Effect of Nitrogen Fertilizers on Zinc Accumulation in Fescue

Abstract

This research evaluated effects of nitrogen fertilizers on availability of zinc (Zn) in soils. Two slit loams of the Hadley series (Typic Udifluvents) were used. Zinc sulfate was mixed with the soils to give Zn at 125, 250, 500, or 1,000 mg/kg and incubated for 14 days. Fertilizers (compost, cow manure, urea) were mixed with the soils to supply N at 200 mg/kg. Fourteen days after the fertilizers were mixed with the Zn‐treated soils, soil samples were taken for analysis of plant‐available Zn by extraction with Morgan's solution or water. After the soil samples were taken, fescue (Festuca arundinacea Schreb.) seeds were placed into pots to assess germination, growth, and Zn accumulation. Higher concentrations of Morgan's extractable Zn were detected in soils treated with compost (201 mg/kg) than with calcium nitrate (179 mg/kg), manure (153 mg/kg), or urea (152 mg/kg). However, with water extraction, higher Zn concentrations were detected in soils treated with calcium nitrate (36 mg/kg) with the lowest concentrations being extracted from soils treated with urea (8 mg/kg). Extraction of Zn by Morgan's solution or water increased as the soil‐Zn levels increased. Fescue germinated and grew at all of the soil‐Zn levels. The highest concentration of Zn occurred in plants grown in soils amended with calcium nitrate or urea, and the lowest concentration was in plants grown in soils amended with compost or manure. Fescue grown in soils amended with urea had the largest dry mass, and plants grown with compost or manure had the smallest. Zinc concentration and accumulation for fescue shoots increased as the soil‐Zn levels increased. These results suggest that accumulation of Zn in fescue can be enhanced by selection of nitrogen‐containing fertilizers that affect the solubility of Zn in soils.     

Phytoextraction Potential of Indian Mustard at Various Levels of Zinc Exposure

ABSTRACT

Indian mustard (Brassica juncea Czern.) has the potential to extract zinc (Zn) and other metals from contaminated soils, but the potential to accumulate metals at different levels of exposure is not well documented. The objectives of this research were to assess plant growth and Zn accumulation for different metal-accumulating accessions of Indian mustard grown with various Zn concentrations. In the experiment, three accessions of Indian mustard (426308, 182921, and 211000) were supplied with 12 levels of Zn (ranging from 0.0 to 7.0 mg L^?1) for three weeks in solution culture. Accession 426308 had a greater capacity for dry-mass accumulation than the others, but differences among accessions lessened as the concentration of Zn in solution increased. Accessions did not differ in Zn concentrations in shoots, but accession 426308 had a greater potential to accumulate Zn than the other accessions. Elevating the Zn supply in solutions had a limited effect on increasing the total Zn accumulation of shoots. Plants suffered Zn-induced iron (Fe) deficiency if the Zn concentration in solution exceeded 2.0 mg Zn L^?1. The level of Zn tolerance of Indian mustard accessions was: 211000 > 182921 > 426308. Maximum Zn accumulation in shoots was approximately 5.0 mg Zn per plant. The phytoextraction potential of Indian mustard may be limited under Zn-contaminated conditions by nutrient disorders and toxic effects of Zn that suppress growth.     

Nutritional Alleviation of Zinc-Induced Iron Deficiency in Indian Mustard and the Effects on Zinc Phytoremediation

ABSTRACT

Indian mustard (Brassica juncea Czern) is a promising species for the phytoextraction of zinc (Zn), but the effectiveness of this plant can be limited by iron (Fe) deficiency under Zn-contaminated conditions. Our objectives were to determine the effects of root-applied Fe and Zn on plant growth, accumulation of Zn in plant tissues, and development of nutrient deficiencies for B. juncea. In the experiment, B. juncea was supplied 6 levels of iron ethylenediamine dihydroxyphenylacetic acid (Fe-EDDHA; 0.625 to 10.0 mg L^?1) and two levels of Zn (2.0 and 4.0 mg L^?1) for 3 weeks in a solution-culture experiment. Nutrient solution pH decreased with decreasing supply of Fe and increasing supply of Zn in solution, indicating that B. juncea may be an Fe-efficient plant. If plants were supplied 2.0 mg Zn L^?1, plant growth was stimulated by increases in Fe supply, but plant growth was not influenced by Fe treatments if plants were supplied 4.0 mg Zn L^?1. Zinc concentration in roots and shoots was suppressed by increasing levels of Fe in solution. Leaf concentrations of Cu, Mn, and P were suppressed also as Fe supply in solutions increased. Iron additions to the nutrient solution were not effective at increasing the Zn-accumulation potential of B. juncea unless plants were supplied the higher level of Zn in solution culture. Even under these conditions, Fe additions were effective only if supplied at low levels in solution culture (1.25 mg Fe L^?1). Results suggest that Fe fertility has limited potential for enhancing Zn phytoextraction by B. juncea, even if plants suffer a suppression in growth from Fe deficiency.     

Arsenic and Cadmium Phytoextraction Potential of Crambe Compared with Indian Mustard

ABSTRACT

The ability to tolerate and accumulate arsenic (As) and cadmium (Cd) was compared between Brassica juncea (Indian mustard) and Crambe abyssinica (Hochst.) (Crambe or Abyssinian mustard). Plants were grown hydroponically and treated with 70 μM sodium arsenate or 50 μ M cadmium chloride for two weeks. When nutrients were omitted during the As treatment, leaves of C. abyssinica accumulated an average of 140 mg As kg^?1, compared with 34 mg kg^?1 for B. juncea. When quarter-strength Hoagland's nutrient solution was provided during As treatment, leaves of C. abyssinica accumulated an average of 270 mg As kg^?1, compared with 13 mg kg^?1 for B. juncea. Cadmium accumulation on a dry-weight basis was approximately two times greater in shoots of B. juncea. Shoot biomass production in the presence or absence of metals was greatest for C. abyssinica. Because of its larger biomass and more efficient accumulation of As, C. abyssinica should be considered for use in phytoremediation research.     

Influence of Ammonium and Nitrate Nutrition on Plant Growth and Zinc Accumulation by Indian Mustard

ABSTRACT

The source of nitrogen (N) used in soil fertility practices affects plant growth, nutrient absorption, and the availability of nutrients. Consequently, the potential of plants to extract zinc (Zn) from soils may be increased by controlling the ratio of NH₄ ⁺ to NO₃ ^? to maximize growth and Zn accumulation. The objectives of this research were to determine the effects of Zn supply and different molar ratios of NH₄ ⁺ to NO₃ ^? on growth and Zn accumulation in Indian mustard (Brassica juncea Czern.). In a factorial experiment with solution culture, Indian mustard (accession 182921) was supplied with two concentrations of Zn (0.05 and 4.0 mg L^?1) in combination with six N treatments with different molar percentage ratios of NH₄ ⁺ to NO₃ ^? (0:100, 10:90, 20:80, 30:70, 40:60, and 50:50) for three weeks. Zinc supplied at 0.05 mg Zn L^?1 represented a common concentration of Zn in solution culture, whereas 4.0 mg Zn L^?1 was excessive for plant nutrition. If the supply of Zn in solution was excessive, plants developed symptoms of foliar chlorosis, which became severe if plants were supplied with 80% of N as NO₃ ^?. Supplying high proportions of NO₃ ^? in the nutrient medium stimulated Zn accumulation, whereas increasing proportions of NH₄ ⁺ (up to 50% of the total N) enhanced shoot growth. The pH of nutrient solutions generally decreased with increasing proportion of NH₄ ⁺ in solutions and with increased Zn supply. The Zn phytoextraction potential of Indian mustard was maximized, at about 15 mg Zn plant^?1, if plants received 10% of the total N as NH₄ ⁺ and 90% as NO₃ ^?.     

高羊茅春化基因FaVRN1亚细胞定位与差异表达分析

高羊茅在生长季出现生殖枝,抑制新枝形成,不利于草坪质量及其持久性生长。研究春化基因的分子特征,探索抑制生殖生长的分子育种新途径,对坪用型高羊茅品种改良具有重要意义。本研究在克隆高羊茅春化基因FaVRN1的基础上,构建高羊茅春化基因FaVRN1与绿色荧光蛋白基因GFP融合的植物表达载体p-FaVRN1-hGFP,利用基因枪转化法转入洋葱表皮细胞,荧光显微镜检测融合基因的瞬时表达,并运用实时荧光定量PCR分析春化基因FaVRN1在春化与非春化条件下的表达差异。研究结果表明,FaVRN1基因编码的蛋白产物位于细胞核,符合它作为转录因子特性;春化条件下,FaVRN1基因的表达随处理时间延长逐渐增加。非春化条件下,FaVRN1基因的表达随处理时间延长而降低。FaVRN1基因在春化条件下的表达水平远高于非春化条件,FaVRN1基因的表达受春化条件正调控。     

微生物对土壤Cd Pb和Zn生物有效性的影响研究

采用土壤盆栽模拟试验方法,研究了接种不同微生物对重金属富集植物——印度芥菜修复土壤中Cd、Pb、Zn的作用效果。结果表明,接入菌株JA27、JC55、JC40不仅显著促进植物的生长,提高印度芥菜的生物量,降低了土壤pH,并且对土壤Cd、Pb、Zn产生活化作用,使土壤Cd、Pb、Zn有效态含量显著增加,增强印度芥菜对土壤Cd、Pb、Zn吸收量,显著提高了富集植物的修复效果。以上3个处理使印度芥菜地上部Cd、Pb、Zn吸收量分别提高了117%～137%、37%～62%、9%～15.1%。接种JB37对土壤Cd、Pb、Zn产生钝化作用,并且抑制印度芥菜对土壤Cd、Pb、Zn的吸收。JB37处理印度芥菜地上部Pb、Zn吸收量分别降低了72.5%、27%,对Cd吸收量无显著影响。     

高羊茅和黑麦草对污染土壤Cd,Pb,Zn的富集特征

以潮褐土为供试土壤,通过模拟试验研究了高羊茅(Festuca arundinacea)和黑麦草(Lolium multif lorum)对复合污染土壤Cd,Pb,Zn的富集特点。结果表明,在土壤Cd,Pb,Zn复合污染处理条件下,高羊茅Cd,Pb,Zn的平均富集量,地上部分别为5.76,19.77,418.18 mg/kg,地下部分别为129.82,256.66,354.66 mg/kg;黑麦草Cd,Pb,Zn的平均富集量,地上部分别为5.57,26.13,467.18 mg/kg,地下部分别为114.53,155.98,513 48 mg/kg。通过方差分析,这两种草坪草的重金属富集量没有显著差异,并且富集规律呈现较为一致的特点。地上部的富集量和土壤重金属含量的离子冲量呈显著的线性相关。这两种草坪草对其重金属的富集能力顺序为:Zn>Cd>Pb,其中对Zn的吸收呈现富集植物的特性规律,当土壤Zn含量>400 mg/kg时,其转运系数>1,地上部对Zn的富集能力很强,可作为Zn污染土壤的修复植物。通过偏相关和多元回归分析表明,这两种草坪草在土壤Cd,Pb,Zn复合污染条件下均未产生复合效应。     

高羊茅FeTOC1基因的克隆、差异表达及亚细胞定位分析

拟南芥TOC1基因是中央振荡器的重要组成部分,其编码的蛋白质TOC1通过光周期途径调控拟南芥对光照的响应.为了揭示高羊茅FeTOC1基因的生物学功能,本研究通过同源克隆获得该基因全长cDNA序列,对其在不同光照水平下的表达模式进行分析,并对其编码的蛋白质进行亚细胞定位.结果显示,高羊茅FeTOC1基因的全长cDNA序列...     

培养基质对印度芥菜Cd、Pb、Zn富集效果的研究

通过温室土培和砂培盆栽对比试验,研究了外源Cd、Pb、Zn复合污染对印度芥菜富集重金属的效果。结果表明,印度芥菜Cd、Pb和Zn的富集量分别与土培和砂培Cd、Pb、Zn的添加量呈极显著正相关。砂培印度芥菜Cd、Pb和Zn的富集量分别远大于土培,前者印度芥菜地上部Cd、Pb、Zn的最高富集量分别达311.3,248.0,2760mg/kg,分别为土培的10.4,12.9,4.67倍;砂培条件下印度芥菜地上部Cd、Pb、Zn的提取量均大于土培,分别为土培的1.29～8.96倍、1.02～8.58倍和1.68～5.62倍;印度芥菜Cd、Pb、Zn的富集系数砂培较土培明显增大,其中富集系数的变化为CdZnPb,对Pb的富集系数除个别处理外均小于1,说明印度芥菜对Cd、Zn具有很强的富集能力,对Pb的富集能力较弱。研究表明,土培条件下Cd、Pb、Zn的生物有效性较低,直接制约着印度芥菜对土壤重金属污染的修复效果。     

Interactive Effects of Lanthanum and Cadmium on Plant Growth and Mineral Element Uptake in Crisped-Leaf Mustard Under Hydroponic Conditions

Plant growth and mineral element accumulation in Brassica juncea var. crispifolia (crisped-leaf mustard) under exposure to lanthanum (La) and cadmium (Cd) were studied by employing a hydroponic experiment with a complete two-factorial design. Four levels of La (0.05–5.0 mg L^?1) and two levels of Cd (1.0 and 10.0 mg L^?1) were used in this experiment. Lanthanum did not improve plant growth in this experiment. Addition of La (≥ 1.0 mg L^?1) or Cd (≥ 10 mg L^?1) to the solution inhibited root elongation. Lanthanum treatments reduced accumulations of iron (Fe), manganese (Mn), and zinc (Zn) in roots, and Mn in shoots. Lanthanum at ≥ 1.0 mg L^?1 limited the Cd translocation from roots to shoots and thus decreased the accumulation of Cd in shoots. Cadmium had no influence on La accumulations in roots, but inhibited the accumulation of La in shoots. The study results suggest that applications of rare earth elements in vegetables would be potentially risky to human health.     

Zinc fractions in soil and uptake by wheat as affected by different preceding crops

Zinc (Zn) deficiency is widespread in alkaline and calcareous soils. Limited information is available on the effect of preceding crops on the distribution of Zn in soil solid phase. This field study was conducted to investigate the changes in Zn chemical forms in soil solid phase as affected by four preceding crops [Sunflower (Heilianthus annuus L. cv. Allstar), Sorghum (Sorghum bicolor L. cv. Speed Feed), Clover (Trifolium pratense L.) and Safflower (Carthamus tinctorius L. cv. Koseh-e-Isfahan)] in a calcareous soil. A control treatment with no preceding crop (fallow) was also used. Our results showed that the preceding crops increased Zn concentration in exchangeable fraction (EXCH-Zn), the organically bound zinc form (ORG-Zn) and zinc bound to iron and manganese oxides (FeMnOX-Zn) while decreased carbonates bound-zinc (CAR-Zn) and residual zinc forms (RES-Zn). However, the changes in Zn fractions were dependent on the preceding crop type. The EXCH-Zn and ORG-Zn pools can be considered labile pools that play significant roles in supplying Zn for plants. Among the preceding crops used in this experiment, clover (Clo) had the highest effect on transforming CAR-Zn form to EXCH-Zn and ORG-Zn labile forms and thus resulted in the highest Zn accumulation in tissues of the target wheat (Triticumaestivum L. cv. Back Cross). Although the changes in chemical forms of Zn in the soil solid phase are complex and dependent on various factors, our findings showed that the preceding crops significantly increased the concentration of Zn in exchangeable and organic matter pools and in turn resulted in higher uptake of Zn by the target wheat.     

Effects of Forms and Rates of Zinc Fertilizers on Cadmium Concentrations in Two Cultivars of Maize

Abstract

A pot experiment was conducted to investigate the effects of three soluble zinc (Zn) fertilizers on cadmium (Cd) concentrations in two genotypes of maize (Zea mays): Jidan 209 and Changdan 374. Zinc fertilizers were added to soil at four levels: 0, 80, 160, and 240 mg kg^?1 soil as nitrate [Zn(NO₃)₂], chloride (ZnCl₂), and sulfate (ZnSO₄). Cadmium nitrate [Cd(NO₃)₂] was added to all the treatments at a uniform rate equivalent to 10 mg kg^?1 soil. The biomass of maize plants was increased with the application of three zinc fertilizers, of which Zn(NO₃)₂ yielded more than others. Under ZnCl₂ treatment, plant growth was promoted at the lower level and depressed at the higher one. All the three fertilizers decreased Cd concentration in shoots in comparison with treatments without Zn, but there were variations with different forms, especially in plants treated with Zn(NO₃)₂, which had the minimal value. The orders of average Cd concentration in shoots with different zinc fertilizers were ZnSO₄>ZnCl₂>Zn(NO₃)₂ for Jidan 209 and ZnCl₂>ZnSO₄>Zn(NO₃)₂ for Changdan 374, respectively (P<0.001). There was no significant difference between ZnSO₄ and ZnCl₂ treatments. The lowest Cd concentration in shoots was found in the 80‐mg‐kg^?1 soil or 160‐mg‐kg^?1 soil treatment. Cadmium concentration in roots in the presence of ZnCl₂ was the lowest and under ZnSO₄ the highest. The mechanism involved needs to be studied to elucidate the characteristics of complexation of Cl^? and SO₄ ^2? with Cd in plants and their influence on transfer from roots to shoots.     

Effects of Nitrogen and Sulfur on Total Phenolics and Antioxidant Activity in Two Genotypes of Leaf Mustard

Leaf mustard (Brassica juncea Coss) is widely used for both fresh and processed markets in southern China. It contains high nutritional and medicinal compounds, which are important for maintaining optimum health. The objective of this study was to determine the influence of nitrogen (N) and sulfur (S) nutrition on total phenolics and antioxidant activity in two genotypes of leaf mustard (cvs. ‘Xuelihong’ and ‘Zhujie’). Plants were greenhouse-grown using nutrient solutions with two levels of nitrogen (10 and 25 mM) and three levels of sulfur (0.5, 1, and 2 mM). Total phenolic concentrations were considerably decreased by increasing nitrogen supply, whereas increased by increasing sulfur supply. Total phenolic concentrations in cv ‘Zhujie’ was higher than in cv ‘Xuelihong’. Three assays including 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, β -carotene bleaching (BCB), and ferric reducing antioxidant power (FRAP) were used to evaluate antioxidant activity. Increasing nitrogen supply reduced DPPH radical scavenging activity and FRAP value, but increased antioxidant activity using BCB assay. Increasing sulfur supply increased antioxidant activity with all three tests. The effects of genotype on DPPH radical scavenging activity and FRAP value were not significant, however, antioxidant activity using BCB assay was significantly higher in cv ‘Zhujie’ than in cv ‘Xuelihong’. A significantly positive correlation was found between DPPH radical scavenging activity and total phenolic concentrations in two genotypes, FRAP value and total phenolic concentrations in cv ‘Xuelihong’.     

新疆石灰性土壤锌有效性及其影响因素

为探讨新疆石灰性土壤锌的组分分布特征及锌有效性的影响因素,对南北疆3种最主要土壤类型农田土壤锌及其组分含量进行研究。结果表明:新疆石灰性土壤有效锌平均含量为潮土(0.69mg/kg)>棕漠土(0.57mg/kg)>灰漠土(0.51mg/kg),变异系数为灰漠土>潮土>棕漠土。在土壤锌组分中,松结有机态锌(WBO)、碳酸盐结合态锌(CARB)、氧化锰结合态锌(OxMn)、紧结有机态锌(SBO)、无定形铁结合态锌(AOFe)平均含量均为潮土>棕壤土>灰漠土。南北疆土壤锌背景值不同,南疆土壤全锌含量高于北疆土壤,而北疆土壤全锌变异较大。土壤碳酸钙含量和物理性粘粒含量与松结有机态、碳酸盐结合态、紧结有机态锌分配率高度相关。松结有机态锌、碳酸盐结合态锌及松结有机态锌分配率与土壤物理性粘粒含量呈(极)显著正相关。交换态锌与松结有机态锌呈显著正相关。松结有机态锌与碳酸盐结合态锌呈显著正相关。石灰性土壤有效锌含量与松结有机态锌、碳酸盐结合态锌含量呈显著正相关,可用方程Y=0.306+0.123WBO+0.116CARB(F=20.095,r2=0.801**)预测。     

Chelate-Assisted Phytoextraction of Cadmium and Lead using Mustard and Fenugreek

A screen-house experiment was conducted to study cadmium (Cd) and lead (Pb) phytoextraction using mustard and fenugreek as test crops. Cadmium was applied at a rate of 20 mg kg^?1 soil for both crops, and Pb was applied at 160 and 80 mg kg^?1 soil for mustard and fenugreek, respectively. The disodium salt of ethylenediamine tetraacetic acid (EDTA) was applied at 0, 0.5, 1.0, and 1.5 g kg^?1 soil. Dry-matter yield (DMY) of both crops decreased with increasing rates of EDTA application. Application of 1.5 g EDTA kg^?1 soil caused 23% and 70% declines in DMY of mustard and fenugreek shoots, respectively, in the soils receiving 20 mg Cd kg^?1 soil. Similarly, in soil with 160 mg Pb kg^?1 soil, application of 1.5 g EDTA kg^?1 resulted in 25.4% decrease in DMY of mustard shoot, whereas this decrease was 55.4% in fenugreek grown on a soil that had received 80 mg Pb kg^?1 soil. The EDTA application increased the plant Cd and Pb concentrations as well as shoot/root ratios of these metals in both the crops. Application of 1.5 g kg^?1 EDTA resulted in a 1.50-fold increase in Cd accumulation and a 3-fold increase in Pb accumulation by mustard compared to the control treatment. EDTA application caused mobilization of Cd and Pb from carbonate, manganese oxide, and amorphous iron oxide fractions, which was evident from decrease in these fractions in the presence of EDTA as compared to the control treatment (no EDTA).     

高羊茅对河道底泥中复合重金属污染的修复

为了治理河道底泥中复合重金属的污染,利用栽培试验研究高羊茅对底泥中复合重金属污染的修复情况。研究发现,高羊茅种植3个月后对底泥中Cr、Cd、Cu、Zn、Mn、Ni污染有较好的去除效果,此时底泥中大部分重金属含量达到最小值,但对Pb的去除效果不明显。重金属去除率的大小顺序为:Cr>Cd>Cu>Zn>Mn>Ni。对底泥中Cr的去除效果最好,去除率高达61.44%。Ni、Zn、Cr、Cu、Mn均在根部的累积量最大,其次是叶和茎。Cd被高羊茅吸收后,主要累积在叶和茎部。从富集系数和转移系数来看,高羊茅尤其适于对Cd和Zn污染的修复。脱氢酶活性在高羊茅种植的过程中表现为先升高后降低,在种植3个月后酶活性达到最高,且脱氢酶活性与重金属浓度均呈负相关关系,其对重金属污染较为敏感。高羊茅根际底泥中微生物种群数量为细菌>放线菌>真菌,对环境的适应能力表现为真菌>细菌>放线菌。     

Effect of Salinity and Nitrogen Status on Nitrogen Uptake by Tall Fescue Turf

ABSTRACT

Nitrogen (N) absorption is inhibited by root zone salinity, which could result in increased NO₃ leaching. Conversely, N absorption is enhanced by moderate N deficiency. Because turfgrasses are grown under N-limiting conditions, it is important to understand the interactive effects of salinity and N deficiency on N uptake. This study examined the effect of N status (replete versus deficient) and salinity on N (¹⁵NO₃ and ¹⁵ NH₄) uptake and partitioning by tall fescue (Festuca arundinacea Schreb.). Two cultivars (‘Monarch’ and ‘Finelawn I’) were grown in nutrient solution culture. Treatments included N level (100% or 25% of maximum N demand) and salinity (0, 40, 80, and 120 meq L^?1) in a factorial arrangement. Absorption of NO₃ and NH₄ was greater in low-N than in high-N cultures, but was reduced by salinity under both N treatments. Salinity reduced partitioning of absorbed N to leaves and increased retention in roots. These results suggest that turfgrass managers should consider irrigation water quality when developing their fertilizer program.     

石灰性褐土中磷锌镉相互作用对其有效性的影响

采用室内培养的方法,研究了石灰性褐土中磷、锌、镉相互作用对土壤中磷、锌、镉有效性的影响。结果表明：（1）磷锌共同培养时,施锌提高了土壤速效磷含量,且随培养时间的延长而降低。在相同锌浓度处理下,土壤中的有效锌含量随施磷量的增加而增加,不同锌浓度处理下,有效锌含量随土壤培养时间的延长而显著降低。（2）磷镉共同培养时,施镉对土壤速效磷含量影响不明显;施磷降低了有效镉含量,但效果不显著;且都随时间的延长而降低。（3）锌镉共同培养时,在培养的前30d,土壤中有效锌含量随施镉浓度增加而降低,但在30d后,有效锌含量有增加的趋势。土壤中有效镉含量在不同锌-镉处理下随培养时间变化有较大差异：在Cd3处理下,加入高浓度锌后显著降低土壤有效镉含量;Cd30处理下,在培养前30d,锌的施入对土壤中有效镉含量影响不明显,但30d以后,土壤有效镉含量随施入锌浓度的增加而显著降低。说明两者的竞争机制随时间的延长发生变化,且施锌能明显降低镉的毒性。     

Mineral composition of kenhy tall fescue as affected by nutrient solution concentrations of Mg and K

Four greenhouse sand culture experiments were conducted with Kenhy tall fescue, a Lolium multiflorum X Festuca arundinacea hybrid derivative. These experiments were conducted to characterize mg accumulation and the chemical composition of Kenhy under various combinations of Mg, K, and N solution concentrations. Of primary interest was the shape and magnitude of response of tissue Mg concentration to solution K levels and potential for Mg accumulation that exists in Kenhy under low solution K levels. Analyses were made for Mg, K, Ca, Na, N, and nitrate.

Increased Kg concentrations were observed with increased solution Mg. Increased solution K was in all cases associated with lower concentrations of Mg. Under conditions of low solution K (0.125 mM) and adequate Mg (0.25 mM), Mg accumulation exceeded 1.0%. Increased solution N was associated with decreased Mg concentrations. Both the linear and quadratic components of Mg solution concentration contributed significantly to increased tissue Mg. Hawever, the linear component of K solution concentration was sufficient to account for decreased tissue Mg. The reduction of tissue Mg to solution K was greater at higher concentrations of K.

Potassium accumulation significantly increased with increased solution K. Increased solution Mg was associated with lower tissue K in which the greatest reduction in K accumulation occurred with the first Mg addition.

Calcium accumulation decreased with increased solution K. Higher solution Mg was associated with lower tissue Ca levels while higher levels of N were associated with increased tissue Ca. Sodium accumulation was significantly reduced by increased K concentrations but neither Mg nor N was effective in consistently altering tissue Na concentrations.

From these experiments it is evident that Kenhy tall fescue has the absorptive capability for high levels of Mg under conditions of low levels of solution K. However, even small increments of solution K were shown to be capable of substantially reducing the Mg content, Thus, the selection of forage grasses for Mg absorptive capability must be conducted under conditions of high solution K, if large improvements on present forage materials are to be obtained. In addition, the inverse relationship between Mg and K present in Kenhy seedlings confirms the need to consider K fertilization recommendations in attempting to increase forage Mg durirg the grass tetany period.