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1.

Purpose  

Iron’s fluctuation between the II (ferrous) and III (ferric) oxidation states has been coined as the “FeIII–FeII redox wheel.” Numerous studies have coupled the “iron redox wheel” with the biogeochemical cycle of carbon (C), nitrogen (N), sulfur (S), or phosphorus (P) individually in soils or sediments, but evidence suggests that the FeIII–FeII redox wheel drives the biogeochemical cycles interactively in a fluctuating redox microenvironment. The interactions of the FeIII–FeII redox wheel with the biogeochemical cycles of C, N, S, and P in the fluctuating redox environments were reviewed in this paper.  相似文献   

2.
The effect of chronic high groundwater nitrate loading on riparian forests is poorly understood. The growth patterns of northern white cedar (Thuja occidentalis) and related plant–soil processes were examined at four riparian sites in southern Ontario, Canada which have similar vegetation, soils, and hydrology but have differed in adjacent land use for >60 years. Fertilized cropland at two riparian sites produced groundwater-fed surface flows with high mean NO3–N concentrations of 9 and 31 mg l−1, whereas mean concentrations were <0.5 mg l−1 at two control sites down slope from forest. Tree-ring analysis at the two nitrate-rich sites indicated a positive growth trend in 1980–2004 and an absence of a positive growth trend in the 1945–1970 period that preceded high rates of synthetic nitrogen fertilizer use on cropland. However, a significant increase in growth also occurred in 1980–2004 at the two control riparian sites suggesting that high groundwater nitrate inputs did not influence tree growth. Cedar foliar and litter N content did not differ significantly between the high nitrate and control sites. Litter decomposition rates measured by the litterbag technique at a nitrate-enriched and control site were similar. Litter from a high nitrate and a control site produced a similar rate of potential denitrification in lab incubations of riparian surface peat. This study indicates that prolonged nitrate inputs in groundwater did not increase nitrogen uptake and growth of white cedar or stimulate decomposition and denitrification as a result of changes in the quality of plant material. In the absence of anthropogenic nitrate inputs, riparian wetland soils are typically high in ammonium and low in nitrate, and as a consequence, white cedar may have a limited ability to utilize nitrate.  相似文献   

3.
Hydraulic conductivity reduction caused by enhanced biological growth in sand was investigated. Studies were conducted using columns packed with three different sand sizes of 0.2, 0.3, and 0.4 mm. Phenol was used as a growth substrate at 15, 50, and 100 mg/L. Variations in piezometric head, substrate concentration, and biomass measured as volatile solids, were monitored in space and time. Reductions in hydraulic conductivity due to microbial growth were found to be 72% for the 0.4 mm, 82% for the 0.3 mm, and 86% for the 0.2 mm sand at phenol concentration of 15 mg/L. Similarly of 50 mg/L, the reductions were 94% for 0.4 mm sand, and 96% for 0.3 mm sand. Finally, at 100 mg/L, the reductions were 96% for 0.3 mm, and 98% for 0.2 mm sand. Phenol removal efficiencies varied from 88% to 94% depending on influent concentration and sand size. Hydraulic conductivity reduction correlated with average biomass density when biofilm density is high and was adversely affected by reduction in specific surface area. Anaerobic biofilms developed at phenol concentrations of 50 and 100 mg/L markedly reduced hydraulic conductivities of all three sand sizes by virtue of their gaseous biodegradation end products. At phenol concentrations of 50 and 100 mg/L hydraulic conductivity correlated with biomass densities per unit mass of sand and was less affected by biofilm thickness and specific surface area.  相似文献   

4.
In order to identify potential ecological risks associated with the environmental release of two Rhizobium meliloti strains, genetically engineered with the firefly-derived luciferase gene (luc), a pre-release greenhouse investigation was conducted. The upper 4 cm of soil columns (30 cm diameter; 65 cm depth), which were filled according to the horizons of an agricultural field (loamy sand), were inoculated with seeds of Medicago sativa (alfalfa) and R. meliloti cells at approximately 5×106 cells·g–1 soil. Four treatments were tested: inoculation with a non-engineered wild type strain (2011), strain L33 (luc +), strain L1(luc +, recA–) and non-inoculated controls. The fate of the engineered strains was followed by two methods: (1) selective cultivation and subsequent detection of bioluminescent colonies and (2) PCR detection of the luc gene in DNA, directly extracted from soil. Strain R. meliloti L33 declined to 9.0×104 cfu·g–1 soil within 24 weeks and to 2.8×103 cfu·g–1 soil within 85 weeks in the upper 25 cm of the soil columns. Decline rates for R. meliloti L1 were not significantly different. Vertical distribution analysis of the recombinant cells after 37 weeks revealed that in three of four columns tested, the majority of cells (>98%) remained above 10 cm soil depth and no recombinant cells occurred below 20 cm depth. However, in one column all horizons below 20 cm were colonized with 2.2×104 to 6.8×104 cfu g–1 soil. Ecological monitoring parameters included organic substance, total nitrogen, ammonium and nitrate, microbial biomass, culturable bacteria on four different growth media and the immediate utilization of 95 carbon sources (BiologGN) by soil-extracted microbial consortia. None of the parameters was specifically affected by the genetically engineered cells. Received: 6 December 1996  相似文献   

5.
 The influence of fertilizer N applied through nitrate and ammoniacal sources on the availability of nitrate, supply of C, and gaseous N losses via denitrification (using acetylene inhibition technique) in a semiarid subtropical soil (Typic Ustochrepts) was investigated in a growth chamber simulating upland [60% water-filled pore space (WFPS)], nearly saturated (90% WFPS), and flooded (120% WFPS) conditions. The rate of denitrification was very low in the upland soil conditions, irrespective of fertilizer N treatments. Increasing water content to nearly saturated and flooded conditions resulted in four- to sixfold higher rates of denitrification within 2 days, suggesting that the denitrifying activity commences quickly. Results of this study reveal that (1) under restricted aeration, these soils could support high rates of denitrification (∼6 mg N kg–1 day–1) for short periods when nitrate is present; (2) application of fertilizer N as nitrate enhances N losses via denitrification (∼10 mg N kg–1 day–1) – however, the supply of available C determines the intensity and duration of denitrification; (3) when fertilizer N is applied as an ammoniacal form, nitrification proceeds slowly and nitrate availability limits denitrification in flooded soil; (4) the nearly saturated soil, being partially aerobic, supported greater nitrification of applied ammoniacal fertilizer N than flooded soil resulting in higher relative rates of denitrification; and (5) under aerobic soil conditions, 26 mg mineral N kg–1 accumulated in control soil over a 16-day period, demonstrating a modest capacity of such semiarid subtropical soils, low in organic matter, to supply N to growing plants. Received: 7 June 1999  相似文献   

6.
Nitrate and nitrite reduction was studied in a waterlogged soil after γ-irradiation with 2.5 Mrad. Before irradiation and mineral-N addition the pH was controlled at 4.5, 6 and 8, and the redox potential controlled at 0, +200 and +400 mV Nitrate reduction rate increased with increasing pH as well as with decreasing redox potential. Nitrate reduction rate was doubled by decreasing the redox potential from +400 to 0 mV. At pH 4.5 almost no nitrite accumulated regardless of redox potential, while at pH 6 and 8 marked nitrite accumulation occurred at low redox potential. In relation to non-irradiation. γ-irradiation had a stimulating effect on nitrate reduction at pH 6 and 8 but a retarding effect at pH 4.5; nitrite reduction proceeded slower at pH 6 and 8 but at the same rate at pH 4.5. It has been demonstrated that nitrate and nitrite reduction can be carried out by radiation-resistant enzyme systems of non-proliferating cells of denitrifying organisms.  相似文献   

7.
In order to investigate the redox condition in soil aggregates, an approach using the inoculation of the soil bacteria Pseudomonas fluorescens C7R12, which affects soil redox, was developed. First, redox modifications were studied at the colony level in pure culture on solid synthetic medium. Then, the effect of strain inoculation on the redox status of soil aggregates was studied under controlled conditions with millimeter size aggregates from a Mollisol. A redox micro-electrode was employed to determine redox intensity (redox potential, E), which ranged from 240±70 to 110±25 mV at the surface of non-inoculated (control) and inoculated aggregates after 3 days. Differential pulse polarography (DPP) was employed to assess redox capacity (amount of electro-active compounds), which was higher (7.17 nA/mV) in inoculated aggregates than in the control samples (3.04 nA/mV). Similarities between redox potential depth profile for P. fluorescens colonies on plates and for some inoculated aggregate profiles suggested a patch colonisation of the surface of the aggregates by the redox effector strain. By comparison with non-inoculated aggregates, the influence of the inoculated strain on the redox status of the aggregates was observed to increase with the amount of some electroactive compounds with potential values from about −110 and +15-40 mV. Lower mean values and the limitation of the redox potential range fluctuation along the profiles from surface to 220 μm depth were also characteristics of the inoculated aggregates.  相似文献   

8.
The massive oil release from the Deep Water Horizon disaster has reemphasized the need to remediate oil impacted marshes. Due to the physically fragile nature of salt water marshes, bioremediation is often proposed as an appropriate technology and nutrient amendment is often proposed as a means of accelerating biodegradation of crude oil. However, no information is currently available concerning the efficacy of in situ nutrient amendments in Gulf Coast salt marshes. An experimental crude oil spill (142 l over 100 m2) was conducted to evaluate the efficacy of nitrogen amendment to stimulate bioremediation in a Spartina alterniflora dominated Louisiana salt marsh. A randomized complete block design with replication (n = 10) was utilized to test the hypothesis that additions of fast-release ammonium nitrate (60 g N/m2) and slow-release urea (30 g N/m2) fertilizers could enhance biodegradation of selected crude oil components in the marsh. Crude oil degradation was monitored by analyzing sediment samples for branched and unbranched alkanes over the 180-day study period. The compound/hopane ratio was used to correct for nonbiological losses. No consistent statistically significant effect of fertilizer addition on degradation rates was observed, despite success in increasing the porewater ammonium and NaCl-extractable ammonium over the time frame of the trial. Intrinsic pseudo-first order degradation rates of alkanes in all plots were substantial (0.003–0.008 day−1). Existing, background levels of N did not appear to limit biodegradation rates in Spartina-dominated salt marshes. These results suggest that nutrient amendments will not be successful in stimulation biodegradation of crude oil in these systems.  相似文献   

9.
In this article, work is presented which highlights the biological processing capacities of urban waste water within porous media of different textures. A comparative study on the growth of biomass coupled with the general mechanisms for gas transfer through two biological beds is undertaken. Infiltration-percolation beds are simulated using columns filled with sands of different origins and structures. These are periodically fed using an influent with a COD load of 525 mg/l and 54 mg/l of Kjeldahl nitrogen. The results obtained show that a balanced development of biomass, including growth and regression phases, is intrinsically related to the physical nature of the material support. Using core samples from the columns and oxymetry probes set at various heights, it is shown that both the vertical distribution of the biofilm in the columns and oxygenation of the porous media during a rest period also correlate with the support structure. The effectiveness of biological treatment is optimum for carbon with alluvial sand rather than crushed sand, with this tendency being significantly reversed for nitrogen abatement.  相似文献   

10.
Laboratory scale porous media biofilm reactors were used to evaluate the effect of biofilm thickness on media porosity and permeability. Media tested consisted of three different sizes of sand (0.4, 0.3, and 0.2 mm). A set of fifteen columns was used in this experiment, five columns for each size of sand. Columns were operated under constant piezometric head (2.5 m) conditions, resulting in a decreasing flow rate with biofilm development. During the experiment, variations in the piezometric head, substrate concentration, and growth in biomass as well as volatile solids were monitored in space and time. Phenol (15 mg/L) was used as a growth substrate. The reductions in hydraulic conductivity were found to be 97% for the coarse sand (0.4 mm), 96% for the medium size sand (0.3 mm), and 93.7% for the fine sand (0.2 mm). The respective removal of phenol in these columns was 96% for the coarser sand, 97.9% for the medium size sand, and 98.8% for the finer sand. Steady-state effluent phenol concentrations occurred simultaneously with uniform hydraulic conductivity reduction after 50 days of operation. The concentration of volatile solids near the column inlets and outlets, after 58 days of operation, ranged between 9.8 and 4.04 mg/g for the coarse sand, 11.2 and 6.2 mg/g for the medium size sand, and 11.8 and 6.2 mg/g of sand for the fine sand, respectively. The number of colonies near the column inlets and outlets was 2800 × 1010/mL and 1480 x 1010/mL for the coarse sand, and 2840 × 1010/mL and 1520 × 1010/mL for the medium sand, and 2890 × 1010/mL and 2120 × 1010/mL for the fine sand.  相似文献   

11.
 We studied the influence of soil compaction in a loamy sand soil on C and N mineralization and nitrification of soil organic matter and added crop residues. Samples of unamended soil, and soil amended with leek residues, at six bulk densities ranging from 1.2 to 1.6 Mg m–3 and 75% field capacity, were incubated. In the unamended soil, bulk density within the range studied did not influence any measure of microbial activity significantly. A small (but insignificant) decrease in nitrification rate at the highest bulk density was the only evidence for possible effects of compaction on microbial activity. In the amended soil the amounts of mineralized N at the end of the incubation were equal at all bulk densities, but first-order N mineralization rates tended to increase with increasing compaction, although the increase was not significant. Nitrification in the amended soils was more affected by compaction, and NO3 –-N contents after 3 weeks of incubation at bulk densities of 1.5 and 1.6 Mg m–3 were significantly lower (by about 8% and 16% of total added N, respectively), than those of the less compacted treatments. The C mineralization rate was strongly depressed at a bulk density of 1.6 Mg m–3, compared with the other treatments. The depression of C mineralization in compacted soils can lead to higher organic matter accumulation. Since N mineralization was not affected by compaction (within the range used here) the accumulated organic matter would have had higher C : N ratios than in the uncompacted soils, and hence would have been of a lower quality. In general, increasing soil compaction in this soil, starting at a bulk density of 1.5 Mg m–3, will affect some microbially driven processes. Received: 10 June 1999  相似文献   

12.
Effect of cropping systems on nitrogen mineralization in soils   总被引：3，自引：0，他引：3  
 Understanding the effect of cropping systems on N mineralization in soils is crucial for a better assessment of N fertilizer requirements of crops in order to minimize nitrate contamination of surface and groundwater resources. The effects of crop rotations and N fertilization on N mineralization were studied in soils from two long-term field experiments at the Northeast Research Center and the Clarion-Webster Research Center in Iowa that were initiated in 1979 and 1954, respectively. Surface soil samples were taken in 1996 from plots of corn (Zea mays L.), soybean (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) that had received 0 or 180 kg N ha–1 before corn and an annual application of 20 kg P and 56 kg K ha–1. N mineralization was studied in leaching columns under aerobic conditions at 30  °C for 24 weeks. The results showed that N mineralization was affected by cover crop at the time of sampling. Continuous soybean decreased, whereas inclusion of meadow increased, the amount of cumulative N mineralized. The mineralizable N pool (N o) varied considerably among the soil samples studied, ranging from 137 mg N kg–1 soil under continuous soybean to >500 mg N kg–1 soil under meadow-based rotations, sampled in meadow. The results suggest that the N o and/or organic N in soils under meadow-based cropping systems contained a higher proportion of active N fractions. Received: 10 February 1999  相似文献   

13.
 Azorhizobium caulinodans was directly inoculated onto rice plants in three short-term pot trials. Addition of increasing amounts of sucrose (23, 46, 92 kg ha–1) did not influence the N economy of the A. caulinodans-rice association during the early vegetative growth stage. A. caulinodans inoculation alone and in combination with the highest amount of sucrose had a significantly positive effect on the N balance, with small but significant N gains in the system. Application of 60 kg urea-N ha–1 had a negative impact on the N economy of the inoculated treatments. N losses increased and the amount of atmospheric N2 fixed and incorporated decreased significantly as compared to the amounts under the 20 kg urea-N ha–1 regime. However, N losses were low – a maximum of 8% – at the early vegetative growth stage under the conditions of the experiments. C limitation does not seem to be a limiting factor for the incorporation of fixed N2 in this bacteria-plant association. Biological N2 fixation caused by A. caulinodans inoculation was responsible for 14% of the plant N at the vegetative growth stage and under low N conditions. Received: 30 January 2000  相似文献   

14.
Biomarker and hydrochemical characteristics of geogenic arsenic-contaminated aquifers at Datong Basin, northern China, were analyzed to better understand the impact of organic matter (OM) biodegradation on arsenic enrichment in groundwater. The hydrochemical characteristics of high arsenic groundwater from the Datong Basin indicate that arsenic mobilization and iron and manganese oxide/hydroxide reduction were controlled by biodegradation of OM. The elevated value of alkalinity produced by microbial oxidation of OM is another important factor for arsenic mobilization via competitive sorption. Bulk geochemistry of the sediments shows that arsenic has close correlation with iron and manganese, indicating iron- and manganese-bearing minerals could be the major pools for arsenic. Results of biomarker analysis reveal that all the sediments contained natural petroleum-sourced hydrocarbons which may have undergone biodegradation, as suggested by the carbon preference index, C29 sterane, and the distribution pattern of hopanes. The presence of unresolved complex mixtures in all samples also indicates the natural petroleum origin of hydrocarbons and the effect of biodegradation. At some depths (5.4–11.8, 31–33.2, and 40–48.4 m below the land surface), the samples have low n-alkane content and no odd-over-even predominance, suggesting that indigenous microbes within the aquifer can preferentially remove the petroleum-sourced n-alkanes. The bioavailability of organic carbon is very important to promote the microbially mediated reductive dissolution of iron oxides/hydroxides and subsequent arsenic release from aquifer sediment into groundwater.  相似文献   

15.
 The response of the microbial community to changes in aeration status, from oxic to anoxic and from anoxic to oxic, was determined in arable soil incubated in a continuous flow incubation apparatus. Soil incubated in permanently oxic (air) and/or anoxic (O2-free N2) conditions was used as the control. Before experiments soil was preincubated for 6 days, then aeration status was changed and glucose added. Glucose concentration, extractable C, CO2 production, microbial biomass, pH and redox potential were determined 0, 4, 8, 12, 16, 24, 36 and 48 h after change of aeration status. If oxic conditions were changed to anoxic, the amount of glucose consumed was reduced by about 60%, and CO2 production was 10 times lower at the end of incubation compared to the control (permanently oxic conditions). Microbial biomass increased by 114% in glucose-amended soil but did not change in unamended soil. C immobilization prevailed over C mineralization. Redox potential decreased from +627 mV to –306 mV. If anoxic conditions were changed to oxic, consumption of glucose and CO2 evolution significantly increased, compared to permanently anoxic conditions. Microbial biomass did not change in glucose-amended soil, but decreased by 78% in unamended soil. C mineralization was accelerated. Redox potential increased from +238 to +541 mV. The rate of glucose consumption was low in anoxic conditions if soil was incubated in pure N2 but increased significantly when incubation was carried out in a CO2/N2 mixture. Received: 6 January 1999  相似文献   

16.
A simple predictive approach to solute transport in layered soils   总被引：1，自引：0，他引：1  
Solute transport through layered columns (repacked aggregates overlying sand) was studied under steady flow conditions. Predictions of transport were simplified by assuming that the distribution of solute travel times in one layer was not correlated with that in the other. The implications of this assumption were developed for the transfer function model (TFM) and the convection-dispersion model (CDM) of solute transport. The parameter values in each model were obtained from experiments carried out on columns containing only aggregates or sand.
The solutes used were nitrate (surface-applied) and chloride (previously distributed); predictions of the chloride movement were made using the parameter values for the nitrate. The predictions were tested against experimental values of drainage effluent concentration and solute concentration with depths in the columns (measured at the end of the experiments). The TFM (with an assumed lognormal distribution of travel times) and the CDM did not differ significantly, mainly because the spatial scale of the experiments was small.
Because the parameter values for the columns of aggregates or sand were determined from the drainage effluent data, they were average values for whole columns. These parameters were satisfactory for predicting drainage effluent concentration from the two-layer columns. However, they were not satisfactory for predicting the depth distribution of solute, particularly in the sand, because the water content of the sand increased with depth, unlike that of the aggregates, which was approximately constant with depth. The overall results of this study on materials of differing transport characteristics suggest that the assumption of uncorrelated travel times between layers has a potentially wide application. The approach taken here needs to be tested on undisturbed layered soils.  相似文献   

17.
Combinations of sequential anaerobic and aerobic process enhance the treatment of textile wastewater. The aim of this study was to investigate the treatment of diazo dye Reactive Black 5 (RB5)-containing wastewater using granular activated carbon (GAC)–biofilm sequencing batch reactor (SBR) as an integration of aerobic and anaerobic process in a single reactor. The GAC–biofilm SBR system demonstrated higher removal of COD, RB5 and aromatic amines. It was observed that the RB5 removal efficiency improved as the concentration of co-substrate in the influent increased. The alternative aeration introduced into the bioreactor enhanced mineralization of aromatic amines. Degradation of RB5 and co-substrate followed second-order kinetic and the constant (k 2) values for COD and RB5 decreased from 0.002 to 0.001 and 0.004 to 0.001 l/mg h, respectively, as the RB5 concentration increased from 100 to 200 mg/l in the GAC–biofilm SBR system.  相似文献   

18.
The changes of soil Eh and pH during decomposition of nitrates at different levels of glucose (0%; 0, 5% and 1.0%) and nitrates (0%; 0,5%; 1% and 2% KNO3) in water saturated soil samples (Ah horizon of a Mollic Gleysol) were examined. It was found that in the presence of 0–2% nitrates and 0,5–1% glucose in the soil with 1–2 days anaerobiosis at 20°C resulted in the increase of reduction processes and a decrease of redox potential up to 500 mV (Eh). Soil pH increased in the range of 2.5 units. The results from the model experiment - implying Eh > 200 mV and pH < 6.5 as range of nitrate stability in the soil studied - can be useful for field conditions both to predict the stability of nitrates in the soil environment and to create proper conditions for the effective use of carbon sources as a main factor of redox transformations.  相似文献   

19.
The effects of several dominant tillage and rotation systems on soil organic C content of different particle-size fractions were studied in Chernozemic soils from southwestern and east-central Saskatchewan, Canada. In an Orthic Brown Chernozem in southwestern Saskatchewan, 7 years of no-till cereal–fallow, imposed on a long-term tillage fallow–wheat rotation soil, resulted in 0.1 Mg C ha−1 more organic C mass in the sand + organic matter (OM) fraction of the 0- to 5-cm layer, whereas organic C associated with coarse silt (CS), fine silt (FS), coarse clay, and fine clay of 0- to 5- and 5- to 10-cm layers was less than that of the comparable tilled cereal–fallow system. Conversion of tilled fallow–wheat rotation soil to continuous cropping had a slight effect, whereas the organic C mass in all the size fractions was significantly increased in both 0- to 5- and 5- to 10-cm layers after alfalfa was introduced on tilled fallow–wheat as perennial forage for 10 years. In an Orthic Black Chernozem in east-central Saskatchewan that was cultivated and tilled using a cereal–fallow rotation for 62 years, organic C mass decreased in sand + OM, CS, and FS of 0- to 10-cm depth. Conversion of the tilled cereal–fallow cropland soil back to seeded grassland resulted in significantly more soil organic C in sand + OM fraction after 12 years of grass seed-down. The sand + OM fraction appears to be the size fraction pool initially most sensitive to adoption of management practices that are liable to sequester carbon in the soil.  相似文献   

20.
 Particle-size fractionation of a heavy metal polluted soil was performed to study the influence of environmental pollution on microbial community structure, microbial biomass, microbial residues and enzyme activities in microhabitats of a Calcaric Phaeocem. In 1987, the soil was experimentally contaminated with four heavy metal loads: (1) uncontaminated controls; (2) light (300 ppm Zn, 100 ppm Cu, 50 ppm Ni, 50 ppm V and 3 ppm Cd); (3) medium; and (4) heavy pollution (two- and threefold the light load, respectively). After 10 years of exposure, the highest concentrations of microbial ninhydrin-reactive nitrogen were found in the clay (2–0.1 μm) and silt fractions (63–2 μm), and the lowest were found in the coarse sand fraction (2,000–250 μm). The phospholipid fatty acid analyses (PLFA) and denaturing gradient gel electrophoresis (DGGE) separation of 16S rRNA gene fragments revealed that the microbial biomass within the clay fraction was predominantly due to soil bacteria. In contrast, a high percentage of fungal-derived PLFA 18 : 2ω6 was found in the coarse sand fraction. Bacterial residues such as muramic acid accumulated in the finer fractions in relation to fungal residues. The fractions also differed with respect to substrate utilization: Urease was located mainly in the <2 μm fraction, alkaline phosphatase and arylsulfatase in the 2–63 μm fraction, and xylanase activity was equally distributed in all fractions. Heavy metal pollution significantly decreased the concentration of ninhydrin-reactive nitrogen of soil microorganisms in the silt and clay fraction and thus in the bulk soil. Soil enzyme activity was reduced significantly in all fractions subjected to heavy metal pollution in the order arylsulfatase >phosphatase >urease >xylanase. Heavy metal pollution did not markedly change the similarity pattern of the DGGE profiles and amino sugar concentrations. Therefore, microbial biomass and enzyme activities seem to be more sensitive than 16S rRNA gene fragments and microbial amino-sugar-N to heavy metal treatment. Received: 21 January 2000  相似文献   

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