Response of nitrogen fixation,nodule activities,and growth to potassium supply in water‐stressed broad bean

Three‐week‐old nodulated faba bean plants were subjected to two levels of water stress (0.5 and 0.25 field capacity; soil water content of 20 and 10%) for five weeks. Half of the stressed plants was treated with potassium chloride (KC1) at 10 (K₁) and 150 mg (K₂)/kg soil at the beginning of water deficit. Nodulation was examined and some nodule activities were assayed. Nodulation, nitrogenase activity, total nitrogen (N), and dry matter yield were significantly decreased by increasing stress but were significantly higher with the two levels of potassium (K) supply. Leghaemoglobin and protein contents of cytosol as well as nodule protease and invertase were severely depressed by drought stress. Soluble carbohydrate contents of nodules, however, was significantly increased. Protein and leghaemoglobin contents and enzyme activities were greater with K fertilization but less soluble carbohydrate was accumulated. The results indicate that K supply, particularly at the 150 mg/kg soil level, increased faba bean resistance to water stress.     

Nodulation and nitrogen fixation by arrowleaf clover: Effects of phosphorus and potassium

“Yuchi” arrowleaf clover (Trifolium vesiculosum Sav.) has a potential for high forage productivity with desirable symbiotic nitrogen fixation within most temperate regions. Our objective was to determine the effects of soil fertility on growth, nodulation, nitrogenase and associated enzyme activities of arrowleaf clover. In greenhouse experiments top growth increased with additions of 300 mg K kg^?1 soil with and without 100 mg P kg^?1 soil to a Cumulic Haplustoll (Port silt loam, pH 6.1). Nodule mass without P fertilizer additions increased linearly up to 400 mg K kg^?1 soil. When both P and K fertilizer additions were combined nodule mass increased significantly only up to the 300 mg K addition. However, nodule weight, increased 4-fold with the PK combination treatments. Nitrogenase activity, as measured by C₂H₂ reduction, more than doubled with P additions and increased linearly up to 400 mg K kg^? soil, with and without the P additions. Aspartate amino-transferase (AST) activity of nodule cytosol more than doubled with P additions but increased only with up to 300 mg K without P. Highest AST activities were recorded with the 400 mg K addition when combined with P. Glutamate synthetase (GS) activity increased with up to 300 mg K without P addition, but when combined with P was approximately 3 times higher, increasing linearly to 400 mg K. Differences in glutamate synthetase (GOGAT) activity were not significant with K additions without P, but when combined with P treatments were almost doubled up to the 400 mg K concentrations. Multiple regression for nitrogenase (C₂H₂ red.) as the dependent variable = 5.89 (AST) + 12.79 (GS) + 21.52 (GOGAT) + 13.53 (GDH); R² = 0.92 and C.V. = 15.6%. Nodule cytosol P and K compositions reflected soil treatment levels and combinations. Reciprocal effects of monovalent cations were highly significant, with increased K concentrations reducing Na content; nitrogenase = 0.12 (P) + 0.01(K) + 0.14(Ca) ?0.34 (Na); R² = 0.86 and C.V. = 21.9%.     

Mycorrhiza and soil fertility effects with growth,nodulation and nitrogen fixation of leucaena grown on a typic eutrustox

Abstract

The rapidly growing, woody perennial legume, Leucaena (Leucaena leucocephala (Lam.) de Wit), is adaptable to a wide range of neotropical soil conditions. Effective Rhizobium inoculation and endophyte mycorrhizal colonization are essential for high levels of production and symbiotic N₂ fixation. The objective of this study was to determine growth, nodulation, nitrogenase activity and nodule composition of inoculated Leucaena as affected by mycorrhizal colonization and factorial soil fertility treatments of a Typic Eutrustox. Highly significant increases in top growth, nodule fresh wt. and nitrogenase activity resulted with Glomus fasciculatum colonization, soil K and linear increases with low‐soluble P fertilization to 300 mg P kg^‐1 soil. Highly significant interactions for increased nodulation and nitrogenase activity resulted with K × mycorrhiza. Interactions of all three factors P, K and mycorrhiza were highly significant for nodule fresh wt. However, responses comparing inoculation with G. fasciculatum and with combined G. fasciculatum, G. microcarpus and G. clavium were not significant. Highly significant increases with applied K levels to 300 mg K kg^‐1 soil resulted with top and root growth, nodulation and nitrogenase when applied with soluble P at 100 mg kg^‐1 soil and 500 mg Ca kg^‐1 soil. Significant and highly significant interactions of P, Ca and K level resulted for all parameters. Plant nutrient element composition of nodules increased with the fertilization treatments for P, Ca and increased K levels. A highly significant inverse relation was apparent with decreased Na resulting with increased K levels. Half or more of total nodule K, P and Mg but less than 20% of Ca and Na were within the nodule cytosol. Sodium, Mg, P, and Ca decreased in the cytosol fraction with increased K content.     

干旱与Cd双重胁迫对土壤-小麦-蚜虫系统Cd转移规律影响的研究

为探究干旱和重金属双重胁迫对土壤-小麦-蚜虫系统内Cd转移规律的影响,为小麦蚜虫的生态调节提供理论依据,本研究以麦长管蚜[Sitobionavenae(Fabricius)]为研究对象,用原子吸收分光光度法分别测定不同土壤Cd含量(100 mg?kg-1、200 mg?kg-1)及不同程度干旱胁迫(无胁迫、中度胁迫、重度胁迫)处理下小麦根茎叶及蚜虫体内的Cd含量。结果表明:土壤Cd含量及干旱单一胁迫均对小麦及蚜虫体内的Cd含量造成了显著影响(P0.05)。两者交互作用对小麦根部及叶部的Cd含量影响显著,而对小麦茎部及蚜虫体内Cd含量影响不显著。在相同胁迫条件下, Cd在小麦中的积累分布为根茎叶。随着干旱胁迫程度增大,小麦根部Cd含量及土壤-根转移系数降低,茎部Cd含量及根-茎转移系数升高,麦长管蚜Cd含量在土壤Cd含量100mg?kg-1下高于土壤Cd含量200 mg?kg-1;中度干旱胁迫增加了麦长管蚜体内Cd累积量,而重度干旱胁迫则降低了其体内Cd累积量。叶-蚜虫的Cd转移系数明显大于土壤-根、根-茎和茎-叶转移系数且大于1,说明Cd在麦长管蚜体内产生了生物富集作用。综上所述,干旱胁迫促进了Cd从土壤向小麦茎部转移和根部Cd累积,但抑制了Cd从根部到茎部转移和茎部Cd累积;中度干旱胁迫促进了麦长管蚜体内Cd的积累,而重度干旱胁迫抑制了麦长管蚜体内Cd的积累。     

Influence of arbuscular mycorrhizae and phosphorus fertilization on growth, nodulation and N2 fixation (15N) inMedicago sativa at four salinity levels

The rose of an isolate of the arbuscular mycorrhizal (AM) fungusGlomus mosseae in the protection ofMedicago sativa (+Rhizobium meliloti) against salt stress induced by the addition of increasing levels of soluble salts was studied. The interactions between soluble P in soil (four levels), mycorrhizal inoculum and degree of salinity in relation to plant growth, nutrition and infective parameters were evaluated. Salt stress was induced by sequential irrigation with saline water having four concentrations of three salts (NaCl, CaCl₂, and MgCl₂).¹⁵N-labelled ammonium sulphate was added to provide a quantitative estimate of N₂ fixation under moderate to high salinity levels. N and P concentration and nodule formation increased with the amount of plant-available P or mycorrhizal inoculum in the soil and generally declined as the salinity in the solution culture increased from a moderate to a high level. The mycorrhizal inoculation protected the plants from salt stress more efficiently than any amount of plant-available P in soil, particularly at the highest salinity level applied (43.5 dS m^?1). Mycorrhizal inoculation matched the effect on dry matter and nutrition of the addition in the soil of 150 mg P kg^?1. Nevertheless the highest saline solution assayed (43.5 dS m^?1) affected more severely plants supplemented with phosphorus than those with the addition of mycorrhizal inoculum. Such a saline-depressing effect was 1.5 (biomass), 1.4 (N) and 1.5 (P) times higher in plants supplied with soluble phosphate than with AM inoculum. Mechanisms beyond those mediated by P must be involved in the AM-protectioe effect against salinity. The¹⁵N methodology used allowed the determination of N₂ fixation as influenced by different P applications compared to mycorrhizal inoculation. A lack of correlation between nodule formation and function (N₂ fixation) was evidenced in mycorrhizal-inoculated plants. In spite of the reduced activity per nodule in mycorrhizal-inoculated In spite of the reduced activity per nodule in mycorrhizal-inoculated plants, the N contents determined indicated the highest acquisition of N occurred in plants with the symbiotic status. Moreover, N and P uptake increased while Ca and Mg decreased in AM-inoculated plants. Thus P/Ca ratios and cation/anion balance in general were altered in mycorrhizal treatments. This study therefore confirms previous findings that AM-colonized plants have optional and alternative mechanisms available to satisfy their nutritive requirements and to maintain their physiological status in stress situations and in disturbed ecosystems.     

Influence of arbuscular mycorrhizae and phosphorus fertilization on growth, nodulation and N2 fixation (15N) inMedicago sativa at four salinity levels

The rose of an isolate of the arbuscular mycorrhizal (AM) fungusGlomus mosseae in the protection ofMedicago sativa (+Rhizobium meliloti) against salt stress induced by the addition of increasing levels of soluble salts was studied. The interactions between soluble P in soil (four levels), mycorrhizal inoculum and degree of salinity in relation to plant growth, nutrition and infective parameters were evaluated. Salt stress was induced by sequential irrigation with saline water having four concentrations of three salts (NaCl, CaCl₂, and MgCl₂).¹⁵N-labelled ammonium sulphate was added to provide a quantitative estimate of N₂ fixation under moderate to high salinity levels. N and P concentration and nodule formation increased with the amount of plant-available P or mycorrhizal inoculum in the soil and generally declined as the salinity in the solution culture increased from a moderate to a high level. The mycorrhizal inoculation protected the plants from salt stress more efficiently than any amount of plant-available P in soil, particularly at the highest salinity level applied (43.5 dS m^–1). Mycorrhizal inoculation matched the effect on dry matter and nutrition of the addition in the soil of 150 mg P kg^–1. Nevertheless the highest saline solution assayed (43.5 dS m^–1) affected more severely plants supplemented with phosphorus than those with the addition of mycorrhizal inoculum. Such a saline-depressing effect was 1.5 (biomass), 1.4 (N) and 1.5 (P) times higher in plants supplied with soluble phosphate than with AM inoculum. Mechanisms beyond those mediated by P must be involved in the AM-protectioe effect against salinity. The¹⁵N methodology used allowed the determination of N₂ fixation as influenced by different P applications compared to mycorrhizal inoculation. A lack of correlation between nodule formation and function (N₂ fixation) was evidenced in mycorrhizal-inoculated plants. In spite of the reduced activity per nodule in mycorrhizal-inoculated In spite of the reduced activity per nodule in mycorrhizal-inoculated plants, the N contents determined indicated the highest acquisition of N occurred in plants with the symbiotic status. Moreover, N and P uptake increased while Ca and Mg decreased in AM-inoculated plants. Thus P/Ca ratios and cation/anion balance in general were altered in mycorrhizal treatments. This study therefore confirms previous findings that AM-colonized plants have optional and alternative mechanisms available to satisfy their nutritive requirements and to maintain their physiological status in stress situations and in disturbed ecosystems.     

Perennial winged bean yield and nitrogen fixation improvement with soil fertility treatments of a typic eutrustox

The perennial legume, Winged Bean (Psophocarpus tetragonolobus (L) DC), has potential as a high protein food crop for the humid, tropical regions of the world. Edible seed pods, oil seed grain, leaves, flowers, and unique high protein tubers provide abundant nutritious components desirable for improved human diets. However, soil characteristics and fertility levels influence plant growth, yields and nitrogen fixation capability of this legume. Objectives of this study were to determine soil‐plant nutrient influences on vigorous regrowth, pod and tuber yields, nitrogenase (C₂H₂ red.) activity levels, and nodule cytosol components of the perennial Siempre cultivar grown on a Typic Eutrustox during three years, 1978–1980.

Available soil phosphorus was a first limiting plant nutrient during all three years of plant age. Effects of combined 100 mg P with 200 mg K/kg soil were highly significant for every parameter and plant age. Pod and seed yields more than doubled with PK addition compared to the check. Tuber growth, nodule mass and nitrogenase activity levels more than trebled with PK treatments as compared to the check. Both elemental P and K were significantly increased within the nodule cytosol of fertilized plants. Cytosol Na was significantly decreased with soil K additions. The best fit multiple regression was: nitrogenase = 1.99 nodule wt. + 6.34 tuber wt. + 0.39 tuber % N + 5.08 cytosol P + 1.55 cytosol K ‐ 0.45 cytosol Na, R² = 95.5, C.V. = 11.2%. The dominant nodule cytosol enzymes, aspartate aminotransferase (AST) and glutamine synthetase (GS), significantly increased with soil K additions regardless of P treatments. Glutamate dehydrogenase (GDH) and glutamate synthase (GOGAT) also contributed significantly with multiple regression for nitrogenase = 1.07 GS + 2.1 AST + 1.74 GOGAT ‐ 1.76 GDH + 12.89 Ureide, R² = .89, C.V. = 17.3%. Highly significant increases in nodule cytosol ureide composition with K soil additions has interest because of the role as a nitrogenous nonprotein component for many legumes. Increases in growth, nodulation and nitrogenase activity levels resulted with increased K levels of 0, 100, 200 and 300 mg K/kg soil when soil P and Ca were not limiting.     

Effect of Silicon on Growth, Physiology, and Cadmium Translocation of Tobacco (Nicotiana tabacum L.) in Cadmium-Contaminated Soil

Silicon(Si) offers beneficial effect on plants under cadmium(Cd) stress such as promoting plant growth and increasing resistance to heavy metal toxicity. In this study, a pot experiment was performed to study the role of Si in alleviating Cd toxicity in tobacco(Nicotiana tabacum L.) plants on a yellow soil taken from Guiyang, China. Nine treatments consisting of three concentrations of Cd(0, 1, and 5 mg kg~(-1)) together with three Si levels(0, 1, and 4 g kg~(-1)) were established. Plant growth parameters, Cd concentration,and the malondialdehyde(MDA), chlorophyll, and carotenoid contents were determined 100 d after transplanting of tobacco seedlings.Application of exogenous Si enhanced the growth of tobacco plants under Cd stress. When 5 mg kg~(-1) Cd was added, Si addition at 1 and 4 g kg~(-1) increased root, stem, and leaf biomass by 26.1%–43.3%, 33.7%–43.8%, and 50.8%–69.9%, respectively, compared to Si addition at 0 g kg~(-1). With Si application, the transfer factor of Cd in tobacco from root to shoot under both 1 and 5 mg kg~(-1) Cd treatments decreased by 21%. The MDA contents in the Si-treated tobacco plants declined by 5.5%–17.1% compared to those in the non-Si-treated plants, indicating a higher Cd tolerance. Silicon application also increased the chlorophyll and carotenoid contents by 33.9%–41% and 25.8%–47.3% compared to the Cd only treatments. Therefore, it could be concluded that Si application can alleviate Cd toxicity to tobacco by decreasing Cd partitioning in the shoots and MDA levels and by increasing chlorophyll and carotenoid contents, thereby contributing to lowering the potential health risks of Cd contamination.     

Behavior and respiration responses of the earthworm Eisenia fetida to soil arsenite pollution

Soil arsenic (As) pollution from mining and industrial sources is a serious issue in China. Earthworms are considered ecosystem engineers and contribute to soil fertility development and maintenance of soil physico-chemical properties. In this study, earthworms were exposed to soils with different sodium arsenite concentrations (0, 5, 20, and 80 mg As kg^-1) for 60 d to investigate the changes in soil properties and the responses of the earthworms (e.g., burrowing activity and respiration). Earthworm burrowing activity decreased with increasing arsenite concentrations, and earthworm respiration was significantly lower in soils with 20 and 80 mg As kg^-1 compared to 0 mg As kg^-1. Changes in soil properties were also observed after incubation of As-amended soil with earthworms. Specifically, soil pH decreased, while soil electrical conductivity and contents of soil NH₃^--N, Olsen-P, and available K increased. Our results suggest that arsenite negatively impacts the metabolic activity of earthworms, leading to reduced burrowing activity, which in turn modifies the effects of earthworms on soil fertility and remediation.     

Effects of Arbuscular Mycorrhizal Inoculation and Phosphorus Application on Yield and Nutrient Uptake of Yam

To be sustainable, production in the traditional yam cropping system, faced with declining soil fertility, could benefit from yam–arbuscular mycorrhizal (AM) symbiosis, which can improve nutrient uptake, disease resistance, and drought tolerance in plants. However, only limited information exists about AM colonization of yam. A pot experiment was conducted to collect information on the response of two genotypes (Dioscorea rotundata accession TDr 97/00903 and D. alata accession TDa 297) to AM inoculation (with and without) and phosphorus (P) (0, 0.05, 0.5, and 5 mg P kg^–1 soil). Factorial combinations of the treatments were arranged in a completely randomized design with four replicates. The percentage of AM colonization was significantly lowered at 5 mg P kg^–1 soil rate in mycorrhizal plants of both genotypes. TDr 97/00903 showed more responsiveness to AM inoculation than TDa 297. The greatest AM responsiveness for tuber yield (52%) was obtained at 0.5 mg P kg^–1 soil rate for TDr 97/00903. Mycorrhizal inoculation significantly increased root dry weight and tuber yield of TDr 97/00903 with the greatest values obtained at the 0.5 mg P kg^–1 soil rate. Arbuscular mycorrhizal inoculation did not lead to significant (P < 0.05) changes in root length and area. Phosphorus application significantly increased the shoot dry weight and root diameter of TDa 297. Uptake of P was greatest at 0.5 mg P kg^–1 soil in both genotypes and was significantly influenced by AM inoculation. Nitrogen (N) and potassium (K) uptake were greatest in mycorrhizal plants at 0.05 mg P kg^–1 soil for TDr 97/00903 but at 0.5 mg P kg^–1 soil of nonmycorrhizal plants of TDa 297. The increased tuber yield and nutrient uptake observed in the mycorrhizal plants indicate the potential for the improvement of nutrient acquisition and tuber yield through AM symbiosis.     

中国亚热带稻田土壤碳氮含量及矿化动态

Dynamics of soil organic matter in a cultivation chronosequence of paddy fields were studied in subtropical China. Mineralization of soil organic matter was determined by measuring CO2 evolution from soil during 20 days of laboratory incubation. In the first 30 years of cultivation, soil organic C and N contents increased rapidly. After 30 years, 0-10 cm soil contained 19.6 g kg^-1 organic C and 1.62 g kg^-1 total N, with the corresponding values of 18.1 g kg^-1 and 1.50 g kg^-1 for 10-20 cm, and then remained stable even after 80 years of rice cultivation. During 20 days incubation the mineralization rates of organic C and N in surface soil （0-10 cm） ranged from 2.2% to 3.3% and from 2.8% to 6.7%, respectively, of organic C and total N contents. Biologically active C size generally increased with increasing soil organic C and N contents. Soil dissolved organic C decreased after cultivation of wasteland to 10 years paddy field and then increased. Soil microbial biomass C increased with number of years under cultivation, while soil microbial biomass N increased during the first 30 years of cultivation and then stabilized. After 30 years of cultivation surface soil （0-10 cm） contained 332.8 mg kg^-1 of microbial biomass C and 23.85 mg kg^-1 of microbial biomass N, which were 111% and 47% higher than those in soil cultivated for 3 years. It was suggested that surface soil with 30 years of rice cultivation in subtropical China would have attained a steady state of organic C content, being about 19 g kg^-1.     

Selenium in geo-ecosystem and its relation to endemic diseases in China

In China, Se deficiency is associated with Keshan disease and Kaschin-Beck disease. This paper further demonstrates this relationship by studying the Se levels in the geo-ecosystem substances, including soil, plant, herbage, food grain, wool and human hair in disease affected areas and in control non-disease areas. Buteha Qi and Tailai counties in Northeast China were selected as the typical areas for these studies. The results show that in affected areas the average Se contents were: for soil, 0.125mg kg¹, plants, 0.057 mg kg^?1; herbage, 0.026 mg kg¹; wheat, 0.012 mg kg^?1; maize, 0.008 mg kg¹; wool, 0.046 mg kg^?; and human hair, 0.144 mg kg¹. In the control area, the substances mentioned above all had higher Se contents compared with those in the affected area. Thus, it was shown that the geo-ecosystem of the affected area was low in Se, an important reason for the occurrence of Keshan disease and Kaschin-Beck disease. In recent years, some increase in the Se level of human hair was also found in the studied areas. This increase coincides with the decline, since the mid 1980's, of the incidence of the two diseases. An elevation in hair Se may, therefore, be a good indication of an improved Se intake of the subject population.

     

Soil fertility effects on nodulation,nitrogen fixation,and yields of guar, (Cyamopsis tetragonoloba (L.) Taub.), grown on a typic eutrustox

Guar (Cyamopsis tetragonoloba (L.) Taub.) is a legume of unusual industrial importance due to increased utilization of Guar gum, ‘Guran,’ in numerous modern manufacturing and food processes. Guar has high tolerance of drought and inhibitory soil characteristics and has been utilized for many centuries within the subhumid regions of the Indo‐Pakistan subcontinent. Nodulation, nitrogen fixation, and yields of high protein seed with desirable Guran content are improved by favorable soil fertility. Plant growth, seed yields, and nodulation are influenced by plant population density.

Top Growth quadratically increased with plant population densities of 10, 25, and 50 plants per meter² for P and P+K treatments. Highest seed yield and nodule development resulted for all soil fertility treatments with 25 plant per meter². Ontogenetic response from anthesis to full seed maturity resulted with increased nodulation significantly correlated (r = 0.67) with top growth. However, nitrogenase activity levels plant‘¹ declined significantly with plant maturity. Nodule cytosol enzyme activity levels at anthesis were: allantoinase (ALTN) 29.5 IU, aspartate transaminase (AST) 19.3 IU, glutamine synthase 12.5 IU, uricase (URC) 2.25 IU, and allantoicase (ALTC) 0.14 IU g^‐1 fresh nodule. Cytosol composition included ureidoglycolates (ureides) 425.8 μmol, amine‐amide content 29.5 μmol, nitrate 1.95 μmol, pyruvate 0.21 μimol, and oketoglutarate 0.09 μmol g‘¹ fresh nodule. Plant nutrient composition of nodule cytosol was K 394.9 jig, P 59.4 μg, Ca 48.9 μg, Mg 39. μg, and Na 19.0 μg g^‐1 fresh nodule. Precise histology with Giemsa and PAS procedures were essential for microscopy with cellular compartmentalization of purine enzymatic transformations governing nitrogenase activity and nodule development.     

Effect of vesicular-arbuscular mycorrhizae and zinc application on dry matter and zinc uptake of greengram (Vigna radiata L. Wilczek)

Summary In a greenhouse study we examined the effects of vesicular-arbuscular mycorrhizae (VAM) inoculation, using Glomus macrocarpum and of Zn application on dry matter production and Zn uptake by greengram in two mollisols. The VAM inoculation significantly increased the dry weight of different plant parts and the Zn uptake in both soils. Inoculated plants showed a greater response to the application of Zn at 2.5 and 5.0 mg kg^-1 soil in a Zn deficient clay loam soil. The inoculated plants also absorbed — more water than the uninoculated plants. Mass flow and diffusion were the principal processes by which Zn reached the plant roots; mass flow was particularly important in the absence of VAM in a sandy soil fertilized with higher Zn doses (5 and 10 mg kg^-1 soil). The greater supply of Zn to inoculated roots was attributed to an apparent diffusion process rather than to mass flow of Zn.     

水氮耦合对黍稷幼苗形态和生理指标的影响

盆栽试验条件下,研究水氮耦合对黍稷幼苗形态和生理指标的影响。结果表明,在供水量相同条件下,黍稷幼苗株高、叶面积、根系总表面积、总体积与总根长均随施氮量的增加而增加,供水量相同时根冠比随施氮量增加而降低;施氮量相同条件下随灌水量的增加黍稷幼苗各指标呈相似变化趋势,各处理与对照差异均达到了显著水平。不同的水氮处理组合,黍稷叶片叶绿素含量差异显著,以高水高氮的W3N3处理[土壤田间持水量70%~80%,尿素用量4.6 g.kg 1(土)]为最大值,低水低氮的W1N1处理[土壤田间持水量30%~40%,尿素用量为0 g.kg 1(土)]为最小值;灌水量相同,叶绿素含量随施氮量增加而增加;施氮量相同,叶绿素含量也随灌水量增加而增加,水分和氮素对叶片叶绿素含量的影响表现为明显的协同效应;黍稷幼苗叶片电解质外渗率的变化趋势则相反。黍稷根系超氧化物歧化酶活性以低水中氮的W1N2处理[土壤田间持水量30%~40%,尿素用量2.3 g.kg 1(土)]为最高,达213.71 U.g 1(FW);W3N3最低,为72.93 U.g 1(FW)。水分相同条件下黍稷幼苗根系过氧化物酶活性、丙二醛含量、可溶性糖含量均随施氮量的增加而降低,施氮量相同时则随灌水量的增加而降低。根系活力则相反,且各处理间差异均达到显著水平。在干旱胁迫条件下,适当的增施氮肥可以提高苗期黍稷的叶绿素含量和根系活力,增加根系总表面积、总体积与总根长,降低根系丙二醛含量,在一定程度上缓解干旱胁迫的影响。     

水稻品种和砷污染对土壤溶解性有机碳氮的影响

选取有机质含量和pH不同的2种水稻土(黄泥田和红泥田),通过盆栽实验研究砷(As)污染条件下,种植9个水稻品种对土壤溶解性有机碳(DOC)和溶解性有机氮(DON)含量的影响,分析水稻品种、As污染和土壤类型的相对影响与交互作用.结果表明,水稻品种显著影响了土壤DOC和DON的变化,在水稻收获后,DOC平均含量的大小顺序为杂交稻(41.09±0.92 mg kg-1)＞籼稻(38.10±1.53 mg kg-1)＞粳稻(37.74± 1.37 mg kg-1);DON平均含量的大小顺序为粳稻(2.94± 0.40 mg kg-1)＞杂交稻(2.61±0.42 mg kg-1)＞籼稻(1.45± 0.17 mg kg-1).As污染降低了土壤DOC和DON的含量,但不同品种水稻的响应不同.与对照相比,As污染条件下,黄泥田和红泥田中DOC平均含量分别下降了14.4％和11.1％,DON平均含量分别下降了65.0％和44.7％;DOC在种植杂交稻后降幅最小,而DON在种植籼稻后降幅最小.在两种水稻土中,黄泥田的DOC和DON平均含量高于红泥田,在没有As污染条件下,分别高22.4％和45.8％,这与黄泥田有机质含量和pH高有关.水稻品种、As污染和土壤类型对DOC和DON变化的影响不同,3个因子对DOC变化的相对贡献率分别为7.7％、15.5％和27.6％,对DON变化的相对贡献率分别为14.7％、24.2％和2.0％.     

Growth,survival, and heavy metal (Cd and Ni) uptake of spinach (Spinacia oleracea) and fenugreek (Trigonella corniculata) in a biochar‐amended sewage‐irrigated contaminated soil

Irrigation of arable land with contaminated sewage waters leads to the accumulation of trace metals in soils with subsequent phyto‐/zootoxic consequences. In this study, biochar derived from cotton sticks was used to amend an agricultural silt‐loam soil that had been previously irrigated with trace metal contaminated sewage waters. Metal accumulation and toxicity to spinach (Spinacia oleracea) and fenugreek (Trigonella corniculata) was investigated by measuring concentrations of Cd and Ni in plant tissues and various photosynthetic and biochemical activities of plants. Positive impacts of biochar on both spinach and fenugreek were observed in terms of biomass production that increased from 29% to 36% in case of spinach, while for fenugreek this increase was 32% to 36%. In the control treatment there was an increase in malondialdihyde, soluble sugar, and ascorbic acid contents, indicating heavy metal stress. Biochar applications increased soluble proteins and amino acids in plants and reduced the uptake of Cd from 5.42 mg kg^?1 at control to 3.45 mg kg^?1 at 5% biochar amended soil and Ni (13.8 mg kg^?1 to 7.3 mg kg^?1 at 5% biochar) by the spinach plants. In fenugreek, the Cd was reduced from 7.72 mg kg^?1 to 3.88 mg kg^?1 and reduction in Ni was from 15.45 mg kg^?1 to 9.46 mg kg^?1 at 5% biochar treated soil, reducing the possibility of transfer up the food chain. This study demonstrates that the use of biochar made from cotton‐sticks, as an amendment to arable soils that have received contaminated irrigation water, could improve plant growth and decrease Cd and Ni uptake to crops, alleviating some of the negative impacts of using sewage waters on arable land.     

铅锌矿区分离丛枝菌根真菌对万寿菊生长与吸镉的影响

盆栽试验研究了土壤不同施Cd水平(0、20、50 mg kg-1)下,接种矿区污染土壤中丛枝菌根真菌对万寿菊根系侵染率、植株生物量及Cd吸收与分配的影响。结果表明:接种丛枝菌根真菌显著提高了Cd胁迫下万寿菊的根系侵染率和植株生物量;随着施Cd水平提高,各处理植株Cd浓度和Cd吸收量显著增加。各施Cd水平下万寿菊地上部Cd吸收量远远高于根系Cd吸收量,尤其在20 mg kg-1施Cd水平下,接种处理地上部Cd吸收量是根系的3.90倍,对照处理地上部Cd吸收量是根系的2.33倍;同一施Cd水平下接种处理地上部Cd吸收量要显著高于对照。总体上,试验条件下污染土壤中分离的丛枝菌根真菌促进了万寿菊对土壤中Cd的吸收,并增加了Cd向地上部分的运转,表现出植物提取的应用潜力。     

Adequate range of boron nutrition is more restricted for root nodule development than for plant growth in young soybean plant

A pot experiment was conducted under growth chamber conditions to determine the lower and upper critical levels of boron (B) for plant growth, nodule development, and nodule acetylene reduction activity (ARA) in young soybean plants. Plants of a soybean cultivar, Tachinagaha, were grown in pots containing river sand to which a nutrient solution with different B levels was added and were inoculated with Bradyrhizobium japonicum A1017. At 8, 12, and 16 d after sowing (DAS), among the plants supplied with the solution at 0, 1.0, and 2.0 mg B L^-1 , plants with 1.0 mg B L^-1 showed the highest values for dry shoot and fresh root weight, root length, total number of developing nodules and meristematic nodules (DMN), and ARA. At 20 DAS plants grown with 11 B levels (0-2.0 mg L^-1) were compared. The B critical deficiency levels for soybean dry shoot weight, fresh root weight, root length, DMN, number of complete nodules, and ARA were approximately 46, 35, 34, 57, 60, and 50 mg B kg^-1 dry matter, and the critical toxicity levels were approximately 114, 137, 134, 97, 104, and 89 mg B kg^-1 dry matter, respectively. The optimum B levels for the growth characters were approximately 34 to 137 mg B kg^-1 dry matter. The optimum range of B levels for nodule formation and function was more restricted than that for the growth characters. Based on the results of treatments with various B concentrations, 0.4 mg B L^-1 was found to be the concentration most beneficial for all the growth characters including nodule formation at the early stage (20 DAS) of development of soybean plants.     

Bioaccumulation of Lead by Indian Mustard in a Loamy Sand Soil Artificially Contaminated with Lead: Impact on Plant Growth and Uptake of Metal

In a screen-house study, the effects of artificially contaminating the soil with lead (Pb) at levels ranging from 0 to 1500 mg kg^?1 soil on the growth and uptake of Pb and micronutrients by Indian mustard [Brassica juncea (L.) Czern.] grown on a loamy sand soil (Typic Ustorthent) were investigated. The crop was grown for 60 days with adequate basal fertilization of nitrogen, phosphorus, and potassium, and dry matter was recorded. The plants were analyzed for total Pb and micronutrients, and the soil was analyzed for diethylenetriaminepentaacetic acid (DTPA)-extractable Pb. The DTPA-extractable Pb measured before sowing of Indian mustard increased consistently and significantly with increase in rates of Pb application to soil. It increased from 0.65 mg kg^?1 in the control to 199.8 mg kg^?1 in soil treated with 1500 mg Pb kg^?1 soil. Significant reduction in the dry-matter yield of Indian mustard occurred with Pb applications of 500 mg kg^?1 soil and greater. The concentration as well as uptake of Pb by Indian mustard increased significantly over control at all rates of its application. It increased from 9.4 μg pot^?1 in the control to 220.6 μg pot^?1 at Pb application of 1500 mg kg^?1 soil. Applications of Pb to the soil decreased the concentration of micronutrients in plants, but a significant reduction occurred only for iron at rates greater than 500 mg Pb kg^?1 soil. However, the uptake of iron, manganese, and copper registered a significant decline at Pb application of 500 mg kg^?1 and greater and that of zinc at 750 mg kg^?1 and greater. In a Typic Ustorthent soil, a DTPA-extractable Pb level of 59.5 mg kg^?1 and plant content of 44.2 μg Pb g^?1 dry matter was found to be the upper threshold levels of Pb for Indian mustard. This study suggests that once the soil is contaminated by Pb, it remains available in the soil for a long time, and such soils, if ingested with food crops, may be a significant source of Pb toxicity to both humans and grazing animals.