   

14.
Abstract

Barley, Hordeum vulgare L., is extremely sensitive to excess soluble or exchangeable aluminum (Al) in acid soils having pH values below about 5.5. Aluminum tolerant cultivars are needed for use in rotations with potatoes which require a soil pH below 5.5 for control of scab disease. They are also potentially useful in the currently popular “low input, sustainable agriculture (LISA)”; in which liming even the plow layer of soil is not always possible or cost effective, or in situations where surface soils are limed but subsoils are acidic and Al toxic to roots. Ten barley cultivars were screened for Al tolerance by growing them for 25 days in greenhouse pots of acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic, typic Hapludult) treated with either 750 or 4000 μg?g‐1 CaCO3 to produce final soil pH values of 4.4 and 5.7, respectively. Based on relative shoot dry weight (weight at pH 4.4/weight at pH 5.7 X 100), Tennessee Winter 52, Volla (England), Dayton and Herta (Denmark) were significantly more tolerant to the acid soil than Herta (Hungary), Kearney, Nebar, Dicktoo, Kenbar and Dundy cultivars. Relative shoot dry weights averaged 28.6% for tolerant and 14.1% for sensitive cultivar groups. Comparable relative root dry weights were 41.7% and 13.7% for tolerant and sensitive cultivars, respectively. At pH 4.4, Al concentrations were nearly three times as high in shoots of sensitive cultivars as in those of the tolerant group (646 vs. 175 μg?g‐1), but these differences were reduced or absent at pH 5.7. At pH 4.4, acid soil sensitive cultivars also accumulated phosphorus concentrations that were twice as high as those in tolerant cultivars (1.2% vs. 0.64%). At pH 5.7, these P differences were equalized at about 0.7% for both tolerant and sensitive groups. At pH 4.4, shoots of the Al‐sensitive cultivar Nebar contained 1067 μg?g‐1 Al and 1.5% P. Concentrations of Al and P in the shoots of acid soil sensitive cultivars grown at pH 4.4 exceeded levels reported to produce toxicity in barley. The observed accumulation of such concentrations of Al and P in the shoots of plants grown under Al stress is unusual and deserves further study.  相似文献   

15.
Toxic levels of aluminum can cause severe yield reductions in many crop species, but sericea lespedeza [Lespedeza cuneata (Dum.‐Cours.) G. Don] has demonstrated considerable tolerance. Aluminum tolerances of six sericea lespedeza cultivars (Am 312, Appalow, AU Lotan, Interstate, Interstate 76, Serala) representing a broad genetic base were evaluated in a Monmouth soil [26.2% Al saturation (pH 4.8) vs. 2.8% Al saturation (pH 5.7)] and in nutrient solutions (0 vs 111 μM Al; pH 4.5). The soil and nutrient culture studies were harvested 30 and 27 d after seeding, respectively.

Aluminum stress did not reduce root and shoot growth significantly, nor were the pooled Al stress x cultivar interactions significant. Cultivars differed significantly in mean shoot and root vigor in nutrient solutions but not in soil. R‐esponses in soil were only weakly correlated with responses in nutrient solutions. Am 312 and Appalow had the lowest relative weight values (dry weight stressed/dry weight unstressed) in both media and Interstate and Interstate 76 the highest. Interstate 76 exhibited a significant positive response (5% level) to Al when evaluated in nutrient solutions.  相似文献   

16.
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.  相似文献   

17.
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.  相似文献   

18.
Aluminum (Al) has many detrimental effects on plant growth, and shoots and roots are normally affected differently. A study was conducted to determine differences among sorghum [Sorghum bicolor (L.) Moench] genotypes with broad genetic backgrounds for growth traits of plants grown at 0,200,400,600, and 800 μM Al in nutrient solutions (pH 4.0). Genotypes were categorized into “Al‐sensitive”, “intermediate Al‐tolerant”, “Al‐tolerant”, and SC 283 (an Al‐tolerant standard). As Al increased, shoot and root dry matter (DM), net main axis root length (NMARL), and total root length (TRL) became lower than controls (0 Al). Aluminum toxicity and/or nutrient deficiency symptoms become more severe, and shoot to root DM ratios and specific RL (TRL/root DM) values also changed as Al in solution increased. Root DM had greater changes among genotypes than shoot DM, and NMARL at 400 μM Al, and TRL at 200 μM Al had greater differences among genotypes than root DM, ratings for toxicity and/or deficiency symptoms, and other DM and RL traits. The wide differences among genotypes for NMARL and TRL could be used more effectively to evaluate sorghum genotypes for tolerance to Al toxicity than the other growth traits.  相似文献   

19.
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.  相似文献   

20.
Soybean [Glycine max (L.) Merr. cv. ‘Ransom'] root elongation under varying concentrations of solution hydrogen (H) and aluminum (Al) was investigated in a vertical split‐root system. Roots extending from a limed and fertilized soil compartment grew for 12 days into a subsurface compartment with solutions adjusted to either different pH values from 3.7 to 5.5 or a factorial combination of pH (4.0,4.6, and 5.2) and Al (0,7.5, 15, and 30 μM) levels. Ionic forms of Al were estimated with GEOCHEM and solution Al was determined with ferron. Boron (B) (18.5 μM) and zinc (Zn) (0.5 μM) were supplied to all solution treatments, in addition to 2000 μM Ca, after preliminary studies at pH 5.2 without Al indicated that their omission inhibited length of tap roots and their laterals in the subsurface compartment. Both H+ and Al inhibited the length of lateral roots more than tap roots. Lateral roots failed to develop on tap roots at pH<4.3 or in treatments with 30 μM Al. Relative tap root length (RRL) among treatments receiving Al correlated with Al as measured by reaction with ferron for 30s. Ferron‐reactive Al was correlated to GEOCHEM‐predicted Al3+ activity (r=0.99). A 50% reduction in RRL occurred with either 2.1 μM Al3+ activity or 4.9 uM ferron‐reactive Al. The absence of shoot and soil‐root biomass differences among solution treatments in the split‐root system indicated that differences in root growth in the subsurface compartment were not directly confounded with differences in top growth.  相似文献   

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