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1.
N dynamics in soil where wheat straw was incorporated were investigated by a soil incubation experiment using 15N-labelled nitrate or 15N-labelled wheat straw. The incubated soils were sampled after 7, 28, 54 days from the incorporation of wheat straw, respectively, and gross rates of N transformations including N remineralization and temporal changes in the amount of microbial biomass were determined.Following the addition of wheat straw into soils, rapid decrease of nitrate content in soil and increase of microbial biomass C and N occurred within the first week from onset of the experiment. Both the gross rates of mineralization and immobilization determined by 15N-ammonium isotope dilution technique were remarkably enhanced by the addition of wheat straw, and gradually decreased with time. Remineralization rate of N derived from 15N-labelled nitrate, and mineralization rate of N derived from 15N-labelled wheat straw was estimated by 15N isotope dilution technique using non-labelled ammonium. Remineralization rates of N derived from 15N-labelled nitrate were calculated to be 0.71 mg N kg−1 d−1 after 7 days, 0.55 mg N kg−1 d−1 after 28 days, and 0.29 mg N kg−1 d−1 after 54 days.Nearly 10% of the 15N-labelled N originally contained in the wheat straw was held in the microbial biomass irrespective of the sampling time. The amount of inorganic N in soil which was derived from 15N-labelled wheat straw ranged between 1.93 and 2.37 mg N kg−1.Rates of N transformations in soil with 15N-labelled wheat straw were obtained by assuming that the k value was equal to the 15N abundance of biomass N, and the obtained values were considered to be valid.  相似文献   

2.
The aim of this greenhouse experiment was the assessment of the influence of H2SeO3 at soil concentrations of 0.05, 0.15 and 0.45 mmol kg−1, on the activity of selected oxidoreductive enzymes in wheat (Triticum aestivum). The wheat plants were grown in 2 dm3 pots filled with dust-silt black soil of pH 7.7. Applied H2SeO3 caused activation of plant nitrate reductase at all concentrations, but activation of plant polyphenol oxidase at only two lower concentrations. The highest concentration caused inhibition of polyphenol oxidase and peroxidase. Plant catalase activity decreased under the influence of 0.15 and 0.45 mmol kg−1 concentration. After the final analysis Se was quantified in plants and soil. The amounts in plants were: control (unamended soil) 1.95 mg kg−1; I dose (0.05 mmol kg−1) 18.27 mg kg−1; II dose (0.15 mmol kg−1) 33.20 mg kg−1 and III dose (0.45 mmol kg−1) 38.37 mg kg−1, in soil: 0.265 mg kg−1; 3.61 mg kg−1; 10.53 mg kg−1; 30.53 mg kg−1; respectively. Simultaneously, a laboratory experiment was performed, where the activity of soil catalase and peroxidase were tested after 1, 3, 7, 14, 28, 56, and 112 days after Se treatment. Peroxidase activity in soil decreased with increasing Se content, over the whole experiment. The lowest dose of Se caused activation a significant 10% increase in catalase activity, but the influence of others doses was unclear.  相似文献   

3.
Physiological groups of soil microorganisms, total C and N and available nutrients were investigated in four heated (350 °C, 1 h) soils (one Ortic Podsol over sandstone and three Humic Cambisol over granite, schist or limestone) inoculated (1.5 μg chlorophyll a g−1 soil or 3.0 μg chlorophyll a g−1 soil) with four cyanobacterial strains of the genus Oscillatoria, Nostoc or Scytonema and a mixture of them.Cyanobacterial inoculation promoted the formation of microbiotic crusts which contained a relatively high number of NH4+-producers (7.4×109 g−1 crust), starch-mineralizing microbes (1.7×108 g−1 crust), cellulose-mineralizing microbes (1.4×106 g−1 crust) and NO2− and NO3− producers (6.9×104 and 7.3×103 g−1 crust, respectively). These crusts showed a wide range of C and N contents with an average of 293 g C kg−1 crust and 50 g N kg−1 crust, respectively. In general, Ca was the most abundant available nutrient (804 mg kg−1 crust), followed by Mg (269 mg kg−1 crust), K (173 mg kg−1 crust), Na (164 mg kg−1 crust) and P (129 mg kg−1 crust). There were close positive correlations among all the biotic and abiotic components of the crusts.Biofertilization with cyanobacteria induced great microbial proliferation as well as high increases in organic matter and nutrients in the surface of the heated soils. In general, cellulolytics were increased by four logarithmic units, amylolytics and ammonifiers by three logarithmic units and nitrifiers by more than two logarithmic units. C and N contents rose an average of 275 g C kg−1 soil and 50 g N kg−1 soil while the C:N ratio decreased up to 7 units. Among the available nutrients the highest increase was for Ca (315 mg kg−1 soil) followed by Mg (189 mg kg−1 soil), K (111 mg kg−1 soil), Na (109 mg kg−1 soil) and P (89 mg kg−1 soil). Fluctuations of the microbial groups as well as those of organic matter and nutrients were positively correlated.The efficacy of inoculation depended on both the type of soil and the class of inoculum. The best treatment was the mixture of the four strains and, whatever the inoculum used, the soil over lime showed the most developed crust followed by the soils over schist, granite and sandstone. In the medium term there were not significant differences between the two inocula amounts tested.These results showed that inoculation of burned soils with alien N2-fixing cyanobacteria may be a biotechnological means of promoting microbiotic crust formation, enhancing C and N cycling microorganisms and increasing organic matter and nutrient contents in heated soils.  相似文献   

4.
The concentrations of Zn, Cd, Pb and Cu in earthworm tissues were compared with the total and DTPA-extractable contents of these heavy metals in contaminated soils. Samples were taken from a pasture polluted by waste from a metallurgic industry over 70 y ago. Three individuals of Aporrectodea caliginosa and Lumbricus rubellus and soil samples were collected at six points along a gradient of increasing pollution. Total metal contents of earthworms, soil, and metals extracted by DTPA from the soil were measured. Total heavy metal contents of the soils ranged from 165.7 to 1231.7 mg Zn kg−1, 2.7 to 5.2 mg Cd kg−1, 45.8 to 465.5 mg Pb kg−1 and 30.0 to 107.5 mg Cu kg−1. Their correlations with metals extracted by DTPA were highly significant. Contents of the metals in earthworm tissues were higher in A. caliginosa than in L. rubellus, with values ranging from 556 to 3381 mg Zn kg−1, 11.6 to 102.9 mg Cd kg−1, 1.9 to 182.8 mg Pb kg−1 and 17.9 to 35.9 mg Cu kg−1 in A. caliginosa, and from 667.9 to 2645 mg Zn kg−1, 7.7 to 26.3 mg Cd kg−1, 0.5 to 37.9 mg Pb kg−1 and 16.0 to 37.6 mg Cu kg−1 in L. rubellus, respectively. Correlations between body loads in earthworms with either total or DTPA-extractable contents of soil metals were significant, except for Cd in L. rubellus and Cu in A. caliginosa. Considering its simple analytical procedure, DTPA-extractable fraction may be preferable to total metal content as a predictor of bio-concentrations of heavy metals in earthworms. Biota-to-Soil Accumulation Factor (BSAF) of these four metals are Cd>Zn>Cu>Pb, with range of mean values between: Cd (6.18-17.02), Zn (1.95-7.91), Cu (0.27-0.89) and Pb (0.08-0.38) in A. caliginosa, and Cd (3.64-6.34), Zn (1.5-6.35), Cu (0.29-0.87) and Pb (0.04-0.13) in L. rubellus. The BSAF of Ca, Fe and Mn are Ca>Mn>Fe, with mean values of: Ca (0.46-1.31), Mn (0.041-0.111), Fe (0.017-0.07) in A. caliginosa and Ca (0.98-2.13), Mn (0.14-0.23), Fe (0.019-0.048) in L. rubellus, respectively. Results of principal component analysis showed that the two earthworm species differ in the pattern of metal bioaccumulation which is related to their ecological roles in contaminated soils.  相似文献   

5.
Enzyme activities and microbial biomass in coastal soils of India   总被引：1，自引：0，他引：1  
Soil salinity is a serious problem for agriculture in coastal regions, wherein salinity is temporal in nature. We studied the effect of salinity, in summer, monsoon and winter seasons, on microbial biomass carbon (MBC) and enzyme activities (EAs) of the salt-affected soils of the coastal region of the Bay of Bengal, Sundarbans, India. The average pH of soils collected from different sites, during different seasons varied from 4.8 to 7.8. The average organic C (OC) and total N (TN) content of the soils ranged between 5.2-14.1 and 0.6-1.4 g kg−1, respectively. The electrical conductivity of the saturation extract (ECe) of soils, averaged over season, varied from 2.2 to 16.3 dSm−1. The ECe of the soils increased five fold during the summer season (13.8 dSm−1) than the monsoon season (2.7 dSm−1). The major cation and anion detected were Na+ and Cl−, respectively. Seasonality exerted considerable effects on MBC and soil EAs, with the lowest values recorded during the summer season. The activities of β-glucosidase, urease, acid phosphatase and alkaline phosphatase were similar during the winter and monsoon season. The dehydrogenase activity of soils was higher in monsoon than in winter. Average MBC, dehydrogenase, β-glucosidase, urease, acid phosphatase and alkaline phosphatase activities of the saline soils ranged from 125 to 346 mg kg−1 oven dry soil, 6-9.9 mg triphenyl formazan (TPF) kg−1 oven dry soil h−1, 18-53 mg p-nitro phenol (PNP) kg−1 oven dry soil h−1, 38-86 mg urea hydrolyzed kg−1 oven dry soil h−1, 213-584 mg PNP kg−1 oven dry soil h−1 and 176-362 mg PNP g−1 oven dry soil h−1, respectively. The same for the non-saline soils were 274-446 mg kg−1 oven dry soil, 8.8-14.4 mg TPF kg−1 oven dry soil h−1, 41-80 mg PNP kg−1 oven dry soil h−1, 89-134 mg urea hydrolyzed kg−1 oven dry soil h−1, 219-287 mg PNP kg−1 oven dry soil h−1 and 407-417 mg PNP kg−1 oven dry soil h−1, respectively. About 48%, 82%, 48%, 63%, 40% and 48% variation in MBC, dehydrogenase activity, β-glucosidase activity, urease activity, acid phosphatase activity and alkaline phosphatase activity, respectively, could be explained by the variation in ECe of saline soils. Suppression of EAs of the coastal soils during summer due to salinity rise is of immense agronomic significance and needs suitable interventions for sustainable crop production.  相似文献   

6.
There is conflicting evidence about toxic effects of heavy metals in soil on symbiotic nitrogen fixation. This study was set-up to assess the general occurrence of such effects. Soils with metal concentration gradients were sampled from six established field trials, where sewage sludge or metal salts have been applied, or from a transect in a sludge treated soil. Additional contaminated soils were sampled near metal smelters, in floodplains, in sludge amended arable land and in a metalliferous area. Symbiotic nitrogen fixation was measured with 15N isotope dilution in white clover (Trifolium repens L.) grown in potted soil that was not re-inoculated, and using ryegrass (Lolium perenne L.) as reference crop. The fraction nitrogen in clover derived from fixation (Ndff) varied from 0 to 88% depending on soil. Pronounced metal toxicity on Ndff was only confirmed in a sludge treated soil where nitrogen fixation was halved from the control value at soil total metal concentration of 737 mg Zn kg−1, 428 mg Cu kg−1 and 10 mg Cd kg−1. The Ndff was significantly reduced by increasing metal concentration in soils from two other sites where Ndff was low throughout and where these effects might be attributed to confounding factors. No significant effects of metals on Ndff were identified in all other gradients even up to elevated total metal concentration (e.g. 55 mg Cd kg−1). The variation of Ndff among all soils (n=48), is mainly explained by the number of rhizobia in the soil (log MPN, log (cells g−1 soil)), whereas correlations with total or soil solution metal concentrations were weak (R2<0.25). The is significantly affected by the presence or absence of the host plant at the sampling site. No effects of metals were identified at even at total Zn concentrations of about 2000 mg Zn kg−1, whereas metal toxicity could be identified at lower most probable number (MPN) values. This survey shows that the metal toxicity on symbiotic nitrogen fixation cannot be generalized and that survival of a healthy population of the microsymbiont is probably the critical factor.  相似文献   

7.
Stable 15N isotope dilution and tracer techniques were used in cultivated (C) and uncultivated (U) ephemeral wetlands in central Saskatchewan, Canada to: (1) quantify gross mineralization and nitrification rates and (2) estimate the relative proportion of N2O emissions from these wetlands that could be attributed to denitrification versus nitrification-related processes. In-field incubation experiments were repeated in early May, mid-June and late July. Mean gross mineralization and nitrification rates (10.3 and 3.1 mg kg−1 d−1, respectively) did not differ between C and U wetlands on any given date. Despite these similarities, the mean NH4+ pool size in the U wetlands (17.2 mg kg−1) was two to three times that of the C wetlands (6.7 mg kg−1) whereas the mean NO3− pool size in U wetlands (2.2 mg kg−1) was less than half that of C wetlands (5.8 mg kg−1). Mean N2O emissions from the C wetlands decreased from 112.8 to 17.0 ng N2O m2 s−1 from May to July, whereas mean U-wetland N2O emissions ranged only from 31.8 to 51.1 ng N2O m2 s−1 over the same period. This trend is correlated to water-filled pore space in C wetlands, demonstrating a soil moisture influence on emissions. Denitrification is generally considered the dominant emitter of N2O under anaerobic conditions, but in the C wetlands, only 49% of the May emissions could be directly attributed to denitrification, decreasing to 29% in July. In contrast, more than 75% of the N2O emissions from the U wetlands arose from denitrification of the soil NO3− pool throughout the season. These land use differences in emission sources and rates should be taken into consideration when planning management strategies for greenhouse gas mitigation.  相似文献   

8.
Long-term diversity-disturbance responses of soil bacterial communities to copper were determined from field-soils (Spalding; South Australia) exposed to Cu in doses ranging from 0 through to 4012 mg Cu kg−1 soil. Nearly 6 years after application of Cu, the structure of the total bacterial community showed change over the Cu gradient (PCR-DGGE profiling). 16S rRNA clone libraries, generated from unexposed and exposed (1003 mg Cu added kg−1 soil) treatments, had significantly different taxa composition. In particular, Acidobacteria were abundant in unexposed soil but were nearly absent from the Cu-exposed sample (P<0.05), which was dominated by Firmicute bacteria (P<0.05). Analysis of community profiles of Acidobacteria, Bacillus, Pseudomonas and Sphingomonas showed significant changes in structural composition with increasing soil Cu. The diversity (Simpsons index) of the Acidobacteria community was more sensitive to increasing concentrations of CaCl-extractable soil Cu (CuExt) than other groups, with decline in diversity occurring at 0.13 CuExt mg kg−1 soil. In contrast, diversity in the Bacillus community increased until 10.4 CuExt mg kg−1 soil, showing that this group was 2 orders of magnitude more resistant to Cu than Acidobacteria. Sphingomonas was the most resistant to Cu; however, this group along with Pseudomonas represented only a small percentage of total soil bacteria. Changes in bacterial community structure, but not diversity, were concomitant with a decrease in catabolic function (BioLog). Reduction in function followed a dose-response pattern with CuExt levels (R2=0.86). The EC50 for functional loss was 0.21 CuExt mg kg−1 soil, which coincided with loss of Acidobacteria diversity. The microbial responses were confirmed as being due to Cu and not shifts in soil pH (from use of CuSO4) as parallel Zn-based field plots (ZnSO4) were dissimilar. Changes in the diversity of most bacterial groups with soil Cu followed a unimodal response - i.e. diversity initially increased with Cu addition until a critical value was reached, whereupon it sharply decreased. These responses are indicative of the intermediate-disturbance-hypothesis, a macroecological theory that has not been widely tested in environmental microbial ecosystems.  相似文献   

9.
The isotopic dilution method developed by Oehl et al. [2001b. Organic phosphorus mineralisation studies using isotopic dilution techniques. Soil Science Society of America Journal 65, 780-787] to measure gross mineralisation of soil organic phosphorus (P) was tested on a range of low-P sorbing soils. This isotopic dilution method relies on accurate prediction of radiolabel behaviour due to soil physicochemical processes. Based on experimental validation of the extrapolation for isotopic dilution due to physicochemical processes using autoclaved soils, a simple power function was used for extrapolation rather than the more complex equation used in the original method. For several soils, however, a potential overestimation of gross mineralisation by 0.1-2.0 mg P kg−1 d−1 was revealed. In addition, the detection limit of P mineralisation ranged between 0.6 and 2.6 mg P kg−1 d−1. The method is likely to be at the detection limit for soils that are high in available P and low in biological activity. The method was modified with respect to the extrapolation and successfully applied to a soil with relatively high microbial P (18 mg P kg−1) and soil respiration rates (29 mg C kg−1 d−1), revealing gross mineralisation rates of organic P of 0.9-1.2 mg P kg−1 d−1. Measurement of uptake of 32P by the microbial biomass allowed derivation of a net organic P mineralisation rate of 0.5-0.9 mg P kg−1 d−1.  相似文献   

10.
The aim of this laboratory study was to investigate the effect of straw and vinasses on the nitrogen (N) mineralization-immobilization turnover of celery residues during two periods (each simulating a time period from autumn till spring) under laboratory conditions. During the first period (1-198 d), 15N-labelled celery residues (1.1 g dry matter (DM) kg−1 soil) were incubated together with straw (8.1 g DM kg−1 soil), aiming to immobilize the N released from celery residues, followed by an incorporation of vinasses (1.9 g DM kg−1 soil) after 84 d, with a view to remineralizing the immobilized celery-N. During the second period (198-380 d), the experimental set-up was repeated, except that non-labelled celery residues were used. Total N, mineral N and their 15N enrichments as well as microbial biomass N were determined at regular time intervals. During both periods, mixing celery residues with straw significantly increased microbial biomass N (90.5 and 40.5 mg N kg−1 extra compared to celery only treatment) and decreased the amount of mineral N (reduction of 56.1 and 45.9 mg N kg−1 soil compared to celery only treatment) and the celery-derived mineral 15N (0% of mineral celery-derived 15N in straw treatment compared to 35% of mineral celery-derived 15N in celery only treatment). After maximum immobilization, a natural remineralization (without addition of vinasses) of 32.2 (at day 198) and 11.1 mg N kg−1 soil (at day 380) occurred in the straw treatment, but the mineral N content remained significantly lower than in the celery only treatment during the complete experiment, and the amount of remineralized celery-15N was very low (5.4% of celery-derived 15N after 380 d). Vinasses caused no real priming effect, although it did slightly increase the amount of remineralized celery-15N (+6.4% of celery-derived 15N at day 380 compared to the straw treatment), probably due an apparent added N interaction caused by displacement reactions with the soil microbial biomass.  相似文献   

11.
To evaluate atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-triazine) ecotoxicology in soil, the effect of atrazine on the activity of antioxidative enzymes (superoxide dismutase, SOD; catalase, CAT; and guaiacol peroxidase, POD) and DNA damage induced by atrazine were investigated in earthworms. Atrazine was added to artificial soil at rates of 0, 2.5, 5 and 10 mg per kg of soil. Earthworm tissues exposed to each treatment were collected on the 7th, 14th, 21st, and 28th day of the treatment. Compared to the controls, the CAT activity was stimulated at 2.5 mg kg−1 treatment except on the 14th day, and inhibited at 5, 10 mg kg−1 atrazine except 5 mg kg−1 on the 28th day and 10 mg kg−1 on the 21st day; the overall SOD activity was inhibited, while the POD activities were stimulated by all atrazine concentrations in 28 days. The olive tail moments of single-cell gel electrophoresis of coelomocytes, as an indication of DNA damage, were increased after treatment with different doses of atrazine on the 7th, 14th, 21st, and 28th day, and significant differences were found compared to the controls. In conclusion, atrazine induces oxidative stress and DNA damage on earthworms, and the adverse effects may be the important mechanisms of its toxicity to earthworms.  相似文献   

12.
The term ‘critical body residue’ (CBR) was defined as the lowest observed total body concentration of a contaminant in an organism, which is associated with the occurrence of adverse toxic effects in either individuals or populations of a defined age or stage of development. In this study, internal toxicity thresholds were determined for copper in the clitellated adult stage of earthworms (Lumbricus rubellus and Aporrectodea caliginosa). The objective was to assess the applicability of CBRs as a practical tool in soil quality assessment of contaminated sites and as a means of a sustainable protection of earthworm fauna. Laboratory studies showed that body concentrations of Cu were generally in agreement with the chemically available CaCl2-extractable fraction in soil, but that there was also some evidence of internal pH-related homeostatic regulation. Toxicological correlates of body Cu concentrations with adverse effects on cocoon production (fecundity) suggested an approximate sublethal internal threshold of about 40 mg kg−1, with mortality occurring at about 60 mg kg−1. Adult L. rubellus sampled from areas with a wide range of metal pollution showed body Cu concentrations with a minimum of 8 mg kg−1 and a maximum of 60 mg kg−1. Beyond this apparent physiological tolerance range, environmental management directed at optimal earthworm population survival may not be sustainable in contaminated fields. Studies of L. rubellus colonizing a metal-contaminated experimental sludge-treated field showed that a reduced rate of colonization can already be associated with an average body Cu concentration of 25 mg kg−1. However, in this particular field situation mixture effects of other metals that were also present in the soil and the occurrence of avoidance behaviour during colonization may have contributed to this low internal toxicity threshold. It is concluded that the CBR approach seems to be a feasible option for use as a tool in a bioavailability-based soil quality assessment, even for essential trace metals like copper, but that further insight may be needed to establish the uncertainty and reliability of the application in environmental quality assessment and decision making.  相似文献   

13.
A phenanthrene-degrading bacterial strain Pseudomonas sp. GF3 was examined for plant-growth promoting effects and phenanthrene removal in soil artificially contaminated with low and high levels of phenanthrene (0, 100 and 200 mg kg−1) in pot experiments. Low and high phenanthrene treatments significantly decreased the growth of wheat. Inoculation with bacterial strain Pseudomonas sp. GF3 was found to increase root and shoot growth of wheat. Strain GF3 was able to degrade phenanthrene effectively in the unplanted and planted soils. Over a period of 80 days the concentration of phenanthrene in soil in which wheat was grown was significantly lower than in unplanted soil (p<0.05). At the end of the 80-d experiments, 62.2% and 42.3% of phenanthrene had disappeared from planted soils without Pseudomonas sp. GF3 when the phenanthrene was added at 100 and 200 mg kg−1 soil, respectively, but 84.8% and 70.2% of phenanthrene had disappeared from planted soils with the bacterial inoculation. The presence of vegetation significantly enhances the dissipation of phenanthrene in the soil. There was no significant difference in soil polyphenol oxidase activities among the applications of 0, 100 and 200 mg kg−1 of phenanthrene. However, the enzyme activities in planted and unplanted soils inoculated with the strain Pseudomonas sp. GF3 were significantly higher than those of non-inoculation controls. The bacterial isolate was also able to colonize and develop in the rhizosphere soil of wheat after inoculation.  相似文献   

14.
The effects of an arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) on atrazine dissipation, soil phosphatase and dehydrogenase activities and soil microbial community structure were investigated. A compartmented side-arm (‘cross-pot’) system was used for plant cultivation. Maize was cultivated in the main root compartment and atrazine-contaminated soil was added to the side-arms and between them 650 or 37 μm nylon mesh was inserted which allowed mycorrhizal roots or extraradical mycelium to access atrazine in soil in the side-arms. Mycorrhizal roots and extraradical mycelium increased the degradation of atrazine in soil and modified the soil enzyme activities and total soil phospholipid fatty acids (PLFAs). Atrazine declined more and there was greater stimulation of phosphatase and dehydrogenase activities and total PLFAs in soil in the extraradical mycelium compartment than in the mycorrhizal root compartment when the atrazine addition rate to soil was 5.0 mg kg−1. Mycelium had a more important influence than mycorrhizal roots on atrazine degradation. However, when the atrazine addition rate was 50.0 mg kg−1, atrazine declined more in the mycorrhizal root compartment than in the extraradical mycelium compartment, perhaps due to inhibition of bacterial activity and higher toxicity to AM mycelium by atrazine at higher concentration. Soil PLFA profiles indicated that the AM fungus exerted a pronounced effect on soil microbial community structure.  相似文献   

15.
The importance of subsoil denitrification on the fate of agriculturally derived nitrate (NO3) leached to groundwater is crucial for budgeting N in an ecosystem and for identifying areas where the risk of excess NO3 is reduced. However, the high atmospheric background of di-nitrogen (N2) causes difficulties in assessing denitrification enzyme activity (DEA) and denitrification potential (DP) in soils directly. Here, we apply Membrane Inlet Mass Spectrometry (MIMS) technique to investigate indirectly DEA and DP in soils by measuring N2/Ar ratio changes in headspace water over soil. Soils were collected from 0-10, 15-25 and 60-70 cm depths of a grazed ryegrass and grass-clover. The samples were amended with helium-flushed deionized water containing ranges of NO3 and carbon (glucose-C) and were incubated for six hours in the dark at 21 °C. The peaks for N2/Ar ratio, declined with increasing soil depth, indicating a reduced substrate requirements to initiate DEA en-masse (15-30 mg NO3-N alone or with 60-120 mg glucose-C, kg−1 soil). The dissolved N2O concentrations were very small (0.004-0.269 μg N kg−1 soil) but responded well to the added N and C, showing a reduction in DEA with soil depth. In three separate studies, only subsoils were incubated for 3 days at 12 °C with 20-30 mg NO3-N ± 40-60 mg glucose-C, kg−1 soil. Denitrification capacity (DC, NO3 only treatment) was not statistically different to the control (no amendment) within a land use (0.03-0.05 vs. 0.07-0.22 mg N kg−1 soil d−1), the highest being in ryegrass subsoils receiving groundwater. The DP was significantly (P < 0.0001) higher in subsoils under ryegrass than under grass-clover (0.50-0.71 vs. 1.15 mg N kg−1 soil d−1). The rates of DP (NO3 + glucose-C) increased significantly (P < 0.0001) in unsaturated and saturated subsoils (0.92 and 2.19 mg N kg−1 soil d−1, respectively) of grass-clover, due to the higher reductive state resulting from the 10 day pre-incubation. Available C accelerated denitrification in soils and superseded the temporary elevation in oxidative state due to NO3 addition. The substrates load differences between the land uses regulated the degree of denitrification rates. Results suggest that both dissolved N2O measured by gas chromatography and N2/Ar ratio measured by MIMS to indirectly determine DEA, and the latter to quantify total DC/DP in soils can be used. However, interference of oxygen in the MIMS system should be considered if available C is added or is naturally elevated in soil or groundwater.  相似文献   

16.
Plasmid transfer among isolates of Rhizobium leguminosarum bv. viciae in heavy metal contaminated soils from a long-term experiment in Braunschweig, Germany, was investigated under laboratory conditions. Three replicate samples each of four sterilized soils with total Zn contents of 54, 104, 208 and 340 mg kg−1 were inoculated with an equal number (1×105 cells g−1 soil) of seven different, well-characterized isolates of R. leguminosarum bv. viciae. Four of the isolates were from an uncontaminated control plot (total Zn 54 mg kg−1) and three were from a metal-contaminated plot (total Zn 340 mg kg−1).After 1 year the population size was between 106 and 107 g−1 soil, and remained at this level in all but the most contaminated soil. In the soil from the most contaminated plot no initial increase in rhizobial numbers was seen, and the population declined after 1 year to <30 cells g−1 soil after 4 years. One isolate originally from uncontaminated soil that had five large plasmids (no. 2-8-27) was the most abundant type re-isolated from all of the soils. Isolates originally from the metal-contaminated soils were only recovered in the most contaminated soil. After 1 year, four isolates with plasmid profiles distinct from those inoculated into the soils were recovered. One isolate in the control soil appeared to have lost a plasmid. Three isolates from heavy metal contaminated soils (one isolate from the soil with total Zn 208 mg kg−1 and two isolates from the soil with total Zn 340 mg kg−1) had all acquired one plasmid. Plasmid transfer was confirmed using the distinct ITS-RFLP types of the isolates and DNA hybridization using probes specific to the transferred plasmid. The transconjugant of 2-8-27 which had gained a plasmid was found in one replicate after 2 years of the most contaminated soil but comprised more than 50% of the isolates. A similar type appeared in a separate replicate of the most contaminated soil after 3 years and persisted in both of these soils until the final sampling after 4 years. After 2 years isolates were recovered from four of the soil replicates with the chromosomal type of 2-8-27 which appeared to have lost one plasmid, but these were not recovered subsequently.Isolate 2-8-27 was among the isolates most sensitive to Zn in laboratory assays, whereas isolate 7-13-1 showed greater zinc tolerance. Acquisition of the plasmid conferred enhanced Zn tolerance to the recipients, but transconjugant isolates were not as metal tolerant as 7-13-1, the putative donor. Laboratory matings between 2-8-27 and 7-13-1 in the presence of Zn resulted in the conjugal transfer of the same small plasmid from 7-13-1 to isolate 2-8-27 and the transconjugant had enhanced metal tolerance. Our results show that transfer of naturally-occurring plasmids among rhizobial strains is stimulated by increased metal concentrations in soil. We further demonstrate that the transfer of naturally-occurring plasmids is important in conferring enhanced tolerance to elevated zinc concentrations in rhizobia.  相似文献   

17.
We established a field trial to assess the impacts on soil biological properties of application of heavy metal-spiked sewage sludge, with the aim of determining toxicity threshold concentrations of heavy metals in soil. Plots were treated with sludges containing increasing concentrations of Cu, Ni and Zn in order to raise the metal concentrations in the soil by 0-200 mg Cu kg−1, 0-60 mg Ni kg−1 and 0-400 mg Zn kg−1, and were then cultivated and sown in ryegrass-clover pasture and monitored annually for 6 years. All biological properties measured (soil basal respiration, microbial biomass C, and sulphatase enzyme activities), except phosphatase activity, increased in all plots over the duration of the experiment. Consequently, it was only possible to assess effects of heavy metals across time if, each year, all data for each metal were normalised by expressing them as percentages of the activities measured in an un-sludged control plot. When this was done, no significant effects of increasing heavy-metal concentrations on basal respiration, microbial biomass C or respiratory quotient (qCO2) were observed, although total Cu and soil solution Cu were significantly negatively related to microbial biomass C when it was expressed as a proportion of soil total C. None of the properties measured were affected by increasing Ni concentrations. Phosphatase and sulphatase activities were significantly negatively related to increasing Zn concentrations, but not usually to increasing Cu unless they were expressed as a proportion of total C. A sigmoidal dose-response model was used to calculate EC20 and EC50 values using the normalised data, but generally, the model parameters had very large 95% confidence intervals and/or the fits to the model had small R2 values. The factors primarily responsible for confounding these results were site and sample variations not accounted for by the normalisation process and the absence of any data points at metal concentrations beyond the calculated EC50 values. In the few instances where reasonable EC20 values could be calculated, they were relatively consistent across properties, e.g., EC20 for total Zn and phosphatase (330 mg kg−1), total Zn and sulphatase (310 mg kg−1), and EC20 for total Cu and sulphatase (140 mg kg−1) and total Cu and microbial biomass C (140 mg kg−1), when both sulphatase and microbial biomass C were expressed as a proportion of total C. Our results suggest that Cu and Zn at the upper concentrations used in this experiment were possibly having adverse effects on some soil biological properties. However, much higher metal concentrations will be needed to accurately calculate EC20 and EC50 and this may not be easily achievable without many applications of sewage sludge, even if the sludge is spiked with heavy metals.  相似文献   

18.
Soil organic carbon (SOC), microbial biomass carbon (MBC), their ratio (MBC/SOC) which is also known as microbial quotient, soil respiration, dehydrogenase and phosphatase activities were evaluated in a long-term (31 years) field experiment involving fertility treatments (manure and inorganic fertilizers) and a maize (Zea mays L.)-wheat (Triticum aestivum L.)-cowpea (Vigna unguiculata L.) rotation at the Indian Agricultural Research Institute near New Delhi, India. Applying farmyard manure (FYM) plus NPK fertilizer significantly increased SOC (4.5-7.5 g kg−1), microbial biomass (124-291 mg kg−1) and microbial quotient from 2.88 to 3.87. Soil respiration, dehydrogenase and phosphatase activities were also increased by FYM applications. The MBC response to FYM+100% NPK compared to 100% NPK (193 vs. 291 mg kg−1) was much greater than that for soil respiration (6.24 vs. 6.93 μl O2 g−1 h−1) indicating a considerable portion of MBC in FYM plots was inactive. Dehydrogenase activity increased slightly as NPK rates were increased from 50% to 100%, but excessive fertilization (150% NPK) decreased it. Acid phosphatase activity (31.1 vs. 51.8 μg PNP g−1 h−1) was much lower than alkali phosphatase activity (289 vs. 366 μg PNP g−1 h−1) in all treatments. Phosphatase activity was influenced more by season or crop (e.g. tilling wheat residue) than fertilizer treatment, although both MBC and phosphatase activity were increased with optimum or balanced fertilization. SOC, MBC, soil respiration and acid phosphatase activity in control (no NPK, no manure) treatment was lower than uncultivated reference soil, and soil respiration was limiting at N alone or NP alone treatments.  相似文献   

19.
Denitrification assays in soils spiked with zinc salt have shown inhibition of the N2O reduction resulting in increased soil N2O fluxes with increasing soil Zn concentration. It is unclear if the same is true for environmentally contaminated soils. Net production of N2O and N2 was monitored during anaerobic incubations (25 °C, He atmosphere) of soils freshly spiked with ZnCl2 and of corresponding soils that were gradually enriched with metals (mainly Zn) in the field by previous sludge amendments or by corrosion of galvanized structures. Total denitrification activity (i.e. the sum of N2O+N2 production rate) was not inhibited by freshly added Zn salts up to 1600 mg Zn kg−1, whereas N2O reduction decreased by 50% (EC50) at total Zn concentrations of 231 mg Zn kg−1 (ZEV soil) and 368 mg Zn kg−1 (TM soil). In contrast, N2O reduction was not reduced by soil Zn in any of the field contaminated soils, even at total soil Zn or soil solution Zn concentrations exceeding more than 5 times corresponding EC50's of the freshly spiked soil. The absence of adverse effects in the field contaminated soils was unrelated to soil NO3 or organic matter concentration. Ageing (2-8 weeks) and soil leaching after spiking reduced the toxicity of Zn on N2O reduction, either expressed as total Zn or soil solution Zn, suggesting adaptation reactions. However, no full recovery after spiking was identified at the largest incubation period in one soil. In addition, the denitrification assay performed with sewage sludge showed elevated N2O release in Zn contaminated sludges (>6000 mg Zn kg−1 dry matter) whereas this was not observed in low Zn sludge (<1000 mg Zn kg−1 dry matter) suggesting limits to adaptation reactions in the sludge particles. It is concluded that the use of soils spiked with Zn salts overestimates effects on N2O reduction. Field data on N2O fluxes in sludge amended soils are required to identify if metals indeed promote N2O emissions in sludge amended soils.  相似文献   

20.
In this study, 13C-labeled rice callus was prepared as a model material for rice straw and was subjected to a DNA-SIP (stable isotope probing) experiment in which the bacterial population was monitored in a soil sample containing decomposing dried callus. Rice callus (13C = 78%) contained the more water-soluble organic carbon and less cellulose and lignin carbon than rice straw. The callus in the soil was 37% decomposed after 56 d of incubation in upland moisture conditions. PCR-DGGE analysis demonstrated that the bacterial community in the soil with the callus changed over time, showing a distinct difference between the first (up to 7 d) and second (14 d and later) stages. After isopycnic centrifugation, DNA in the fractions with a buoyant density between 1.759 and 1.734 g ml−1 was subjected to population analysis (13C-assimilating populations). Diverse groups of bacterial sequences were retrieved from the 13C-labeled DNA fractions: Actinobacteria, Bacilli, γ-Proteobacteria, Chloroflexi, Sphingobacteria, Flavobacteria, Clostridia, Acidobacteria, Cyanobacteria and Candidate Division. Bacilli were detected mainly in the first stage, and Actinobacteria were detected throughout the incubation period. Several DGGE bands in the light fractions became more prominent in the soil with callus, which suggested that the addition of callus promoted the growth of bacteria that fed on soil organic matter, including α-Proteobacteria, γ-Proteobacteria, Bacilli, Actinobacteria, Nitrospira and Gemmatimonadetes.  相似文献   

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