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1.
This study compares the effect of aluminum (Al) on the shoot morphology, root distribution and plant chemical content of selections made for Al tolerance and an unselected population of Huia white clover (Trifolium repens L.). Seedlings from the two seed sources were sown into trays of soil to which had been added 400 μg Al/g soil as aluminum sulphate. The two seed sources were, (1) progeny from a polycross of genotypes previously selected for Al tolerance from the cultivar Huia and, (2) a previously unselected accession of Huia. After selection of genotypes capable of producing large shoots when grown in soil containing 400 μg g‐1 added Al, plants were grown in artificial soil profiles where soil Al content increased with depth. Selections from first generation Al‐tolerant germplasm were smaller leaved, with more leaves per unit length of stolon, with larger stolons, heavier shoots and a slightly deeper root distribution, but lower root/shoot ratio than selections from previously unselected germplasm. The proportion of root weight below 100 mm (i.e., the proportion of root growing in Al‐toxic soil) was poorly related to other characters measured. From an analysis over all 100 genotypes tested, proportion of root weight below 100 mm was significantly (P <0.05) but weakly (r=0.19) correlated with shoot [potassium/(calcium + magnesium) (K/(Ca + Mg))] ratio. Selection for Al tolerance in white clover can cause associated changes in other plant characters.  相似文献   

2.
Abstract

Increased demand for wheat (Triticum aestivum L.) cultivars tolerant to acid‐soil stress has accelerated genetic research on aluminum (Al) tolerance in soil and solution media. Our objective was to characterize the genetic segregation of tolerant and susceptible plants from two populations in an Al‐toxic Porters soil (coarse‐loamy, mixed, mesic Umbric Dystrochrepts), and in nutrient solutions with 0.09, 0.18, 0.36, 0.72, and 0.90 mM Al. Rapid bioassays were applied to determine seedling responses of two Al‐tolerant (Cardinal and Becker) and two susceptible cultivars (GK Zombor and GK Kincso) and their F2 progenies. In the Al‐toxic soil, Becker/Kincso F2 and Cardinal/Zombor F2 exhibited contrasting segregation patterns but with similar heritability values (0.60 and 0.57, respectively). Higher values of root length in soil were dominant in Cardinal/Zombor F2 (degree of dominance, d = 0.98), but dominance was absent (d = 0.07) for Becker/Kincso F2. The results of the soil and nutrient‐solution experiments were not entirely consistent; gene expression appeared to be influenced by the concentration of Al in the nutrient solution. The frequency of susceptible F2 plants increased proportionately to the increase in Al concentration for both populations. This unexpected pattern provides further evidence that segregation in wheat populations cannot always be explained by single‐gene inheritance.  相似文献   

3.
Abstract

Better understanding of soil aluminum has had dramatic effects on the interpretation of many aspects of soil chemistry. Aluminum is a Group III element, metallic in nature, and exhibits both ionic and cuvaient bonding. It is the most plentiful of all metallic cations of the earth's crust. It is released from octahedral coordination with oxygen in minerals by weathering processes. Once released, the trivalent Al ion assumes octahedral coordination with six OH2 groups each of which dissociates a H ion in sequence as pH increases. The resulting hydroxy‐Al ions are absorbed to the cation exchange capacity of the soil. Here they polymerize on charged surfaces and in the interlayers of the clay minerals obstructing both the contraction of the clay lattice and the exchange of cations. Soluble Al is toxic to most plants, and reacts readily with soluble phosphates converting them to relatively insoluble and plant‐unavailable forms. Adsorbed and polymerized aluminum affects actual lime requirements of soils by its acidic nature and indicated lime requirements by its effect on the buffers of the lime requirement test. The level of exchangeable Al has been suggested as an Index of lime requirement of acid soils, but this may be an adequate Index for liming only on highly weathered soils.  相似文献   

4.
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.  相似文献   

5.
Abstract

Macadamia (Macadamia integrifolia) is increasingly becoming an important tree crop in many parts of the world. However, knowledge about the plant's nutritional behavior, especially under adverse soil conditions, has been deficient. To address this deficiency, a pot experiment was conducted to study the effects of Al, Mn and Ca (soil acidity and liming) on macadamia seedlings. Three soils having different mineralogy and fertility were used; soil pH was adjusted based on lime requirement curves so that several pH levels ranging from 4.5 to 7.5 were obtained for each soil. Chemical composition of the soil solution and of recently fully mature leaves was monitored periodically to assess the growth response.

Results suggested that Al was detrimental to physiological processes of macadamia seedlings when leaf Al was greater than 275 mg kg and soil‐solution Al exceeded 1.2 mg L‐1. Furthermore, Al seemed to have reduced Mn uptake by the plant, although macadamia could accumulate as much as 1200 mg Mn kg‐1 in leaves without apparent toxic symptoms. The internal Ca requirement of the plant was not clearly defined; however, maximum growth could be expected when soil solutions contained 160 mg Ca L‐1 , which corresponded to 0.9 cmol(+)kg‐1 of exchangeable Ca (or 10% of CEC) in a highly weathered Oxisol.  相似文献   

6.
Durum wheat, Triticum durum Desf., is reportedly more sensitive to aluminum (Al) toxicity in acid soils than hexaploid wheat, Triticum aestivum L. em. Thell. Aluminum‐tolerant genotypes would permit more widespread use of this species where it is desired, but not grown, because of acid soil constraints. Durum wheat germplasm has not been adequately screened for acid soil (Al) tolerance. Fifteen lines of durum wheat were grown for 28 days in greenhouse pots of acid, Al‐toxic Tatum subsoil at pH 4.5, and non‐toxic soil at pH 6.0. Aluminum‐tolerant Atlas 66 and sensitive Scout 66 hexaploid wheats were also included as standards. Based on relative shoot and root dry weight (wt. at pH 4.5/wt. at pH 6.0 X 100), durum entries differed significantly in tolerance to the acid soil. Relative shoot dry weight alone was an acceptable indicator of acid soil tolerance. Relative dry weights ranged from 55.1 to 15.5% for shoots and from 107 to 15.8% for roots. Durum lines PI 195726 (Ethiopia) and PI 193922 (Brazil) were significantly more tolerant than all other entries, even the Al‐tolerant, hexaploid Atlas 66 standard. Hence, these two lines have potential for direct use on acid soils or as breeding materials for use in developing greater Al tolerance in durum wheat. Unexpectedly, the range of acid soil tolerance available in durum wheat appears comparable to that in the hexaploid species. Hence, additional screening of durum wheat germplasm for acid soil (Al) tolerance appears warranted. Durum lines showing least tolerance to the acid soil included PI 322716 (Mexico), PI 264991 (Greece), PI 478306 (Washington State, USA), and PI 345040 (Yugoslavia). The Al‐sensitive Scout 66 standard was as sensitive as the most sensitive durum lines. Concentrations of Al and phosphorus were significantly higher in shoots of acid soil sensitive than in those of tolerant lines, and these values exceeded those reported to cause Al and phosphorus (P) toxicities in wheat and barley.  相似文献   

7.
Abstract

Shallow rooting and susceptibility to drought are believed to be caused, at least in part, by strongly acidic (pH <5.5, 1:1 soil‐water), aluminum (Al)‐toxic subsoils. However, this hypothesis has not been clearly confirmed under field conditions. The Al toxicity hypothesis was tested on a map unit of Matawan‐Hammonton loam (0–2% slope) on unlimed and limed field plots (pH range 5.1 to 5.8) at Beltsville, MD, during 1994 to 1998. Aluminum‐tolerant and sensitive pairs of barley (Hordeum vulgare L.), wheat [Triticum aestivum (L.)], snap bean (Phaseolus vulgaris L.), and soybean [Glycine max (L.) Merr.] cultivars were used as indicator plants. Eastern gamagrass [Tripsacum dactyloides (L.) L.], cultivar ‘Pete’, reported to tolerate both chemical and physical stress factors in soils, was grown for comparison. Shoots of Al‐sensitive ‘Romano’ snap beans showed a significant response to liming of the 0–15 cm surface layer, but those of Al‐tolerant ‘Dade’ did not, indicating that Al toxicity was a growth limiting factor in this acid soil at pH 5.1. Lime response of the Al‐tolerant and sensitive cultivars of barley, wheat, and soybean were in the same direction but not significant at the 5% level. Aluminum‐tolerant and sensitive cultivars did not differ in abilities to root in the 15–30 cm soil depth. Only 9 to 25% of total roots were in this layer, and 75 to 91% were in the 0–15 cm zone. No roots were found in the 30–45 cm zone which had a pH of 4.9. Soil bulk density values of 1.44 and 1.50 g cm?3 in the 15–30 and 30–45 cm zones, respectively, indicated that mechanical impedance was a primary root barrier. Results indicated that restricted shoot growth and shallow rooting of the Al‐indicator plants studied in this acid soil were due to a combination of Al toxicity and high soil bulk density. Confounding of the two factors may have masked the expected response of indicator plants to Al. These two growth restricting factors likely occur in many, if not most acid, problem subsoils. Studies are needed to separate these factors and to develop plant genotypes that have tolerance to multiple abiotic stresses. Unlike the Al indicator cultivars, eastern gamagrass showed high tolerance to acid, compact soils in the field and did not respond to lime applications (pH 5.1–5.8).  相似文献   

8.
Two genotypes of Old world bluestems from the species Bothriochloa intermedia (R. Br.), A. Camus, shown earlier to differ in tolerance to acid, Al‐toxic Tatum subsoil at pH 4.1, were characterized further with respect to growth in pots of Tatum soil over a wider pH range and tolerance to Al in nutrient solutions. The two genotypes studied were acid‐soil tolerant P. I. 300860 (860) and acid soil sensitive P. I. 300822 (822).

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

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

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

9.
Abstract

Al toxicity in plants is related to the activity of Al3+ and Al‐hydroxy monomers in the soil solution, whereas Al complexed with ligands such as fluoride (F), sulphate (SO4 2‐), and oxalate is not toxic. Estimation of toxic Al relies on measurement of “labile”; Al after short contact times with colorimetric reagents or cation‐exchange resins. However, shifts in equilibrium may result in non‐toxic forms of Al reacting with the complexing agent or resin.

A series of laboratory experiments tested the degree to which labile Al is related to Al3+ in simplified media and compared methods of estimating labile Al in the presence of organic ligands and in soils. Cation‐exchange resins extracted more than the theoretical concentration of Al3+ from solutions containing a range of concentrations of OH‐ and SO4 2‐. More Al was extracted in 15 s by 8‐hydroxy‐quinoline than by Chelex‐100 from solutions of Al‐humate at pH 4. In sands which had been spiked with Al and organic matter, the estimation of labile Al varied with both the method of measurement and type of extract. The cations present in commonly used soil‐extracting chloride solutions can decrease the proportion of organically complexed Al.  相似文献   

10.
Abstract

Aluminum (Al)–humus complexes are abundant in the A horizons of non-allophanic Andosols and contribute to the unique properties of volcanic ash soils, such as high reactivity with phosphate ions and a low bulk density. Natural non-allophanic Andosols commonly show Al toxicity to plant roots. There have been very few studies examining the contribution of Al–humus complexes to the Al toxicity of plant roots, although the complexes are the probable source of the toxic Al. We extracted humic substances from the A horizon of a non-allophanic Andosol using NaOH solution and reacted the humic substances and partially neutralized the AlCl3 solution at three pH conditions (pH 4.0, 4.5 and 5.5) to prepare pure Al–humic substance complexes. The Al solubility study (equilibrium study in 10?2 mol L?1 CaCl2) and the Al release study (a stirred-flow method using 10?3 mol L?1 acetate buffer solution adjusted to pH 3.5) indicated that all the synthetic complexes easily and rapidly release monomeric Al into the liquid phase with slight changes in pH and ion strength, although the Al contents and their extent of polymerization are considerably different among the complexes. A plant growth test was conducted using a medium containing the Al–humic substance complexes and perlite mixture. Root growth in burdock (Arctium lappa) and barley (Hordeum vulgare L.) was reduced equally by all three complex media, and the roots showed the typical injury symptoms of Al toxicity. These results indicate that in soils dominated by Al–humus complexes the Al released from the Al–humus complexes, as well as the exchangeable Al adsorbed by soil minerals, is definitely toxic to plant roots.  相似文献   

11.
Abstract

A comparison of corncob compost with lime on plant growth was studied in acid red soil with pH of 4.07. Lettuce, pea, and corn were selected as test plants for their varying tolerance to acid soil. The pot experiment compared six soil treatments and a check. Soil amendments were 1, 2, and 4 cmol calcium carbonate (CaCO3) kg‐1 and 5, 10, and 20 g corncob compost kg‐1 soil. Results showed higher manganese (Mn) than aluminum (Al) content of the shoot in all check group plants. Reduced shoot Mn content increased shoot dry weight in all test plants, regardless of acid soil tolerance or soil treatment. The higher the test plant resistance to soil acidity, the weaker the detoxification effect of corncob compost was on Al uptake when compared with the check group. Liming was more effective at reducing shoot Mn content than corncob compost with the exception of the more acidity sensitive lettuce. Shoot phosphorus (P) content, however, increased with corncob compost from enhanced organic matter rates. Corncob compost treatments significantly increased shoot dry weight over liming in the acid soil. This study demonstrated an environmentally acceptable use for an agricultural waste.  相似文献   

12.
Abstract

Lines of Leucaena leucocephala (Lam.) de Wit were grown in greenhouse pots of an acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic typic Hapludult) treated with 0 or 3000 ppm CaCO3 to give final soil pH values of 4.1 and 5.3, respectively. Lines of L. leucocephala, plus those of other Leucaena species, were also tested on an acid, Monmouth soil (clayey, mixed, mesic, typic Hapludult) treated with 0 or 1500 ppm CaCO3 to give final soil pH values of 4.8 and 6.6, respectively. The major index of acid soil tolerance used was relative root yield (unlimed/limed %).

Relative root yields of 117 L. leucocephala lines on Tatum soil ranged from 34 to 246%. Hence, liming the soil from pH 4.1 to 5.3 was highly beneficial to some lines and highly detrimental to others. Because Tatum subsoil is 89% Al saturated at pH 4.1, line tolerance to unlimed soil indicates tolerance to Al. Causes of yield depression at pH 5.3 were not determined.

On Monmouth soil, in a test involving 148 lines of 6 Leucaena species, relative root yields (unlimed/limed %) ranged from 23 to 386%. The line showing highest tolerance to the acid soil (P.I. 279578) and that showing lowest tolerance (P.I? 281636) are both L,. leucocephala. The majority of lines used on Monmouth soil (124 of a total of 148) were from this species. Average performances of the 6 species indicated that L. diversifolia Benth. (5 lines) was most tolerant to the acid Monmouth soil and liming the soil from pH 4.8 to 6.6 actually decreased root yields. The species L.. leucocephala (124 entries) and L. pulverulenta Benth. (4 lines) were intermediate, and L. lanceolata S. Wats. (3 lines) and I., retusa Benth. (1 line) appeared more sensitive to acid Monmouth soil. The Al saturation of Monmouth soil at pH 4.8 was only 23% (compared with 89% for Tatum at pH 4.1). The major growth limiting factor in acid Monmouth soil is believed to be Al toxicity, but this soil has not been as throughly characterized as has Tatum, and other factors may well be involved in explaining differential tolerances of Leucaena lines on the unlimed versus limed soil.

Results of these studies indicate that Leucaena species and lines within species differ significantly in tolerance to acid soils having high levels of exchangeable Al. Acid soil tolerant lines of Leucaena may be useful in expanding the acreage of this crop on oxisols and ultisols of the tropics and subtropics.  相似文献   

13.
Literature suggests that nitrogen (N) metabolism is involved in differential acid soil (Al) tolerances among wheat (Triticwn aestivum L. en Thell) genotypes. Atlas 66 wheat is characterized by acid soil and aluminum (Al) tolerance, nitrate (NO3 ‐) preference, pH increase of the rhizosphere, high nitrate reductase activity, and high protein in the grain. Atlas 66 has been used as a high protein gene donor in the development of new high protein wheat lines at Lincoln, NE. The objective of our study was to determine the acid soil tolerances of such lines and to relate such tolerances to their abilities to accumulate grain protein when grown on near‐neutral, non‐toxic soils. Twenty‐five experimental lines, nine cultivars not previously classified as Al‐tolerant or ‐sensitive and three cultivars previously classified according to acid soil tolerance, were grown for 28 days in greenhouse pots of acid, Al‐toxic Tatum subsoil. Relative shoot dry weight (pH 4.35/pH 5.41%) varied from 83.2% for Atlas 66 to 19.3% for Siouxland. Atlas 66 was significantly more tolerant to the acid soil than all other entries except Edwall. Yecorro Roja and Cardinal were intermediate in tolerance. None of the high protein lines approached Atlas 66 in tolerance, but two lines (N87U106 and N87U123) were comparable to Cardinal (relative shoot yield = 54%) which is used on acid soils in Ohio. At pH 4.35, the most acid soil tolerant entries contained significantly lower Al and significantly higher potassium (K) concentrations in their shoots than did sensitive entries. Shoots of acid soil sensitive entries, Scout 66, Siouxland, Plainsman V, and Anza contained deficient or near deficient concentrations of K when grown at pH 4.35. Acid soil tolerance was not closely related to calcium (Ca), magnesium (Mg), phosphorus (P), manganese (Mn), or iron (Fe) concentrations at pH 4.35. Liming the soil to pH 5.41 tended to equalize Al and K concentrations in shoots of tolerant and sensitive entries. Results indicated that acid soil tolerance and grain protein concentrations were not strongly linked in the wheat populations studied. Hence, the probability of increasing acid soil tolerance by crossing Atlas 66 with Nebraskan wheat germplasm is low. However, the moderate level of acid soil tolerance in N87U106 and N87U123 (comparable to that of Cardinal) may be useful in further studies.  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.
In greenhouse experiments with small pots, seeds of cowpea (Vigna unguiculata) were planted into an acid soil (Oxic Paleudult from Onne, South-East Nigeria) which had been treated with Al2(SO4)3-Cowpea genotypes showed varying seedling growth inhibition within 7 days when grown in soil containing 2.2 meq Al/100 g soil. Soil and plant analysis confirmed, that Al toxicity, and consequently differences in Al tolerance, were responsible for the genotypically different seedling growth responses. 783 genotypes showed a wide range of Al tolerance when screened using this technique. In a long-term pot experiment the effect of Al application to the soil on seed yields of 9 genotypes was studied. Although no significant correlation could be found between depression by Al of seedling growth and grain yield of the genotypes, the same genotypes were classified as most tolerant and most sensitive in both cases. The results show that the simple and quick screening method using Al-treated soil allows the identification of genotypes adapted to soils with high Al supply.  相似文献   

16.
Although aluminum (Al) is abundant in soil environments, it is not an essential element and it is toxic to most organisms. Since the toxicity of Al depends on their chemical forms, the importance of Al speciation has been recognized worldwide. Difficulties in Al speciation are caused by the complex coordination chemistry of Al for the hydrolysis and formation of polynuclear species with a variable degree of solubility in aqueous solution. Nondestructive analyses, such as nuclear magnetic resonance (NMR) spectroscopy, could supply primarily im-portant information on the chemical forms of Al and may enable to evaluate the results ob-tained by other methodologies. In the present report, NMR spectral characteristics of environmentally important Al-containing components, such as hydoxyaluminum ions, Alinorganic complexes, Al-organic complexes, and primary and secondary minerals, are summarized for the nuclei of 27Al and 29Si determined by solution NMR and solid-state magic angle spinning (MAS) NMR. Applications of NMR techniques to soil science, including speciation of phytotoxic Al in soil environments and whole soil NMR studies, are described.  相似文献   

17.
Elevated aluminum (Al) availability limits plant growth on acidic soils. Although this element is found naturally in soils, acidic conditions create an environment where Al solubility increases and toxic forms of Al impact plant function. Plant resistance to Al is often attributed to organic acid exudation from plant roots and the chelation of cationic Al in the rhizosphere. The association of arbuscular mycorrhizal (AM) fungi with the roots of plants may alleviate Al toxicity by altering soil Al availability or plant exposure through the binding of Al to fungal structures or through the influence of fungi on exudation from roots. Diverse communities of AM fungi are found in soil ecosystems and research suggests that AM fungi exhibit functional diversity that may influence plant performance under varying edaphic environments. In the present study, we evaluated acidic isolates of six AM species in their responses to Al. Andropogon virginicus (broomsedge), a warm-season grass that commonly grows in a range of stressful environments including acidic soils, was used as a plant host for Acaulospora morrowiae, Glomus claroideum, Glomus clarum, Glomus etunicatum, Paraglomus brasilianum, and Scutellospora heterogama. Fungal spores were germinated and exposed to 0 or 100 μM Al on filter paper in sand culture or were grown and exposed to Al in sand culture in association with A. virginicus. Short- and long-term responses to Al were evaluated using direct measurements of fungal spore germination, hyphal elongation, and measurements of A. virginicus colonization and plant growth as a phytometer of AM function in symbio. Spore germination and hyphal elongation varied among AM species in response to Al, but patterns were not consistent with the influences of these AM species on A. virginicus under Al exposure. Exposure to Al did not influence colonization of roots, although large differences existed in colonization among fungal species. Plants colonized by G. clarum and S. heterogama exhibited the least reduction in growth when exposed to Al, produced the highest concentrations of Al-chelating organic acids, and had the lowest concentrations of free Al in their root zones. This pattern provides evidence that variation among AM fungi in Al resistance conferred to their plant hosts is associated with the exudation of Al-binding organic acids from roots and highlights the role that AM fungal diversity may play in plant performance in acidic soil environments.  相似文献   

18.
Abstract

Cyanide at levels of 50 to 100 μg NaCN/g soil was not only toxic to bush bean plants, but also resulted in increased uptake of Cu, Co, Ni, Al, Ti, and, to a slight extent, of Fe. Either the phytotoxicity from the cyanide or the metals resulted in increased transport of Na to leaves from roots. In studies with 14C‐cyanide the transport of some cyanide into plants and to leaves simultaneously with the metals was demonstrated. There was a root, stem, leaf gradient for 14C. From solutions, cyanide resulted in increased plant uptake somewhat of Cu, Zn, and Fe. The results have bearing on the use of cyanide as a metabolic inhibitor as well as on phytotoxicities of metals.  相似文献   

19.
Abstract

Additions of several categories of organic materials including fresh plant materials, compost, manure, coal derived products, and peat have been shown to ameliorate soil acidity. The main effect is increased soil pH and the corresponding decrease in soil solution and exchangeable aluminum (Al). The organic matter addition is expected to decrease the solubility of soil aluminum so that lower activities are maintained at a given pH value, but this effect has not been tested. Aluminum solubility was investigated after addition of brown coal and peat to an acid soil. Root length was used as a bioassay for the acid ameliorating properties of the organic materials. Addition to soil of brown coal and peat resulted in changes in Al activity in the soil solution. The negative log of Al activity (pAl) was directly proportional to the soil solution pH. A single pAl‐pH line could describe the control, calcium chloride and organically treated soil samples. This line was parallel to that of gibbsite. The intercept was greater suggesting undersaturation with respect to that mineral. The coal and peat applied at the rate of 1 and 2% had little effect on the solubility of soil Al. Any decrease in Al activity was solely dependent on increased soil pH. Relative root length was inversely related to Al activity. This relationship was improved by including base cations in the index of Al phytotoxicity. This index could provide the basis for evaluating the value of brown coal and peat in ameliorating soil acidity.  相似文献   

20.
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.  相似文献   

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