Al Concentration In Nutrient Solution Research Articles

Depicting the physiological and ultrastructural responses of soybean plants to Al stress conditions

Aluminium (Al) is a toxic element for plants living in soils with acidic pH values, and it causes reductions in the roots and shoots development. High Al concentrations can cause physiological and structural changes, leading to symptoms of toxicity in plant tissue. The aim of this study was to describe the Al toxicity in soybean plants through physiological, nutritional, and ultrastructure analyses. Plants were grown in nutrient solution containing increasing Al concentrations (0; 0.05; 0.1; 1.0, 2.0 and 4.0 mmol L−1). The Al toxicity in the soybean plants was characterized by nutritional, anatomical, physiological, and biochemical analyses. The carbon dioxide assimilation rates and stomatal conductance were not affected by the Al. However, the capacity for internal carbon use decreased, and the transpiration rate increased, resulting in increased root biomass at the lowest Al concentration in the nutrient solution. The soybean plants exposed to the highest Al concentration exhibited lower root and shoot biomass. The nitrate reductase and urease activities decreased with the increasing Al concentration, indicating that nitrogen metabolism was halted. The superoxide dismutase and peroxidase activities increased with the increasing Al availability in the nutrient solution, and they were higher in the roots, showing their role in Al detoxification. Despite presenting external lesions characterized by a damaged root cap, the root xylem and phloem diameters were not affected by the Al. However, the leaf xylem diameter showed ultrastructural alterations under higher Al concentrations in nutrient solution. These results have contributed to our understanding of several physiological, biochemical and histological mechanisms of Al toxicity in soybean plants.

Aluminum exclusion from root zone and maintenance of nutrient uptake are principal mechanisms of Al tolerance in Pisum sativum L.

Our study aimed to evaluate intraspecific variability of pea (Pisum sativum L.) in Al tolerance and to reveal mechanisms underlying genotypic differences in this trait. At the first stage, 106 pea genotypes were screened for Al tolerance using root re-elongation assay based on staining with eriochrome cyanine R. The root re-elongation zone varied from 0.5mm to 14mm and relationships between Al tolerance and provenance or phenotypic traits of genotypes were found. Tolerance index (TI), calculated as a biomass ratio of Al-treated and non-treated contrasting genotypes grown in hydroponics for 10days, varied from 30% to 92% for roots and from 38% to 90% for shoots. TI did not correlate with root or shoot Al content, but correlated positively with increasing pH and negatively with residual Al concentration in nutrient solution in the end of experiments. Root exudation of organic acid anions (mostly acetate, citrate, lactate, pyroglutamate, pyruvate and succinate) significantly increased in several Al-treated genotypes, but did not correlate with TI. Al-treatment decreased Ca, Co, Cu, K, Mg, Mn, Mo, Ni, S and Zn contents in roots and/or shoots, whereas contents of several elements (P, B, Fe and Mo in roots and B and Fe in shoots) increased, suggesting that Al toxicity induced substantial disturbances in uptake and translocation of nutrients. Nutritional disturbances were more pronounced in Al sensitive genotypes. In conclusion, pea has a high intraspecific variability in Al tolerance and this trait is associated with provenance and phenotypic properties of plants. Transformation of Al to unavailable (insoluble) forms in the root zone and the ability to maintain nutrient uptake are considered to be important mechanisms of Al tolerance in this plant species.

Tolerance to aluminum toxicity by tropical leguminous plants used as cover crops

The objectives of this work were to compare Al tolerance among 17 species of tropical leguminous plants and to evaluate the most appropriate plant characteristic and Al concentration in nutrient solution for tolerance assessment. In addition, three soybean cultivars were included for comparison purposes. There was a great difference among the 17 plant materials tested, when compared by relative root elongation and critical Al activity to reduce 50% of root net elongation. Based on these parameters and on the comparison of two tropical maize genotypes differing in Al tolerance, the following classification was established: highly tolerant, for Mucuna nivea, M. deeringiana, M. aterrima Vigna unguiculata cv. BR 17 and Lablab purpureus cv. Rongai; tolerant for Cajanus cajan cv. IAPAR 43, Canavalia brasiliensis, Calopogonium mucunoides, Cajanus cajan cv. Fava larga, and Crotalaria paulina; moderately tolerant for Crotalaria ochroleuca, Canavalia ensiformis, Crotalaria spectabilis, and C. mucronata; and sensitive for Neonotonia wightii, Crotalaria breviflora and C. juncea cv.IAC-KR1. The three soybeans cultivars were classified as moderately tolerant (Biloxi) and tolerant (IAC 13 and IAC 9).

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.

Tolerance of eastern gamagrass to excess aluminum in acid soil and nutrient solution

Eastern gamagrass, Tripsacum dactyloides L., has been reported to tolerate a wide variety of soil conditions, including drought, flooding, and acidity, but its specific tolerance to aluminum (Al) has not been tested. One strain of this species, PMK Select Lot 94 SFG‐1, was tested for its tolerance to excess Al in an acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic, Typic Hapludult) and in nutrient solutions containing Al. Roots were able to penetrate unfertilized Tatum subsoil at pH levels as low as 4.1–4.2 (1:1 soil‐water), at Al saturations of 64 to 77% of CEC, and to tolerate Al concentrations in nutrient solution that would be lethal for many crop plants. For example, with 4 mg Al L‐1 and a final solution pH of 4.67, shoot and root dry weights were 75 and 76%, respectively, of those with no Al. Even with 24 mg Al L‐1 and a final solution pH of 4.13, shoot and root dry weights were 45 and 46%, respectively, of those for the no Al check treatment. Hence, this strain of gamagrass shows promise for use on soils having acidic, Al‐toxic subsoil layers that act as root barriers and predispose plants to injury by drought. Roots of gamagrass are also reported to penetrate hard clay pans and to create root channels for subsequent crops that lack this ability. Current studies indicate that the strain tested was susceptible to a chlorosis resembling iron (Fe) deficiency when grown in a Jiffy Mix potting mixture or with excess Al in nutrient solutions. Hence, gamagrass is tentatively being classified as a calcifuge [Al tolerant‐Fe‐inefficient]. In the current experiment, considerable plant to plant variability was noted regarding susceptibility to this chlorosis factor and to a purpling symptom resembling phosphorus (P) deficiency. Results indicate that an exhaustive screening of gamagrass populations could identify strains that are more suitable for specific soil situations.

Responses to Aluminium Toxicity Effects of Two Populations of Piptatherum miliaceum (L.) Cosson

AbstractThe effects of different aluminium (Al) concentrations (0 (control), 5 and 25 ppm) and pH levels (4.5 and 10.0) on two Piptatherum miliaceum populations, one from a bauxite area (population 1) and the other from pasture soil (population 2) were studied. Root length of both populations was severely inhibited at 25 ppm Al concentration and pH 4.5. Positive correlations between the Al content of roots of the two populations and increasing Al concentrations and pH levels in the nutrient solution were observed. Increase of Al concentrations in nutrient solution resulted in the decrease of calcium (Ca) content of the roots of the two populations in both pH values, while potassium (K) concentrations in the roots slightly differed from those of the control. Leaf chlorophyll content increased with increasing Al concentrations and pH values of nutrient solution in population 1 but decreased in population 2.Based on relative values at different treatments of root length (R.L.), Ca and K content of roots and leaf chlorophyll content, it is concluded that population 1 is more tolerant to Al than population 2.The chlorophyll content, under Al influence, may serve to distinguish Al‐tolerant and non‐tolerant ecotypes.

Differential response of citrus rootstocks to aluminum levels in nutrient solutions: II. Plant mineral concentrations2

Abstract 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.

Aluminum Tolerance of Spring Rye Inbred Lines1

Three hundred seventeen spring rye (Secale cereale L.) inbred lines, 15 cultivars of wheat (Triticum aestivum L.), and three lines of triticale (✕ trlticosecale Wittmack) were tested for Al tolerance. The seedlings were grown in solution‐paper medium and the roots were exposed for 48 hours to Al at different concentrations. The ability of roots to regrow after Al treatment was assessed. Approximately 75% of the rye lines tested showed root regrowth after exposure to Al concentrations of at least 30 ppm. The irreversible inhibition of root growth at a particular level of Al concentration in nutrient solution was associated with a significant increase in Al concentration in roots. The more tolerant rye lines were able to tolerate a significantly higher concentration of Al in their roots than those less tolerant. Variability in the reaction to Al was found within some inbred rye lines even though thye were S5 to S8 inbreds. No rye lines showed a greater tolerance to Al than the most tolerant wheat cultivars. Alumininm concentration in roots of tolerant wheat cultivars was lower than in rye lines. Two of the three triticale lines tested were highly tolerant to Al. The screening method is suitable for selecting homozygous tolerant lines.