Iron oxide‐humic acid coprecipitates as iron source for cucumber plants

In soil, iron (Fe) solubility depends on complex interactions between Fe minerals and organic matter, but very little is known about plant availability of Fe present in Fe oxides associated with humic substances. For this purpose, this study investigates the effect of Fe mineral crystallinity in the presence of humic acids (HA) on Fe availability to plants. Four Fe–HA mineral coprecipitates were prepared, either in the presence or absence of oxygen, i.e., two goethite (G)‐HA samples containing large amounts of Fe as nanocrystalline goethite and ferrihydrite mixed phases, and two magnetite (M)‐HA samples containing crystalline magnetite. Bioavailability studies were conducted in hydroponic systems on cucumber plants (Cucumis sativus L.) grown under Fe deficient conditions and supplied with the Fe–HA coprecipitates containing goethite or magnetite. Results showed that plants grown in the presence of Fe–HA coprecipitates exhibited a complete recovery from Fe deficiency, albeit less efficiently than plants resupplied with Fe‐chelate fertilizer used as control (Fe‐diethylene triamine penta acetic acid, Fe‐DTPA). However, the supply with either G‐ or M–HA coprecipitates produced different effects on plants: G–HA‐treated plants showed a higher Fe content in leaves, while M–HA‐treated plants displayed a higher leaf biomass and SPAD (Soil–Plant Analysis Development) index recovery, as compared to Fe‐DTPA. The distribution of macronutrients in the leaves, as imaged by micro X‐ray fluorescence (µXRF) spectroscopy, was different in G–HA and M–HA‐treated plants. In particular, plants supplied with the poorly crystalline G–HA coprecipitate with a lower Fe/HA ratio showed features more similar to those of fully recovered plants (supplied with Fe‐DTPA). These results highlight the importance of mineral crystallinity of Fe–HA coprecipitates on Fe bioavailability and Fe uptake in hydroponic experiments. In addition, the present data demonstrate that cucumber plants can efficiently mobilize Fe, even from goethite and ferrihydrite mixed phases and magnetite, which are usually considered unavailable for plant nutrition.     

Effect of cultivation on physical speciation of humic substances and plant nutrients in aggregate fractions of crusting soil from Zimbabwe

The effects of clearing and cultivation of Rhodic Kandiustalf from Mazowe (Zimbabwe) were studied by quantifying humic substances and plant nutrients (available and exchangeable cations) in aggregate fractions. It was found that cultivation was associated with a relative depletion of plant nutrients in coarse aggregate fractions (i.e. a virtual migration of soil fertility towards microaggregate soil compartments). This effect was connected with the organic matter distribution patterns in the physical fractions: cultivation has led to a relative concentration of the colloidal fractions (humic acids and fulvic acids) in the microaggregates, accompanied by a selective depletion of the latter organic fraction. It is suggested that the increased physicochemical importance of the microaggregate fractions after cultivation may be an index for the disruption of the original soil structure leading to crust formation and it may also be related to the effect of ploughing on the humification processes and the mobility of the colloidal organic fractions. Received: 1 August 1996     

Effects of fractions of coal-derived humic substances on seed germination and growth of seedlings (Lactuga sativa and Lycopersicum esculentum)

Summary Lettuce and tomato seeds were treated in Petri dishes with a humic acid derived from an oxidized coal and with fractions of the same humic acid obtained by ultrafiltration through membranes of known molecular cutoff and by extracting with buffers set at pH 4 and pH 5. The unfractionated humic acid was applied at 40, 100, 1000, and 5000 mg l^-1 whereas the humic fractions were applied at 40, 100, and 200 mg l^-1. Germination parameters such as the number of total germinated seeds, the velocity of seed germination, the fresh weight and dry weight of total seedlings were measured and related to the chemical and physicochemical properties of the humic material. No increase in the germination percentage or the germination rate was observed for either lettuce or tomato seeds. The fresh weight of total seedlings and per seedling increased in treatments with unfractionated humic acid with increasing concentrations for both lettuce and tomato plants without showing signs of growth inhibition up to 5000 mg l^-1. This was attributed to cell elongation and more efficient water uptake. For the lettuce, the fresh weight both of total seedlings and per seedling was enhanced by treating the seeds with fractions of low molecular weight and high content of acidic functions, whereas the dry weight both of total seedlings and per seedling did not change with the humic fraction used. For the tomato seeds in contrast, the dry weight both of total seedlings and per seedling was increased by the use of unfractionated humic acid and by some of the humic fractions. An uptake of humic material by growing tomato seedlings was inferred.     

溶液培养条件下腐殖酸对铁异化还原的影响

腐殖酸对土壤和水体环境中铁(Fe)的还原过程有重要影响。本文采用从山西大同风化煤、河南巩县褐煤、云南昆明滇池底泥中提取制备的腐殖酸,通过布置培育试验并接种土壤悬液,研究了不同来源的腐殖酸对无定形氧化铁异化还原的影响。结果表明:单独添加腐殖酸对氧化铁的还原几乎没有影响;而当同时添加腐殖酸与葡萄糖时,培养基质中氧化铁的还原过程显著加强;腐殖酸浓度越高对氧化铁还原的促进作用越明显。不同来源的腐殖酸因其复杂程度和结构不同,对氧化铁还原的促进作用有明显差异,其中山西大同风化煤提取的腐殖酸促进作用最大,云南昆明滇池底泥和河南巩县褐煤提取的腐殖酸之间则无显著差异。     

Isoelectric focusing of humic substances on ultrathin polyacrylamide gels: evidence of fingerprint performance

Differentiated interactions between humic substances and isoelectric focusing-carrier ampholytes were demonstrated by comparing specific absorption ratios from the supernatant after precipitation with 2 M HCl and with acid ampholytes (pH 2–4) containing both carboxylic and sulphate groups. An increasingly stronger interaction was observed when comparing soil humic substances to those of synthetic origin or those extracted from young reclaimed soil material. Electrofocusing of the humic substances under study revealed a fingerprint-like quality; the band patterns observed were consistent with the concept of three main fractions.     

A comparative survey of recent results on humic-like fractions in organic amendments and effects on native soil humic substances

The main scope of the wide use of organic amendments of various origin and nature in modern agriculture is to increase and/or restore the organic matter content in organically poor or depleted soils in order to maintain and/or increase crop production and reduce soil exposure to degradation, erosion, desertification and pollution. The agronomically efficient and environmentally safe use of any organic amendment requires, however, an adequate control not only of the chemical quality of the humic substance (HS)-like fractions contained, which is an important indicator of the maturity and stability achieved by organic matter in the amendment, but also of the effects that these HS may have on native soil HS. In this review, the most recent results obtained on this topic by the research groups operating in Bari, Italy, and in Madrid, Spain, are discussed comparatively with results recently published by other research groups. Overall, HS-like components of organic amendments are characterized by higher aliphatic character and molecular heterogeneity, lower contents of O, acidic functional groups and organic free radicals, and lower degrees of aromatic ring polycondensation, polymerization and humification than native soil HS. These differences are less evident for composted materials. The composition, structure and functionalities of HS in amended soils may be affected in different ways and at various extents on dependence of the nature, origin and rate of amendment. In general, these properties are intermediate between those of the unamended soil HS and the HS-like fractions in the amendment, but generally resemble more the former than the latter, especially with increasing time after amendment application.     

Methane suppression by iron and humic acids in soils of the Arctic Coastal Plain

Methane–climate interactions are reasonably well understood; the biogeochemical controls on net methane fluxes are less so. Within anoxic soils, alternative electron acceptors such as iron and humic substances influence microbial metabolic function, and thus affect the amount of carbon lost as methane (CH₄). We present three years of data from wet sedge tundra landscapes near Barrow, Alaska that show an inverse relationship between dissolved iron and CH₄ concentrations. We found increasing organic layer thickness related to increases in active layer organic matter content, and decreases in both bulk density and extractable iron. Organic layer depth was also a good proxy for carbon dioxide (CO₂) and CH₄ dynamics, with increasing organic layer depths relating to lower dissolved iron, higher amounts of dissolved CH₄, and lower CO₂:CH₄ ratios in the upper active layer. Net CH₄ fluxes were also significantly suppressed following the experimental addition of iron and humic acids. Iron and humic acid treatment effects were indistinguishable for CH₄ net flux; in contrast, post-treatment CH₄ fluxes were an average of 0.74-fold the control treatment flux rates. These results suggest that in-situ CH₄ production is tied to alternative electron acceptor availability, and that organic layer thickness is a good predictor of biogeochemical controls on CH₄ fluxes in wet-sedge Arctic Alaskan tundra.     

淹水还原条件下红壤中葡萄糖及腐殖酸对铁锰形态的影响

通过设置不同的葡萄糖/腐殖酸配比模拟还原性土壤体系,考察长期(约74 d)淹水培养过程中铁锰元素在土壤溶液/矿物相中的分布形态演变。结果表明:在淹水培养初期,葡萄糖的添加可以促进铁锰离子的还原溶出,同时土壤中可交换态和酸可提取态铁、以及可交换态锰的含量也会随之增加;而腐殖酸的添加则会促进土壤中可氧化态铁/锰含量的升高。随着培养时间的增加,铁锰离子浓度及各个土壤提取形态的铁锰含量大多呈现降低趋势,铁锰元素逐渐转化成提取性更低的矿物形态。因此,淹水环境中铁锰还原溶出-分布形态演变受到土壤中有机物质种类和含量的显著影响,呈现出不同的金属移动性和生物有效性。     

水稻根尖铁的积累及附着形态研究

以铁毒耐性水稻(Oryza sativa L.)品种"9308"为材料, 利用火焰原子吸收光谱法和化学浸提法研究0～10 mm段水稻根尖铁的积累及附着形态.结果表明: 高Fe2+(400 -mol·L-1)胁迫下, 0～2 mm段水稻根尖铁含量最高; 随着Fe2+浓度的升高, 根边缘细胞铁含量也明显增大; 初生根上不同形态铁的含量为铁锰氧化物态>残渣态>有机态>可交换态>碳酸盐态.以上结果表明, 水稻根尖0～2 mm段是过量铁的主要作用位点, 铁的附着形态以紧密结合态为主, 包围在外的根边缘细胞能固定过量铁.     

Effect of commercial amino acids on iron nutrition of tomato plants grown under lime‐induced iron deficiency

The objective of this work was to study the effect of root and foliar application of two commercial products containing amino acids from plant and animal origin on iron (Fe) nutrition of tomato seedlings cultivated in two nutrient media: lime and normal nutrient solutions. In the foliar‐application experiment, each product was sprayed with 0.5 and 0.7 mL L^–1 2, 7, 12, and 17 d after transplanting. In the root application experiment, 0.1 and 0.2 mL L^–1 of amino acids products were added to the nutrient solutions. In both experiments, untreated control plants were included as well. Foliar and root application of the product containing amino acids from animal origin caused severe plant‐growth depression and nonpositive effects on Fe nutrition were found. In contrast, the application of the product from plant origin stimulated plant growth. Furthermore, significantly enhanced root and leaf Fe^III‐chelate reductase activity, chlorophyll concentration, leaf Fe concentration, and Fe^II : Fe ratio were found in tomato seedlings treated with the product from plant origin, especially when the amino acids were directly applied to the roots. These effects were more evident in plants developed under lime‐induced Fe deficiency. The positive results on Fe uptake may be related to the action of glutamic acid, the most abundant amino acid in the formulation of the product from plant origin.     

Contribution of humic substances as a sink and source of carbon in tropical floodplain lagoons

Purpose

We evaluated the decay of humic (HA) and fulvic acids (FA) in order to discuss the contribution of these substances as a sink and source of carbon in a tropical lagoon.

Materials and methods

Experiments were conducted under aerobic and anaerobic conditions using FA and HA isolated from decomposition of Oxycaryum cubense submitted to 10 and 60 days of degradation. HA and FA were added to water samples from a tropical floodplain oxbow system, the Infernão Lagoon. The mineralization chambers were incubated in the dark at 21.0 °C. The carbon balance, electrical conductivity, pH, and optical density were measured over 95 days.

Results and discussion

The results from the carbon budget were fitted with a first-order kinetics model. The mineralization of refractory fractions predominated for both FA and HA. Overall, although the mineralization pathway yields varied according to the type of resource and oxygen availability, the mineralization half-lives were quite similar (49 to 64 days), suggesting a similar microbial catabolism efficiency during the decay of humic substances. The short-term routes are represented by biochemical oxidations, and the immobilization and labile fractions (varying from 0 to 30%) of FA and HA supported these processes. A yield varying from 61.0 to 91.3% represents a carbon source degradation in the middle term (ca. 2 months) considering the ecosystem.

Conclusions

In tropical floodplain lagoons, there are three carbon routes: (i) the IN₁, representing a short-term pathway (hours to days) in the carbon transformation and (ii) IN₃, a middle-term carbon source from HA and FA mineralization to the water column and subsequently to the atmosphere. A third route (IN₂) supported the heterotrophic metabolism of the lagoon acting as a transitory sink of carbon.

     

Behavior of iron‐inefficient plants when grown in combinations of calcareous and noncalcareous soils

Abstract

When Fe‐inefficient plants were grown in mixtures of calcareous Hacienda loam soil and noncalcareous Yolo loam soil compared with plants grown in unmixed soils, characteristics and composition of the plants including Fe deficiency were generally intermediate to those with either soil alone. Noncalcareous soil adjacent to calcareous soil allowed PI 54619–5–1 soybeans (Glycine max L.) to obtain sufficient Fe.     

Critical nitrate levels for squash,cucumber and melon plants

Abstract

Squash (Cucurbita pepo), cucumber (Cucumis sativus) and sweet melon (Cucumis dudain) plants were grown in sand culture with N as the variable and were harvested at the early flowering stage. The plants at this time showed a definite gradation of symptoms from severe to no deficiency of N. The tops were separated into leaves and stems. Leaves were separated into young, mature and old and then subdivided respectively into petioles and blades. The petioles were analyzed for NO₃‐N. The critical NO₃‐N concentration for squash, cucumber and melon on a dry basis was 1000, 2000 and 3000 ppm, respectively. A relatively high concentration of NO₃‐N in the nutrient solution decreased the growth of squash and cucumber plants significantly, but had no effect on melon plants. Melon plants can tolerate relatively high concentrations of N0,‐N in the plant tissues, while squash and cucumber cannot.     

Dynamics of humic fractions and microbial activity under no-tillage or reduced tillage,as compared with native pasture (Pampa Argentina)

Humic fractions, arginine ammonification and soil respiration were monitored in spring, summer and autumn 1999 in natural pasture soil and in no-tillage or reduced-tillage soil under maize. The Typic Argiudoll soils, typical of the Argentine rolling pampa, can be structurally unstable, particularly when conventionally tilled, a form of soil management affecting the humification process. The no-tillage soil had a lower content of fulvic acids than the reduced-tillage soil in spring and summer, probably because the humification process was favored by residue management in no-tillage soil, with a significant increase in the most stable fraction. Both arginine ammonification and CO₂ were significantly correlated with the humic acids and humin contents. No significant correlation was found with fulvic acids,probably due to the lability and high variability of this fraction. A high correlation was found between arginine ammonification and CO₂. The highest index values were generally observed in natural pasture soil, whereas no-tillage soils showed a higher index value than reduced-tillage soils throughout, confirming the hypothesis that humification is more intense in the presence of organic residues.     

腐殖酸对钾在褐土中迁移和转化的影响

采用室内土柱实验研究了腐殖酸与钾共施时腐殖酸对钾在褐土施肥点附件微域中迁移和形态转化的影响。研究结果表明,与单施KCl处理相比,共施腐殖酸没有明显改变肥料钾在褐土中的迁移距离,在培养7天时增加了肥际微域中的水溶性钾含量,而在培养28天时则降低了其含量;共施腐殖酸明显增加了交换性钾含量以及在土壤中的迁移量,但减少了非交换性钾的含量和迁移量。说明共施腐殖酸减少了土壤晶格对钾离子的固定,提高了外源钾在褐土中的有效性。     

Depth distribution of humic substances in Andosols in relation to land management and soil erosion

Although Andosols are relatively resistant to water erosion, they can be severely affected by changes in land use, resulting in accelerated erosion and loss of soil organic matter (SOM). We hypothesized that if the contents of specific components of SOM and organo–metallic complexes (humic acids –HAs–, fulvic acids –FAs–, sodium pyrophosphate extractable carbon –C_p–, aluminium –Al_p–, and iron –Fe_p–) consistently tend towards certain ratios in A and B horizons, they could be used to identify soils denuded by erosion. To test this hypothesis, we investigated the vertical distribution of humus components and certain ratios, namely C‐HA/C‐FA, C‐FA/total organic C (TOC), C_p/TOC and (Fe_p + Al_p)/C‐FA, in representative profiles of andic soils located in natural ecosystems with different degrees of human disturbance. Furthermore, we analysed these parameters in the topsoil of a natural protected area and in adjacent soils under different land use scenarios (natural reserve vs. traditional exploitation). We found that the ratios of C‐HA/C‐FA and, to a lesser extent, of C‐FA/TOC and C_p/TOC changed with depth in the selected soil profiles, but the values were characteristic of each type of soil horizon. The values of these ratios in the topsoils of the disturbed areas were closer to a B horizon than an A horizon. This pattern may be superimposed on pre‐existing gradients, such as those related to the type of natural vegetation. The use of these indices emerges as a possible land use and erosion indicator.     

Digestion of peptidic residues in humic substances by an alkali-stable and humic-acid-tolerant proteolytic activity in the gut of soil-feeding termites

Previous feeding experiments have shown that soil-feeding termites (Termitidae: Termitinae) preferentially mineralize the peptidic component of synthetic humic acids, but nothing was known about the mechanism involved in digestion. Here, we studied the hydrolysis of humus-stabilized peptides in gut extracts of Cubitermes orthognathus by measuring the release of radiolabel from ¹⁴C-peptide-labeled synthetic humic acids. Gut extracts exhibited proteolytic activity over a wide pH range (from 4 to 12) with a maximum at about pH 8. The highest activity was located in the gut section containing the midgut and the extremely alkaline (up to pH 12) mixed segment. Chemical hydrolysis at in situ pH (up to pH 12) was negligible. Proteolytic activity in the hindgut fluid was generally relatively low, but alkaline proteases dominated in the anterior hindgut. When compared to other alkaline proteases, the proteolytic activity of gut extracts had a higher alkali-stability and tolerance to humic acids than subtilisin and an alkaline protease of Streptomyces griseus. Gut extracts also hydrolyzed the peptidic component of synthetic humic acids more efficiently than the commercial enzymes. Together with previous results, this study strongly supports the hypothesis that soil-feeding termites mobilize and digest the peptidic component of organic nitrogen in soil humic substances by a combination of proteolytic activities and extreme alkalinity in their intestinal tract.     

健康与罹病黄瓜根际微生物数量及真菌区系研究

对健康与罹病黄瓜根际微生物数量及真菌区系研究结果表明 ,健康与罹病黄瓜植株根际微生物数量存在明显差异 ,其中罹病黄瓜植株根际真菌、细菌数量明显高于健康黄瓜植株 ;而健康与罹病黄瓜植株放线菌数量无明显差异 ;健康黄瓜植株根系真菌种类为 8种左右 ,常见真菌 3～ 4种 ,优势种的菌落数占总菌落数的 2 5 %～ 5 6 %。罹病植株根系真菌种类为 2～ 4种 ,仅有稀少真菌和优势种 ,且优势种的菌落数占其总菌落数的 88%以上 ,处于绝对优势 ,经证明其系引起黄瓜枯萎病的尖孢镰刀菌     

特定pH条件下Ca2+/Cu2+引发胡敏酸胶体凝聚的比较研究

土壤腐殖质颗粒与金属离子间的相互作用深刻地影响着土壤中的微观过程和宏观现象的发生。而胡敏酸是土壤腐殖质的主要组成物质,本文利用光散射技术研究了不同浓度的Ca(NO3)2和Cu(NO3)2溶液中胡敏酸胶体颗粒的凝聚过程和形成凝聚体的结构,并在此基础上进行比较分析。结果表明:由于Ca2+和Cu2+在带电胶体表面的吸附方式不同而对胡敏酸胶体的凝聚的影响表现出很大差异。(1)散射光强的稳定与否可以反映体系的稳定性,Ca(NO3)2体系中散射光强可以在较宽的电解质浓度范围从0 mmol L-1至20 mmol L-1内保持稳定,而Cu(NO3)2体系中光强稳定的电解质浓度范围较窄,只有0 mmol L-1至3 mmol L-1。(2)随电解质浓度的提高,两种电解质体系中凝聚体的有效粒径随时间先呈线性增长再呈幂函数增长,但胡敏酸胶体凝聚过程对Cu(NO3)2体系浓度变化的敏感性远大于Ca(NO3)2体系,并且1 mmol L-1Cu2+吸附下胡敏酸胶体的凝聚速率为69.55 nm min-1,近乎是7.5 mmol L-1Ca2+吸附下凝聚速率23.94 nm min-1的3倍,可见Cu2+作用下颗粒的平均凝聚速率远远高于Ca2+作用的情况。(3)Ca(NO3)2体系中,电解质浓度越高形成凝聚体的结构越开放,但放置50 d后分形维数变小,结构变得更加疏松,说明该凝聚过程具有可逆性;而Cu2+作用下形成的凝聚体初期结构开放度较高,在放置50 d后分形维数变大,结构更加致密紧实,说明该凝聚过程具有不可逆性。这些信息为研究腐殖质超分子聚合物的形成机制提供了新思路。