Effects of humic substances on iron nutrition of lupin

Poorly crystalline Fe oxides and organic matter are two important factors affecting Fe nutrition of plants. The main objective of this work was to study the contribution of humic substances to Fe nutrition of a typical Fe-chlorosis sensitive plant (white lupin, Lupinus albus L.). An experiment was performed involving two growing media (siliceous and calcareous) and different Fe sources: control without additional Fe added to the growing media, ferrihydrite (FH), FH + humic substances (HS, at two rates, 0.1 and 0.3 g C kg⁻¹ growing media), Fe complexed to humic substances (Fe–HS), and Fe–EDDHA (as an effective Fe source in calcareous media). Chlorophyll meter readings and dry matter production (DM) were significantly greater with Fe–EDDHA and Fe–HS when compared with the other treatments in calcareous media. The positive effect of complexed Fe (to EDDHA or HS) on Fe nutrition can be, at least partially, related to an increase in Fe(III)-reducing capacity by roots, which seems to be improved by an enhanced root development. No positive effect on Fe nutrition was observed with the application of HS in a ferrihydrite enriched growing media (FH + HS) at 4 weeks, particularly with the application of HS at 0.3 g C kg⁻¹ in calcareous media. Thus, the effect of HS on Fe availability was only positive if some Fe is complexed to HS. The efficiency of HS with Fe complexed (Fe–HS) in preventing Fe chlorosis was found to be similar to Fe–EDDHA. This is important not only for the knowledge of factors affecting Fe availability in soils, but also with a view of using Fe–HS complexes as effective products to correct this nutritional problem.     

Formation and mineralization kinetics of dissolved humic substances from aquatic macrophytes decomposition

Purpose

Aquatic macrophytes are an important source of autochthonous dissolved organic carbon in aquatic ecosystems. Yield and mass loss of aquatic humic substances released from macrophytes decomposition could be affected by the plant species and oxygen availability. Our aim was to describe the kinetics of dissolved fulvic and humic acids formed from decomposition of four aquatic macrophytes under aerobic and anaerobic conditions.

Materials and methods

Samples of Eichhornia azurea (Sw.) Kunth, Egeria najas Planch, Oxycaryum cubense (Poepp. and Kunth), and Salvinia molesta (Mitchell) were incubated under aerobic and anaerobic conditions. On sampling days, the remaining particulate detritus were weighted and were measured for the pH, the electrical conductivity, and the organic carbon in the dissolved fraction. Humic substances were extracted from the dissolved fraction, separated into fulvic and humic acids, and then quantified. The mass loss of particulate and dissolved fractions were fitted to first order kinetic models.

Results and discussion

Aerobic environment favored mineralization of aquatic macrophyte detritus and humification of organic dissolved carbon. Incubations under aerobic conditions formed 3.6 times more humic acid than incubations under anaerobic conditions. However, incubations in an anaerobic environment formed 1.84 times more fulvic acid. The dissolved humic compounds presented low mineralization rates probably due to the presence of the macrophyte detritus in the incubation representing a more attractive source of resource for microorganisms.

Conclusions

In many cases, the mineralization of HS was not noticed, leading to an increase in humic and fulvic acid concentration in the water. O. cubense detritus presented the highest carbon concentration, were related to refractory features, and generated the highest amounts of dissolved HA (mainly under aerobic condition). Egeria najas detritus presented the lowest carbon concentration, were related to labile features, and generated the highest amounts of dissolved FA (mainly under anaerobic condition). Besides that, high humic substance concentrations in the dissolved organic carbon were related to low mineralization of this fraction.

     

烤烟根系分泌物对烤烟幼苗生长和养分吸收的影响

连作是烟草栽培中的普遍现象,已引起生长抑制、产量下降和品质恶化等问题。本试验采用溶液培养的方法,在培养液中分别加入未分组和分组后的烤烟根系分泌物,研究根系分泌物对烤烟幼苗生长和养分吸收的影响。结果表明,加入未分组的烤烟根系分泌物显著抑制幼苗的生长,降低根系活力,并随加入量的增加抑制作用增强;加入酸溶性、碱溶性、中性组分的根系分泌物,均降低幼苗根系活力,以中性组分的抑制作用较强。三种不同组分的根系分泌物均显著降低根系对NO3-、PO43-、K+离子的吸收,其中中性组分对NO3-吸收的影响最大,而酸溶性组分对K+的吸收抑制作用较强。推测在烤烟根系分泌物中,可能存在多种抑制烤烟生长和养分吸收的化学物质。     

稀土镧和铈元素对西红柿幼苗生长及其根系分泌物的影响

稀土是具有生理活性的元素,能够对植物的生长发育产生影响,而植物根系可以对外源植物生长调节剂做出响应,调节植物生长。采用水培试验,以西红柿幼苗为材料,分析了稀土镧、铈对西红柿生长和根系分泌物的影响。结果显示,稀土元素的施加浓度为0.05 mmol/kg时,能够促进西红柿株高和叶面积的增加,浓度达到0.1 mmol/kg时则会产生抑制作用;而施加稀土元素后,植物根系生长均受到抑制作用;对西红柿根系分泌物成分和含量进行鉴定分析,稀土处理与空白组对比差异显著的代谢物共有110种,隶属于10个二级分类、38个三级分类,其中三级分类中的Fatty Acyls分类、Carboxylic acids and derivatives分类和Organooxygen compounds分类差异最为显著,但各类根系分泌物对西红柿生长的影响机理仍需要进一步的研究。     

Effect of root mucilage and modelled root exudates on soil structure

Plant roots release in the rhizosphere diverse organic materials which may have different effects on soil structure. We have evaluated the effect of natural and modelled root‐released materials on soil aggregates and the biodegradation of carbon from roots in the soil. The effects of root mucilage from maize and of a modelled soluble exudate were compared with those of simple compounds (glucose, polygalacturonic acid). For all treatments, soil was amended with 2 g C kg^?1 soil and incubated for 30 days at 25°C. The biodegradation of mucilage was similar to that of polygalacturonic acid, and slower than the decomposition of modelled exudates and glucose. Addition of all substrates increased the stability of aggregates, but the duration of this effect depended on the chemical nature of the material. Compared with the control, the proportion of stable aggregates after 30 days of incubation was multiplied by 3.8 for root mucilage, by 4.2 for modelled soluble exudates, by 2.5 for polygalacturonic acid and by 2.0 for glucose. The different fractions of root exudates in the rhizosphere evidently affected the aggregate stability.     

Long-term kinetics study and quantitative characterization of the antioxidant capacities of humic and humic-like substances

Purpose

Humic substances (HS) play important functions in the environment by radical scavenging in biogeochemical redox reactions, thus influencing behavior of pollutants and preventing damage to cell membranes; this is due to antioxidant properties of HS. Previous studies focused primarily on assessing endpoint antioxidant capacity (AOC) of HS. Our work aimed to estimate long-term kinetics of the antioxidant capacities of humic and humic-like substances under different pH in relation to their specific structural features.

Materials and methods

The 10-h kinetic profiles of four standard HS and two fungi-produced humic-like substances (HLS) were established with Trolox equivalent antioxidant capacity (TEAC) approach using the ABTS decolorization assay. Three pH levels (3.75, 4.25, and 6.80) and a broad range of humic material concentrations (0.5–10 mg L^?1) were examined. The data were divided into intervals and fit using exponential functions to evaluate the endpoint AOCs as well as rate constants for the reaction of humic materials with the ABTS radical cation. To further explore the nature of the antioxidant activities of humic materials, the physicochemical features and antioxidant activities of humic compounds were subjected to correlation analysis.

Results and discussion

Our results demonstrated that during the first 40 min, the determined AOCs did not exceed 50 % of the endpoint AOCs for studies of humic materials, indicating that short-term measures of the AOCs of humic materials provide artificially low values due to the presence of slow-acting antioxidant compounds. Due to the instability of ABTS^?+ at neutral and alkaline pH values, only the fast antioxidant moieties of humic materials can be assessed with ABTS decolorization approach under these conditions. Our results show that at acidic pH, the antioxidant activity of HLS is mainly related to the presence of nitrogen-containing groups rather than phenols. However, for HS, both nitrogen-containing compounds and phenolic compounds should be considered.

Conclusions

To obtain clearer information concerning the AOC of humic materials, kinetic profiles should first be established, and then endpoint measurements should be taken at a time when the reaction has reached, or at least neared, the endpoint.

     

Effects of some dicarboxylic acids on the association of dissolved humic substances

Changes in molecular size distributions of four different humic materials were evaluated through high performance size-exclusion chromatography (HPSEC), before and after treating humic solutions with naturally occurring dicarboxylic (oxalic, malonic, succinic and glutaric) acids. Chromatograms of dissolved humic substances showed a decrease in peak absorbance as well as an increase in peak elution volume when the solution pH was lowered from 7 to 3.5 by addition of dicarboxylic acids before HPSEC analysis. The resulting reduction in molecular size is explained by the disruption of unstable humic superstructures into smaller-sized associations stabilized by the formation of strong intra- and inter-molecular hydrogen bonds among humic molecules. The extent of humic size variation was in the order: oxalic相似文献   

Effects of mineral and monocarboxylic acids on the molecular association of dissolved humic substances

The conformational structure of dissolved humic substances is an important property that controls the reactivity of humus in the soil solution. High performance size-exclusion chromatography was used here to study the changes in molecular size of different humic substances brought about by addition of mineral (HCl) and monocarboxylic (formic, acetic, propionic, and butyric) acids. The CPMAS-NMR spectra showed that humic substances had varying chemical composition and that the ratio of hydrophilic to hydrophobic carbon (HI/HB) was greater for a humic acid from soil than for ones from oxidized coal and lignite. All humic substances showed a decrease in UV absorbance of chromatographic peaks when treated with either HCl or monocarboxylic acids. This was due to the hypochromic effect by which the absorptivity of associated molecules is decreased when they are separated. We attributed the molecular separation upon acid treatment to the formation of intermolecular hydrogen bonding that alters the original conformation stabilized mainly by weaker hydrophobic interactions. Addition of organic acids not only further decreased peak absorbances of humic acids but also caused their shift to larger elution volumes, indicating a larger conformational disruption than with HCl. The extent of the molecular size changes showed a relation to the number of carbons of monocarboxylic acids and to the HI/HB ratios of humic materials. The larger the carbon content of organic acids and the smaller the HI/HB ratio of humic materials, the larger was the decrease of the average molecular size of humic acids. These results suggest that dissolved humic substances associate predominantly by hydrophobic forces and that the apolar components of humic substances largely control their aggregation and reactivity in the environment.     

Soil–root cross‐talking: The role of humic substances

The biological activity of humic substances (HS) has been elucidated in the last 40 years. Growth enhancement from HS has been demonstrated in several plants in the laboratory and the field. Morphogenesis effects have also been investigated and include induction of lateral root formation and root hair initiation in intact plants and stimulation of root and shoot development in treated cell calluses. HS enhance nutrient use efficiency, aiding assimilation of both macro and microelements and promoting plant growth by the induction of carbon, nitrogen, and secondary metabolism. The review aims are to: (1) shed light on the mechanism by which plants “talk” with soil through humic substances, (2) elucidate the plant responses to the stimulatory effects of HS, the regulatory circuits that allow plants to cope with humus, and the feedback between plant community structures, and (3) show (in light of recent debate about the alkaline extraction of soil humic substances) the plant capability to acquire biologically active substances from soil. It will be shown that plants modify soils, creating and maintaining favorable habitats for growth and survival. Therefore, organic substances exuded by roots are not a wasteful loss of carbon and energy. They represent an evolved strategy by which plants “talk” to the soil. The mobilization of bioactive organic/humic substances from bulk soil or bulk humus is critical to plant and soil health.     

Fate of humic acids isolated from natural humic substances

Composition of humic acids (HA) is a function of plant-derived inputs, degradation processes regulated by microorganisms, organo-mineral interactions and age. Characterization of different origin humic substances is important for evaluation of their contribution to stabile and labile carbon pool in the environment. The relative abundance of chemical components in HA isolated from soils, compost, commercial lignohumates, alginite, acadiane and lignite was studied with aim to quantify content of important biomarkers such as amino acid, lipids and polyphenols. HA were considered as a heterogeneous complex and high concentration of peptides, polyphenols and lipids was determined in acadian-HA to compare with soil-HA. Compost-HA contained much more amino acids to compare with soil-HA samples. Alginite-HA and lignite-HA were similar in biomarkers content to soil-HA. Fourier transform infrared spectroscopy confirmed that chemical composition and functional groups content differs with the origin, humification degree and the age of studied samples. Soil-HA are typically composed of a variety of ?OH, COOH?, C–O, C–H₂, (aliphatic and aromatic) groups, quinines, lignin fragments, polysaccharide, monosaccharide and proteins fragments, which are linked together by ?O?, ?NH?, ?H=, >C=O, metal ions and –S? groups. ¹³C NMR spectroscopy showed that aromatic carbon content was the highest in lignite-HA and soil-HA.     

长期施肥对黑土团聚体中腐殖物质组成的影响

腐殖物质(HS)是土壤有机质的主体,在土壤固碳方面具有重要作用[1],近些年来,在土壤有机质化学研究中越来越受到重视。团聚体是土壤有机质(SOM)分解转化和HS形成的最主要“场所”,土壤中的一切生物化学活动均在这一骨架内进行(包括土壤腐殖化作用)。在正常的或特定的条件下,不仅微生物主导的腐殖化作用需要合适的“场所”,而且所形成的HS也只有在合适的“场所”或者说与土壤矿质部分相结合才能长时间保存[2-3]。这种“场所”或者说有机无机结合状况,是制约整个土壤固碳反应的关键。但至今为止关于这种“场所”(团聚体)的固碳机制尚不清楚,特别是很少注重HS化学方面。团聚体和HS二者关系密切,不可分割。可以假     

Effects of coal derived humic substances on water retention and structural stability of Mediterranean soils

Abstract. The potential for using coal-derived humic substances to improve the available water holding capacity (AWC) and aggregate stability of typical Mediterranean soils was evaluated in the laboratory using an agricultural surface (0–20 cm) soil from each of three regions of Italy, (Sicily, Tuscany and Venetia) and five rates of humic acids (HA), 0,0.05,0.10,0.50 and 1.00 g/kg. There were significant ( P < 0.05) differences between the field capacity (FC), permanent wilting point (PWP), and available water capacity (AWC) values of the controls and those treated with 0.05 g/kg of the HA. Beyond this rate, differences in these properties were not significant. At the 1.00 g/kg HA rate, the relative improvements in AWC over the three controls were 30%, 10% and 26%. Low rates (0.05 to 0.10 g/kg) of HA were also needed to obtain a 40 to 120% improvement in aggregate stability of these soils relative to the controls. These results indicate that the addition of highly humified organic matter such as coal-derived humic substances can improve the structural and water retention properties of degraded arable soils. However, since there is not yet any direct evidence that these humic materials can ameliorate soils under field conditions, field studies will be needed to validate these results.     

Physiological action of humic substances on microbial cells

By incorporating molecular weight fractions of humic acids of various origins into selective substrates designed for the enumeration of physiological groups of microorganisms, it was found that the presence of humic acids at concentrations of up to 30mgl^?1 normally resulted in increased numbers of soil microbes active within a particular physiological group. Observed increases could be as much as 2000-fold. Microbes in an organic humus-rich soil were more stimulated by humic substances than organisms from a sandy soil.In certain microbes humic substances appeared to induce a change in metabolism, allowing the organisms to proliferate on substrates which previously they could not utilize. Indications were obtained that within the 10–30 mgl^?1 concentration range lower molecular weight humic fractions (approx. 5500 dallons) were more effective than higher molecular weight material. At higher concentrations the reverse was sometimes noticed. Similarly, fulvic acids at concentrations of up to approximately 50mgl^?1 would appear to have a more pronounced physiological effect than humic acids, whereas the latter might be more effective at higher concentrations.The response of certain physiological groups to humic products of natural origin appeared to be comparable to that of surfactants such as Tween and Brij. This would suggest that the physiological action of humic substances is, at least partly, the result of their surface activity, making the membrane one of the prime targets of the physiological action of humics on living cells.     

The alkaline hydrolysis of humic substances

A humic and a fulvic acid were subjected to four successive hydrolyses with 2NNaOH solution at 170°C for 3 h. Following each hydrolysis, the degradation products were extracted into ethyl acetate, methylated, separated by chromatographic techniques and identified by mass spectrometry and micro-IR spectrophotometry.One g of humic acid yielded 113.5 mg of aliphatic compounds (mainly n-C₁₆ and n-C₁₅) fatty acids), 72.1 mg of phenolics (principally guaiacyl and syringyl derivative) 17.1 mg of benzenepolycarboxylic acid esters and 30.4 mg of N-containing compounds (mainly secondary aromatic amides). Repeated attacks by the alkali on 1.0 g of fulvic acid released 103.8 mg of aliphatics, 133.8 mg of phenolics, 27.0 mg of benzenecarboxylic but 181.8 mg of N-containing compounds. Most of the latter appeared to have been formed during the second, third and fourth hydrolysis which produced reactive compounds that could abstract N from diazomethane which was used as methylating reagent. While 25.0% of the initial humic acid resisted repeated attacks by the alkali, practically all of the fulvic acid was converted into ethyl acetate-soluble products. The alkali-resistant humic acid residue produced high yields of benzenepolycarboxylic acids on alkaline permanganate oxidation.Alkaline hydrolysis, which is known to cleave CO bonds, was found to be relatively specific, although not very efficient, for the degradation of structural phenolic humic and fulvic acid components and for the concomitant liberation of adsorbed aliphatics and N-containing compounds, but was relatively ineffective for degrading aromatic structures linked by CC bonds.     

微量元素亏缺对人参根系分泌物组成的影响

以3年生人参幼苗为试验材料,在室内用正常以及缺少硼、锰、锌、铁元素的1倍Hoagland营养液进行水培养试验,研究不同微量元素亏缺处理对人参根系分泌物主要成分的影响.结果表明:在包括对照在内的5个处理中分别检测到23～30种化合物,包括醇类、脂肪酸、脂肪酸酯、酚酸及其衍生物、醛类和其他类化合物.进一步研究发现,除20种化合物在上述5种不同处理中均检测到外,与对照相比,在微量元素亏缺胁迫下,人参根系分泌物中其他类化合物有所减少,有机酸及酚酸类化合物增多.试验结果表明,微量元素亏缺对根系分泌物组成有显著影响.     

氮肥减施对玉米幼苗根系分泌物影响的根际代谢组学分析

植物根系分泌物的根际代谢组学分析有助于更好地理解土壤根际微域内植物根系与土壤和土壤生物之间化学信号交流的根际过程。本文采用核磁共振氢谱(~1H nuclear magnetic resonance,~1H NMR)技术,对基于不同施氮处理下[常规施氮(180 kg×hm~(-2))、80%常规氮量和55%常规氮量]土壤培养收集的玉米幼苗的根系土壤沥出液(soil leachate,SL)、根鞘土浸提液(rhizosheath soil,RS)和根系水培液(distilled water cultivation,DWC)内的根系分泌物进行检测,并结合多维统计分析对比了不同收集方法以及不同施氮量下玉米幼苗根系分泌物的不同。结果表明:3种不同方法收集的玉米幼苗根系分泌物的核磁共振氢谱谱图轮廓及主要标志物明显不同。其中SL法的谱图峰信号及检测到的根系分泌物数目少,而RS和DWC法的谱图峰信号较多且可检测到玉米幼苗根系分泌物中的糖、有机酸和氨基酸等组分。与常规施氮量比较,在85%施氮量下,玉米幼苗根系分泌物中的α-葡萄糖、苹果酸、亮氨酸、缬氨酸水平显著增加;而当施氮量减少到55%时,玉米幼苗根系分泌物水平不再显著增加并呈现下降趋势。上述根系分泌物的变化可能和玉米根系对土壤氮营养供应水平的适应性调节有关。采用~1H NMR技术,结合RS和DWC收集方法进行根际代谢组学分析,可为根际生态及根际氮素营养研究提供重要理论依据。     

连作对花生根系分泌物化感作用的影响

采用连续收集法提取连作5 年、3 年和轮作处理的花生结荚期根系分泌物, 研究其对土壤微生物及花生种子发芽、幼苗生长发育和细胞膜过氧化的化感作用及连作对花生根系分泌物化感作用的影响。结果表明,花生结荚期根系分泌物对花生根腐镰刀菌36194 菌丝的生长、叶片超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性及丙二醛(MDA)含量存在促进作用, 对固氮菌14046 的生长, 花生种子胚根的伸长、幼苗的苗高、茎叶鲜重、根系鲜重、叶片叶绿素含量等有抑制作用, 促进和抑制作用均随根系分泌物添加浓度和连作年限的增加呈增强趋势。连作花生结荚期根系分泌物化感物质在土壤中的累积, 很可能是导致花生连作障碍的原因之一。     

Interactions of humic substances with allophanic compounds

Abstract

Organic matter from two Chilean Andisols, Vilcun and Osorno soils, were extracted and fractionated into humic (HA) and fulvic acids (FA). Humic acid were chemically characterized and their molecular weight (MW) distribution was obtained by gel permeation chromatography. The HA from the Vilcun soil had a lower MW than the HA from the Osorno soil and consequently had a higher acidity. Humic acid were used to coat synthetic allophanic materials which carried ferrihydrite coatings. The isoelectric point (IEP) of the synthetic allophanic materials was reduced from 8.6 to near 3.0 and surface area was reduced from 450 m²/g to 120 m²/g depending on the HA level. The surface pKa values showed that the HA buffer capacity generally reduced the surface acidity of allophahic materials, but the HA from the Vilcun soil at a higher HA level which slightly increased the surface acidity due to an observed lower condensation degree. Phosphate (P) adsorption capacity was reduced to a greater degree in the HA from the Osomo soil model than in the HA Vilcun one, indicating a positive correlation with surface acidity. The differential isosteric heat of P adsorption (?H) showed similar energy sites at lower P adsorbed levels in the Osorno and Vilcun soil models, but that with over 40% surface coverage, the Vilcun soil model had higher energetic reaction than the Osorno one.     

Enzymatic transformation of humic substances by NDO

Enzymatic transformation of humic acids (HA), fulvic acids (FA) and indole was examined using naphthalene 1,2-dioxygenase (NDO). NDO was used as a model for dioxygenase enzymes found in various microbial species. Indole was used as a model substrate for NDO-catalyzed reactions resulting in condensation products. Although NDO is not classified as a soil enzyme, all HA and FA tested were susceptible to NDO-induced transformation. The extent of NDO-specific NADH oxidation in solutions containing HA and FA paralleled the percent aromaticity of the HA and FA. Furthermore, the UV–Vis absorptive properties of NDO-treated HA and FA were altered in a manner suggesting condensation reactions similar to the formation of indigo from indole. Condensation reactions were enhanced in NDO-treated mixtures containing indole and an FA. NDO retained activity for 2 weeks under ambient conditions, and retained some enzymatic activity for 9 days based on detection of specific metabolites by HPLC, suggesting prolonged extracellular activity. Humic substances have not previously been known to be substrates for dioxygenases; even more significant was that dioxygenase enzymes can facilitate condensation reactions between indole-like functional groups well-known to be present in HA and FA. These results illustrate how dioxygenases can be potential humic-modifying enzymes when released into the environment upon microbial death and concurrent cell lysis which could alter the bioavailability of organic contaminants associated with dissolved organic matter through specific modulation of enzyme activity involving substrate competition.