Al In Nutrient Solution Research Articles

NCED expression is related to increased ABA biosynthesis and stomatal closure under aluminum stress

Aluminum (Al)-induced decrease in leaf hydration has been associated with low gas exchange, especially stomatal conductance (gs). However, the mechanisms explaining these responses are unclear. Citrus limonia was exposed to 0 and 1480 μM Al in nutrient solution for 90 days to test whether the low gs and leaf hydration in plants exposed to Al is associated with increased 9-cis-epoxycarotenoid dioxygenase (NCED) gene expression and abscisic acid (ABA) biosynthesis. Relative leaf water content (RWC), water potential (Ψw) and gas exchange in the leaves, as well as leaf and root ClNCED3, ClNCED1 and ClNCED5 expression and accumulation of ABA and its metabolites (phaseic acid, dihydrophaseic acid, (+)-7′-hydroxy-ABA and ABA-β-d-glucosyl ester) were measured. Aluminum up-regulated ClNCED3 and induced ABA accumulation in the roots before impairments in leaf water status (low Ψw, RWC and gs) could be observed. Leaf ABA concentration increased from 7 to 90 days and this could be partially explained by the up-regulation of ClNCED3, ClNCED1 and ClNCED5 in this organ. Stomatal closure occurred concomitantly with the increase of ABA concentration, and this result provides further evidence of the role of ABA modulation of plant hydration under Al stress.

Aluminum-induced stomatal closure is related to low root hydraulic conductance and high ABA accumulation

Many studies ask how aluminum (Al) reduces the root growth, but as Al is mostly retained in the root system, physiological explanations for the also expected Al-induced decrease in stomatal conductance (gs) are unclear, mainly in well-watered conditions. We exposed tomato plants (Solanum lycopersicum) to 0, 25, 50 and 100 μM Al in nutrient solution to investigate whether Al impairs root hydraulic conductance (Lpr), affecting leaf water potential (Ψleaf) and possibly inducing abscisic acid (ABA) accumulation in roots and/or leaves. We also measured ABA delivery rate, xylem sap pH and the root/leaf area ratio in order to explain the low gs in plants exposed to Al. Declines in Lpr and gs were proportional to the increase in Al concentration, and all Al treatments similarly decreased Ψleaf, indicating the plant’s attempt to reduce water loss through transpiration while accumulating more ABA. Despite Al-induced increases in root ABA, the root-to-shoot delivery of ABA did not enhance, but Al caused root xylem sap alkalization. Despite the stability of root/leaf area ratio across a range of Al concentrations (0, 25 and 50 μM Al), the leaf hydration and stomatal opening was not conserved. Here we provide the first evidence that decreases in Lpr and increases in ABA might explain Al-induced stomatal closure.

Physiological, anatomical and ultrastructural effects of aluminum on Styrax camporum, a native Cerrado woody species.

Styrax camporum Pohl. (Styracaceae) is a woody species that grows on acidic soils from the Brazilian savanna with high aluminum (Al) saturation (m% > 50%), where it accumulates ~ 1500mg Al per kg dry leaves. Using nutrient solution, a previous study showed that 1480μM Al causes toxicity symptoms, which raises the question whether less than 1480μM Al could cause beneficial effects on this species. Here, we checked possible altered gas exchange rates, damage to organelles in root tips and the association between Al exposure and mitochondria occurrence in cells of root tips, once organic acids from Krebs cycle exuded by the roots of this species when exposed to Al have been recently evidenced. Five-month-old plants were grown in nutrient solution with 0, 740 and 1480μM Al for 90days. Plants exposed to 1480μM Al showed less developed root system, reduced plant height and low gas exchange rates in relation to those exposed to 0 and 740μM Al, confirming that 1480μM Al is toxic to S. camporum. However, plants exposed to 0 and 740μM Al had similar number of leaves, plant height, root biomass, root length, total plant biomass and gas exchange rates, indicating that no beneficial effects from 740μM Al could be noted on this species. In plants exposed to 0 and 740μM Al, mitochondria were noted at the root tip, while at 1480μM Al these organelles were not evident due to the conspicuous vacuolation of root cells. S. camporum shows limited tolerance to Al in nutrient solution. In addition, this species is not dependent on Al to grow and develop because the plants grew well under 0 and 740μM Al.

Low root PIP1-1 and PIP2 aquaporins expression could be related to reduced hydration in 'Rangpur' lime plants exposed to aluminium.

In acidic soils, aluminium (Al) occurs as Al3+, which is phytotoxic. One of the most conspicuous symptoms of Al toxicity is the root growth inhibition, which can lead to low water uptake and consequent reduction in leaf hydration and gas exchange. However, fibrous xylem vessels have been observed in roots of 'Rangpur' lime plants (Citrus limonia L.) when exposed to Al, which could affect the functioning of aquaporins, ultimately reducing their expression. We confirmed a decrease of CO2 assimilation (A), stomatal conductance (gs), transpiration (E) and relative leaf water content (RWC) in 3-month-old C. limonia plants exposed to 1480 μM Al in nutrient solution for 90 days. The estimated hydraulic conductivity from soil to the leaf (KL) and leaf water potential (Ψw) also showed low values, although not consistently reduced over time of Al exposure. The relative expression of aquaporin genes belonging to PIP family (PIP1-1, PIP1-2 and PIP2) showed downregulation for ClPIP1-1 and ClPIP2 and upregulation for ClPIP1-2 in plants exposed to Al. Furthermore, ClPIP1-1 was positively correlated with A and gs in plants exposed to Al. Therefore, downregulation of ClPIP1-1 and ClPIP2 in roots of 'Rangpur' lime plants could be associated with the low leaf hydration of this species when exposed to Al.

Macronutrients accumulation and growth of pineapple cultivars submitted to aluminum stress

ABSTRACT The objective was to determine the growth and accumulation of macronutrients of two pineapple cultivars submitted to different concentrations of aluminum (Al). For this, a study was conducted in plastic pots containing 4 L of nutrient solution, in a randomized block design, in a 2 x 5 factorial scheme, corresponding to two pineapple cultivars (‘IAC Fantástico’ and ‘Vitória’) and five Al concentrations (0, 21.6, 43.2, 64.8 and 86.4 mg of Al plant-1), with four replicates. The following variables were evaluated: root length, dry matter of root, stem and leaf, stem diameter, number of leaves, chlorophyll content and accumulation of macronutrients at 60 days after treatment. The cv. ‘Vitória’ showed a linear decrease in chlorophyll content, root dry matter, root length and accumulation of N, P, K, Ca and Mg in most plant components promoted by the increase of Al concentration in the nutrient solution. The cv. ‘IAC Fantástico’ had lower total dry matter, stem dry matter, stem diameter and accumulation of N, Ca and Mg. However, the evaluated characteristics were not influenced by the increase of Al concentration, showing greater tolerance of this cultivar to Al in nutrient solution.

Low doses of exogenous methyl jasmonate applied simultaneously with toxic aluminum improve the antioxidant performance of Vaccinium corymbosum

The effect of different MeJA doses applied prior to or simultaneously with toxic Al on biochemical and physiological properties of Vaccinium corymbosum cultivars with contrasting Al resistance was studied. Legacy (Al-resistant) and Bluegold (Al-sensitive) plants were treated with and without toxic Al under controlled conditions: a) without Al and MeJA, b) 100 μM Al, c) 100 μM Al + 5 μM MeJA, d) 100 μM Al + 10 μM MeJA and e) 100 μM Al + 50 μM MeJA. MeJA was applied to leaves 24 h prior to or simultaneously with Al in nutrient solution. After 48 h, Al-concentration, lipid peroxidation (LP), H2O2, antioxidant activity, total phenols, total flavonoids, phenolic compounds and superoxide dismutase activity (SOD) of plant organs were analyzed. Al-concentrations increased with Al-treatment in both cultivars, being Al, LP and H2O2 concentrations reduced with low simultaneous MeJA application. Higher MeJA doses induced more oxidative damage than the lowest. Legacy increased mainly non-enzymatic compounds, whereas Bluegold increased SOD activity to counteract Al3+. Low MeJA doses applied simultaneously with Al3+ increased Al-resistance in Legacy by increasing phenolic compounds, while Bluegold reduced oxidative damage through increment of SOD activity, suggesting a diminution of its Al-sensitivity. Higher MeJA doses could be potentially toxic. Studies are needed to determine the molecular mechanisms involved in the protective MeJA effect against Al-toxicity.

Theoretical and experimental assessment of nutrient solution composition in short-term studies of aluminium rhizotoxicity

Many recent studies examining aluminum (Al) toxicity have failed to consider its complex chemistry, thereby leading to erroneous results. Using modelling and experimental approaches, we focussed on the key effects of pH, P, and ionic strength on Al in nutrient solutions and resultant root elongation rate (RER) of soybean (Glycine max). A review of the literature showed that the composition of nutrient solutions (ionic strength =3 to 26 mM) in many studies differs markedly from solutions (mean ionic strength =5 mM) extracted from acid soils. Nutrient solutions should have a pH ≤ 4.5 to ensure that Al remains soluble and that the toxic Al3+ ion is the dominant species. Solutions should contain ≤5 μM P to ensure that Al is not precipitated and should have an ionic strength of < ca. 5 mM. Finally, we have shown that soybean RER is more closely related to the activity of Al3+ at the outer surface of the root-cell plasma membrane than its activity in the bulk solution. This study has highlighted the crucial consideration of the kinetic and thermodynamic chemistry of Al in experiments designed to study the rhizotoxic effects of Al.

Effects of Toxic Levels of Aluminium on Seedling Parameters of Rice under Hydroponic Culture

The presence of Al in the rhizosphere of rice in acid soil restricts root growth and significantly reduces crop productivity. In this study, the effects of Al (30, 60 and 90 µg/mL) on seedling root growth, number of primary roots per seedling, seedling shoot length, number of leaves per seedling, seedling fresh weight, and seedling dry weight were studied. Rice genotypes were classified into three different classes, namely, tolerant, moderately tolerant, and susceptible, based on root tolerance index. The method of hydroponic culture was modified, and elaborated in the text. Toxic levels of Al in nutrient solution significantly decreased seedling root growth, number of primary roots, seedling shoot length, number of leaves per seedling, seedling fresh weight, and seedling dry weight. Few genotypes showed longer root length at 30 µg/mL Al in nutrient solutions compared with the control. High levels of Al in nutrient solutions were highly toxic for rice seedlings. Based on root tolerance index, Radhunipagal, Gobindobhog, Badshabhog, Kalobhog, UBKVR-11, UBKVR-16, UBKVR-18, Khasha and IVT4007-B were classified as tolerant genotypes, and these genotypes may be used as donors for breeding of Al-toxicity tolerance.

Novel barley (Hordeum vulgare L.) germplasm resistant to acidic soil

Improving the resistance of barley (Hordeum vulgare L.) to acidic soils is an important goal of several barley breeding programs around the world. The identification and utilisation of novel barley sources resistant to aluminium (Al) may provide a significant and rapid advance towards that goal. Barley standards and screening protocols for selecting barley germplasm resistant to Al in nutrient solution and acidic soil were reevaluated. The assays used were quantitative in nature and were suitable for genotypic- and seedling-based selections. Although there was a broad agreement between the solution culture assays and soil assays in the ranking of genotypes it obscured the fact that misclassification of genotypes is common. Brindabella was shown to be better suited than Dayton (the current barley standard resistant to Al) as the Australian standard for resistance to acidic soils. A seedling-based Al pulse-recovery assay and an acidic soil assay were used to characterise 41 genotypes from the South and East Asian Barley Core Collection (SEA-BCC). In addition, in the acidic soil assays several standard barley and wheat genotypes were included. Three SEA-BCC genotypes were more resistant than Dayton to acidic soil while several others were similar to Dayton. The most resistant SEA-BCC genotypes Honen, Ohichi and Zairai Tanbo were of Japanese origin. Misclassification of barley genotypes and wheat genotypes for resistance to soil acidity between solution culture and acid soil assay provided strong evidence for the unsuitability of solution culture assay. Although in solution culture several barley genotypes were sensitive relative to wheat, in acidic soil they were not different from wheat. While the quest for resistant barley to acidic soils similar or better than resistant wheat still continues, it may be an unnecessary endeavour.

Constitutive and aluminium-induced patterns of phenolic compounds in two maize varieties differing in aluminium tolerance

Aluminium tolerance in maize is mainly due to more efficient Al exclusion. Nonetheless, even in tolerant varieties Al can gain access into the cells. Detoxification by binding to strong organic ligands should therefore play a role also in plants with high Al exclusion capacity. To test this hypothesis in this study the concentrations of soluble, free and bound, phenolics were analyzed in roots of two maize varieties differing in Al tolerance. Exposure for 24 h to 50 microM Al in nutrient solution strongly inhibited root elongation in the sensitive variety 16 x 36, but not in the Al-tolerant variety Cateto. Cateto accumulated about half the concentration of Al in roots than 16 x 36 (analysis performed after root desorption with citrate). Roots of Al-tolerant Cateto contained higher concentrations of caffeic acid, catechol and catechin than roots of the sensitive variety. Exposure to Al induced the accumulation of taxifolin in roots of both varieties. However, Al-tolerant Cateto accumulated about twice the concentration than Al-sensitive 16 x 36 of this pentahydroxyfavonol. The molar ratio for phenolics with catecholate groups to Al was about unity in roots of Cateto, while in those of 16 x 36 the ratio was ten times lower. Both the fact that these phenolics are strong ligands for Al and their high antioxidant and antiradical activity suggest that these compounds may provide protection against the Al fraction that is able to surpass the exclusion mechanisms operating in the tolerant maize variety.

Identification of aluminum resistant Andean common bean (Phaseolus vulgaris L.) genotypes

Aluminum (Al) toxicity is the principal abiotic constraint in acid soils of the tropics. Common bean, meanwhile, is for the most part very sensitive to this stress although certain genotypes within the species show some level of resistance, justifying screening of germplasm from both the Andean and Mesoamerican genepools to identify better performing sources. The objective of this study was to evaluate 36 genotypes of common bean under hydroponic conditions to identify root morphological traits that could be associated with Al resistance. A total of five root traits (elongation rate of the primary root, total root length, root biomass, average root diameter and specific root length) were measured using a simple nutrient solution with or without Al (20 µM) over a 48 hour growth period with the experiments conducted in five replicates. We found that genotypes from the Andean gene pool were more resistant to Al than Mesoamerican genotypes under these conditions, based on a smaller decrease in the elongation rate of the primary root, total root length, specific root length and a lesser increase in root diameter in the presence of Al in nutrient solution. These root traits but not root biomass can serve as selection criteria to distinguish between Al-resistant and Al-sensitive genotypes.

Ketenggangan Genotipe Jagung (Zea mays L.) Terhadap Cekaman Aluminium

Aluminum (Al) toxicity is the main yield-limiting factor for maize growing on acid soils of tropical regions. This experiment was conducted to screen maize ( Zea mays L) genotypes under Al stress in culture solution. The experiment was arranged in a split plot design with three replications. The main plots were Al concentrations (0, 2.5, 5 10, 20, and 40 ppm Al), and the sub plots were 22 maize genotypes. The results indicated that the genotype AMATL-(HS).C2, SATP-(S2)-C6-S0, MRSS-1(S1).C1-29-1, and MRSS-1(S1).C1-57-1 were more tolerant to Al-toxicity than the other genotypes including Antasena. The growth of Al-tolerant genotypes under low concentration of Al (2.5 ppm Al) was stimulated. The Concentration of 5 - 10 ppm Al in nutrient solution was adequate to separate genotypes between tolerant and sensitive genotypes in screening maize genotypes under Al stress. Relative net root length and relative root length were the best variable to be used as Al-tolerance indicators. Key words: Maize, Al-tolerance, Al-toxicity

Variation in aluminum resistance among arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal (AM) fungi mediate interactions between plants and soils, and are important where nutrient or metal concentrations limit plant growth. Variation in fungal response to edaphic conditions may influence the effectiveness of the plant-mycorrhizal association in some soil environments. Andropogon virginicus (broomsedge) colonizes disturbed sites in the eastern United States, including acidic mine soils where aluminum (Al) is phytotoxic, and Al resistance in broomsedge has been associated with colonization by the AM fungus Glomus clarum. In the present study, inter- and intra-specific variation to confer Al resistance to broomsedge was assessed among selected species of AM fungi. Broomsedge seeds were grown in sand culture inoculated with one of five isolates of three species of fungi (G. clarum, Acaulospora morrowiae, and Scutellospora heterogama). Plants were exposed to 0 or 400 microM Al in nutrient solution and harvested after 4 or 9 weeks of growth. Mean infection percentage, plant biomass, and plant tissue Al and phosphorus (P) concentrations were measured. G. clarum conferred the greatest Al resistance to broomsedge, with the lowest variability among isolates for colonization and growth inhibition by Al [tolerance indices (TI) between 22.4 and 92.7%]. Broomsedge plants colonized by A. morrowiae were consistently the most sensitive to Al, with little variation among isolates (TI between 1.6 and 12.1%). Al resistance by S. heterogama isolates was intermediate and wide-ranging (TI between 3.9 and 40.0%). Across all AM fungal isolates, resistance was associated with high rates of colonization and low tissue Al concentrations of broomsedge plants. The functional diversity in Al resistance displayed by these AM fungi reflect variation in acclimation mechanisms operating in the mycorrhizal symbiosis under environmental stress.

Identification of Aluminum Resistant Genotypes Among Madeiran Regional Wheats

Forty‐eight genotypes representing wheat diversity from the Island of Madeira were screened for resistance to aluminum (Al) in nutrient solution. Seeds of wheat used in the experiments were obtained from local farmers. The soil pH and content of ionic Al of plots cultivated with wheat were analyzed. The pH of topsoils varied between 3.83 and 6.59. The amount of ionic Al in soil samples varied between 0.38 and 1.36 cmol Al3 + per kg of soil and was positively correlated with the altitude of a plot. Eriochrome cyanine staining was used to evaluate the effect of Al ions on the root elongation. Seventy‐two hour exposure of 3‐day‐old seedlings to 100 and 200 µM Al in nutrient solution revealed a high number of Al resistant genotypes among wheat germplasm. After withdrawal of Al stress, survival and root regrowth was observed in 28 and 23 genotypes screened at 100 and 200 µM Al in nutrient solution, respectively. Enhanced resistance to Al among Madeiran genotypes was associated with the amount of ionic Al in the soils. Complexity and various patterns of responses of tested cultivars to Al stress may suggest that Madeiran germplasm could be a valuable source of genes controlling Al resistance for conventional breeding programs and for studies of molecular bases of mechanisms of Al resistance.

Differential Ability of the Root to Change Rhizosphere PH Between Chamaecyparis Obtusa Sieb . (Hinoki) and Quercus Serrata Thumb.(Konara) Under Aluminium Stress

Aluminium has a strong effect on many plant species, and there are reports of differing responses to Al between coniferous and broadleaf trees. A study was conducted on the effect of various concentrations of Al in nutrient solutions on tree root systems, using Chamaecyparis obtusa Sieb. (hinoki) and Quercus serrata Thumb. (konara) seedlings. Konara showed a tendency to enhance its root growth with increasing Al concentration in nutrient solution. The ability to change the rhizosphere pH decreased for both hinoki and konara with increasing Al concentration, but konara showed a higher pH change ability. It is suggested that konara and hinoki have different strategies to adjust the pH of acid soil.

Is The Ca + K + Mg/Al Ratio in the Soil Solution a Predictive Tool for Estimating Forest Damage?

The ratio between (Ca +K +Mg) and Al in nutrientsolution has been suggested as a predictive tool forestimating tree growth disturbance. However, the ratiois unspecific in the sense that it is based on severalelements which are all essential for plant growth;each of these may be growth-limiting. Furthermore,aluminium retards growth at higher concentrations. Itis therefore difficult to give causal and objectivebiological explanations for possible growthdisturbances. The importance of the proportion ofbase-cations to N, at a fixed base-cation/Al ratio, isevaluated with regard to growth of Picea abies.The uptake of elements was found to be selective;nutrients were taken up while most Al remained insolution. Biomass partitioning to the roots increasedafter aluminium addition with low proportions of basecations to nitrogen. We conclude that the low growthrates depend on nutrient limitation in thesetreatments. Low growth rates in the high proportionexperiments may be explained by high internal Alconcentrations. The results strongly suggest thatgrowth rate is not correlated with the ratio in therooting medium and question the validity of usingratios as predictive tools for estimating forestdamage. We suggest that growth limitation of Picea abies in the field may depend on lowproportions of base cations to nitrate. It istherefore important to know the nutritional status ofthe plant material in relation to the growth potentialand environmental limitation to be able to predict andestimate forest damage.

Hematoxylin staining as a phenotypic index for aluminum tolerance selection in tropical maize (Zea mays L.)

Hematoxylin staining is an early indicator of Aluminum (Al) toxicity effects on the apices of young, developing roots grown in nutrient solution. In this work, the potential of this technique as a reliable and reproducible phenotypic index for Al tolerance in tropical maize genotypes was assessed, with its performance systematically compared to two other parameters widely used in breeding programs – relative seminal-root length (RSRL) and net seminal-root length (NSRL). Seeding roots from contrasting genotypes for Al sensitivity stained remarkably different after 24- and 48-h and 7-day exposures to 222 μM Al in nutrient solution, with the Al-dye complex being detected in both the outer (epidermis) and inner (cortex) portions of the roots from the sensitive cultivar. Hematoxylin staining was compared to the RSRL and NSRL parameters using 20 families from the third generation of selfing (S3) following the cross between two contrasting inbred lines that had been previously classified by the RSRL index in an independent procedure. The coloration technique showed the highest capacity to discriminate among tolerant and sensitive genotypes and displayed significant correlation coefficients to the other two indexes. Evaluation of the results from diallel crosses involving nine inbred lines proved that hematoxylin staining was also particularly adequate for identifying expressive hybrid vigor, as demonstrated by the general (GCA) and specific (SCA) combining ability estimates obtained by using the three indexes simultaneously. Hence, hematoxylin staining of Al-stressed root apices appears to be a powerful tool to assist in Al-tolerance selection in tropical maize breeding programs.

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.

Growth traits among sorghum genotypes in response to aluminum

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.

Eastern gamagrass (Tripsacum dactyloides) root penetration into and chemical properties of claypan soils

Claypans restrict rooting depth and availability of moisture and nutrients to plants during periods of drought. Eastern gamagrass [Tripsacum dactyloides var. dactyloides (L.) L] often remains green during summer droughts, while other plants turn brown. Questions arose whether eastern gamagrass roots could penetrate claypans to obtain needed moisture. Pits were dug (2m deep) under eastern gamagrass plants that had been growing 50+ and 5+ years at two sites in Missouri. Clay contents were 30 to 50% in soil layers below 30 cm, and moisture was not limiting in these deep soil layers. Soil pHCa, in the lower soil layers, except at 180 cm, was below 5.0, and in some cases near 4.0. Extractable Al was especially high in the 90 and 120 cm deep soil layers where pH was low. Extractable Ca, Mg, and K increased with soil depth. The eastern gamagrass roots effectively penetrated claypan soils. Root lengths and root weights were extensive to 180 cm depth, and decreased from the surface with soil depth. Roots of eastern gamagrass were aerenchymous (having cellular compartments which allow air movement) at all depths, were mycorrhizal to at least 150 cm depth, and had relatively high tolerance to acidic Al toxic Tatum subsoil (Typic Hapludult) and toxic levels of Al in nutrient solution. The eastern gamagrass roots also provided root channels through claypans, which could enable new eastern gamagrass or other plant roots to grow into deeper soil layers.