有机酸和磷对两种污染土壤铅的释放作用研究

用土壤培养和化学浸提法研究了不同低分子量有机酸和磷对污染土壤中铅释放的影响。结果表明,随有机酸浓度增加,铅污染红壤、棕壤中可溶出铅量均增加。当供试有机酸浓度≥1mmol·L-1时,相同浓度有机酸溶出铅量为柠檬酸〉乙酸〉草酸;当有机酸浓度≤0.5mmol·L-1时,溶出铅量为草酸〉柠檬酸〉乙酸。将2g·kg-1磷及50mmol·kg-1有机酸与铅污染红壤以不同方式混合后,柠檬酸处理的溶出铅比率（在污染土壤中加入P、有机酸后溶出铅含量与单加有机酸溶出铅含量之比）为66%（先加有机酸再加磷）、58%（有机酸与磷同时加入）、70%（先加磷再加有机酸）,草酸处理（方式同上）的溶出铅比率为90%、89%、94%,乙酸处理（方式同上）的为10%、8%、10%。铅污染棕壤上,以上处理的溶出铅比率分别为106.46%、104.43%、105.19%（柠檬酸）;43%、48%、58%（草酸）;38%、42%、55%（乙酸）。供试条件下,红壤最低溶出铅比率低于棕壤。     

低分子有机酸/盐对森林暗棕壤铁的释放效应

模拟森林凋落物淋洗液中草酸/草酸盐和柠檬酸/柠檬酸盐的浓度范围,设计了不同浓度草酸/草酸盐和柠檬酸/柠檬酸盐溶液一次性浸提和多次连续浸提等系列实验,结果表明,草酸/草酸盐和柠檬酸/柠檬酸盐对暗棕壤铁具有活化作用,活化作用大小因有机酸/盐种类、浓度和土壤性质而异。随着低分子有机酸/盐浓度的增加,A1层和B层暗棕壤活化释放的铁也逐渐增多。pH 5.16的低分子有机盐溶液对A1层和B层暗棕壤铁的活化作用强于同浓度的相应低分子有机酸,即柠檬酸盐>柠檬酸,草酸盐>草酸,因此推断草酸盐和柠檬酸盐溶液促进暗棕壤铁活化释放的机理主要在于低分子有机酸阴离子的配位反应。柠檬酸/柠檬酸盐对A1层和B层暗棕壤铁的活化作用强于同浓度的草酸/草酸盐,即柠檬酸>草酸,柠檬酸盐>草酸盐,这主要与柠檬酸对铁较强的络合能力及较大的离解常数有关。A1层与B层相比,草酸/草酸盐和柠檬酸/柠檬酸盐均对B层暗棕壤释放的铁量较高。另外,低分子有机酸对暗棕壤铁的释放并不是一次就能完成的,第一次以后的连续4次浸提仍源源不断释放出数量可观的铁。     

Remediation of Metal Contaminated Soil by Organic Metabolites from Fungi I—Production of Organic Acids

Investigations were made on living strains of fungi in a bioremediation process of three metal (lead) contaminated soils. Three saprotrophic fungi (Aspergillus niger, Penicillium bilaiae, and a Penicillium sp.) were exposed to poor and rich nutrient conditions (no carbon availability or 0.11 M d-glucose, respectively) and metal stress (25 µM lead or contaminated soils) for 5 days. Exudation of low molecular weight organic acids was investigated as a response to the metal and nutrient conditions. Main organic acids identified were oxalic acid (A. niger) and citric acid (P. bilaiae). Exudation rates of oxalate decreased in response to lead exposure, while exudation rates of citrate were less affected. Total production under poor nutrient conditions was low, except for A. niger, for which no significant difference was found between the poor and rich control. Maximum exudation rates were 20 µmol oxalic acid g^?1 biomass h^?1 (A. niger) and 20 µmol citric acid g^?1 biomass h^?1 (P. bilaiae), in the presence of the contaminated soil, but only 5 µmol organic acids g^?1 biomass h^?1, in total, for the Penicillium sp. There was a significant mobilization of metals from the soils in the carbon rich treatments and maximum release of Pb was 12% from the soils after 5 days. This was not sufficient to bring down the remaining concentration to the target level 300 mg kg^?1 from initial levels of 3,800, 1,600, and 370 mg kg^?1in the three soils. Target levels for Ni, Zn, and Cu, were 120, 500, and 200 mg kg^?1, respectively, and were prior to the bioremediation already below these concentrations (except for Cu Soil 1). However, maximum release of Ni, Zn, and Cu was 28%, 35%, and 90%, respectively. The release of metals was related to the production of chelating acids, but also to the pH-decrease. This illustrates the potential to use fungi exudates in bioremediation of contaminated soil. Nonetheless, the extent of the generation of organic acids is depending on several processes and mechanisms that need to be further investigated.     

Impact of low-molecular-weight organic acids on the availability of phenanthrene and pyrene in soil

The impact of low-molecular-weight organic acids (LMWOAs) on the availability of phenanthrene and pyrene was investigated using laboratory batch assays. Experiments were conducted with two types of soil with different organic contents. The LMWOAs used were citric and oxalic acid. A mild solvent extraction procedure and a sorption-desorption experiment were used to predict the availability of phenanthrene and pyrene. Results showed that the extractable amounts of phenanthrene and pyrene in both soil types increased with increased citric or oxalic acid concentration. Citric acid addition promoted phenanthrene and pyrene extraction to a greater degree than oxalic acid. Compared with freshly spiked soils, the extractable amounts of phenanthrene and pyrene with the addition of LMWOAs decreased significantly after 60 days of cultivation. Soils with higher values of soil organic carbon content (f_oc) showed decreased phenanthrene and pyrene availability after the addition of LMWOAs. The sorption and desorption results also demonstrated the enhanced availability of PAHs with LMWOA addition. Phenanthrene sorption could be described using a linear model, regardless of the addition of LMWOAs. The simulated distribution constants (K_d) for phenanthrene sorption decreased significantly with the addition of LMWOAs. In contrast, phenanthrene desorption clearly increased with the addition of LMWOAs. These results suggest that the availabilities of phenanthrene and pyrene can be increased with the addition of suitable LMWOAs.     

Fermentation of sugar beet waste by Aspergillus niger facilitates growth and P uptake of external mycelium of mixed populations of arbuscular mycorrhizal fungi

Sugar beet waste has potential value as a soil amendment and this work studied whether fermentation of the waste by Aspergillus niger would influence the growth and P uptake of arbuscular mycorrhizal (AM) fungi. Plants were grown in compartmentalised growth units, each with a root compartment (RC) and two lateral root-free compartments (RFC). One RFC contained untreated soil while the other RFC contained soil, which was uniformly mixed with sugar beet waste, either untreated (SB) or degraded by A. niger (ASB) in a rock phosphate (RP)-supplied medium. The soil in each pair of RFC was labelled with ³³P and ³²P in order to measure P uptake by the AM fungal mycelium, of which length density was also measured. Whole cell fatty acid (WCFA) signatures were used as biomarkers of the AM fungal mycelium and other soil microorganisms. The amount of biomarkers of saprotrophic fungi and both Gram-positive and Gram-negative bacteria was higher in SB than in ASB treatments. Whilst ASB increased growth and activity of AM mycelium, SB had the opposite effect. Moreover, shoot P content was increased by the addition of ASB, and by inoculation with AM fungi. Modification of soil microbial structure and production of exudates by A. niger, as a consequence of fermentation process of sugar beet waste, could possibly explain the increase of AM growth in ASB treatments. On the other hand, the highest P uptake was a result of the solubilisation of rock phosphate by A. niger during the fermentation.     

低分子有机酸去除土壤中重金属条件的研究

采用化学萃取实验,以湖南郴州柿竹园和湖南衡阳水口山矿区的重金属污染农田土壤为研究对象,采用柠檬酸、草酸、酒石酸作为低分子有机酸萃取剂,在一定的条件下对污染土壤中重金属进行萃取实验,确定各个单因素的适宜条件。结果表明,对于湖南郴州和衡阳两个污染地区土壤运用化学萃取技术萃取重金属来进行土壤修复是实际可行的;柠檬酸、酒石酸、草酸对各种土壤中的重金属都表现出了良好的萃取能力,是高效的土壤重金属萃取剂;单因素的适宜萃取条件为100mmol·L^-1有机酸溶液,固液比1∶5,恒定温度35℃,pH为3,反应时间24h,且萃取率随着电解质浓度的增大而提高;土壤中重金属存在形态与萃取效果有一定的相关性,稳定态（残渣态、硫化物和有机结合态、铁-锰氧化物结合态）金属含量高,表现为较低的萃取率;反之,萃取率高;柠檬酸、草酸、酒石酸3种萃取剂均能有效地降低衡阳污染土壤中的重金属浓度,3种萃取剂的萃取效率依次为酒石酸〉草酸〉柠檬酸。     

低分子量有机酸强化烟草修复镉污染土壤的适用性研究

采用盆栽试验,以0.125mmol/kg EDTA为对照,研究3种低分子量有机酸(酒石酸、柠檬酸和草酸)在强化烟草修复镉污染土壤中应用的可行性。3种低分子量有机酸(LMWOA)均可显著降低土壤pH,提高镉的有效含量,酒石酸和草酸对镉在烟草中转运有抑制作用,柠檬酸在酸性土壤中促进镉在烟草中转运,在中性土壤中则起抑制作用。31.25mmol/kg LMWOA对烟草地上部的生长有一定的促进作用,该浓度的柠檬酸和草酸使酸性土壤中烟草地上部镉累积量分别提高42.95%和28.67%,柠檬酸还使中性土壤中烟草地上部镉的累积量提高40.91%,所有酒石酸处理镉在烟草地上部的累积量均降低,EDTA使酸性土壤中烟草地上部镉的累积量提高24.56%,对中性土壤中烟草地上部镉累积量的影响不显著。表明柠檬酸和草酸具有强化烟草地上部对镉的吸收、提高烟草提取土壤镉效率的作用,但要获得与EDTA相当的效果,需大大提高其用量,这必然导致修复成本大大提高,故不宜用于强化烟草修复镉污染土壤。     

Effect of low-molecular-weight organic acids on Cl- adsorption by variable charge soils

Low-molecular-weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes.The objective of the present paper was to evaluate effect of two LMW organic acids, citric acid and oxalic acid, on Cl^- adsorption by three variable charge soils, a latosol, a lateritic red soil and a red soil, using a batch method. The results showed that the presence of citric acid and oxalic acid led to a decrease in Cl- adsorption with larger decreases for citric acid. Among the different soils Cl- adsorption in the lateritic red soil and the red soil was more affected by both the LMW organic acids than that in the latosol.     

Remediation of Metal-Contaminated Soil by Organic Metabolites from Fungi II—Metal Redistribution

Exudation of low molecular weight organic acids by fungi was studied in a project focusing on bioremediation of metal-contaminated soils. The production of acids (mainly oxalic and citric acid) as a response to nutrient variations and presence of metals has recently been reported (Arwidsson et al. 2009). A significant release of metals was observed and was related not only to the production of organic acids but also to the resulting pH decrease in the systems. The processes governing the release and redistribution of metals in the soil–water fungus system were the focus of the present continuation of the project, based on observations of Aspergillus niger, Penicillium bilaiae, and a Penicillium sp. The release of lead was 12% from the soil with the second highest initial load (1,600 mg kg^?1), while the release of copper was 90% from the same soil (140 mg kg^?1). The dominating mechanism behind the release and subsequent redistribution was the change in pH, going from near neutral to values in the range 2.1–5.9, reflecting the production of organic acids. For some of the systems, the formation of soluble complexes is indicated (copper, at intermediate pH) which favors the metal release. Iron is assumed to play a key role since the amount of secondary iron in the soils is higher than the total load of secondary heavy metals. It can be assumed that most of the heavy metals are initially associated with iron-rich phases through adsorption or coprecipitation. These phases can be dissolved, or associated metals can be desorbed, by a decrease in pH. It would be feasible to further develop a process in technical scale for remediation of metal-contaminated soil, based on microbial metabolite production leading to formation of soluble metal complexes, notably with copper.     

低分子量有机酸对石灰性土壤有机磷组成及有效性的影响

为探索提高土壤磷素有效性的途径,采用室内培养的方法,研究不同有机酸对土壤速效磷含量及有机磷组分的影响。结果表明,添加有机酸后土壤速效磷含量发生显著变化,其中草酸处理下土壤速效磷含量显著高于其他处理,而柠檬酸和苹果酸对土壤速效磷含量具有抑制作用,其活化量为负值;随着培养时间的延长,速效磷含量缓慢降低。速效磷含量随着草酸浓度的升高而升高,随着苹果酸、柠檬酸浓度的升高而降低;有机酸处理后,土壤活性、中活性、中稳性有机磷升高,高稳性有机磷降低,这说明有机酸能促进土壤有机磷由有效性低的形态逐步向有效性高的形态转化,其中草酸的作用效果总体上较柠檬酸和苹果酸强。     

The effect of low-molecular-weight organic acids and inorganic phosphorus concentration on the determination of soil phosphorus by the molybdenum blue reaction

Low-molecular-weight organic acids play an important role in the mobilization of soil phosphorus (P). The molybdate blue colorimetric method, based on the formation of P molybdenum blue compound, is commonly used for analysis of phosphate in soil and environmental samples. However, some organic acids can act as a ligand to bond with molybdenum acid, which subsequently interfere with the colorimetric reaction. The recoveries of P were inhibited by the addition of oxalic (>2 mM) and citric acids (>3 mM) both in standard P solutions and soil extracts, but formic and maleic acids did not interfere with the P determination. The inhibition of oxalic and citric acids on P recovery remained even at higher level of P (up to 100 μg P 100 ml⁻¹) though such interferences decreased by increasing P concentration. Comparison between oxalic and citric acids revealed the more pronounced interference by the addition of oxalic acid. The results suggested that the interference of organic acids with P determination is related to the types of organic acids and the ratio of organic acid ligands to P anions in the solutions. Thus, analysis of P using the molybdate blue colorimetric method should be undertaken cautiously in the presence of relative strong ligands like oxalic and citric acids.     

Role of beneficial microbial gene pool in mitigating salt/nutrient stress of plants in saline soils through underground phytostimulating signalling molecules

Soil salinity diminishes soil health and reduces crop yield, which is becoming a major global concern. Salinity stress is one of the primary stresses, leading to several other secondary stresses that restrict plant growth and soil fertility. The major secondary stresses induced in plants under saline-alkaline conditions include osmotic stress, nutrient limitation, and ionic stress, all of which negatively impact overall plant growth. Under stressed conditions, certain beneficial soil microflora ...     

低分子量有机酸对可变电荷土壤铝活化动力学的影响

从动力学角度研究了几种低分子量有机酸对2种酸性土壤中铝的活化和活化铝在土壤固/液相之间分配的影响。结果表明:对于络合能力弱的醋酸和乳酸,主要通过质子作用活化铝,且活化作用明显小于盐酸。而络合能力较强的苹果酸、草酸和柠檬酸,主要通过络合作用促进铝的释放,且这种作用随有机酸根阴离子络合能力的增强而增加。在氧化铁含量较高的砖红壤中,苹果酸、草酸和柠檬酸通过专性吸附增加土壤表面负电荷,从而增加土壤交换态铝;但在氧化铁含量较低的红壤中,草酸和柠檬酸主要通过形成可溶性铝络合物降低交换态铝。活化铝在土壤固/液相间的分配主要决定于溶液中有机阴离子与土壤固相表面对铝离子的竞争。醋酸和乳酸活化的铝主要以交换态铝存在;而草酸和柠檬酸活化的铝主要以有机酸-铝络合物存在于溶液中,特别是在氧化铁低的红壤中,这将促进铝在土壤-水体中的迁移。     

Alkalinity exacerbates phosphorus deficiency in subtropical red soils: Insights from phosphate-solubilizing fungi

Red soils in subtropical regions are often low in available phosphorus (P), a vital plant nutrient. Phosphate-solubilizing microorganisms (PSMs) can release P from phosphate reservoir, making it accessible to plants. However, the complex interactions between PSMs and minerals in red soils are not yet fully understood. In this study, we investigated the effects of Aspergillus niger, a typical phosphate-solubilizing fungus (PSF), on phosphate dissolution in two representative red soils – an acidic soil and an alkaline soil. In the acidic red soil, the fungal abundance reached 3.01 × 10 ⁷ cfu g⁻¹ after a 28-day incubation period, with respiration of ~2000 mg C kg⁻¹. The secretion of oxalic acid promoted P release from inorganic phosphate (from ~1 to 187 mg kg⁻¹). Additionally, the contents of amorphous Fe/Al oxides decreased, which otherwise could have contributed to P sorption in the soil. In contrast, P availability declined in the alkaline red soil after the addition of A. niger, regardless of the P source (inorganic or organic phosphate). Meanwhile, the fungal respiration decreased to ~780 mg C kg⁻¹. Therefore, alkaline red soils with abundant carbonates are susceptible to P deficiency due to both the diminished function of PSMs and strong soil buffering. These findings have important implications for sustainable agriculture on alkaline red soils, as they suggest that the use of PSMs to improve P availability may be limited.     

Lead Phytostabilization and Cationic Micronutrient Uptake by Maize as Influenced by Pb Levels and Application of Low Molecular Weight Organic Acids

ABSTRACT

Phytoremediation is a promising technique to clean up toxic heavy metals including lead (Pb). A greenhouse trial was conducted to evaluate the effectiveness of citric, succinic, malonic and oxalic acids on micronutrient uptake and phytoremediation of Pb contaminated soil by maize under different Pb levels. Mean root and shoot dry weights of maize decreased with increasing Pb levels. At the lowest Pb level, application of citric and oxalic acids caused increase effects on root and shoot dry weight, respectively, as compared to the absence of organic acid. As Pb levels increased, micronutrient uptake in maize shoot decreased. Among the studied organic acids, only the application of oxalic acid increased uptake of all micronutrients in maize shoot as compared to control at the lowest Pb level. Mean root and shoot Pb concentration and uptake and also uptake index noticeably increased at the highest Pb level. All tested acids increased Pb concentration and uptake in maize root. At the highest Pb level, organic acids, except for citric acid, significantly increased shoot Pb uptake and uptake index as compared to the absence of organic acid. Translocation factors less than 1, demonstrated that most of Pb taken up by maize accumulated in root as compared to shoot. According to results reported herein, application of malonic, succinic and oxalic acids is a good strategy to enhance phytostabilization potential of Pb by maize in pb-polluted soils.     

Effect of Oxalic and Citric Acids on Zinc Release Kinetic in Two Calcareous Soils

Rate of zinc (Zn) release from solid to solution phase by organic acids can influence Zn availability in calcareous soils. The objective of the present study was to investigate the effect of different concentrations (1.1, 2.2, and 3.3 mM) of oxalic acid and citric acid on the kinetic release of Zn from two calcareous soils from Eastern Iran. The two organic acids showed significant difference in Zn release from studied soils. Cumulative Zn release during 72 h ranged from 5.85 to 10.4 mg kg^?1 in soil 1 and ranged from 8.7 to 16.9 mg kg^?1 in soil 2 using different concentrations of oxalic acid. The amount of cumulative Zn release after 72 h in soil 1 ranged from 13.65 to 28.77 mg kg^?1 and from 17.63 to 23.13 mg kg^?1 when different concentrations of citric acid was used. In general, Citric acid released 38% more Zn from soils than oxalic acid. The release of Zn from soils increased with citric acid concentration but decreased with increasing of oxalic acid concentrations in the solution. The simplified Elovich equation best described Zn release as a function of time (r² = 0.93 and SE = 0.78). From the present study, Zn release from soils can be limited by the higher concentration of oxalic acid, while citric acid is suitable for enhancing soil lability of Zn.     

溶磷真菌液体培养条件下对磷矿粉的溶解效果

Rock phosphate （RP） is a low efficiency P fertilizer that is directly applied to the soil and can be solubilized by phosphate-solubilizing microorganisms （PSMs） in fermentation or soil conditions. This study investigated dynamic solubilization of 2 concentrations of rock phosphate in a liquid culture with different dosages of glucose by two fungal isolates,Aspergillus niger P39 and Penicillium oxalicum P66, from soybean and wheat rhizosphere soil. Although during the 20 day culture period A. niger P39 had a stronger ability to acidify the culture media than P. ozalicum P66, soluble P concentrations at glucose dosages of 30 and 50 g L^-1 with RP of 15 g L^-1 in the culture solution were much higher by P. oxalicum P66. The greater effectiveness of P. oxalicum P66 compared to A. niger P39 in the solubilization of RP was strongly associated with the production of organic acids. This study suggested that for RP solubilization the type rather than the concentration of PSM-produced organic acids was more important.     

Production of L-lactic acid and oligomeric compounds from apple pomace by simultaneous saccharification and fermentation: a response surface methodology assessment

The potential of apple pomace for lactic acid production by simultaneous saccharification and fermentation (SSF) was evaluated. The effects of the cellulase to solid ratio (CSR), the liquor to solid ratio (LSR), and the beta-glucosidase to cellulase ratio (BCR) on the kinetics of lactic acid generation were assessed, and a set of mathematical models was developed to reproduce and predict the lactic acid concentration of fermentation broths. Operating at low cellulase and cellobiase charges (1 FPU/g and 0.25 IU/FPU, respectively) and short reaction times (10 h), SSF media containing 27.8 g of lactic acid/L were obtained with a volumetric productivity of 2.78 g/Lh. Material balances showed that the SSF processing of 100 kg of dry apple pomace results in the production of 36.6 kg of lactic acid, 18.3 kg of oligomeric carbohydrates (which can be used as ingredients for functional foods), 8.4 kg of microbial biomass, and 8 kg uronic acids.     

螯合剂对铀镉污染土壤中蚕豆幼苗生理特性影响

通过盆栽试验研究了在不同浓度EDTA、柠檬酸、草酸3种螯合剂作用下不同浓度铀镉复合污染（分别用W1、W2表示）对土壤中蚕豆（ViciafabaL.）幼苗体内叶绿素、丙二醛和细胞质膜透性的影响。结果表明,在所设的两个土壤污染浓度下,较高土壤污染浓度（W2）中植物受损伤程度高于较低土壤污染浓度（W1）中的植物受损伤程度,由此得出较高土壤污染浓度可能更有利于蚕豆对铀镉的吸收;蚕豆的整个生长过程中,对于叶绿素而言,在污染土壤中添加5mg.kg-1的草酸,对其含量影响最大,可能有利于促进蚕豆对土壤中铀和镉的吸收,添加2.5mg.kg-1的柠檬酸次之;对于丙二醛,向污染土壤中添加10mg.kg-1的草酸,对其含量影响最大,可能有利于蚕豆对土壤中铀和镉的吸收,添加2.5mg.kg-1的柠檬酸次之;在细胞质膜透性上,向土壤中添加5mg.kg-1草酸,对其含量影响最大,可能更有利于促进蚕豆吸收土壤中的铀和镉,而添加5mg.kg-1的柠檬酸次之。而EDTA在整个试验中都表现出了对植物较大的生物毒性。     

Citric acid enhances the mobilization of organic phosphorus in subtropical and tropical forest soils

Low-molecular-weight organic acids are considered to be effective in the release of inorganic phosphorus (P) but their effectiveness to mobilize organic P is not well understood. The aim of this study was to examine the role of three common organic acids (maleic, oxalic, and citric acids) in mobilizing organic P in forest soils. Soil samples tested in this study were collected from either native or plantation forests in subtropical and tropical Australia with 16–87% of soil total P being in organic form. At a concentration of 10 mM organic acid kg^?1 soil, all three organic acids did not enhance the release of inorganic P as compared with water, whereas the three organic acids displayed different capacities in mobilizing organic P. Citric acid significantly enhanced the solubilization of organic P by 34.7% as compared with water; whereas no significant differences were observed in the mobilization of organic P among maleic acid, oxalic acids, and water. The amount of organic P solubilized by citric acid was not correlated with soil pH but increased with increasing soil organic P as the values were below 200 mg kg.^?1 The possible mechanisms of the effective mobilization of organic P by citric acid were discussed. Our results implied that organic P might play an important role in P nutrition of plants in subtropical and tropical forests due to its substantial proportion in soil P and the effective mobilization by organic acids.