霍甫水丝蚓（Limnodrilus hoffmeisteri）扰动对表层沉积物细菌群落结构和多样性的影响

为研究大型底栖动物霍甫水丝蚓（Limnodrilus hoffmeisteri）对表层沉积物中细菌群落结构和多样性的影响,设计了沉积物-水微宇宙的实验,模拟太湖梅梁湾霍甫水丝蚓（Limnodrilus hoffmeisteri）的自然分布特征,运用末端限制性片段长度多态性技术（T-RFLP）比较了有无霍甫水丝蚓（Limnodrilus hoffmeisteri）分布的沉积物样品中细菌群落的动态变化。结果表明,水丝蚓组和对照组沉积物细菌群落结构相似性无显著差异（P〉0.05）,可见太湖梅梁湾目前的水丝蚓生物量引起的生物扰动对表层沉积物细菌群落结构影响不明显;实验中后期只在处理组中出现的206 bp以及处理组含量高于对照组的370 bp T-RFs都可能是Nitrosomonas属的氨氧化细菌,提示大型底栖动物霍甫水丝蚓的存在可能为氨氧化细菌提供了适合的生态位。     

Harsh summer conditions caused structural and specific functional changes of microbial communities in an arable soil

The mineralization of the herbicide 3-(4-isopropylphenyl)-1,1-dimethylurea (isoproturon) was reduced after the dry and hot summer 2003 in a soil profile placed in a field lysimeter. A different isoproturon mineralization pattern remained in soil material taken at two different soil depths (0–5 cm and 15–20 cm), although soil material was re-equilibrated at adequate climatic conditions. Special soil microcosms were designed to determine if the changes in this special soil function 'isoproturon mineralization' were related to the climatic scenario of summer 2003. These microcosms were filled with lysimeter soil from the 15–20 cm depth and the temperature and dryness of summer 2003 were simulated. Afterwards, soil samples were taken from the microcosms and re-equilibrated under controlled conditions for 4 weeks. Subsequently, isoproturon mineralization was investigated. The soil microbial community reduced drastically its original capability of isoproturon mineralization in the course of the model experiments.
Analysis of 16S-rRNA by denaturing gel gradient electrophoresis (DGGE) revealed substantial differences in the band patterns of the bacterial communities from both depths of the field lysimeter soil and from the soil incubated in microcosms. The different soil microbial biomass determined by microcalorimetry reinforced these results. In conclusion, the factors higher temperature and smaller soil moisture content generated important and enduring changes in the microbial community structure and therefore in specific soil functions of the community, as shown here by the function of isoproturon degradation. Results are discussed in connection with environmental conditions and conservation tillage.     

Shifts in bacterial community structure associated with inputs of low molecular weight carbon compounds to soil

Low molecular weight carbon (C) substrates are major drivers of bacterial activity and diversity in the soil environment. However, it is not well understood how specific low molecular weight C compounds, which are frequently found in root exudates and litter leachates, influence bacterial community structure or if there are specific groups of soil bacteria that preferentially respond to these C inputs. To address these knowledge gaps, we added three simple C substrates representative of common root exudate compounds (glucose, glycine, and citric acid) to microcosms containing three distinct soils from a grassland, hardwood forest, and coniferous forest. CO₂ production was assessed over a 24 h incubation period and, at the end of the incubation, DNA was extracted from the samples for assessment of bacterial community structure via bar-coded pyrosequencing of the 16S rRNA gene. All three C substrates significantly increased CO₂ production in all soils; however, there was no relationship between the magnitude of the increase in CO₂ production and the shift in bacterial community composition. All three substrates had significant effects on overall community structure with the changes primarily driven by relative increases in β-Proteobacteria, γ-Proteobacteria, and Actinobacteria. Citric acid additions had a particularly strong influence on bacterial communities, producing a 2-5-fold increase in the relative abundance of the β-Proteobacteria subphylum. These results suggest that although community-level responses to substrate additions vary depending on the substrate and soil in question, there are specific bacterial taxa that preferentially respond to the substrate additions across soil types.     

Biodegradation of biodiesel and toluene under nitrate-reducing conditions and the impact on bacterial community structure

Purpose

Biodiesel is a renewable fuel that can be mixed with toluene and be accidentally released into anoxic ecosystems and impact soil microbial communities. Therefore, the aim of the present work was to examine, under nitrate-reduction conditions, the biodegradation of toluene in the presence of two different types of biodiesel (sunflower and rapeseed), and their impact on the bacterial community structure.

Materials and methods

Sediment samples were spiked individually with toluene, biodiesel, and their blends in laboratory-designed microcosms. Sunflower oil biodiesel was produced in the laboratory, while rapeseed oil biodiesel was a commercial product. Degradation of biodiesels and blends was monitored by directly measuring the substrate or indirectly by determining nitrate removal during the course of the experiment. Denitrification rates were estimated with the acetylene inhibition technique. Denaturing gradient gel electrophoresis was used to assess impacts on the bacterial community structure exposed to biodiesels, blends, and toluene.

Results and discussion

The results of this study showed that toluene and biodiesel were completely degraded within 10 days. Biodiesel significantly affected the bacterial community structure at a similar magnitude, independently of its origin. Additionally, toluene impacted the bacterial community and denitrification process to a lower extent than biodiesel and a clear decrease in the relative bacterial richness and diversity was shown in samples with biodiesel and blends. To the best of our knowledge, this is one of the first reports describing degradation of biodiesel alone and blends under nitrate-reducing conditions, and also the effects of these compounds on the denitrification process. In addition, due to the recently discovered “oxygenic denitrification” process, the acetylene inhibition technique and nitrous oxide quantification may not be the most adequate tool to estimate denitrification rates. Further detailed studies are advised to understand whether the identified bacterial community shift impacts ecosystem functions.

Conclusions

Our results help to understand the biodegradation of toluene, biodiesel, and their blends in sediments under nitrate-reducing conditions and might be important in implementing bioremediation strategies in anoxic environments.

     

Impact of sulfadiazine and chlorotetracycline on soil bacterial community structure and respiratory activity

Veterinary medicines enter agricultural soils by the use of animal excrements as fertilizers. To study their impact on soil bacterial communities, microcosms containing orthic luvisol soil were spiked with the antimicrobial agents sulfadiazine (SDZ) and chlorotetracycline (CTC) at three different concentrations (1, 10, 50 mg kg⁻¹ soil) and incubated for 48 days at 20 °C. The impact on the microbial respiratory activity was measured continuously in a respirometer (Sapromat). Changes in bacterial community structure were visualized by means of PCR-denaturing gradient gel electrophoresis (DGGE) of 16S rDNA derived from soil samples after 1, 7, 11 and 48 days. Additionally, growth inhibitory effects of SDZ and CTC on bacteria previously isolated from the same soil were tested in agar diffusion tests. In microcosms with soil and antibiotics only, no effects could be observed, either on respiratory activity or on bacterial population structure. Therefore, further incubations were conducted in the presence of an additional assimilable carbon source (5 g glucose kg⁻¹ soil). In the presence of glucose, SDZ affected soil respiration as well as the bacterial community structure: Additional bands appeared and some bands already visible at the beginning of incubations increased in intensity. A clear relationship between SDZ concentrations and changes in DGGE patterns became visible. During 48 days of incubation, changes in DGGE patterns were minimal in microcosms with 50 mg SDZ kg⁻¹soil indicating an inhibition of strains, which were capable of growing on glucose in the presence of lower SDZ concentrations. Only a few soil bacterial isolates (5 out of 47 strains tested) were weakly inhibited by SDZ in agar diffusion disk tests. Contrastingly, CTC inhibited growth of 12 soil bacterial isolates significantly in disk tests, but no effects on soil respiration and bacterial community structure could be observed. In the presence of the soil matrix the growth inhibitory potential of CTC decreased due to adsorption or complexation. This was confirmed in growth inhibition experiments with soil suspensions and time-dependent sampling.     

Recovery of Amoebae Community in the Root Soil of <Emphasis Type="Italic">M. sativa</Emphasis> after a Strong Contamination Pulse with n-Hexane

Microbial food webs tolerate toxic compounds depending on individualistic species resistance and their ability of using alternate food sources. Soil polluted with low-molecular weight volatile organics, such as hexane, diminishes bacterial and fungal communities despite its short residence time. Survival of microbial species depends on perturbation intensity, which in turn restricts resources for amoebae survival in polluted soil. Soil functional recovery from anthropogenic perturbations depends on microbial organic matter (OM) metabolization of pollutants. However, reconfiguration of amoebae community after soil exposure remains largely unknown. A microcosms study was carried out to determine the effects of hexane on the community structure of soil amoebae as well as the importance of Medicago sativa on amoebae community recovering. Hexane had a negative impact on species richness and structure of the amoebae community 24 h after pollution. There was a significant increase in species richness and number of amoebae 30 days after contamination. These two parameters further increased after 60 days from contamination. After 30 days of the initial trophozoites extinction caused by Hexane, M. sativa’s. Root zone showed a significant increase of both species richness and number of individuals. This recovery trend was kept after 60 days when the highest values in species richness and abundance of individuals were shown in both polluted and non-polluted microcosms. In conclusion, M. sativa’s root zone speeds up recovery of the amoebae community structure after pollution exposure.     

Characterization of rhizosphere microbial communities in continuous cropping maca (Lepidium meyenii) red soil,Yunnan, China

ABSTRACT

Continuous cropping maca systems are widespread in Yunan Province, China. However, the relationships between continuous cropping maca systems and microbes are not well understood. The objective of this study was to determine the effects of continuous cropping maca systems (Maca with 0, 1, 2, and 3 years of continuous cultivation) on the soil microbial community. The results showed that the soil organic matter, total N, total P, and total K contents, as well as maca fresh and dry weight, decreased significantly with increased continuous cropping years. Interestingly, qPCR analysis showed that the bacterial and fungal abundance (DNA levels) decreased and active bacterial and fungal abundance (RNA levels) increased with cropping years from the first to the third cropping (p < 0.05). Moreover, the abundance of actinomycetes in the CK soil was significantly higher than that in the other maca soils. In addition, the continuous cropping system resulted in rich diversity in the fungal structure and had little effects on the bacterial and actinomycete communities. Acidobacteria (50%) and Ascomycota (58.3%) were detected in the continuous cropping maca soils. Based on the present results, continuous cropping of maca not exceeding two years could be optimal to maintain soil nutrition and microbial community.     

Factors controlling the removal of sulfate and acidity from the waters of an acidified lake

Although Lake Anna, an impoundment in Central Virginia, receives acid mine drainage (AMD) from Contrary Creek, the effects of the AMD pollution on the lake are less severe than expected. Previous work at Lake Anna has shown that bacterial sulfate reduction in the lake sediments plays an important role in the recovery of the lake from the AMD inputs. Sulfate removal rates were measured in sediment microcosms under a variety of experimental conditions to determine the factors controlling the rate of sulfate and acidity removal from the lake water. Sulfate removal rates were not significantly different over the short term (3 weeks) in summer sediment microcosms incubated at 6 vs 26 °C. Winter sediment microcosms showed no significant sulfate removal during the 18 day experiment when incubated at either 6 or 28 °C. Thus there is a strong seasonal temperature effect in Lake Anna sediments but no significant short term effect. Simulated AMD, with and without Fe, was added to sediment microcosms collected from an unpolluted part of the lake. The microcosms with Fe had significantly higher rates of sulfate removal indicating that Fe plays an important role in transporting sulfate to the sediment and/or in preventing oxidation of the reduced sulfide. After 27 days, from 54 to 96% of the added sulfate in the simulated AMD was recovered as FeS or S⁰ in the top 4 cm of sediment. In a separate experiment, ³⁵S-SO _inf4 ^sup2? was found to attach to precipitating Fe oxyhydroxides (1.5 to 4.7 mol SO _inf4 ^sup2? mol^?1 Fe precipitate) upon mixing Contrary Creek (AMD) and Lake Anna waters. Results of this study suggest that sulfate removal may be more rapid in metal rich AMD systems thans in metal poor systems characteristic of those which receive acidic deposition.     

Influx and concentration of triazine pesticides in the Amaterska cave system,Moravian Karst,Czech Republic

Purpose

The aim of this study was to detect three triazine pesticides and their metabolites in the drip water and the sediment of the Amaterska cave system. Diversity of the bacterial community in the sediment was also assessed, and the potential role of bacteria in degradation of these pesticides was evaluated.

Materials and methods

Triazines and their metabolites were analyzed in the soil, drip water, and sediment of the Amaterska cave system area in seven sampling sites (S1–S7) based on the above ground cover that included forest, permanent grassland, and agriculture cropland. The bacterial community in the cave sediments (S1–S6) was also analyzed using the Illumina sequencing of the V3 and V4 regions of 16S rDNA.

Results and discussion

Triazines were present in the soil and drip water in all sites below grassland and agricultural land but not under the forest area. Only atrazine metabolites were detected in the surface soil. In contrast, atrazine was detected in all cave sediments regardless of above ground cover, and this is likely due to the occasional alluvial influx. The overall prevalence of bacteria potentially capable of atrazine degradation in the cave sediment ranged from 13.4 to 64.0% of the entire bacterial community. The concentrations of atrazine in the cave sediment were 16 to 70 times higher than in those in drip water.

Conclusions

High concentrations of atrazine in the cave sediment indicate a slow degradation rate of triazines in the cave likely due to low temperatures and absence of photolysis. The main source of atrazine in the Amaterska cave system is likely not drip water but the alluvial influx. Bacteria potentially capable of triazine degradation in the cave sediment were detected; however, their role in this process remains to be investigated.

     

Characteristics of bacterial community in the water and surface sediment of the Yellow River,China, the largest turbid river in the world

Purpose

Few studies have described the bacterial community structures of turbid rivers. In this paper, the characteristics of the bacterial community in the water and surface sediment of the Yellow River, China, the largest turbid river in the world, were studied.

Materials and methods

Water and sediment samples were collected from six sites along the river. Bacterial community composition was determined using the 16S ribosomal RNA (rRNA) gene clone library technique. The relationship between environmental parameters and bacterial diversity was analyzed.

Results and discussion

A total of 1,131 gene sequences were obtained and clustered into 639 operational taxonomic units (at the 97 % identity level), with Proteobacteria as the predominant phylum. The Shannon index for water samples ranged from 3.39 to 4.40 and was generally higher than that in other rivers; this was probably due to the high suspended particulate sediment (SPS) concentration in the Yellow River, which can provide more habitats for both aerobic and anaerobic bacteria. Also, the bacterial diversity of the water samples was slightly higher than that of the surface sediment samples. The bacterial diversity of water increased along the river in the downstream direction, while there was no trend for the sediment. Redundancy analysis indicated that pH, dissolved organic carbon (DOC), and SPS were the main factors controlling the water bacterial community in the Yellow River, and pH, nitrate–nitrogen, and water content were the main factors for the surface sediment bacterial community.

Conclusions

This study indicated that the bacterial diversity of the Yellow River is generally higher than that in other rivers, suggesting that SPS plays an important role in regulating bacterial diversity and community structure in aquatic environments.     

Plant growth promoting bacteria increases biomass,effective constituent,and modifies rhizosphere bacterial communities of Panax ginseng

Purpose: The main aim of this study was to introduce and explore plant growth-promoting bacteria (PGPB) indigenous to ginseng, and to evaluate their ability to improve production and quality, and effect on rhizosphere niche in ginseng.

Materials and methods: Endophytic bacteria were isolated from root, stem, and leaf of ginseng from different sites and genotype in China and Korea, screened based on their beneficial properties as PGPB. Nine bacterial isolates were selected according to their plant growth properties including soluble phosphate and potassium, ammonia, auxin and siderophore producing, ACC deaminase, and antagonistic pathogen as well. Changes in ginseng after PGPB inoculation were evaluated with respect to the non-inoculated control.

Results and Conclusions: The PGPB isolates were identified as genera Bacillus, Lysinibacillus, Rhizobium, Stenotrophomonas, Erwinia, Ochrobactrum, Enterobacter and Pantoea based on 16S rRNA sequences. Inoculation of G209 and G119 increased not only plant height, root length, fresh weight, and dry weight, but also root activity and the amount of ginsenosides significantly. In particular, using the Illumina Miseq platform, the native bacterial community of rhizospheric soil maintained high community diversity and increased abundance of specific bacteria. Therefore, they may be play a crucial role in sustainable ginseng cultivating in farmland.     

RESPONSES OF TOMATO VAR. TINY TOM TO APPLICATION OF COPPER AND ZINC FERTILIZERS IN THREE LIMED TROPICAL PEAT SOILS OF SARAWAK

We assessed the response of the tomato variety “Tiny Tom” to the application of copper (Cu) and zinc (Zn) fertilizers in three tropical peat soils of Sarawak: mixed swamp forest, Alan forest and Padang Alan forest. Limed soils were used because peat soils in their natural condition are unsuitable to sustain healthy growth of most crops. Yield responses were correlated with added Cu and Zn using Mitscherlich model. Adequate levels of applied Cu and Zn were calculated as those which resulted in 90% of the maximum obtainable shoot dry weight. Application of Cu and Zn significantly (P ≤ 0.05) increased the shoot dry weight and the shoot Cu and Zn concentrations of tomato. Application of the equivalent of 8.3 kg Cu and 5.2 kg Zn per ha was required to achieve 90% of the maximum shoot dry weight. In tomato shoots, the critical concentration for Cu was 18 mg/kg and for Zn, 92 mg/kg. The corresponding concentrations for diethylenetriaminepentaaceticacid (DTPA) extractable Cu and Zn in the soils were 2.3 mg Cu kg ^?1 and 3.6 mg Zn kg ^?1 . However, the addition of Cu fertilizer also increased Zn uptake by tomato plant, probably by displacing native Zn that was weakly sorbed to the soil solid phase.     

Effects of soil‐surface microbial community phenotype upon physical and hydrological properties of an arable soil: a microcosm study

The nature of the first few millimetres of the soil surface strongly affects water infiltration rates, generation of run‐off, soil detachment and sediment transport. We hypothesized that the phenotypic community structure of the soil‐surface microbiota affects the physical and hydrological properties of an arable soil. A range of contrasting microbial community phenotypes were established in microcosms by manipulating the wavelength of light reaching the soil surface, with the microcosms being incubated in the field for approximately 6 months. Phenotypes were characterized by phospholipid fatty acid (PLFA), ergosterol and chlorophyll analysis. The microcosms were then subjected to simulated rainfall at an intensity of 60 mm hour⁻¹ for 20 minutes at a slope gradient of 9°. Water infiltration rates, run‐off generation, soil loss (including a particle‐size analysis of the sediment) and soil‐surface shear strength were quantified. Distinct microbial phenotypes developed on the soil surfaces with UV‐A and restricted‐UV treatments when compared with subsurface layers. There was significantly greater fungal biomass in the no‐light treatment when compared with all other treatments, with approximately 4.5 times more ergosterol being extracted from the subsurface layer of the no‐light treatment when compared with other treatments. The no‐light treatment produced the greatest amount of run‐off, which was approximately 15% greater than the restricted photosynthetically‐active radiation (PAR) treatment. Significant differences between treatments were also found in shear strengths, with increasing strength being correlated with increasing ergosterol concentration. Water infiltration, erosion and the sediment concentrations in run‐off were not significantly different between treatments. This work demonstrates that the quality of light reaching the soil surface affects the microbial phenotype, in turn producing functional consequences with regard to the physical and hydrological properties of arable soil surfaces.     

Influence of Rainfall and Basic Water Quality Parameters on the Distribution of Endocrine-Disrupting Chemicals in Coastal Area

Occurrence and distribution of three typical endocrine-disrupting chemicals (EDCs), nonylphenol mixture (NPs), bisphenol A (BPA), and 17α-ethynilestradiol (EE2), were investigated in the seawater, suspended solid, and sediment around the coastline of Shenzhen city. Field surveys were conducted in both dry season and rainy season to access the influence of rainfall and basic water quality parameters on the distribution of target EDCs. In the seawater, NPs, BPA, and EE2 ranged from 31 to 1,777 ng/l, from 11 to 777 ng/l, and from 10 to 269 ng/l, respectively. In the suspended solid, NPs, BPA, and EE2 were in the range from 3 to 289 ng/l, from 1 to 75 ng/l, and from 1 to 29 ng/l, respectively. In the sediment, NPs, BPA, and EE2 varied from 9 to 355 ng/g dry weight (dw), from 3 to 156 ng/g dw, and from 7 to 144 ng/g dw, respectively. With the increasing rainfall, the concentrations of target EDCs decreased in seawater and sediment and increased in suspended solid at all the sampling locations. Among the six measured basic water quality parameters, the volatile suspended solid value was positively related with the partition property of target EDCs between suspended solid and seawater. Based on the results of principal component analysis, dissolved organic carbon, total nitrogen, and total phosphorous had close relationships with the distribution of target EDCs in the seawater. Temperature and dissolved oxygen had little relationship with the distribution of target EDCs in the coastal area.     

Response of microbial communities to different doses of chromate in soil microcosms

The toxic effect of chromate on soil microbial communities is not well documented, although microorganisms control biogeochemical cycling, contribute to formation of soil structure, regulate the fate of organic matter applied to soil. In this study the effects of short- and middle-term chromate on the soil microbial community were investigated. The shifts in the size and in the diversity of culturable heterotrophic bacterial community, the resistance to Cr(VI) of heterotrophic bacteria, the presence of cyanobacteria, the activity of 19 enzymes, and the ATP content were monitored over time (120 days) in soil microcosms artificially contaminated with three concentrations of chromate (50, 250 and 1000 mg kg⁻¹ soil). The chromate contamination affected the structure and the diversity of the soil bacterial community. Bacterial strains isolated from the microcosm contaminated with the highest concentration of chromate were identified by 16S rDNA gene sequencing. All isolates belonged to the genus Pseudomonas, were able to reduce Cr(VI), and showed a high resistance to chromate. To our knowledge, this is the first report that shows Pseudomonas strains having the capability to resist up to 40 mM of Cr(VI) on minimal medium. The cyanobacterial group was more sensitive to chromate contamination than culturable heterotrophic bacteria. No cyanobacterial growth was detected in enrichment cultures from the soil polluted with the highest chromate concentration. Some enzymes were inhibited by high concentrations of chromate, whereas others were stimulated. The ATP content in microcosms was strongly affected by chromate. We conclude that the soil microbial community responds to chromate pollution through changes in community structure, in metabolic activity, and in selection for Cr(VI)-resistance.     

Iron and manganese transformation in louisiana salt and brackish marsh sediment

Abstract

The kinetics of the release of dissolved iron [Fe(II)], manganese [Mn(II)], and phosphate in salt and brackish marsh sediment and the exchange with the overlying water column were investigated. Sediment was incubated in laboratory microcosms and in sediment water columns in studying these exchanges. The rate constants of the dissolved Fe(II), Mn(II), and phosphate release in sediment suspensions were 2.02–2.28,0.08–0.117, and 4.18–5.38 μmol g^‐1 dry sediment d^‐1, respectively. In sediment‐water column studies, the rate constants (K) of dissolved Fe(II), Mn(II), and phosphate removal from the overlying water into the sediment were 0.755–0.989,0.0695–0.0949, and 0.315–0.448, day^‐1, respectively. The flux of dissolved Fe(II), Mn(II), and phosphates from the salt and brackish marsh sediment to the overlying water in the column studies were 2.56–4.93,1.05–1.689, and 208.6–428.9 mg m^‐2 d^‐1, respectively. The fluxes from salt marsh were slightly greater than those measured in brackish marsh, although these differences were not statistically significant.     

模拟人工湿地中硫酸盐氯霉素处理对细菌数量、湿地酶活性和生化作用的影响

【目的】细菌被认为是人工湿地中最重要的微生物成分,因为湿地中的一些生化过程均与细菌群落有关。然而,这一结论都是通过将细菌群落动态与湿地具体生化过程和废水净化效率进行比较得出的,因而是间接的,直接证据尚缺乏。本研究试图通过国际上通用的选择性抑制手段,再结合细菌数量、酶活性和生化过程分析,进一步认识细菌在人工湿地中的重要性。【方法】本研究依托垂直流模拟人工湿地进行。湿地从上至下,顺序地填充细砂（直径1~2 mm）、粗砂（直径6~12 mm）和石块（直径50~120 mm）3种填料。植物为香附子 （Cyperu srotundus L.）。废水为来自养猪场的排出液,废水灌溉采用间歇方式进行。废水的滞留时间为7 d,排空时间为0.5 d。共设置6个浓度的硫酸链霉素处理（0、 1.0、 1.5、 2.0、 2.5和3.0 mg/kg沙子）,调查了硫酸链霉素处理浓度与湿地填料中细菌数量、 酶活性和生化作用之间的关系。细菌数量用平板计数法测定,纤维素酶、 -葡糖糖苷酶、 蔗糖酶、 蛋白酶、 脲酶、 硝酸还原酶和酸性磷酸酶活性采用常规的酶学方法分析;纤维素降解作用、 氨化作用、 硝化作用、 反硝化作用、 有机磷降解作用和无机磷转化作用用室内培养分光光度法测定。【结果】随着硫酸链霉素处理浓度的增加,CMC纤维素酶、 -葡糖糖苷酶和蛋白酶活性未发生明显改变（P0.05）,而细菌数量、 脲酶、 硝酸还原酶和酸性磷酸酶活性却显著下降（P0.05）。在6种生化作用中,除了纤维素降解作用和无机磷转化作用没有发生显著变化外（P0.05）,其余4种生化作用（氨化作用、 硝化作用、 反硝化作用和有机磷降解作用）均随着硫酸链霉素浓度的增加而显著下降（P0.05）。主成分分析表明, 生化作用的总体变化清楚地区分了链霉素的不同浓度 (P 0.05),而酶活性的总体变化则未能区分。【结论】本研究突出了细菌在人工湿地氮和有机磷转化方面的重要性,因为细菌的逐渐抑制导致了与氮和磷循环有关的酶以及生化作用的显著降低。另一方面,还发现土壤生化作用的总体变化对链霉素的浓度梯度比酶活性敏感,这一规律是否具有普遍性还需进一步验证。     

Forest soil community responses to plant growth-promoting rhizobacteria and spruce seedlings

The influence of plant-growth-promoting rhizobacteria (PGPR) and spruce seedlings on the composition and activity of forest soil microbial communities was studied in a microcosm experiment in which sterile, sand-filled 25mm×150mm glass tubes were treated with a forest soil suspension containing Bacillus or Pseudomonas PGPR and 2-week-old spruce seedlings. Eighteen weeks after treatments were established, bacterial, actinomycete and fungal population sizes were determined by dilution plating, as were seedling dry weights and soil carbon substrate utilization profiles using Biolog plates. PGPR inoculation had little influence on the population sizes of actinomycetes or fungi. However, significant effects were detected on the total bacterial population size, primarily in microcosms without seedlings. Euclidean distances between treatments plotted on two dimensions by multidimensional scaling showed that the introduction of PGPR strains changed the type of microbial community, particularly when inoculated into soil without seedlings. Significant changes were also detected in one soil type in the presence of seedlings. Our results suggest that the type of soil community and the presence of seedlings are significant factors influencing the responses of soil communities to bacterial inoculation, and that for some soil communities, the presence of seedlings may mitigate perturbations caused by the introduction of PGPR. Received: 24 February 1997     

Development of pollution-induced community tolerance is linked to structural and functional resilience of a soil bacterial community following a five-year field exposure to copper

Copper (Cu) is accumulating in agricultural soils worldwide creating concern for adverse impacts on soil microbial communities and associated ecosystem services. In order to evaluate the structural and functional resilience of soil microbial communities to increasing Cu levels, we compared a Cu-adapted and a corresponding non-adapted soil microbial community for their abilities to resist experimental Cu pollution. Laboratory soil microcosms were set-up with either High-Cu soil from Cu-amended field plots (63 g Cu m⁻²) or with Low-Cu control soil from the same five-year field experiment. Laboratory treatments consisted of Cu amendments in the presence or absence of pig manure. Microbial activities (soil respiration, substrate-induced respiration, [³H]leucine incorporation), bacterial community structure (terminal restriction fragment length polymorphism, T-RFLP), community-level physiological profiles, and pollution-induced bacterial community tolerance (PICT detected using the [³H]leucine incorporation technique) were monitored for 12 weeks. The High-Cu and Low-Cu soil microbial communities initially exhibited almost identical structure and function and could only be distinguished from each other by their differential Cu tolerance. Experimental Cu pollution inhibited microbial activities, affected bacterial community structure, and induced further bacterial community tolerance to Cu. However, Low-Cu and High-Cu soil microbial communities showed essentially identical responses. Manure amendment did not protect against Cu toxicity and slightly increased Cu bioavailability as measured by a Cu-specific whole-cell bacterial biosensor. Our results indicate convergence of bacterial community structure and function in the High-Cu and Low-Cu soils during the five-year field experiment. We conclude that soil bacterial communities can exhibit structural and functional resilience to a five-year Cu exposure by virtue of their ability to develop Cu tolerance without affecting overall community structure. The observed increased Cu tolerance may involve phenotypic adaptation or selection at the micro-diversity level, for example an increased proportion of Cu-resistant strains within each bacterial species, which go undetected by T-RFLP community fingerprinting. Finally, our results indicate that Cu-dissolved organic matter complexes contribute to microbial toxicity in manure-amended soils implying that free Cu may comprise a poor predictor of metal toxicity.     

Horticultural Use of Copper-Based Fungicides Has Not Increased Copper Concentrations in Sediments in the Mid- and Upper Yarra Valley

The use of Cu-based fungicide can pose a risk to nearby surface water bodies due to the run-off of accumulated Cu from agricultural soils. In 2008, we conducted a reconnaissance survey of the presence and concentration of copper in sediments at 18 sites within the Yarra River Catchment, an important horticultural production system in south-eastern Australia. Observed Cu concentrations in sediment samples from the study sites (mean (95 % confidence interval) 12.0 (10.6–13.6)? mg/kg dry weight) were similar to the concentrations present in the samples from the reference sites (mean (95 % confidence interval) 12.0 (6.7–16.8)? mg/kg dry weight). The data on Cu and other metals in the sediments suggest that that there is unlikely to have been wide spread, diffuse, off-site transport of Cu from the soils of horticultural properties to nearby surface waterways in the Yarra River Catchment and that that observed sediment metal concentrations are unlikely to pose an ecological risk to sediment-dwelling organisms at the study sites.