Rhizosphere microbial community and Zn uptake by willow (Salix purpurea L.) depend on soil sulfur concentrations in metalliferous peat soils

On numerous occasions, rhizosphere microbial activities have been identified as a key factor in metal phytoavailability to various plant species and in phytoremediation of metal-contaminated sites. For soil bioremediation efforts in heavy metal contaminated areas, microbes adapted to higher concentrations of heavy metals are required. This study was a field survey undertaken to examine rhizosphere microbial communities and biogeochemistry of soils associated with Zn accumulation by indigenous willows (Salix purpurea L.) in the naturally metalliferous peat soils located near Elba, NY. Soil and willow leaf samples were collected from seven points, at intervals 18 m apart along a willow hedgerow, on four different dates during the growing season. Soil bacterial community composition was characterized by terminal restriction fragment length polymorphism (T-RFLP) analysis and a 16S clone library was created from the rhizosphere of willows and soils containing the highest concentrations of Zn. Bacterial community composition was correlated with soil sulfate, but not with soil pH. The clone library revealed comparable phylogenetic associations to those found in other heavy metal-contaminated soils, and was dominated by affiliations within the phyla Acidobacteria (32%), and Proteobacteria (37%), and the remaining clones were associated with a wide array of phyla including Actinobacteria, Gemmatimonadetes, Planctomycetes, Verrucomicrobia, Bacteriodetes, and Cyanobacteria. Diverse microbial populations were present in both rhizosphere and bulk soils of these naturally metalliferous peat soils with community composition highly correlated to the soil sulfate cycle throughout the growing season indicative of a sulfur-oxidizing rhizosphere microbial community. Results confirm the importance of soil characterization for informing bioremediation efforts in heavy metal contaminated areas and the reciprocity that microbial communities uniquely adapted to specific conditions and heavy metals may have on an ecosystem.     

Changes in microbial biomass C, soil carbohydrate composition and aggregate stability induced by growth of selected crop and forage species under field conditions

The effects of growth of various crop and forage species on microbial biomass C, soil carbohydrate content and monosaccharide composition, and mean weight diameter (MWD) were investigated in two field experiments. One experiment was conducted over one growing season (4 months) whereas the other had been conducted for three consecutive growing seasons (32 months). In the four-month experiment, aggregate stability (estimated as MWD) of soil from experimental plots followed the order Italian ryegrass > prairie grass > phacelia = pea = maize. At the 32-month site the order was perennial ryegrass > annual ryegrass > perennial white clover = barley. At both sites crops with the greatest root mass and root length density had the greatest effect on increasing MWD. In all cases, rhizosphere soil had a significantly higher microbial biomass and MWD than non-rhizosphere soil. However, organic C, total content of acid-hydrolysable carbohydrate and content of individual monosaccharides in acid hydrolysates were similar in rhizosphere and non-rhizosphere soil. The fraction of soil carbohydrate extractable with hot water (representing about 6-8% of the total carbohydrate content) was significantly higher in the rhizosphere soil. This fraction has a galactose plus mannose over arabinose plus xylose ratio of 2.1–2.3 indicating that it was predominantly of microbial origin. It is suggested that the carbohydrate fraction extractable with hot water is made up of exocellular microbial polysaccharides that are involved in stabilizing soil aggregates in the rhizosphere. By comparison with arable crop species, grass species have a larger root mass and root length density, and therefore a higher microbial biomass and larger production of carbohydrate extractable with hot water. As a result they have a more marked effect on improving soil aggregate stability.     

EPIC Evaluation of the Impact of Poultry Litter Application Timing on Nutrient Losses

Recently, changes in the utilization practices of animal manures for fertilization have been encouraged to reduce the potential of nonpoint pollution of lakes and streams from agricultural land. However, the potential impact of changing some of these practices has not been fully studied. The objective of this study was to examine the potential impact of limiting poultry litter application times on nutrient movement important to water quality. The WinEPIC model was used to simulate poultry litter applications during the winter months and chemical fertilizer application, with both cool season and warm season grass pastures on the major soil regions of Alabama. With the warm season grass, soluble nitrogen (N) losses could be reduced if the application of poultry litter was made after 30 December. With the cool season grasses, there was no significant difference in application dates for poultry litter for soluble N losses for any soil region, and no improvement could be noted for limiting applications in northern Alabama compared to southern Alabama. No significant difference was observed for soluble phosphorus (P) losses for application date for either warm season or cool season grass pastures. This indicates that factors other than plant P uptake during the growing season were the dominant regulators of the amount of soluble P lost in runoff. Also, the results would indicate that best management practices such as are administered with the P index are more important than plant growth factors in determining N and P losses to the environment.     

Bioavailability of Reversibly Sorbed and Desorption-Resistant 1,3-Dichlorobenzene from a Louisiana Superfund Site Soil

Microcosm batch studies were conducted to study the biodegradation of 1,3-dichlorobenzene (1,3-DCB) from the aqueous (soil free) and soil phases. For soil phase experiments, a freshly contaminated soil and a soil containing only the desorption-resistant or irreversibly bound or non-labile fraction of the contaminant were used. These experiments were designed to simulate biodegradation at Superfund site assuming sorption/desorption equilibrium was reached. The presence of the soil reduced the rates of biodegradation significantly. Nearly 100% of the total 1,3-DCB in the aqueous phase was biodegraded by enriched bacterial cultures within 7 days compared to about 55% over a 6-week incubation period from the freshly contaminated soil. The biodegradation in the soils containing only the desorption-resistant fraction of the contaminant was considerably lower (about 30%). It is believed that for freshly contaminated soil, 1,3-DCB readily desorbed into the aqueous phase and was available for microbial consumption whereas for soils containing mostly the desorption-resistant fraction of 1,3-DCB, the contaminant availability was limited by the mass transfer into the aqueous phase. Our earlier studies concluded that about 20–30% of the sorbed contaminant is tightly bound (even larger for weathered or aged soils) and is not easily extractable. This fraction is typically present in micropores or chemically bound to soil humic matter and thus is not readily accessible for microbial utilization. The findings presented here for 1,3-DCB are in agreement with those reported for other chemicals in the literature and could have implications to the current remedy, the monitored natural attenuation at the Petro Processors Inc. Superfund site in Louisiana.     

Using sod to manage nitrogen in orchard floors

Abstract

Irrigation of untilled orchard floors can lead to substantial leaching losses of nitrate‐nitrogen (NO₃‐N). Soil NO₃ that remains after cool weather in the fall is subject to leaching in the spring. Nitrate losses can be controlled through growing ground cover vegetation to cycle residual nitrogen (N) and/or limiting the amount of water applied. A study was initiated in lysimeters to compare sodded soil surfaces versus bare soil for controlling NO₃ leaching losses. Cool season vegetation (orchardgrass, western wheatgrass, white clover) and warm season grasses (bahiagrass and buffalograss) were compared for then‐effect on grapefruit seedling growth. A field verification in pecan orchards was conducted where clean‐till versus a grass soil cover was used to compare the relative movement of NO₃ through the profile. The presence of vigorously growing sods greatly reduced NO₃ losses the first year in the lysimeter study. The second year a shade screen was placed over the lysimeters, resulting in greatly reduced cool season sod growth and substantially reduced warm season sod growth. The best grapefruit growth occurred on bare soil; vigorous sod growth greatly reduced grapefruit tree growth. In the second year of the experiment, tree growth on bare soil began to absorb substantial amounts of N. The presence of even reduced receding sod growth still adversely affected grapefruit tree growth. In commercial pecan orchards, NO₃ distributions in a clean‐tilled orchard soil showed large quantities of NO₃ entering the water table (the highest quantity at the lowest depth of the soil profile) while in the presence of a sod much less NO₃ (highest profile NO₃ near the soil surface) was being lost to the water table. However, the NO₃ leaching patterns were of large leaching losses in clean tilled surfaces and small controlled leaching losses with sod surfaces.     

Effects of PAH-Contaminated Soil on Rhizosphere Microbial Communities

Bacterial associations with plant roots are thought to contribute to the success of phytoremediation. We tested the effect of addition of a polycyclic aromatic hydrocarbon contaminated soil on the structure of the rhizosphere microbial communities of wheat (Triticum aestivum), lettuce (Lactuca sativa var. Tango), zucchini (Cucurbita pepo spp. pepo var. Black Beauty), and pumpkin (C. pepo spp. pepo var. Howden) 16S rDNA terminal restriction fragment length polymorphism (T-RFLP) profiles of rhizosphere microbial communities from different soil/plant combinations were compared with a pairwise Pearson correlation coefficient. Rhizosphere microbial communities of zucchini and pumpkin grown in the media amended with highest degree of contaminated soil clustered separately, whereas communities of these plants grown in unamended or amended with lower concentrations of contaminated soil, grouped in a second cluster. Lettuce communities grouped similarly to cucurbits communities, whereas wheat communities did not display an obvious clustering. The variability of 16S rDNA T-RFLP profiles among the different plant/soil treatments were mostly due to the difference in relative abundance rather than presence/absence of T-RFLP fragments. Our results suggest that in highly contaminated soils, the rhizosphere microbial community structure is governed more by the degree of contamination rather than the plant host type.     

Structure and function of microbial communities in the rhizosphere of Scots pine after tree-felling

We evaluated changes occurring in the rhizosphere microbial communities of Scots pine (Pinus sylvestris L.) due to tree-felling and decrease of the photosynthetic C flow into the soil under field conditions over one growing season. Samples were taken from tree rhizospheres, freshly felled stump rhizospheres and bulk soil. We used culture dependent (CFU counts, community level physiological profiles, CLPPs) and independent methods (fluorogenic MUF-substrates, PLFA pattern and PCR-DGGE) to monitor the microbial communities in soil samples. The numbers of cultivable bacteria and amounts of phosphatase activity in the rhizosphere of trees were significantly higher compared with those in the bulk soil. The organic C consuming community measured by CLPP was stimulated directly after the tree-felling in stump rhizospheres; utilization of the disintegration components of cellulose, hemicellulose and chitin increased. Furthermore, bacterial and fungal biomass as well as chitin decomposers (CFU) increased in the stump rhizosphere. After 11 weeks of tree-felling the stump rhizosphere soluble PO₄-P and NH₄-N as well as amounts of total C and N began to resemble the concentrations measured in the bulk soil. However, the stump rhizosphere community structure detected by PLFA and PCR-DGGE still resembled that of the tree rhizosphere.     

红壤丘陵区不同种草模式的水土保持效果与生态环境效应

研究探讨了红壤丘陵区将牧草纳入不同利用方式后的水土保持效果及对生态环境的影响。 3年的试验结果表明 :种植牧草能明显地减少径流量和泥沙量 ,截留雨水 ,提高土壤水分含量 ,降低高温干旱期地表温度 ,提高土壤有机质含量 ,培肥土壤。然而 ,梯田果园区种植暖季型禾本科牧草将在高温干旱期影响果树生长 ,果园牧草应以根系浅的豆科牧草罗顿豆或夏季枯死的冷季型牧草为主。在梯田作物区的梯边上种植牧草不仅没有产生明显的水土保持效果 ,而且引起牧草和作物竞争而减产 ,因而不宜提倡。     

Effects of subsurface aeration and trinexapac-ethyl application on soil microbial communities in a creeping bentgrass putting green

The sensitivity of creeping bentgrass (Agrostis palustris Huds.) to the extreme heat found in the southeastern United States has led to the development of new greens-management methods. The purpose of this study was to examine the effects of subsurface aeration and growth regulator applications on soil microbial communities and mycorrhizal colonization rates in a creeping bentgrass putting green. Two cultivars (Crenshaw and Penncross), a growth regulator (trinexapac-ethyl), and subsurface aeration were evaluated in cool and warm seasons. Total bacterial counts were higher in whole (unsieved) soils than in sieved soils, indicating a richer rhizosphere soil environment. Mycorrhizal infection rates were higher in trinexapac-ethyl (TE) treated plants. High levels of hyphal colonization and relatively low arbuscule and vesicle occurrence were observed. Principal components analysis of whole-soil fatty acid methyl ester (FAME) profiles indicated that warm-season microbial populations in whole and sieved soils had similar constituents, but the populations differed in the cool season. FAME profiles did not indicate that subsurface aeration and TE application affected soil microbial community structure. This is the first reported study investigating the influences of subsurface aeration and TE application on soil microorganisms in a turfgrass putting green soil.     

镉污染土壤根际环境的调节与植物修复研究进展

简要回顾了近年来土壤镉污染现状,介绍了根际环境的调节作用、镉污染土壤的植物修复技术的类型、特点及植物修复情况,并对今后植物修复发展前景作了进一步展望,为实现对镉污染土壤进行有效的生态整治与安全高效益的利用提供了新的技术途径。     

Phospholipid fatty acid composition of a 2,4,6-trinitrotolune contaminated soil and an uncontaminated soil as affected by a humification remediation process

Analysis of phospholipid fatty acids (PLFAs) was performed to investigate effects of 2,4,6-trinitrotoluene (TNT) contamination and soil remediation on microbial biomass and community structure. A TNT-contaminated and an uncontaminated soil from a former ammunition plant were analysed before and after a humification/remediation process. TNT contamination reduced microbial biomass but indicated only minor differences in PLFA composition between the contaminated and uncontaminated soils. The humification process increased microbial biomass and altered soil PLFA patterns to a larger degree than did TNT contamination.     

Plant nitrogen uptake drives rhizosphere bacterial community assembly during plant growth

When plants establish in novel environments, they can modify soil microbial community structure and functional properties in ways that enhance their own success. Although soil microbial communities are influenced by abiotic environmental variability, rhizosphere microbial communities may also be affected by plant activities such as nutrient uptake during the growing season. We predicted that during the growing season, plant N uptake would explain much of the variation in rhizosphere microbial community assembly and functional traits. We grew the invasive C₃ grass Bromus tectorum and three commonly co-occurring native C₃ grasses in a controlled greenhouse environment, and examined rhizosphere bacterial community structural and functional characteristics at three different plant growth stages. We found that soil N availability and plant tissue N levels strongly correlated with shifts in rhizosphere bacterial community structure. It also appeared that the rapid drawdown of soil nutrients in the rhizosphere during the plant growing season triggered a selection event whereby only those microbes able to tolerate the changing nutrient conditions were able to persist. Plant N uptake rates inversely corresponded to microbial biomass N levels during periods of peak plant growth. Mechanisms which enable plants to influence rhizosphere bacterial community structure and function are likely to affect their competitive ability and fitness. Our study suggests that plants can alter their rhizosphere microbiomes through influencing nutrient availability. The ways in which plants establish their rhizosphere bacterial communities may now be viewed as a selection trait related to intrinsic plant species nutrient demands.     

接种微生物对土壤中Cd、Pb、Zn生物有效性的影响

针对提高植物修复土壤重金属污染的效果,以印度芥菜作为重金属富集植物,通过盆栽试验研究了巨大芽胞杆菌和胶质芽胞杆菌的混合微生物制剂(A处理)和黑曲霉发酵液(B处理)对植物修复Cd、Pb、Zn污染土壤的作用效果。结果表明:巨大芽胞杆菌和胶质芽胞杆菌的混合微生物制剂,不仅可以促进富集植物的生长,使其印度芥菜的生物量提高24.73%,并且可促进土壤Cd、Pb、Zn的活化,使土壤Cd、Pb、Zn有效态含量分别提高15.02%、7.65%和2.23%,增强富集植物对土壤的Cd、Pb、Zn富集吸收,使印度芥菜对土壤Cd、Pb、Zn的提取量分别提高52%、121%和23%,显著提高其植物修复效果。从对植物生理生化指标的影响来看,A处理对植株的伤害程度要低于B处理,它是一种有助于植物修复Cd、Pb、Zn污染土壤的微生物制剂,在植物修复领域有较高的利用价值。然而,黑曲霉混合发酵液不适于促进植物修复应用。     

Influence of grass species and soil type on rhizosphere microbial community structure in grassland soils

A number of studies have reported species specific selection of microbial communities in the rhizosphere by plants. It is hypothesised that plants influence microbial community structure in the rhizosphere through rhizodeposition. We examined to what extent the structure of bacterial and fungal communities in the rhizosphere of grasses is determined by the plant species and different soil types. Three grass species were planted in soil from one site, to identify plant-specific influences on rhizosphere microbial communities. To quantify the soil-specific effects on rhizosphere microbial community structure, we planted one grass species (Lolium perenne L.) into soils from three contrasting sites. Rhizosphere, non-rhizosphere (bulk) and control (non-planted) soil samples were collected at regular intervals, to examine the temporal changes in soil microbial communities. Rhizosphere soil samples were collected from both root bases and root tips, to investigate root associated spatial influences. Both fungal and bacterial communities were analysed by terminal restriction fragment length polymorphism (TRFLP). Both bacterial and fungal communities were influenced by the plant growth but there was no evidence for plant species selection of the soil microbial communities in the rhizosphere of the different grass species. For both fungal and bacterial communities, the major determinant of community structure in rhizospheres was soil type. This observation was confirmed by cloning and sequencing analysis of bacterial communities. In control soils, bacterial composition was dominated by Firmicutes and Actinobacteria but in the rhizosphere samples, the majority of bacteria belonged to Proteobacteria and Acidobacteria. Bacterial community compositions of rhizosphere soils from different plants were similar, indicating only a weak influence of plant species on rhizosphere microbial community structure.     

Microbial community structure and abundance in the rhizosphere and bulk soil of a tomato cropping system that includes cover crops

Understanding microbial responses to crop rotation and legacy of cropping history can assist in determining how land use management impacts microbially mediated soil processes. In the literature, one finds mixed results when attempting to determine the major environmental and biological controls on soil microbial structure and functionality. The objectives of this research were to: (1) Qualitatively and quantitatively measure seasonal and antecedent soil management effects on the soil microbial community structure in the rhizosphere of a subsequent tomato crop (Solanum lycopersicum) and (2) Determine phylum scale differences between the rhizosphere and bulk soil microbial community as influenced by the antecedent hairy vetch (Vicia villosa), cereal rye (Secale cereale), or black plastic mulch treatments. In this report, we use terminal restriction fragment length polymorphisms in the 16s rDNA gene to characterize changes in microbial community structure in soil samples from a field replicated tomato production system experiment at USDA-ARS Beltsville Agricultural Research Center, Beltsville, MD, USA. We found season of the year had the strongest influence on the soil microbial community structure of some of the major microbial phyla. Although we monitored just a few of the major microbial phyla (four Eubacteria and Archaea), we found that the effects of the tomato plant on the structural composition of these phyla in the rhizosphere differed dependent on the antecedent cover crop. Increased understanding of how agricultural factors influence the soil microbial community structure under field conditions is critical information for farmers and land managers to make decisions when targeting soil ecosystem services that are microbially driven.     

Effects of initial plant spacing and applied nutrients on stand development and productivity of Texas bluegrass in the Louisiana coastal plain

The native rhizomatous cool‐season perennial grass, Texas bluegrass (Poa arachnifera Torn), has recently been recognized again as a plant with considerable potential for range and pasture plantings. Throughout the first half of this century, sporadic efforts at evaluation and commercial use of Texas bluegrass were thwarted primarily by slow stand establishment and difficulties with seed processing. Subsequent advances in seed harvesting, processing, and planting equipment and selection of superior plant genotypes could reduce effects of these limitations. In much of the southern mid‐ and tall‐grass prairie regions and lower southeastern states where Texas bluegrass appears to have potential, there is no currently available sustainable cool‐season forage grass. Effects of initial plant spacing and lime, phosphorus (P), and nitrogen (N) application were evaluated in a field and a green house experiment on acid infertile Louisiana Coastal Plain soils. Stands from transplanting on 10‐ and 30‐cm spacings were comparable by the third growing season as the sparsely planted stand spread aggressively. The only consistent response to soil amendment was enhanced forage production from N fertilization in the spring. A plant photoperiodic response appears to limit potential to respond to N in autumn and winter. Forage production of dense stands and responses to spring application of N indicate that Texas bluegrass has considerable potential as a productive, sustainable cool‐season forage grass for at least some soils on the southeastern Coastal Plain as well as that recently reported for the southern mid‐ and tall‐grass prairie regions.     

Toxicity of hexyl to<Emphasis Type="Italic">F. candida and E. crypticus</Emphasis>

Aim, Scope and Background  Hexyl is along with TNT a possible pollutant of ammunition contaminated soils. To assess the ecological risk of a pollutant biotests are obligatory to gain information of the effects on the habitat function of the contaminated soil. The effect of Hexyl was investigated using the standardised biotests for the springtailFolsomia Candida and the enchytraeidEnchytraeus crypticus. Method  The tests with Hexyl were performed in spiked standard soil (Lufa 2.2). The toxic endpoints were mortality (short-term test, exposure time 7 days) and reproduction rate (long-term test, exposure time 28 days). The effect on the reproduction was further investigated by transferring animals from contaminated soil material onto uncontaminated substrate. Then the number of offspring was determined for the collembola and the cocoon- and hatching rates for the enchytraeid. Results. The mortality of the collembola was not influenced by Hexyl, but the number of offspring was significantly reduced. On the bases of these data the influence of the contaminant on the fertility of the adults itself was investigated. Therefore a reproduction test was performed with adult springtails transferred from contaminated onto uncontaminated soil material. It was shown that the fertility of the adults was not affected by Hexyl indicating a strong lethal effect on the juveniles. In case of the enchytraeid the mortality as well as the reproduction was affected. The surviving enchytraeids turned yellow and rigid in the mortality tests. They were also reduced in size compared to individuals in the uncontaminated control soil material. Thus the cocoon and hatching rates of worms transferred from contaminated soil material onto agar-agar was further investigated. Indeed, the reproduction (both cocoon production and juvenile hatching) was affected by the contaminant. However, the effect was not as strong as might have been suggested by their change in colour and size. A rapid recovery of the worms was observed, too. Conclusion  Hexyl is toxic for the two terrestrial invertebrates, although in comparison to other explosives tested it is less toxic than TNT, but more toxic than the other explosives such as Hexogen (RDX) and Octogen (HMX) or TAT, the end product of the microbial reduction of TNT. So far, all these substances have only been tested with the luminescent bacteriaVibrio fischeri, for which Hexyl and TNT were classified as very toxic to aquatic organisms. With earthworms (Eisenia fetida andEisenia andrei) only TNT, Hexogen and Octogen have been investigated. TNT was also the most toxic of these substances. Outook  Hexyl is one of the main pollutants of ammunition-contaminated sites and has to be considered as a toxic compound. Therefore an assessment of its full ecological impact is necessary and should include tests with animals from different trophic levels as well as biotests with plants and microorganisms.     

香薷植物修复铜污染土壤的研究进展

土壤铜污染有自然来源和人为来源。铜污染土壤中有机质、Fe／Al氧化物对铜的专性吸附，是影响土壤中铜生物有效性的主要因素。近年来，我国原生植物修复材料如海州香薷、鸭跖草、酸模、紫花香薷在国内铜污染土壤的研究中得到广泛应用。其中．采用海州香薷开展铜污染土壤植物修复机理和修复技术的研究，已从实验室水培、盆栽试验的生长反应特性、耐及解铜毒的生理生化反应，进展到室外大田修复的示范工程及技术推广阶段。紫花香薷在重金属复合污染土壤上，也有修复前景。开展植物修复材料的产后处置研究，综合利用和深加工，增大植物修复材料价值，对加强植物修复工程的示范和推广步伐，有重要意义。     

生草不同条件还田对桃园土壤微生物、酶活性及养分供应的影响

为探讨桃园生草不同条件还田对土壤微生物、酶活性及有效态养分的影响,以清耕为对照,设置生草自然还田、生草刈割还田、生草刈割配施有机物料腐熟剂还田3个处理,连续开展3年定位试验。采集根际和非根际土壤,研究桃园生草不同条件还田对土壤微生物数量、土壤酶活性以及土壤不同形态氮、钾含量的影响。结果表明:生草不同条件还田提高了根际土壤微生物的数量,生草刈割配施有机物料腐熟剂还田显著提高了根际和非根际土壤细菌和真菌的数量,较其他处理分别提高21.2%～48.2%和11.7%～17.0%,生草刈割后,配施有机物料腐熟剂能加速秸秆的腐熟与微生物繁殖;与清耕对照相比,桃园生草不同条件还田均能显著提高土壤酶活性,生草刈割配施有机物料腐熟剂的土壤脲酶活性、过氧化氢酶活性、蔗糖酶活性较其他处理分别提高10.2%～45.4%,26.8%～56.9%,20.5%～30.7%;桃园生草还田对土壤养分的积累具有正效应,以生草刈割配施有机物料腐熟剂还田效果明显,其不仅增加了土壤无机态氮和有机态氮含量,减少了氮素损失,同时还显著提高土壤速效钾和水溶性钾含量,较其他处理的土壤速效钾和水溶性钾含量分别提高12.6%～15.6%和11.4%～39.1%。综上,桃园生草刈割配施有机物料腐熟剂还田为提高土壤微生物数量、土壤酶活性及氮钾养分供应的较好途径,为果园生草精细化管理提供科学依据。     

Field-Scale Assessment of Phytotreatment of Soil Contaminated with Weathered Hydrocarbons and Heavy Metals (9 pp)

Background, Aim and Scope   Phytoremediation is a remediation method which uses plants to remove, contain or detoxify environmental contaminants. Phytoremediation has successfully been applied for the removal of fresh hydrocarbon contamination, but removal of aged hydrocarbons has proven more difficult. Biodegradation of hydrocarbons in the subsurface can be enhanced by the presence of plant roots, i.e. the rhizosphere effect. Phytostabilization reduces heavy metal availability via immobilization in the rhizosphere. Soils contaminated by both hydrocarbons and heavy metals are abundant and may be difficult to treat. Heavy metal toxicity can inhibit the activity of hydrocarbon-degrading microorganisms and decrease the metabolic diversity of soil bacteria. In this experiment, weathered hydrocarbon- and heavy metal- contaminated soil was treated using phytoremediation in a 39- month field study in attempts to achieve both hydrocarbon removal and heavy metal stabilization. Materials and Methods: A combination of hydrocarbon degradation and heavy metal stabilization was evaluated in a field-scale phytoremediation study of weathered contaminants. Soil had been contaminated over several years with hydrocarbons (11400±4300 mg kg dry soil)-1 and heavy metals from bus maintenance activities and was geologically characterized as till. Concentrations of soil copper, lead and zinc were 170±50 mgkg-1, 1100±1500 mg kg-1 and 390±340 mg kg-1, respectively. The effect of contaminants, plant species and soil amendment (NPK fertilizer or biowaste compost) on metabolic activity of soil microbiota was determined. Phytostabilization performance was investigated by analyses of metal concentrations in plants, soil and site leachate as well as acute toxicity to Vibrio fischeri and Enchtraeus albidus. Results: Over 39 months hydrocarbon concentrations did not decrease significantly (P=0.05) in non-amended soil, although 30% of initial hydrocarbon concentrations were removed by the last four months of study. In soil amended with NPK fertilizer and municipal biowaste compost, 65 % and 60 % of hydrocarbons were removed, respectively. The soil contained metabolically diverse bacteria, measured as carbon source utilization and extracellular enzymatic activities. Compost addition resulted in a slight increase in enzymatic activities. Diesel fuel utilization potential in Biolog MT2 plates inoculated with a soil suspension was enhanced by both compost and NPK compared to non-amended soil. Soil toxicity to V. fischeri and E. albidus was low. The leachate was not toxic to V. fischeri. Pine (Pinus sylvestris), poplar (Populus deltoides x Wettsteinii), grasses and clover (Trifolium repens) survived to varying degrees in the contaminated soil. All plants suffered from phytotoxicity symptoms and some trees died during the study period. Plants formed a dense cover over the compost-amended soil, whereas non-amended soil had areas devoid of vegetation throughout the study. Vegetation coverage in the NPK-amended quarter was about 50 % after the first four months of study, but increased gradually to 100 %. Heavy metals did not accumulate in plant tissue. Discussion: Removal of hydrocarbons from weathered unfertilized hydrocarbon-contaminated soil was not statistically significant despite the presence of a viable hydrocarbon-degrading microbial community. This effect is attributed to soil heterogeneity and low bioavailability of hydrocarbons. Hydrocarbon concentrations were not reduced to the desired level, i.e., 1500 mg hydrocarbons (kg of dry soil)-1, in any treatment. . The presence of clay minerals and organic matter within the compost may have limited heavy metal transfer to leachate and plant tissue. Conclusions: Weathered hydrocarbons were partly decomposed in soil fertilized with NPK fertilizer or biowaste compost, but not from unfertilized soil. The active hydrocarbon-degrading microbiota and low toxicity of soil to V. fischeri and E. albidus indicates low availability of contaminants to microorganisms. Despite high heavy metal concentrations, the soil contained metabolically diverse bacteria, measured as carbon source utilization and extracellular enzymatic activities. Heavy metals did not accumulate in test plants. Pine and poplar suffered from phytotoxicity symptoms in the soil and could not enhance hydrocarbon removal in compost-amended soil. Compost addition combined with a grass and legume crop is suggested for stabilization of combined hydrocarbon- and metal-contaminated soil. Recommendations and Perspectives: Both compost and NPK fertilizers can be used to enhance phytoremediation of soil contaminated with weathered hydrocarbons in the presence of heavy metals; however, compost addition is recommended since it enables greater vegetative coverage. This in turn may decrease heavy metal mobility. Phytoremediation can be used for remediation of soil contaminated with weathered hydrocarbons in the presence of heavy metals. However, phytoremediation of weathered contaminants requires extended periods of time; thus, other remediation methods should be considered in the event of soil contamination posing an immediate public health and/or environmental threat.