Response of cotton cultivars to aluminum in solutions with varying silicon concentrations

Abstract

Cotton (Gossypium hirsutum L.) is extremely sensitive to Al toxicity. Increasing Si concentration in solution has been reported to alleviate AI toxicity. In this investigation the effects of varying Si concentrations (700, 1400, and 2800 μM Si) on reactive Al (defined as Al reactive with aluminon during 10‐s reaction time, without acidification and heating) was studied in solutions containing either 50, 100 or 200 μM Al during 50 d of aging. An increase in Si concentration had negligible effects on the reactive Al in solutions with 50 or 100 μM Al. However, in solutions with 200 μM Al the reactive Al decreased by 6 to 15% with an increase in Si concentration from 0 to 2800 μM.

The effects of either 700, 1400 or 2800 μM Si on root growth of Coker 208, Coker 315, DPL 90, McNair 235, Stoneville 506 and Tifcot 56 cotton cultivars were investigated in solutions containing either 0, 10, 20 or 40 μM Al with 500 μM Ca at pH 4.5. In solutions containing no Al, addition of 700 μM Si improved root growth by 69–87% in Coker 315, DPL 90 and McNair 235 cultivars but not in the other cultivars. In solutions containing 10 μM Al, an increase in Si concentration from 0 to 2800 μM improved the root growth by 15–17% in DPL 90 and McNair 235 cultivars only. An increase in Si additions failed to improve root growth of any of the cultivars in solutions with 20 or 40 μM Al.     

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.     

Influence of surface‐applied poultry manure on topsoil and subsoil acidity and salinity: A leaching column study

It has been suggested that surface applications of animal manure can ameliorate both top and subsoil acidity. For that reason, the effects of surface incorporation (0–5 cm) of a high rate of poultry manure to an acid soil on pH and exchangeable and soluble Al in the top‐ and subsoil were investigated in a leaching column study. During the experimental period of 108 d, columns received a total of 875 mm with leaching events occurring after 9, 37, 58, and 86 d. Incorporation of poultry manure into the surface 5 cm resulted in a large rise in pH measured in both 1M KCl and in soil solution. This liming effect was attributed primarily to the substantial CaCO₃ content of poultry manure. In the 15–45 cm layer, pH_KCl was not significantly different between poultry manure and control treatments but surprisingly, soil‐solution pH was substantially less in the poultry‐manure treatments. Exchangeable Al was significantly less in poultry manure than in control in all soil layers although the effect was most marked in the 0–5 cm layer. However, although concentrations and activities of monomeric Al (Al_mono), and the proportion of total Al present as Al_mono, in soil solution were lower under poultry manure than in control in the 0–5 cm layer, the reverse was, in fact, the case in lower soil horizons. This was attributed to a soluble‐salt effect, originating from the large cation content of poultry manure, displacing exchangeable Al³⁺ and H⁺ back into soil solution. Indeed, electrical conductivity and concentrations of Ca²⁺, Mg²⁺_, K⁺, and Na⁺ in soil solution were substantially higher in the poultry‐manure than in the control treatments at all soil depths. Poultry‐manure applications also resulted in substantial increases in the concentrations of Ca²⁺_, Mg²⁺_, K⁺, Na⁺, Al_mono, NH , and NO in leachates, particularly at the fourth leaching. It was concluded that although surface application of poultry manure can raise soil pH in the topsoil, increases in soluble‐salt concentrations in soil solution can greatly modify this effect in the subsoil.     

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.     

The liming effect of five organic manures when incubated with an acid soil

A laboratory incubation experiment of 6 months duration was carried out to investigate the liming effects of five organic manures (poultry, pig, and cattle manure, soybean residues, and sewage sludge) when added to an acid soil at a rate of 10 mg g^–1. Soils were sampled after 1, 7, 13, 19, and 25 weeks of incubation. For the animal manures and sewage sludge, soil pH was highest after 1 week incubation and it declined thereafter. However, for soybean residues, pH increased over the first 7 weeks of incubation after which it declined. The decreases in pH were accompanied by accumulation of NO ‐N in the soil. The addition of organic residues to the soil resulted in decreases in the concentrations of exchangeable Al and in both total (Al_t) and monomeric (Al_mono) Al present in the soil solution. The effect was most marked for poultry manure, least marked for cattle manure, and more evident after 7 than 25 weeks incubation. Concentrations of soluble C in the soil solution were elevated in manure‐amended soils. Manure additions resulted in a decrease in the percentage of Al_t present in solution as Al_mono, and this was attributed to complexation of Al by soluble organic matter originating from the manures. It was concluded that organic wastes can act as liming materials when added to acid soils and that the resulting increase in pH and decrease in Al_mono concentrations might provide a window of opportunity for establishment and early growth of crop plants.     

Effects of phosphogypsum or calcium sulfate on aluminon reactive aluminum in solutions at varying pH

Abstract

Growing evidence of positive crop responses to gypsum or phosphogypsum (PG) application in acid soils strongly support the use of these amendments as an ameliorant of subsoil acidity. Although gypsum improves Ca availability in subsoils, its role in alleviation of Al toxicity needs careful attention. In the current study, either PG, CaSO₄.2H₂O or CaCl₂.2H₂O was added (to supply 12 mM Ca) to solutions containing 40 μM Al at pH 4.1 + 0.1. Solution pH was gradually raised to 4.5, 4.8 and then to 5.3 at various time intervals during 25 d aging of the solutions at 25 + 1^OC.

Concentration of Al measured by aluminon method without preacidification and preheating, referred to as “reactive Al”; in this paper, was 16 μM in 2 g L^‐1PG solution without added Al. This accounted 38% of total soluble Al in PG solution. Addition of 2 g L^‐1PG to solution containing 40 μM Al, resulted in only 42% of total Al in solution present in forms reactive with aluminon. According to MINTEQ speciation model, Al in solution was present as an entirely complexed form with F^‐. An increase in solution pH up to 5.3 had no effect on measured concentration of reactive Al or predicted distribution of Al species.

Addition of CaSO₄.2H₂O to 40 μMAl solutions had no effect on the concentration of reactive Al within pH 4.1 ‐4.8, however, up to 62% of total Al was in a form complexed with SO₄ ^2‐, as predicted by MINTEQ model. The concentration of reactive Al decreased by 60% at pH 5.3. Addition of CaCl₂.2H₂O also had no effect on the concentration of reactive Al within pH 4.1 ‐ 4.8. Nearly 73 ‐ 94% of total Al was present in Al³⁺form. An increase in pH to 5.3, decreased the concentration of reactive Al by 27%. The results suggest that ion‐pairing of Al with F^‐would appear to be a possible mechanism for alleviation of Al toxicity by PG at pH range 4.1 ‐ 5.3. With regard to CaSO₄.2H₂O, at pH 4.1 ‐ 4.8 ion‐pairing with SO.₄ ^2‐appears to be possible mechanism for the alleviation of Al toxicity. In addition, at pH 5.3 a considerable decrease in reactive Al was evident which would further alleviate Al toxicity.     

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

Abstract

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

Root exudation,organic acids,and element distribution in roots of Norway spruce seedlings treated with aluminum in hydroponics

Seedlings of Norway spruce (Picea abies [L.] Karst.), which had been grown under sterile conditions for three months, were treated for one week in a hydroculture system with either 500 μM AlCl₃ or 750 μM CaCl₂ solutions at pH 4. Organic acids were determined in hot‐water extracts of ground root tissue. Oxalate (3.3—6.6 μmol (g root dry weight)^—1) was most abundant. Malate, citrate, formate, acetate, and lactate concentrations ranged between 1—2 μmol (g root dry weight)^—1. Organic substances and phosphate found in the treatment solutions at the end of the experimental period were considered to be root exudates. Total root exudation within a 2‐day period ranged from 20—40 μmol C (g root weight)^—1. In root exudates, organic acids, and total carbohydrates, total amino acids, and total phenolic substances were quantified. Citrate and malate, although present in hot‐water extracts of root tissue, were not detected in root exudates. Phosphate was released from Ca‐treated plants. In Al treatments, there was indication of Al phosphate precipitation at the root surface. Oxalate and phenolics present in the exudates of Norway spruce seedlings are ligands that can form stable complexes with Al. However, concentrations of these substances in the treatment solutions were at micromolar levels. Their importance for the protection of the sensitive root apex under natural conditions is discussed.     

Elemental patterns in roots and foliage of mature spruce across a gradient of soil aluminium

Tissue concentrations of Al in red and Norway spruce trees were compared across 5 sites in North America and Europe as part of an investigation of Al biogeochemistry in forested ecosystems (ALBIOS). Fine roots and foliage were sampled and analyzed for Al, Ca, Mg, and P, and the chemistry of soil and soil solutions was characterized at each plot by horizon. Sites exhibited a wide range in soil Al saturation and in concentrations of Al and sulfate in lysimeter solutions. Aluminium concentrations in roots were two orders of magnitude higher than those in foliage. Fine roots (<1.0 mm) from B horizons had the highest Al concentrations and appeared to be the best phytoindicators of plant-available Al. Aluminium concentrations in fine roots from B horizons were highly correlated with soil solution monomeric Al, and with Al in 0.01 M SrC₂. soil extracts. Stronger soil Al extractants were generally poor predictors of concentrations of Al in plant tissue. Sites with higher levels of plant-available Al supported spruce trees with correspondingly lower foliar levels of Ca and Mg. As such, these field sites provided circumstantial evidence that Al may be interfering with Ca and Mg uptake and transport. No evidence was found of Al interference with P uptake or transport at these sites.     

Increases in pH and soluble salts influence the effect that additions of organic residues have on concentrations of exchangeable and soil solution aluminium

It has been suggested that additions of organic residues to acid soils can ameliorate Al toxicity. For this reason the effects of additions of four organic residues to an acid soil on pH and exchangeable and soil solution Al were investigated. The residues were grass, household compost, filter cake (a waste product from sugar mills) and poultry manure, and they were added at rates equivalent to 10 and 20 t ha^?1. Additions of residues increased soil pH measured in KCl (pH_(KCl)) and decreased exchangeable Al³⁺ in the order poultry manure > filter cake > household compost > grass. The mechanism responsible for the increase in pH differed for the different residues. Poultry manure treatment resulted in lower soil pH measured in water (pH_(water)) and larger concentrations of total (Al_T) and monomeric (Al_mono) Al in soil solution than did filter cake. This was attributed to a soluble salt effect, originating from the large cation content of poultry manure, displacing exchangeable Al³⁺ and H⁺ back into soil solution. The considerably larger concentrations of soluble C in soil solution originating from the poultry manure may also have maintained greater concentrations of Al in soluble complexed form. There was a significant negative correlation (r = ?0.94) between pH_(KCl) and exchangeable Al. Concentrations of Al_T and Al_mono in soil solution were not closely related with pH or exchangeable Al. The results suggest that although additions of organic residues can increase soil pH and decrease Al solubility, increases in soluble salt and soluble C concentrations in soil solution can substantially modify these effects.     

Long-Term Effects of Aluminum and Cadmium on Growth,Leaf Anatomy,and Photosynthetic Pigments of Cotton

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.     

Screening wheat and sorghum cultivars for aluminum sensitivity at low aluminum levels

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.     

Sand culture of mycorrhizal plants

In this work, a sand culture system for ecto- or arbuscular mycorrhizal plants was developed. Nutrients were added into the sand at a constant rate using solutions with similar concentrations of nutrients as those found in forest soil solutions. Plants grew well in the system and inoculated plants developed abundant ecto- or arbuscular mycorrhizas. To test the suitability of the culture system for studies on metal toxicity, aluminium was added to the nutrient solutions of non-mycorrhizal and mycorrhizal spruce seedlings. Measurments of labile Al in the solution draining from the sand revealed that Al was mainly present as phytotoxic monomeric Al. In addition, concentrations of Ca²⁺, Mg²⁺ and SO₄^2— ions which have the potential to alleviate Al toxicity, were similar in the draining as in the nutrient solutions. After 10 weeks of exposure to 400 μM Al, taproot growth as well as Ca and Mg uptake of the seedlings were impaired by Al. Mycorrhizal colonization had no effect on the degree of inhibition of these processes. We conclude that this culture system is suitable for investigations on effects of Al and other toxic metals on mycorrhizal tree seedlings.     

Changes in the concentrations and speciation of aluminum in response to an experimental addition of ammonium sulfate to the bear Brook Watershed,Maine, USA

An understanding of the biogeochemistry of aluminum (Al) in acid-sensitive terrestrial and aquatic ecosystems is critical to assessments of the effects of acidic deposition. Bear Brook Watershed, Maine, USA includes paired watersheds, East Bear and West Bear. Starting in November 1989, experimental additions of ammonium sulfate ((NH₄)₂SO₄; 900 mol/ha-yr) have been made to West Bear Brook Watershed. Chemical analysis of soil and stream waters were conducted to evaluate the speciation of Al prior to (1987–89) and following (1989–92) the experimental treatments. Before the treatments, soilwater Al occurred largely as inorganic monomeric Al (Ali). Concentrations of organic monomeric Al (Alo), Ali and dissolved organic C (DOC) were high in soil solutions draining the E horizon, and decreased in the lower mineral soilwater (Bs horizon) and streamwater. Streamwater concentrations of monomeric Al (Alm) were largely in the form of Alo. After the (NH₄)₂SO₄ treatments were initiated in the West Bear Brook Watershed, concentrations of Alm increased in soilwater and streamwater, largely as Ali. These increases in Al accompanied decreases in pH and increases in concentrations of SO₄ ^2? and NO₃ ^? in drainage waters. Increases in stream concentrations of Al were particularly evident during high flow events. This pattern, coupled with the increases in concentrations of Ali in upper soilwaters in response to the (NH₄)₂SO₄ addition, suggests that episodic increases in Ali were due to inputs of water entering the stream from shallow hydrologic flowpaths.     

Changes in Cell Wall Polysaccharides and Hydroxycinnamates in Wheat Roots by Aluminum Stress at Higher Calcium Supply

The present study was conducted to investigate the cell-wall polysaccharides and hydroxycinnamates in wheat plants (Triticum aestivum L.) under aluminum (Al) stress at a higher level of calcium (Ca) supply. Seedlings were grown in nutrient solution for 7 d and then subjected to treatment solutions containing Al (0 or 100 μM) and Ca (0 or 2500 μM) in a 500 μM CaCl ₂ solution at pH 4.5 for 8 d. Calcium treatment (2500 μM) improved root growth significantly under Al-stress conditions. The contents of pectin and hemicellulose in roots were increased under Al-stress conditions, and this increase was conspicuous in the hemicellulosic fraction. The increase in the hemicellulose was attributed to increases in arabinose, xylose, and glucose in neutral sugars. High Ca treatment decreased these contents in Al-stressed cell walls. Aluminum treatment increased the content of ferulic acid, whereas Ca treatment with Al reduced the content. These results suggest that Al may modify the mechanical properties of cell-wall polysaccharides by enhancing the synthesis of arabinoxylan, β-glucan, and ferulic acid in the cell wall. High Ca treatment may maintain the normal synthesis of these materials even under Al-stress conditions.     

Boron-Calcium Synergically Alleviates Aluminum Toxicity in Wheat Plants (Triticum aestivum L.)

The effects of B and Ca treatments on root growth, nutrient localization and cell wall properties in wheat ( Triticum aestivum L.) plants with and without Al stress were investigated. Seedlings were grown hydroponically in a complete nutrient solution for 7 d and then treated with B (0, 40 μM), Ca (0, 2,500 μM), and Al (0, 100 μM) in a 500 μM CaCl₂ solution for 8 d. The cell wall materials (CWM) were extracted with a phenol: acetic acid: water (2:1:1 w/v/v) solution and used for subsequent pectin extraction with trans -1,2-diami-nocyclohexane- N,N,N,N -tetraacetic acid (CDTA) and Na₂CO₃ solutions. Boron, Ca, and B + Ca treatments enhanced root growth by 19.5, 15.2, and 27.2%, respectively, compared to the control (pH 4.5). Calcium and B+Ca treatments enhanced root growth with Al stress by 43 and 54%, respectively, while B did not exert any effect. The amounts of CWM and pectin per unit of root fresh weight increased by Al treatment, whereas the Ca and B+Ca treatments slightly reduced the contents of these components. Seventy-four percent of total B, 69% of total Ca, and 85% of total Al were located in the cell wall in the B, Ca, and Al treatments, respectively and 32% of total B, 33% of total Ca, and 33% of total Al were located in the CDTA-soluble and Na₂CO₃-soluble pectin fractions. A more conspicuous localization of B was observed in the presence of Al. Aluminum treatment markedly decreased the Ca content in the cell wall as well as pectin fractions, mainly in the case of the CDTA-soluble pectin fraction. Boron + Ca treatment decreased the Al content in the cell wall and pectin fractions compared to the Ca treatment alone in the presence of Al. It is concluded that the B+Ca treatment enhanced root growth and, B and Ca uptake, and helped to maintain a normal B and Ca metabolism in the cell walls even in the presence of Al.     

IS CHLOROPHYLL FLUORESCENCE TECHNIQUE A USEFUL TOOL TO ASSESS MANGANESE DEFICIENCY AND TOXICITY STRESS IN OLIVE PLANTS?

A 130-day hydroponic experiment was carried out in a glasshouse to examine whether manganese (Mn) concentration in the nutrient solution affects the nutritional status of olive plants and to find out whether the chlorophyll fluorescence technique is suitable to assess Mn toxicity and/or deficiency stress in olive plants prior to the appearance of these two nutritional disorders. For this purpose, chlorophyll fluorescence parameters (F_v/F_m and F_v/F₀ ratios) were recorded every 40 days in the leaves of ‘Kothreiki’ and ‘FS-17’ olive cultivars, which were irrigated with Hoagland's nutrient solutions containing various Mn concentrations. In parallel the elongation of the main shoot of all experimental plants, as well as the concentrations of Mn, iron (Fe), zinc (Zn), boron (B), phosphorus (P), calcium (Ca), magnesium (Mg), and potassium (K) in their leaves were recorded. The following Mn treatments were applied: 0 μM Mn (to induce Mn deficiency), 40 μM Mn (to promote normal growth), and 640 μM Mn (to induce Mn toxicity). Our results indicated that not only the rate of shoot elongation but also the fluctuation with time of the leaf concentrations of all determined mineral elements (except for Mn) was not significantly affected by the Mn concentration in the nutrient solution, irrespectively of the cultivar. This was not observed with regard to the time variation of the F_v/F_m and F_v/F₀ ratios, where the values of these parameters were significantly reduced in the 640 μM Mn treatment at the 80th and 130th day of the experiment in both olive cultivars, compared to the relevant previous ones (those of the days 0 and 40th), something which did not happen in the other two Mn treatments (0 and 40 μM). However, in none of the two cultivars tested and in any of the three Mn treatments (0, 40 and 640μM) the F_v/F_m and F_v/F₀ ratios did not drop below the critical values of 0.8 and 4, respectively, even at the end of the experiment, where high Mn concentrations were found in the leaves of both cultivars treated with 640 μM Mn (616 μg g^?1 d.w. in ‘FS-17’ and 734 μg g^?1 d.w. in ‘Kothreiki’). Symptoms of Mn toxicity (curling and brown speckles) were observed in the top leaves of both cultivars, after the 90th day of the experiment. At the same time, the final leaf Mn concentrations (those of the 130th day of the experiment) in plants grown under 0 μM Mn were 23 μg g^?1 d.w. in ‘FS-17’ and 20 μg g^?1 d.w. in ‘Kothreiki’, i.e., a little above of the deficiency range (<20 μg g^?1 d.w.). At the 130th day, Mn concentration in nutrient solution, as well as Mn concentration in the leaves of both olive cultivars was negatively correlated with the leaf concentration of Fe and the values of the F_v/F_m and F_v/F₀ ratios, and positively with the concentrations of Zn and P in the leaves. Finally, the periodical measurement of the F_v/F_m and F_v/F₀ ratios was proved to be a non-reliable means to predict the appearance of the visible symptoms of Mn toxicity in olive leaves (although their values declined significantly at the 80th and 130th day of the experiment in both olive cultivars).     

不同改土物料对苏打碱土磷素吸附解吸及磷素形态的影响

  目的  通过研究不同改土物料对苏打碱土中磷（P）素的吸附、解吸及P素形态的影响,为科学改良苏打碱土提供理论依据。  方法  以东北松嫩平原苏打碱土为研究对象,设置不添加改土物料（CK）和添加有机肥（M）、硫酸铝（Al）、石膏（Ca）、硫酸铝 + 有机肥（Al + M）、石膏 + 有机肥（Ca + M）六个处理,研究了不同改土物料对土壤P素的吸附解吸和P素形态的影响。  结果  有机肥处理会降低苏打碱土对P素的吸附,增加对P素的解吸,其它四个处理均会增加土壤对P素的吸附,降低对P素的解吸,其中以Al和Al + M处理差异较大。不同改土物料处理土壤无机P含量均有不同程度增加,其中M、Ca和Ca + M处理均显著提高了土壤中Ca₂-P含量（P < 0.05）,以Ca + M处理增幅最大,达到21.43%;不同改土物料处理均可增加缓效态P（Ca₈-P、Al-P和Fe-P）含量,增幅为1.00%-112.03%,其中Ca、Al、Ca + M和Al + M处理均可显著提高Al-P和Ca₈-P含量,增幅为66.37% ~ 250.1%和18.06% ~ 74.36%。与Ca处理相比,Ca + M处理显著增加了Ca₂-P含量（P < 0.05）,显著降低了Al-P和O-P含量（P < 0.05）。  结论  在苏打碱土中石膏和有机肥配施可减少土壤对P素的吸附,增加土壤有效态P含量,是提高苏打碱土P素有效性的最佳措施。     

Uptake of Al,Ca, and P in black spruce seedlings: Effect of organic versus inorganic al in nutrient solutions.

Two-year old black spruce seedlings (Picea mariana [Mill.] B.S.P.) of greenhouse-grown paper-pot stock were subjected to chemically well-characterized nutrient solutions for 28 days to assess the elemental uptake (A1,P,Ca) of these plants in response to organic versus inorganic Al in the rooting medium (pH=3.0; 0 ≤ total Al ≤ 48 mg L^?1). Oxalate additions to the nutrient solutions (0 ≤ Ox ≤ 2.4 mmol) served as organic Al-complexing agent. The results indicated that the plants took up Al in proportion to the Al concentration of the rooting medium, with Al uptake from the Al-Ox treatments somewhat more extensive than the Al uptake from the inorganic Al treatments. Furthermore, root Al ? shoot Al for both cases. The pattern of P uptake was similar to that of Al uptake but for the roots only, i.e. root P was proportional to root Al.Increased root P was not associated with increased shoot P. Calcium content of the roots was slightly reduced with increased inorganic and organic Al, but increased strongly with increasing oxalate in the rooting medium.     

Effect of varying solution calcium or magnesium concentrations in the presence or absence of aluminum on yield and plant calcium or magnesium concentrations in wheat

The effect of varying solution calcium (Ca) and magnesium (Mg) concentrations in the absence or presence of 10 μM aluminum (Al) was investigated in several experiments using a low ionic strength (2.7 × 10^‐3 M) solution culture technique. Aluminium‐tolerant and Al‐sensitive lines of wheat (Triticum aestivum L.) were grown. In the absence of Al, top yields decreased when solution Ca concentrations were <50 μM or plant Ca concentrations were <2.0 mg/g. Top and root yields decreased when solution Mg concentrations were <50 μM or plant Mg concentrations were <1.5 mg/g. There were no differences between the lines in solution or plant concentrations at which yield declined. Increasing solution Ca concentrations decreased plant Mg concentrations in the tops (competitive ion effect) but increased plant Mg concentrations in the roots of wheat. This suggests that Ca is competing with Mg when Mg is transported from the roots. Increasing solution Mg concentrations decreased plant Ca concentrations in the tops and the roots (competitive ion effect). In the roots, increasing solution Mg concentrations decreased plant Ca concentrations at a lower solution Ca concentration in the Al‐sensitive line than the Al‐tolerant line. In the presence of Al, increasing solution Ca and Mg concentrations increased yield (Ca and Mg ameliorating Al toxicity). Yield increased until the sum of the solution concentrations of the divalent cations (Ca+Mg) was 2,000 μM for the Al‐tolerant line or 4,000 μM for the Al‐sensitive line. The exception was that yield decreased when solution Mg concentrations were > 1,500 μM and the solution Ca concentration was 100 μM (Mg exacerbating Al toxicity). The ameliorative effects of solution Ca or Mg on Al tolerance were not related to plant Ca or Mg concentrations per se.