外来种互花米草对江苏省潮间带生物地球化学过程的影响研究

Spartina alterniflora Loisel, a species vegetating in intertidal flats along the eastern coast of the United States, was introduced in China almost 30 years ago and has become an urgent topic due to its invasiveness in the coastal zone of China. The impacts of this alien species S. alterniflora on intertidal ecosystem processes in the Jiangsu coastland were investigated by comparing the sediment nutrient availability and trace element concentration characteristics in a mud flat and those of a four-year old Spartina salt marsh that had earlier been a mudflat. At each study site, fifteen plots were sampled in different seasons to determine the sediment characteristics along the tidal flats. The results suggested that Spartina salt marsh sediments had significantly higher total N, available P, and water content, but lower pH and bulk density than mudflat sediments. Sediment salinity, water content, total N, organic C, and available P decreased along a seaward gradient in the Spartina salt marsh and increased with vegetation biomass. Furthermore, the concentrations of trace elements and some metal elements in the sediment were higher under Spartina although these increases were not significant. Also, in the Spartina marsh, some heavy metals were concentrated in the surface layer of the sediment. The Spartina salt marsh in this study was only four years old; therefore, it is suggested that further study of this allen species on a longer time frame in the Jiangsu coastland should be carried out.     

外源铬对小白菜(Brassica chinensis L.)根际土壤微生物生物量和磷脂脂肪酸的剖面分布特征的影响

The effects of root activity on microbial response to cadmium （Cd） loading in the rhizosphere are not well understood. A pot experiment in greenhouse was conducted to investigate the effects of low Cd loading and root activity on microbial biomass and community structure in the rhizosphere of pakchoi （Brassica chinensis L.） on silty clay loam and silt loamy soil. Cd was added into soil as Cd（NO3）2 to reach concentrations ranging from 0.00 to 7.00 mg kg-1. The microbial biomass carbon （MBC） and community structure were affected by Cd concentration, root activity, and soil type. Lower Cd loading rates （〈 1.00 mg kg-1） stimulated the growth of pakchoi and microorganisms, but higher Cd concentrations inhibited the growth of microorganisms. The content of phospholipid fatty acids （PLFAs） was sensitive to increased Cd levels. MBC was linearly correlated with the total PLFAs. The content of general PLFAs in the fungi was positively correlated with the available Cd in the soil, whereas those in the bacteria and actinomycetes were negatively correlated with the available Cd in the soil. These results indicated that fungi were more resistant to Cd stress than bacteria or actinomycetes, and the latter was the most sensitive to Cd stress. Microbial biomass was more abundant in the rhizosphere than in the bulk soil. Root activity enhanced the growth of microorganisms and stabilized the microbial community structure in the rhizosphere. PLFA analysis was proven to be sensitive in detecting changes in the soil microbial community in response to Cd stress and root activity.     

Microbial Activity Indices： Sensitive Soil Quality Indicators for Trace Metal Stress

Physicochemical properties, total and DTPA （diethylenetriaminepentaacetic acid）-extractable Cu, Zn, Pb and Cd contents, microbial biomass carbon （C） content and the organic C mineralization rate of the soils in a long-term trace metal-contaminated paddy region of Guangdong, China were determined to assess the sensitivity of microbial indices to moderately metal-contaminated paddy soils. The mean contents of total Cu, Zn, Pb and Cd were 251, 250, 171, and 2.4 mg kg^-1 respectively. DTPA-extractable metals were correlated positively and significantly with total metals, CEC, and organic C （except for DTPA-extractable Cd）, while they were negatively and highly significantly correlated with pH, totall Fe and Mn. Metal stress resulted in relatively low ratios of microbial biomass C to organic C and in remarkable inhibition of the microbial metabolic quotient and C mineralization rate, which eventually led to increases in soil organic C and C/N. Moreover, microbial respiratory activity showed a stronger correlation to DTPA-extractable metals than to total metal content. Likewise, in the acid paddy soils some “linked” microbial activity indices, such as metabolic quotient and ratios of basal respiration to organic C, especially during initial incubation, were found to be more sensitive indicators of soil trace metal contamination than microbial biomass C or basal respiration alone.     

氧化势影响下的滇池沉积物孔隙水磷浓度变化

The sediment redox potential was raised in the laboratory to estimate reduction of internal available phosphorus loads, such as soluble reactive phosphorus （SRP） and total phosphorus （TP）, as well as the main elements of sediment extracts in Dianchi Lake. Several strongly reducing substances in sediments, which mainly originated from anaerobic decomposition of primary producer residues, were responsible for the lower redox potential. In a range of -400 to 200 mV raising the redox potential of sediments decreased TP and SRP in interstitial water. Redox potentials exceeding 320 mV caused increases in TP, whereas SRP maintained a relatively constant minimum level. The concentrations of Al, Fe, Ca^2＋, Mg^2＋, K^＋, Na^＋ and S in interstitial water were also related to the redox potential of sediments, suggesting that the mechanism for redox potential to regulate the concentration of phosphorus in interstitial water was complex.     

长期施肥黑土微生物区系及功能多样性的变化

Black soil （Mollisol） is one of the main soil types in northeastern China. Biolog and polymerase chain reactiondenaturing gradient gel electrophoresis （PCR-DGGE） methods were used to examine the influence of various fertilizer combinations on the structure and function of the bacterial community in a black soil collected from Harbin, Heilongjiang Province. Biolog results showed that substrate richness and catabolic diversity of the soil bacterial community were the greatest in the chemical fertilizer and chemical fertilizer＋manure treatments. The metabolic ability of the bacterial community in the manure treatment was similar to the control. DGGE fingerprinting indicated similarity in the distribution of most 16S rDNA bands among all treatments, suggesting that microorganisms with those bands were stable and not influenced by fertilization. However, chemical fertilizer increased the diversity of soil bacterial community. Principal com- ponent analysis of Biolog and DGGE data revealed that the structure and function of the bacterial community were similar in the control and manure treatments, suggesting that the application of manure increased the soil microbial population, but had no effect on the bacterial community structure. Catabolic function was similar in the chemical fertilizer and chemical fertilizer＋manure treatments, but the composition structure of the soil microbes differed between them. The use of chemical fertilizers could result in a decline in the catabolic activity of fast-growing or eutrophic bacteria.     

长期重金属胁迫下的土壤微生物特征: 沈阳张士污灌区的案例研究

Soil samples were collected from Zhangshi Wastewater Irrigation Area in the suburb of Shenyang City, China, an area with a 30-year irrigation history with heavy metal-containing wastewater. The chemical properties and microbial characteristics of the soils were examined to evaluate the present situation of heavy metal pollution and to assess the soil microbial characteristics under long-term heavy metal stress. In light of the National Environmental Quality Standards of China, the soil in the test area was heavily polluted by Cd and to a lesser degree by Zn and Cu, even though wastewater irrigation ceased in 1993. Soil metabolic quotient （qCO2） had a significant positive correlation, while soil microbial quotient （qM） had a negative correlation with content of soil heavy metals. Soil microbial biomass carbon （MBC） had significantly negative correlation with Cd, but soil substrate~induced respiration （SIR）, dehydrogenase activity （DHA）, cellulase activity, and culturable microbial populations had no persistent correlations with soil heavy metal content. Soil nutrients, except for phosphorous, showed positive effects on soil microbial characteristics, which to a certain degree obscured the adverse effects of soil heavy metals. Soil Cd contributed more to the soil microbial characteristics, but qM and qCO2 were more sensitive and showed persistent responses to heavy metals stress. It could be concluded that qM and qCO2 can be used as bioindicators of heavy metal pollution in soils.     

温室集约化生产系统对土壤质量的影响

Composite top- and subsoil samples were collected from the greenhouses in the Al-Balawneh area,Jordan,where intensive greenhouse production system（IGPS） has been practiced since 1998,to study the impact of IGPS on soil quality as measured by the chemical and biological properties to develop a sustainable production system.The study showed that IGPS led to higher electrical conductivity in top- and subsoils compared to an uncultivated soil（control）.Quality and amount of irrigation water,lack of efficient drainage,and quantity and types of applied fertilizers were major factors resulting in salt buildup.IGPS resulted in lower total N（TN） and NO₃-N in the soil compared to the control.The lower TN was due to crop uptake,microbial immobilization,volatilization,and irregular application of composted animal manure or poultry manure.In contrast,higher residual Olsen-P content was detected in both soil layers of greenhouses than in the control.Residual P was classified as very high in the topsoil layers and sufficient to high in the subsoil layers.Residual available K in the soils of greenhouses was relatively lower than that in the control and it was,however,classified as high to very high.A large increase of Cl and a considerable decrease in the bacterial count were observed in both soil layers of IGPS compared to the control treatment.Economically sustainable soil management practices need to be adopted by farmers to achieve a sustainable and profitable production.This can be accomplished through education,targeted towards the farming community in the central Jordan Valley.     

黄河三角洲退化湿地微生物群落特性研究

Five different sites with a soluble salt gradient of 3.0--17.7 g kg-1 dry soil from the coast to the inland were selected, and the microbial population size, activity and diversity in the rhizospheres of five common plant species and the adjacent bulk soils (non-rhizosphere) were compared in a degraded wetland of the Yellow River Delta, Shandong Province, China to study the effects of soil environment (salinity, seasonality, depth, and rhizosphere) on microbial communities and the wetland’s ecological function, thus providing basic data for the bioremediation of degraded wetlands. There was a significant negative linear relationship between the salinity and the total number of microorganisms, overall microbial activity, or culturable microbial diversity. Salinity adversely affected the microbial community, and higher salinity levels resulted in smaller and less active microbial communities. Seasonal changes were observed in microbial activity but did not occur in the size and diversity. The microbial size, activity and diversity decreased with increasing soil depth. The size, activity and diversity of culturable microorganisms increased in the rhizospheres. All rhizospheres had positive effects on the microbial communities, and common seepweed had the highest rhizosphere effect. Three halophilic bacteria (Pseudomonas mendocina, Burkholderia glumae, and Acinetobacter johnsonii) were separated through BIOLOG identification, and common seepweed could be recommended for bioremediation of degraded wetlands in the Yellow River Delta.     

挪威北部土壤微生物活性的季节变化

Seasonal development of soil microbial activity and bacterial biomass in sub-polar regions was investigated to determine the impacts of biotic and abiotic factors, such as organic matter content, temperature and moisture. The study was performed during spring thaw from three cultivated meadows and two non-cultivated forest sites near Alta, in northern Norway. Samples from all five sites showed increasing respiration rates directly after the spring thaw with soil respiration activity best related to soil organic matter content. However, distributions of bacteria] biomass showed fewer similarities to these two parameters. This could be explained by variations of litter exploitation through the biomass. Microbial activity started immediately after the thaw while root growth had a longer time lag. An influence of root development on soil microbes was proposed for sites where microorganisms and roots had a tight relationship caused by a more intensive root structure. Also a reduction of microbial activity due to soil compaction in the samples from a wheel track could not be observed under laboratory conditions. New methodological approaches of differential staining for live and dead organisms were applied in order to follow changes within the microbial community. Under laboratory conditions freeze and thaw cycles showed a damaging influence on parts of the soil bacteria. Additionally, different patterns for active vs. non-active bacteria were noticeable after freeze-thaw cycles.     

土壤微生物群落结构与多样性对农田集约化管理程度降低的响应

Using a scheme of agricultural fields with progressively less intensive management （deintensification）, different management practices in six agroecosystems located near Goldsboro, NC, USA were tested in a large-scale experiment, including two cash-grain cropping systems employing either tillage （CT） or no-tillage （NT）, an organic farming system （OR）, an integrated cropping system with animals （IN）, a successional field （SU）, and a plantation woodlot （WO）. Microbial phospholipid fatty acid （PLFA） profiles and substrate utilization patterns （BIOLOG ECO plates） were measured to examine the effects of deintensification on the structure and diversity of soil microbial communities. Principle component analyses of PLFA and BIOLOG data showed that the microbial community structure diverged among the soils of the six systems.Lower microbial diversity was found in lowly managed ecosystem than that in intensive and moderately managed agroecosystems, and both fungal contribution to the total identified PLFAs and the ratio of microbial biomass C/N increased along with agricultural deintensification. Significantly higher ratios of C/N （P 〈 0.05） were found in the WO and SU systems, and for fungal/bacterial PLFAs in the WO system （P 〈 0.05）. There were also significant decreases （P 〈 0.05） along with agricultural deintensification for contributions of total bacterial and gram positive （G＋） bacterial PLFAs.Agricultural deintensification could facilitate the development of microbial communities that favor soil fungi over bacteria.     

Effect of organic mulches on soil bacterial communities one year after application

The application of organic mulches as a soil cover is effective in improving the quality of soil. However, very little information is available on the effect of mulches on the soil microbial community. In this study, we investigated the effect of various organic mulches on soil dehydrogenase activity (DHA) and microbial community structures in the top 1 cm and 5 cm below the soil surface 1 year after application of the mulches. DHA was stimulated at both depths in plots mulched with grass clippings (GC), but was not significantly different from the control for the other mulch treatments. Fatty acid methyl ester (FAME) analysis and denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction-amplified 16S rDNA fragments were used to assess changes in the soil microbial community structure. Cluster analysis and principle component analysis of FAME profiles showed that only soil mulched with pine chips distinctively clustered from the other treatments. At the soil surface, bacterial DGGE profiles revealed that distinct shifts in several bacterial populations occurred in soils mulched with GC and eucalyptus yardwaste (EY), while DGGE profiles from soil at the 5 cm depth revealed no distinct changes. Changes in bacterial diversity at the soil surface under different mulches were calculated based on the number of bands in the DGGE profile using the Shannon-Weaver index of diversity ( H). Compared to the control ( H =0.9), the GC- and EY-treated soils showed slightly increased bacterial diversity, with an H of 1.1 and 1.0, respectively. These results indicate that the long-term effect of organic mulches on the soil microbial activity and community structure is highly dependent upon the type of mulch and is mostly exerted in the top few centimeters of the soil profile.     

Salt marsh rhizosphere affects microbial biotransformation of the widespread halogenated contaminant tetrabromobisphenol-A (TBBPA)

Estuarine sediments are the repository for a wide range of contaminants. Anthropogenic impacts and variations in the belowground biomass of salt marsh plants potentially select for different sediment microbial communities with different functional capabilities, including the ability to biotransform anthropogenic contaminants. There are large differences in both root morphology and the amount of fine root biomass of Spartina alterniflora and Phragmites australis; Spartina is the species commonly used to replace Phragmites in northeastern US salt marsh restoration projects. Our study compared the effect of these two macrophyte species on sediment microbial communities responsible for the biotransformation of the halogenated flame retardant tetrabromobisphenol A (TBBPA). Sediments were obtained from contaminated and uncontaminated salt marsh field sites in New Jersey. Anaerobic methanogenic sediment microcosms were established and incubated for up to 130 days. TBBPA was reductively dehalogenated resulting in the transient formation of two intermediates, identified as tribromobisphenol A and dibromobisphenol A, and the formation and accumulation of bisphenol A (BPA) as the end product. Spartina sediments from both sites were found to dehalogenate TBBPA more rapidly than the Phragmites or unvegetated sediments, resulting in greater production of BPA. Microbial community diversity as measured by in situ sediment phospholipid fatty acid (PLFA) composition prior to TBBPA exposure, was found to be higher in the uncontaminated sediments; differences in microbial PLFA diversity were not seen in contaminated sediments associated with either the different plant species or unvegetated sediment. The results of this study demonstrate that these two plant species affected sediment microbial community function with respect to dehalogenation capabilities, even though the disturbed and undisturbed sediments varied in microbial community composition.     

Chemical and Microbiological <Emphasis Type="Italic">in situ</Emphasis> Characterization of Benthic Communities in Sediments with Different Contamination Levels

Background  River sediments are natural habitats of complex bacterial and fungal communities and therefore play a decisive role in the mineralization process of organic matter in freshwater systems. By means of comparative temporal and spatial analyses of microbial communities, the in situ impact of anthropogenically generated pollutants on these biofilm associations can be assessed and discriminated from seasonal variations. Aim  The aim was the adaptation of hybridization with fluorescently labelled rRNA-targeted oligonucleotides (FISH) for the in situ characterization of the structural and functional diversity of native microbial communities in complex lotic sediments. The impact of qualitatively and quantitatively different water pollutants on the microbial diversity, metabolic potential, and relative abundance of characteristic bacterial groups was assessed by oligonucleotide probes on different phylogenetic levels. In particular, sulfate reducing bacteria (SRB) were investigated to evaluate their potential applicability as microbial biomonitors in sediments. Methods  Sediment samples from the German lowland rivers Elbe and Oder were investigated over 12 months with regard to physico-chemical parameters and the composition of the attached microbial communities. Mechanical treatment including ultrasonification and sagitation under aerobic conditions combined with the use of pyrophosphate ensured the equal dispersion of fixed microbial cells within the sediment samples. The optimized whole-sediment FISH-technique was combined with an improved cell extraction procedure and applied, due to the specific grain size fraction distribution, at the different sampling sites. Resultsand discussion  Up to 85.6% of the total bacterial cell counts as determined by DAPI (4’, 6-diamidino-2-phenylindole) staining could be successfully monitored by the eubacterial oligonucleotide probe set EUB338, EUB338-II and EUB338-III, simultaneously indicating a high proportion of Eubacteria and the high metabolic potential of the bacterial community. Desulfobacteriaceae could be detected by the specific probe SRB385Db in various relative percentages ranging from 2.4 to 16.0% of the total bacterial cell counts. The total number of bacteria and the metabolic potential of sediment related bacteria were barely affected by the different pollution pattern of the sampling sites. Conclusions  The pre-treatment step as conducted by cell extraction as well as the FISH hybridization procedure was successfully optimized to the specific conditions present within freshwater sediments. Beside seasonal variations, particularly occurring at hydrologically influenced sites, sampling sites with different pol lution levels could be successfully distinguished by the relative abundance of Desulfobacteriaceae used as microbial indicator organisms. Outlook  The integration of ongoing insights into pollution induced changes of natural bacterial consortia should result in a system of ecotoxicological classes representing the different ecological status of riverine systems. Physiological directed methods like Community Level Physiological Profiling (CLPP) or Pollution Induced Community Tolerance (PICT), and structural techniques as FISH or microarrays should be used to investigate the influence of harmful substances on the biodiversity in natural microbial sediment communities.     

CLPP and EEA profiles of microbial communities in salt marsh sediments

Objective  Microbial communities are a central component of trophic dynamics and biogeochemical processes on coastal systems, since most of the processes in sediments are mediated by microorganisms and carried out by enzymes. Microorganisms play a key role in decomposition processes in salt marsh sediments, although the significance of microbial dynamics is largely unexplored. A culture-dependent (Ecoplate) and a culture-independent (extracellular enzyme activity [EEA]) approaches were evaluated in their ability to distinguish the catabolic potential among sediments from Tagus estuary salt marshes with different proximities to anthropogenic sources. Methods  Ecoplate was used to analyse the salt marsh community-level physiological profiles (CLPPs). Results were expressed as the net area under the curve for each of the 31 response wells over a 3-day incubation period in two sediment horizons. The catabolic profiles for salt marsh samples were analysed by Principal Component Analysis (PCA) and hierarchic clustering methods. EEA was analysed by fluorescein diacetate (FDA) hydrolysis in two sediment horizons. The FDA is catalysed by extracellular enzymes, i.e. esterases, lipases and partially by proteases. Results were expressed as μg g⁻¹d wt h⁻¹. Results and Discussion  In this study the CLPP and EEA data were not generally correlated. In Corroios salt marsh only in surface sediments higher net areas corresponded to higher extracellular enzymatic activity, and in Alcochete deep sediments lower net areas corresponded to lower enzymatic activity. Although EEA profiles more directly reflect the inherent activity of resident community in each salt marsh sample, the CLPP profiles provide better assessments of diversity. ESS-Submission Editor: Prof. Dr. Peter Schroeder, Institute of Soil Ecology, Department of Rhizosphere Biology, GSF — National Research Center for Environment & Health, Ingolstaedter Landstrasse 1, 85758 Neuherberg, Germany (peter.schroeder@gsf.de)     

Indication of Soil Microbial Activity by Electrical Signals of Microbial Fuel Cells with Re-Vegetated Red Soils

Electrical signals generated by microbial fuel cells (MFCs) may potentially indicate overall soil microbial activity. This study aimed to validate whether a significant correlation existed between soil microbial activity and electrical signals in different soils. Re-vegetated red soils with four vegetation types and unplanted eroded red soil were collected and packed into MFCs. The voltage of the MFCs was recorded during operation. Electrical signals including start-up time (ST), peak voltage, and coulomb quantity were extracted from the voltage curves. Soil dehydrogenase activity (DHA) was determined as a reference method to verify the reliability of the electrical signals. After MFC operation, the anodic bacterial community was analyzed by Illumina sequencing based on the 16S rRNA gene. The results indicated that ST was significantly correlated with DHA, along with soil organic carbon content. The linear regression model described the optimal relationships for ST and DHA. Clostridium and Acinetobacter constituted the dominant genera on the anode of the MFCs. The results demonstrated that ST may indicate soil microbial activity in re-vegetated red soils.     

Evaluation of two bacterial delivery systems for in-situ remediation of PAH contaminated sediments

Intention, Goal and Background  Contaminated sediments represent a significant, worldwide environmental problem since they contain a mixture of different xenobiotics and heavy metals. The presence of mixed contamination presents a unique set of obstacles for remediation efforts. Often sediment remediation occurs as an ex-situ application (i.e., after dredging) in an attempt to minimize some of the problems. However, dredging poses it’s own issues. It does not address contaminated water and often material is not completely removed thereby leaving a long-term residual contamination source in the waterway. Objective  The potential of bio remediation to treat sediments contaminated with polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, and heavy metals was addressed. The primary objective was to assess two delivery mechanisms for microbial inoculation to facilitate in-situ remediation of PAH contaminated sediments. Methods  Simulated river beds were constructed to mimic the Mahoning River. Contaminated sediment from the river was added to each reactor at a uniform depth, followed by the addition of river water. Fifteen inoculation points were used in each simulated river bed to ensure adequate microbial populations. One tank was inoculated with an acclimated bacteria solution as a free suspension. The other tank was inoculated with an attached growth biofilm system. Sediment samples were taken throughout the experiment and the percent PAH degradation determined. Water characteristics (DO, pH, bacterial activity, etc.) were also tracked as corroborating evidence. Results and Discussion  The monitoring sites indicated that an attached growth system was more effective, and achieved a 99% PAH degradation efficiency at some of the sampling sites. Tracking individual PAH compounds also indicated a higher overall microbial activity with the attached growth system. This activity was evident by the formation and subsequent biodegradation of lower molecular weight degradation byproducts. However, more of the sediment area was treated by the free suspension inoculum due to the ease of microbial migration. Conclusions  The applicability of using an aerobic microbial consortium composed ofMycobacterium sp., Pseudomonas aeruginosa, andPseudomonas flourescens to treat contaminated sediment was demonstrated. In addition, it was found that introducing the consortium as an attached growth was more effective than when delivered as a free suspension. Recommendation and Outlook  The results demonstrated that the consortium was effective at treating the PAHs present in the contaminated soil. An additional study to evaluate the consortium’s effectiveness at remediating the PCB present in the sediment is warranted. Optimization of the consortium-nutrient combination could enable a treatment approach to effective for all the organic contaminants present. Although this would not address the heavy metals present in the sediment, it would afford a great opportunity at remediating a severely contaminated sediment system.     

Relating microbial community structure and environmental variables in mangrove sediments inside Rhizophora mangle L. habitats

This study aimed to access the structure of microbial communities in sediments in the root zone of the red mangrove (Rhizophora mangle) in three sites with an increasing distance from the sea inside a mangrove forest in two distinct periods (dry and wet seasons) using denaturing gradient gel electrophoresis (DGGE). These data were correlated to environmental variables and sediments characteristics by using redundancy analysis (RDA) which revealed that the distribution of the microbial communities is significantly (p < 0.05) influenced by the silt–clay percentages for both Bacteria and Archaea and organic matter content significantly influences the distribution of Archaea. The archaeal community also exhibited an annual clustering pattern. The sites had only 30% and 35% of similarity of bacterial and archaeal communities, respectively, and this could be interpreted as being the core microbiome of R. mangle. Thus the spatial distribution of microbial communities inside the red mangrove habitats seems to be primarily controlled by the abiotic variables of each habitat.     

不同底栖生物扰动对沉积物渗透性的影响

[目的]探讨不同生物扰动对沉积物成分、粒径分布和渗透性的影响,为河流污染治理与潜流带修复提供科学依据。[方法]通过室内模拟沉积物中摇蚊幼虫(Chironomid larvae),颤蚓(Tubificid)和尖膀胱螺(Physa acuta)的生物扰动过程,研究不同底栖生物扰动对河流潜流带沉积物渗透系数的影响。[结果]混合生物组中,摇蚊幼虫和尖膀胱螺组合为渗透性能加强最大的一组。生物扰动作用通过改变沉积物的物理特性促使其结构疏松,孔隙增大,从而对沉积物颗粒粒径大小和分布区域产生明显干预作用,从而影响沉积物的渗透性。摇蚊幼虫对沉积物成分变化及粒径分布影响最大,使沉积物渗透性增强;颤蚓的淤塞作用主要发生在水-沉积物界面以下3~9cm,导致渗透性减弱;尖膀胱螺对沉积物粒径分布的影响不明显。[结论]在同一沉积物环境条件下,单一物种组中摇蚊幼虫和尖膀胱螺对沉积物的渗透性呈促进作用,摇蚊幼虫的促进效果比尖膀胱螺更显著,颤蚓对沉积物渗透性呈削弱作用。     

Microbial biomass and activity in salt affected soils under arid conditions

The effects of salinity on the size, activity and community structure of soil microorganisms in salt affected arid soils were investigated in Shuangta region of west central Anxi County, Gansu Province, China. Eleven soils were selected which had an electrical conductivity (EC) gradient of 0.32–23.05 mS cm⁻¹. There was a significant negative exponential relationship between EC and microbial biomass C, the percentage of soil organic C present as microbial biomass C, microbial biomass N, microbial biomass N to total N ratio, basal soil respiration, fluorescein diacetate (FDA) hydrolysis rate, arginine ammonification rate and potentially mineralizable N. The exponential relationships with EC demonstrate the highly detrimental effect that soil salinity had on the microbial community. In contrast, the metabolic quotient (qCO₂) was positively correlated with EC, and a quadratic relationship between qCO₂ and EC was observed. There was an inverse relationship between qCO₂ and microbial biomass C. These results indicate that higher salinity resulted in a smaller, more stressed microbial community which was less metabolically efficient. The biomass C to biomass N ratio tended to be lower in soils with higher salinity, reflecting the bacterial dominance in microbial biomass in saline soils. Consequently, our data suggest that salinity is a stressful environment for soil microorganisms.