水稻(Oryza sativa L.)铝毒害与耐性机制及铝毒害的缓解作用

铝 (Al) 毒是广泛存在于热带亚热带地区酸性土壤上的主要的生产力限制因子之一。水稻Al毒害主要发生在新开垦的旱地酸性土壤上。本文较详细地总结了: (1) 水稻发生Al毒的环境条件,水稻Al毒害的可见症状和Al毒害的部位;(2) 水稻耐Al指标,营养元素的吸收与分配对水稻耐受Al毒害的影响,以及Al胁迫下根系分泌物、根际pH的变化等对水稻耐Al的贡献,水稻耐Al基因的定位等;(3) 水稻Al毒害的缓解作用机理及可能的解决措施。最后对水稻Al毒害和水稻耐Al机制研究中存在问题进行了分析探讨,同时对今后的研究作了展望。     

Differential aluminum tolerance in some tropical rice cultivars: I. Growth performance

Ten‐day‐old seedlings of 22 rice (Oryza sativa.L) cultivars originated from various tropical countries were subjected to six levels of aluminum (Al) [0, 74, 148, 222, 296, and 370 μM] to test their tolerance to Al toxicity in nutrient solutions at pH 4.0±0.l. Seedlings were grown in the presence of Al under controlled environmental conditions in growth chambers. The nutrient solutions were replenished once a week. After 30 days, treatments were terminated and the differences in their growth patterns were compared. Standard growth parameters such as plant growth, dry matter production, relative growth reduction in roots (RGRS) and shoots (RGRS), root tolerance index (RTI) and shoot tolerance index (STI) have been used as markers of Al toxicity.

Rice cultivars studied exhibited wide range of responses in their tolerance to Al. Though, the rice cultivars were subjected to six levels of Al, a good degree of separation in their responses was observed only at 222 μM Al. Therefore, this concentration was chosen to analyze and compare the performances of the cultivars. Further, only six cultivars showed significant changes in their expression in the presence of Al compared to control, and so data have been presented only for those cultivars for clarity. The cultivars BW 196, Bhura Rata, Basmati 370 and Co 37 recorded increases in growth, while Damodar and ADT 36 showed severe inhibitions in the presence of Al. Furthermore, in RTI and STI also Co 37 and Basmati 370 registered their tolerance to Al by showing increased growth in the presence of Al. Whereas, Damodar and ADT 36 recorded severe reductions. The RGRR and RGRS data also substantiates this finding. Based on the growth parameters, the six rice cultivars were ranked based on their tolerance to Al: Co 37 > Basmati 370 > BW 196 > Bhura Rata > Damodar > ADT 36. Co 37 and Basmati 370 are the two most tolerant cultivars which performed extremely well in the presence of Al, and Damodar and ADT 36 are the most susceptible cultivars. Therefore, the Al‐tolerant cultivars can be used for future breeding programes to develop Al‐tolerant, cultivars that subsequendy can be recommended for planting in acidic, infertile soils of the tropics.     

Differential tolerances of oat cultivars to aluminum in nutrient solutions and in acid soils of Poland

Aluminum tolerant oat cultivars are needed for use on acid soil sites where neutralization of soil acidity by liming is not economically feasible. Oat germplasm in Poland has not been examined for range of Al tolerance. Eleven Polish oat cultivars were screened for Al tolerance in nutrient solutions containing 0, 5 and 15 mg L^‐1 Al. Three of these cultivars showing high to moderate tolerance to Al in nutrient solutions were also grown in greenhouse pots of soil and in field plots of soil over a pH range of 3.8 to 5.5 as determined in 1 N KC1.

The eleven oat cultivars differed significantly in tolerance to Al in nutrient solutions. Based on relative root yield (15 mg L^‐1 Al/no A1%), the cultivars ‘Solidor’ and ‘Diadem’ were most tolerant and ‘Pegaz’ and ‘B‐20’ were least tolerant. For these three cultivars, the order of tolerance to acid soil agreed with the order of tolerance to Al in nutrient solution ‐ namely, Solidor > Diadem > Leanda. Hence, for these cultivars, the nutrient solution methods used appear adequate for selecting plants that are more tolerant to Al in strongly acid soils. Additional study is needed to assess the value of this method for screening a broad range of germplasm.

Superior tolerance of the Solidor cultivar to acid soil was associated with significantly higher concentrations of N in the grain. Hence, results suggest that selecting for acid soil or Al tolerance may increase N efficiency in oats.     

Differential aluminum tolerance in some tropical rice cultivars. II. mechanism of aluminum tolerance

Ten‐day‐old seedlings of 22 rice (Oryza sativa L.) cultivars were subjected to aluminum (Al) stress in nutrient solutions with an initial pH of 4.0±0.1. The rice cultivars exhibited a wide range of response by changing the rhizosphere pH, and the uptake and efficiency ratio (ER) of utilization of nutrients both in the presence (222 μM Al) and absence of Al. In the presence of Al, the cultivars Co 37 and Basmati 370 recorded maximum uptake and highest ER's for calcium (Ca), potassium (K), magnesium (Mg), manganese (Mn), phosphorus (P), and iron (Fe). The cultivars Damodar and ADT 36 performed very poorly in terms of nutrient uptake. The tolerant cultivars (Al‐insensitive) efficiently took up and utilized Ca and P in the presence of Al. The susceptible (Al‐sensitive) and intermediate cultivars exhibited less Ca and P uptake and utilization. There was no apparent relationship between foliar Al content and the efficiency ratios. However, the Al‐tolerant cultivars, Co 37 and Basmati 370, accumulated less Al in their foliage which was the reverse in case for the Al‐susceptible cultivars. Among the 22 rice cultivars tested, Co 37 and Basmati 370 emerged as the most Al‐tolerant. Hence, they would be recommended for cultivation in acidic, infertile soils of the tropics. The results of this study are discussed in terms of identifying the mechanism of Al tolerance or sensitivity among the studied rice cultivars as related to their nutrient metabolism.     

Symbiotic effectiveness of Bradyrhizobium japonicum in acid soils can be predicted from their sensitivity to acid soil stress factors in acidic agar media

In acid soil, low pH, reduced availability of nutrients, and toxicity of Al and Mn limit plant growth and the survival and effectiveness of rhizobia. The symbiosis between legumes and rhizobia is particularly sensitive to acid soil stress. A pot experiment evaluated whether Bradyrhizobium japonicum strain growth on acidic agar media would predict ability to colonize the rhizosphere and form effective nodules in acidic soils. Three Indonesian strains of B. japonicum with similar effectiveness at neutral pH in sand culture but with different tolerance of acid soil stress factors in agar media, and an acid-tolerant commercial strain (CB1809) of comparable effectiveness, were tested in three acid soils using the Al tolerant soybean (Glycine max cv PI 416937). At 7 days after inoculation all strains had achieved large rhizosphere populations, but by day 14 the rhizosphere population of the acid-sensitive strain had decreased, while the more acid-tolerant strains increased. The acid-tolerant strains had significantly greater nodulation and symbiotic effectiveness than plants inoculated with the acid-sensitive strain. Laboratory prescreening of B. japonicum for acid, Al and Mn tolerance in acid media successfully identified strains which were symbiotically competent in low pH soils.     

Variation of tolerance to manganese toxicity in Australian hexaploid wheat

High concentrations of manganese (Mn), iron (Fe), and aluminium (Al) induced in waterlogged acid soils are a potential constraint for growing sensitive wheat cultivars in waterlogged‐prone areas of Western Australian wheat‐belt. Tackling induced ion toxicities by a genetic approach requires a good understanding of the existing variability in ion toxicity tolerance of the current wheat germplasm. A bioassay for tolerance to high concentration of Mn in wheat was developed using Norquay (Mn‐tolerant), Columbus (Mn‐intolerant), and Cascades (moderately tolerant) as control genotypes and a range of MnCl₂ concentrations (2, 250, 500, 750, 1000, 2000, and 3000 μM Mn) at pH 4.8 in a nutrient solution. Increasing solution Mn concentration decreased shoot and root dry weight and intensified the development of toxicity symptoms more in the Mn‐intolerant cv. Columbus than in Norquay and Cascades. The genotypic discrimination based on relative shoot (54% to 79%) and root dry weight (17% to 76%), the development of toxicity symptoms (scores 2 to 4) and the shoot Mn concentration (1428 to 2960 mg kg^–1) was most pronounced at 750 μM Mn. Using this concentration to screen 60 Australian and 6 wheat genotypes from other sources, a wide variation in relative root dry weight (11% to 95%), relative shoot dry weight (31% to 91%), toxicity symptoms (1.5 to 4.5), and shoot Mn concentration (901 to 2695 mg kg^–1) were observed. Evidence suggests that Mn tolerance has been introduced into Australian wheat through CIMMYT germplasm having “LERMO‐ROJO” within their parentage, preserved either through a co‐tolerance to Mn deficiency or a process of passive selection for Mn tolerance. Cultivars Westonia and Krichauff expressed a high level of tolerance to both Mn toxicity and deficiency, whereas Trident and Janz (reputed to be tolerant to Mn deficiency) were intolerant to Mn toxicity, suggesting that tolerance to excess and shortage of Mn are different, but not mutually exclusive traits. The co‐tolerance for Mn and Al in ET8 (an Al‐tolerant near‐isogenic line) and the absence of Mn tolerance in BH1146 (an Al‐tolerant genotype from Brazil) limits the effectiveness of these indicator genotypes to environments where only one constraint is induced. Wide variation of Mn tolerance in Australian wheat cultivars will enable breeding genotypes for the genetic solution to the Mn toxicity problem.     

Differential Soil Acidity Tolerance of Tropical Legume Cover Crops

In tropical regions, soil acidity and low soil fertility are the most important yield‐limiting factors for sustainable crop production. Using legume cover crops as mulch is an important strategy not only to protect the soil loss from erosion but also to ameliorate soil fertility. Information is limited regarding tolerances of tropical legume cover crops to acid soils. A greenhouse experiment was conducted to determine the differential tolerance of 14 tropical legume cover crops to soil acidity. The acidity treatments were high (0 g lime kg^?1 soil), medium (3.3 g lime kg^?1 soil), and low (8.3 g lime kg^?1 soil). Shoot dry weight of cover crops were significantly affected by acidity treatments. Maximum shoot dry weight was produced at high acidity. Jack bean, black mucuna, and gray mucuna bean species were most tolerant to soil acidity, whereas Brazilian lucern and tropical kudzu were most susceptible to soil acidity. Overall, optimal soil acidity indices were pH 5.5, hydrogen (H)+ aluminum (Al) 6.8 cmol_c kg^?1, base saturation 25%, and acidity saturation 74.7%. Species with higher seed weight had higher tolerance to soil acidity than those with lower seed weight. Hence, seed weight was associated with acidity tolerance in tropical legume species.     

Soil Aluminum Effects on Growth and Nutrition of Cacao

In acid soils, Al toxicity and nutrient deficiencies are main constraints for low yield of cacao ( Theobroma cacao L.). A controlled growth chamber experiment was conducted to evaluate the effect of three Al saturations (0.2, 19, and 26%) adjusted by addition of dolomitic lime on growth and nutrient uptake parameters of cacao. Overall, increasing soil Al saturation decreased shoot and root dry weight, stem height, root length, relative growth rate, and net assimilation rate. However, increasing soil Al saturation increased leaf area, specific leaf area (total leaf area/total leaf dry wt), and leaf area ratio (total leaf area/shoot+root wt). Increasing soil Al saturation decreased uptake of elements. Nutrient influx (IN) and transport (TR) decreased significantly for K, Ca and Mg, and showed an increasing trend for S and P as soil Al saturation increased. However, increasing soil Al saturation significantly increased nutrient use efficiency ratio (ER, mg of shoot weight produced per mg of element in shoot) of Ca, Mg and K and decreased ER for other elements. Reduction of soil acidity constraints with addition of lime and fertilizers appear to be key factors in improving cacao yields in infertile, acidic, tropical soils.     

Soil Aluminum Effects on Growth and Nutrition of Cacao

In acid soils, Al toxicity and nutrient deficiencies are main constraints for low yield of cacao (Theobroma cacao L.). A controlled growth chamber experiment was conducted to evaluate the effect of three Al saturations (0.2, 19, and 26%) adjusted by addition of dolomitic lime on growth and nutrient uptake parameters of cacao. Overall, increasing soil Al saturation decreased shoot and root dry weight, stem height, root length, relative growth rate, and net assimilation rate. However, increasing soil Al saturation increased leaf area, specific leaf area (total leaf area/total leaf dry wt), and leaf area ratio (total leaf area/shoot+root wt). Increasing soil Al saturation decreased uptake of elements. Nutrient influx (IN) and transport (TR) decreased significantly for K, Ca and Mg, and showed an increasing trend for S and P as soil Al saturation increased. However, increasing soil Al saturation significantly increased nutrient use efficiency ratio (ER, mg of shoot weight produced per mg of element in shoot) of Ca, Mg and K and decreased ER for other elements. Reduction of soil acidity constraints with addition of lime and fertilizers appear to be key factors in improving cacao yields in infertile, acidic, tropical soils.     

Aluminum,manganese, and iron tolerance improves performance of wheat genotypes in waterlogged acidic soils

Waterlogging results in high shoot concentrations of iron (Fe), aluminum (Al), and manganese (Mn) in wheat grown in acidic soil. The verification of this observation in several acidic soils, development of screening techniques, and identification of genotypes differing in tolerance made it possible to test whether tolerance of ion toxicities improves performance of wheat in waterlogged acid soils. Six wheat varieties selected for tolerance/intolerance of Al, Mn, and Fe were grown in three acidic soils (pH_CaCl2 4.1–4.3) with or without waterlogging for 40 d. In terms of relative shoot dry weight, Al‐, Mn‐, and Fe‐tolerant genotypes tolerated waterlogging better, outperforming intolerant genotypes by 35%, 53%, and 32%, respectively, across the soils. The Al‐tolerant genotype had up to 1.8‐fold better root growth than the intolerant genotype under waterlogging. Waterlogging increased DTPA‐extractable soil Mn (71%) and Fe (89%), and increased shoot Fe (up to 7.6‐fold) and Al (up to 5.9‐fold) for different genotypes and soils. The Al‐tolerant genotype maintained lower tissue concentrations of Al as compared to intolerant genotypes during waterlogging. Waterlogging delayed crop development but distinctly less so in the tolerant than in the intolerant genotypes, thus jeopardizing the capacity of intolerant genotypes to produce yield in Mediterranean climates with dry finish of the season. Pyramiding multiple ion tolerances into current wheat varieties with desirable agronomic and quality characteristics to enhance their performance under waterlogged acid soils should be considered.     

Magnetic resonance imaging of absorbed aluminum in alfalfa roots

An estimated 30% of the world's arable soils are acidic and aluminum (Al) toxicity is often the primary growth‐limiting factor. Excess Al is especially undesirable in sub‐soils because it reduces rooting depth and branching and predisposes plants to drought injury. Liming the plow layer does not generally neutralize subsoil phytotoxicity and Al‐tolerant cultivars offer an alternative or supplemental solution to the problem. Genetic diversity for acid soil tolerance in alfalfa (Medicago sativa L.) is limited and a better understanding of the basic tolerance mechanisms would facilitate the design of more efficacious breeding procedures. Evidence is accumulating that organic acids and proteins elicited by Al stress may complex and detoxify Al either within, or external to, the root. Because Al is a paramagnetic element that can reduce T2 relaxation times (inter‐proton interactions) markedly, the mechanism of Al tolerance in alfalfa was investigated through T2‐based Magnetic Resonance Imaging (MRI) of young lateral root sections of an Al‐sensitive and an Al‐tolerant alfalfa clone grown in nutrient solution (0 or 111 μmol Al; pH 4.5). Root sections that developed under phytotoxic levels of Al accumulated considerable Al in the epidermis and internal root tissue. Aluminum may have been complexed by low molecular weight proteins and organic acids in the tolerant clone whereas the sensitive clone appeared to have abundant free Al; however, variation among replications indicates that free Al may still have been present in tolerant roots and that other tolerance mechanisms may also be important. Root buds accumulated little Al compared to the remainder of the root, indicating that the pronounced effects of Al on lateral root development are indirect. Magnetic Resonance Imaging images evaluated in this study provided clues to the basic mechanisms of Al tolerance in alfalfa and, with further refinement, could be used as one criterion for selecting Al‐tolerant plants.     

不同水稻品种磷利用效率与耐铝性的关系研究

铝毒和磷缺乏是酸性土壤上作物生产的主要限制因子。本研究中我们探究了5个粳稻和5个籼稻品种的磷利用效率和耐铝性之间的相互关系。结果表明,粳稻品种的耐铝性显著高于籼稻品种。对于耐铝性强的水稻品种,施加磷肥后地上部生物量显著增加,而铝敏感的品种对磷肥响应较小,这可能是由于其耐铝性差而酸性土壤中的铝毒导致根系结构和功能受损,从而影响养分的吸收和利用。不同水稻品种的耐铝性和磷吸收效率呈正比而与磷利用效率呈反比,且粳稻的地上部磷浓度及磷吸收效率高于籼稻,但磷利用效率则低于籼稻。这些结果对于酸性土壤中筛选耐铝和磷高效利用的水稻品种具有重要意义。     

植物耐铝机理研究进展

铝毒是酸性土壤上作物生产的主要限制因子,植物耐铝机理以及与耐铝有关基因的研究是近十多年来研究的热点。本文对植物耐铝的生理、遗传及分子机理的研究进展作了综述。明确了目前取得的突破性进展已使通过植物遗传育种及生物技术手段提高粮食作物耐铝性成为可能;同时,本文对今后的研究方向作了简要的讨论。     

Tolerance of durum wheat lines to an acid,aluminum‐toxic subsoil

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.     

Effects of aluminum stress on alfalfa root proteins 1

An estimated 40% of arable soils worldwide contain phytotoxic levels of aluminum (Al). Recent evidence indicates that Al‐stress‐induced low molecular weight proteins may bind Al in Al‐tolerant plants. The objective of this study was to investigate protein patterns in young roots of two Al‐sensitive and two Al‐tolerant alfalfa (Medicago sativa L.) clones grown at 0 and 111 μmol Al in pH 4.5 nutrient solution. Based on SDS‐PAGE of supernatant, Al stress resulted in an increase in detectable root proteins in all clones and results are consistent with results reported for other plant species. A proliferation of new low‐molecular‐weight proteins in the tolerant clones could be related to Al tolerance. One protein (18.7 kD) was produced in both tolerant clones yet not detected in the sensitive clones. Protein levels were more often reduced than enhanced under Al stress and reduction was more prevalent in sensitive than in tolerant clones. Aluminum stress may initiate the production of some of the same proteins in alfalfa and wheat (Triticum aestivum L. Thell.). General stress proteins could be produced in reaction to a variety of chemical, environmental, and pathological stresses.     

Acid soil tolerances of wheat lines selected for high grain protein content

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.     

Manganese deficiency in wheat genotypes: Physiological responses and manganese deficiency tolerance index

Manganese (Mn) deficiency limits wheat productivity on sandy loam, calcareous and alkaline soils cropped with rice. Variation of wheat genotypes to sustain production and Mn use from Mn deficient condition was investigated to screen efficient genotypes. Forty-seven diverse wheat genotypes were evaluated on Mn sufficient (0.195 µM) and Mn deficient (0 µM) nutrient solution to elucidate physiological basis of Mn deficiency tolerance and to develop manganese deficiency tolerance index (MDTI). Shoot dry weight and mean Mn accumulation was 136.7% and 76.5% enhanced when Mn nutrition was improved, respectively. Efficient genotypes under limited Mn had lower root length/shoot weight ratio but higher relative shoot growth rate with higher shoot demand on root which reflected higher Mn influx. Genotypes were classified as tolerant (>0.66), semi-tolerant (0.33–0.66) and sensitive (<0.33) on the basis of MDTI (0–1 scale). Manganese efficient genotypes are most desirable for sustainable production of wheat under low Mn.     

Varietal diversity of upland rice in sensitivity to aluminium

A rapid and simple nutrient addition technique was used for evaluating Al tolerance of six local upland rice (Oryza sativa L.) cultivars (BG35, BR21, DA25, DA26, DA14, and DA22) from Bangladesh and three IRRI rice, IR46, IR97, and IR45, cultivars from the Philippines. The plants were grown for 21 days with Al (0 μM, 140 μM, 280 μM or 560 μM) at pH 4.1. The roots were more affected by Al than the shoots. In rating cultivars for Al sensitivity, relative shoot weight (RSW) was found to be the best parameter due to the severe damage of the roots, irrespective of Al sensitivity. The cultivars were rated as Al tolerant (BG35, BR21, DA25, and DA26), mid‐tolerant (DA14, DA22, and IR46) and sensitive (IR97 and IR45) . More Al was retained in the roots of tolerant cultivars than in the mid‐tolerant or sensitive cultivars. In shoots, the Al concentration of tolerant cultivars was less than in the mid‐tolerant or in the sensitive cultivars and the inhibition of growth was proportional to Al concentration irrespective of Al tolerance. Therefore, the variation among cultivars in Al sensitivity could be related to the capacity of roots to retain Al from transport to the shoots.     

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.     

大豆种质耐低磷与耐铝毒部分指标及其相互关系的研究

通过溶液培养试验 ,对来源于华南酸性土壤的 5个大豆品种的地上部及根部耐低磷及耐酸铝部分指标进行了系统的研究。研究结果表明 ,大豆在磷效率和耐铝毒特性方面存在着一定的差异 ,大豆品种 6 2号、乐昌及广州大粒具有较高的磷效率和耐铝毒特性。在低磷及铝毒胁迫下它们具有较高的生物量、磷含量、叶面积、叶绿素含量、总酸分泌量以及主根长。低磷和铝毒胁迫严重影响地上部磷的吸收 ,高磷能缓解铝毒。铝浓度不同处理大豆的地上部无显著差异 ;但在铝毒胁迫下 ,根部的铝浓度比地上部高 5～ 6倍 ,且品种间存在显著差异。本研究初步确定了大豆耐低磷与耐铝毒的相关关系