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1.
Pesticide contamination of soil and groundwater at agricultural chemical distribution sites is a widespread problem in the USA. Alternatives to land-farming or solid waste disposal include biostimulation and phytoremediation. This research investigated the ability of compost, corn stalks, corn fermentation byproduct, peat, manure, and sawdust at rates of 0.5% and 5% (w/w) to stimulate biodegradation of atrazine [6-chloro-N-ethyl-N'-(1-methyethyl)-1,3,5-triazine-2,4-diamine], metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] added as a mixture to soil. Initial concentrations were 175ᆾ mg atrazine kg-1 soil, 182ᆭ mg metolachlor kg-1 soil, and 165ᆫ mg trifluralin kg-1 soil. After amendment addition, 30% of the atrazine, 33% of the metolachlor, and 44% of the trifluralin was degraded over 245 days, which included 63 days' aging prior to amendment additions. Atrazine degradation was enhanced by 0.5% manure, 5% peat, and 5% cornstalk amendments compared to nonamended soils. Metolachlor degradation was enhanced by all amendments at the 5% level, except for compost and peat. Amendments had no effect on trifluralin degradation. The 5% addition of compost, manure, and cornstalks resulted in significant increases in bacterial populations and dehydrogenase activity. A second experiment compared the persistence of atrazine, metolachlor, and trifluralin applied in a mixture to their persistence in soil individually. A combined average of 123 mg atrazine kg-1 remained in soil treated with the three-herbicide mixture compared to 31 mg atrazine kg-1 remaining in soil treated with atrazine only. Atrazine mineralization and atrazine-degrading microorganisms were suppressed by high concentrations of metolachlor, but not by trifluralin.  相似文献   

2.
A comparison of three atrazine-degrading bacteria for soil bioremediation   总被引：3，自引：0，他引：3  
The ability of three atrazine-degrading bacteria, Pseudomonas sp. strain ADP, a Pseudaminobacter sp., and a Nocardioides sp., to degrade and mineralize this herbicide in a loam soil was evaluated in laboratory microcosms. These bacteria all hydrolytically dechlorinate atrazine, and degrade atrazine in pure culture with comparable specific activities. The Pseudaminobacter and Nocardioides can utilize atrazine as sole carbon and nitrogen source, whereas the Pseudomonas can utilize the compound only as a nitrogen source. The Pseudomonas and Pseudaminobacter mineralize the compound; the end product of atrazine metabolism by the Nocardioides is N-ethylammelide. At inoculum densities of 105 cells/g soil, only the Pseudaminobacter and Nocardioides accelerated atrazine dissipation. The Pseudaminobacter mineralized atrazine rapidly and without a lag, whereas atrazine was mineralized in the Nocardioides-inoculated soil but only after a lag of several days. The Pseudaminobacter remained viable longer than did the Pseudomonas in soil. PCR analysis of recovered bacteria indicated that the genes atzA (atrazine chlorohydrolase) and atzB (hydroxyatrazine ethylaminohydrolase) were less stable in the Pseudaminobacter than the Pseudomonas. In summary, this study has revealed important differences in the ability of atrazine-hydrolyzing bacteria to degrade this compound in soil, and suggests that the ability to utilize atrazine as a carbon source is important to establish "enhanced degradation" by ecologically meaningful inoculum densities.  相似文献   

3.
An incubation experiment was conducted to study N2O emissions from a Typic Ustochrept, alluvial soil, fertilized with urea and urea combined with different levels of two nitrification inhibitors, viz karanjin and dicyandiamide (DCD). Karanjin [a furano-flavonoid, obtained from karanja (Pongamia glabra Vent.) seeds] and DCD were incorporated at rates of 5, 10, 15, 20 and 25% of applied urea-N (100 mg kg-1 soil), to the soil adjusted to field capacity moisture content. The highest N2O flux (366 µg N2O-N kg-1 soil day-1) was obtained on day 1 after incubation from soil fertilized with urea without any inhibitor. The presence of the inhibitors appreciably reduced the mean N2O flux from the urea-treated soils. The application of karanjin resulted in a higher mitigation of total N2O-N emission (92-96%) compared to DCD (60-71%). Rates of N2O flux ranged from 0.9 to 140 µg N2O-N kg-1 soil day-1 from urea combined with different levels of the two inhibitors (coefficient of variation=24-272%). Karanjin (62-75%) was also more effective than DCD (9-42%) in inhibiting nitrification during the 30-day incubation period.  相似文献   

4.
Despite growing concerns about the potential adverse effects of elevated mercury concentrations in the environment, only a few toxicity data are available for soil invertebrates. The chronic toxicity of mercury (II) was therefore assessed for Eisenia fetida, Enchytraeus albidus and Folsomia candida using standard test protocols. The 21-day EC50 (the concentration causing 50% effect) for the cocoon production of E. fetida was 9.16 mg Hg kg-1 dry wt. Based on the reproduction, a 42-day EC50 of 22.0 mg Hg kg-1 dry wt was observed for E. albidus while for F. candida the 28-day EC50 was 3.26 (2.45-4.05) mg Hg kg-1 dry wt. Although these data can be considered as a step forward in the assessment of the potential risks of mercury in terrestrial environments, further research is needed to evaluate the influence of soil parameters on the toxicity of mercury and to quantify the effect of ageing on the bioavailability.  相似文献   

5.
To identify the key soil parameters influencing N2O emission from the wheat-growing season, an outdoor pot experiment with a total of 18 fertilized Chinese soils planted with wheat was conducted in Nanjing, China during the 2000/2001 wheat-growing season. Average seasonal N2O-N emission for all 18 soils was 610 mg m-2, ranging from 193 to 1,204 mg m-2, approximately a 6.2-fold difference between the maximum and the minimum. Correlation analysis indicated that the seasonal N2O emission was negatively correlated with soil organic C (r2=0.5567, P<0.001), soil total N (r2=0.4684, P<0.01) and the C:N ratio (r2=0.4530, P<0.01), respectively. A positive dependence of N2O emission on the soil pH (r2=0.3525, P<0.01) was also observed. No clear relationships existed between N2O emission and soil texture, soil trace elements of Fe, Cu and Mg, and above-ground biomass of the wheat crop at harvest. A further investigation suggested that the seasonal N2O-N emission (E, mg m-2) can be quantitatively explained by E=1005-34.2SOC+4.1Sa (R2=0.7703, n=18, P=0.0000). SOC and Sa represent the soil organic C (g kg-1) and available S (mg kg-1), respectively.  相似文献   

6.
The mineralisation of green manure from agroforestry trees was monitored with the objective to compare the temporal dynamics of mineralisation of litter from different species. Green manures from five agroforestry tree species were used on a fallow field during the long rainy season of 1997 (March-August) and from two species in the following short rainy season (September-January) in western Kenya. Different methods, i.e. measurements of isotopic ratios of C in respired CO2 and of soil organic matter (SOM) fractions, soil inorganic N and mass loss from litterbags, were used in the field to study decomposition and C and N mineralisation. Soil respiration, with the separation of added C from old soil C by using the isotopic ratio of 13C/12C in the respired CO2, correlated well with extractable NH4+ in the soil. Mineralisation was high and very rapid from residues of Sesbania sesban of high quality [e.g. low ratio of (polyphenol+lignin)/N] and low and slow from low quality residues of Grevillea robusta. Ten days after application, 37% and 8% of the added C had been respired from Sesbania and Grevillea, respectively. Apparently, as much as 70-90% of the added C was respired in 40 days from high quality green manure. Weight losses of around 80%, from high quality residues in litterbags, also indicate substantial C losses and that a build-up of SOM is unlikely. For immediate effects on soil fertility, application of high quality green manure may, however, be a viable management option. To achieve synchrony with crop demand, caution is needed in management as large amounts of N are mineralised within a few days after application.  相似文献   

7.
Atrazine and metolachlor degradation in subsoils   总被引：6，自引：0，他引：6  
Degradation of atrazine [2-chloro-4-etylamino-6-isopropylamino-1,3,5-triazine] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)-acetamide] in sterile and non-sterile soil samples collected at two different soil depths (0-20 and 80-110 cm) and incubated under aerobic and anaerobic conditions was studied. Under aerobic conditions, the half-life of atrazine in non-sterile surface soil was 49 days. In non-sterile subsoil, the half-life of atrazine (119 days) was increased by 2.5 times compared in surface soils and was not statistically different from half-lives in sterile soils (115 and 110 days in surface soil and subsoil, respectively). Metolachlor degradation occurred only in non-sterile surface soil, with a half-life of 37 days. Under anaerobic conditions, atrazine degradation was markedly slower than under aerobic conditions, with a half-life of 124 and 407 days in non-sterile surface soil and non-sterile subsoil, respectively. No significant difference was found in atrazine degradation in both sterile surface soil (693 days) and subsoil (770 days). Under anaerobic conditions, degradation of metolachlor was observed only in non-sterile surface soil. Results suggest that atrazine degraded both chemically and biologically, while metolachlor degraded only biologically. In addition, observed Eh values of soil samples incubated under anaerobic conditions suggest a significant involvement of soil microorganisms in the overall degradation process of atrazine under anaerobic conditions.  相似文献   

8.
The objectives of this study were to determine the variability in mineralization of dairy manure N, to determine if N mineralization can be predicted by compositional factors or by near- or mid-infrared reflectance spectroscopy. Dairy manures (n =107) were collected from farms in Maryland, Virginia, Pennsylvania, New York, and Connecticut. The composition of these manures ranged from 14 to 386 g dry matter kg-1, 0.9 to 9.5 kg total N/m3, and 0.3 to 4.7 kg NH4+-N/m3. Manure-amended soil was aerobically incubated at 25°C and concentrations of NH4+-N and NO3--N were determined at day 2 and day 56. The manures were highly variable in their N mineralization characteristics, ranging from a net mineralization of 54.9% to a net immobilization of 29.2% of the organic N. When compositional parameters were individually regressed against percentage mineralized organic N, the highest correlation coefficient (r) was 0.164. A stepwise regression of all 11 variables yielded a maximal r of 0.486. These results suggest that the availability of dairy manure organic N is highly variable and that the availability cannot be predicted from simple compositional parameters. No relationship was found between near-infrared spectral characteristics and N mineralization suggesting that no simple relationship exists between N mineralization and compositional characteristics. There appears to be some potential for the use of mid-infrared for determining the mineralization potential of manures.  相似文献   

9.
The carbon dioxide efflux to the atmosphere and the concentrations at various depths in two soils were measured, for more than a year, under pure stands of silver fir ( Abies alba Mill.) and European beech ( Fagus sylvatica L.) in central Italy. Microbial biomass and activity at the monitored depths were determined in the laboratory and the CO2 evolved from incubated samples was submitted to radiocarbon analysis to assess the mean residence time of the organic matter degraded by microorganisms. The CO2 efflux showed similar trends in the two soils, with highest values in October and lowest in January. The efflux depended more on air and soil temperatures than soil moisture, and was related to these variables better under fir than under beech. In both soils, the CO2 concentration increased with depth: in the top horizon it was low and similar to that of the atmosphere, while in the deeper horizons it often amounted to considerable values (up to more than 1% by volume in the BC horizon under fir). The subsoil of the fir stand generally showed much higher CO2 concentrations than that of the beech. The basal respiration as determined in the laboratory was at a maximum in the topsoil and decreased sharply downwards. Therefore, the high CO2 concentrations measured in the field at the bottom of the profiles--where roots were few, and microbial biomass and available C pool were at a minimum--appeared to be due more to slow diffusivity of the soil matrix rather than to heavy release of the gas by the biota. The organic matter respired by microorganisms in incubated soil samples showed positive values of j14C that revealed a recent synthesis. The estimated mean residence time increased with depth, suggesting a generally higher degree of stabilisation of the organic pool in the subsoil.  相似文献   

10.
Changes in sorption/bioavailability of two metabolites, imidacloprid-urea {1-[(6-chloro-3-pyridinyl)methyl]-2-imidazolidinone} and imidacloprid-guanidine {1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-1H-imidazol-2-amine} of the insecticide imidacloprid {1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine} with aging in different soils were determined. Soil moisture was adjusted to -33 kPa and 14C- and analytical-grade imidacloprid-urea and imidacloprid-guanidine were added to the soil at a rate of 1.0 mg kg-1. Spiked soils were incubated at 25°C for 8 weeks. Replicate soil samples were periodically extracted successively with 0.01 N CaCl2, acetonitrile, and 1 N HCl. Imidacloprid-urea sorption, as indicated by sorption coefficient values, was highest in the soil with highest organic C content, and increased by an average factor of 2.6 in three soils during the 8-week incubation period. Imidacloprid-guanidine sorption increased by a factor of 2.3 in the same soils. The increase in sorption was the result of a decrease in the metabolite extractable with CaCl2 (solution phase); the amount of metabolite extractable with acetonitrile and HCl (sorbed phase) did not significantly change with incubation time. It appears the increase in sorption was because the rate of degradation in solution and on labile sites was faster than the rate of desorption from the soil particles. It may have also been due to metabolite diffusion to less accessible or stronger binding sites with time. Regardless of the mechanism, these results are further evidence that increases in sorption during pesticide aging should be taken into account during characterization of the sorption process for mathematical models of pesticide degradation and transport.  相似文献   

11.
Net N mineralization was studied in three different forest sites (Belgium): a mixed deciduous forest with oak (Quercus robur L. and Quercus rubra L.) and birch (Betula pendula Roth) as dominant species, a deciduous stand of silver birch (Betula pendula) and a coniferous stand of Corsican pine (Pinus nigra ssp. Laricio). The organic (F + H) layer and mineral soil at different depths (0-10, 10-20 and 20-30 cm) were sampled at three locations in the mixed deciduous forest (GE, GF1, GF2), at one location in the silver birch stand (SB) and one in the Corsican pine stand (CP). All samples were incubated over 10 weeks under controlled temperature and moisture conditions. The net N mineralization rates in the organic and upper mineral layer (0-10 cm) were found to be significantly different from the other layers and accounted for 66-95% of the total mineralization over the first 30 cm. Net N mineralization rates in the organic layer ranged from 4.2 to 27.3 mg N m-2 day-1. Net N mineralization and nitrification rates were positively correlated. For the mineral soil, net N mineralization rates decreased with depth and the upper 10 cm showed significantly higher rates, ranging from 8.9 to 33.5 mg N m-2 day-1. The rates of the 10-20 cm and 20-30 cm sublayers were similar, ranging from 1.2 to 7.4 mg N m-2 day-1. The net N mineralization rates for the total mineral layer (0-30 cm) ranged from 17.4 mg N m-2 day-1 (SB) to 36.1 mg N m-2 day-1 (CP). Both from PCA and multiple regression analysis, we could conclude that net N mineralization rates were closely related to the initial mineral N content (Ninitial). Furthermore, significant correlations were observed between the net N mineralization rate, the total carbon (TC) and NH4+-N content for the mineral layers and between net N mineralization rate, total nitrogen (TN), hemicellulose content and C/N for the organic layers.  相似文献   

12.
Controlled-environment chambers were used to study the effects of elevated CO2 concentrations on biological N fixation, N mineralization and C decomposition in rice soil. In three chambers, CO2 concentration was maintained at 353ᆣ/396ᆫ µmol mol-1 (day/night; ambient CO2), while in another three, CO2 was maintained at 667ᆸ/700ᆽ µmol mol-1 (day/night; elevated CO2) throughout the growing season. Rice (var. Nipponbare) seedlings were grown under either ambient or elevated CO2 concentrations, and then transplanted into the soils in the corresponding chambers. At different growth stages, soil samples were taken from surface (0-1cm) and sub-surface (1-10cm) layers at the centre of four hills, then sieved (<1 mm) to remove root residues. Fresh soil was used to measure N fixation activity (using the acetylene reduction assay), NH4+ content and organic C. Separate sets of soil samples were transferred to serum bottles and anaerobically incubated at 30°C for 30 days to measure potential rates of N mineralization and C decomposition. Under an elevated atmospheric CO2 concentration, acetylene reduction activity significantly increased in the surface soil layer during the early cultivation stages and in the sub-surface soil layer during the latter part of cultivation. There was no difference in the amount of NH4+ in fresh soils between elevated and ambient CO2 chambers, while the rate of N mineralization was increased by elevated CO2 during the latter part of cultivation. Soils from the elevated CO2 chambers had obviously higher rate of C decomposition than that from the ambient CO2 chambers. CH4 production gradually increased with the growth of rice plants. These results suggest that elevated CO2 affected biological N fixation, N mineralization and C decomposition in submerged rice soil during the different growth stages of rice.  相似文献   

13.
A plant growth-promoting bacterial strain, GRC2, was isolated from potato rhizosphere and characterized as fluorescent Pseudomonas. It produced a hydroxamate-type siderophore in iron-deficient tryptic soy medium. The production of hydrocyanic acid and indole acetic acid was also recorded under normal growth conditions. The strain showed a strong antagonistic effect against Macrophomina phaseolina, a charcoal rot pathogen of peanut, when co-cultured on tryptic soy agar medium. The growth inhibition of M. phaseolina was 74% after 5 days of incubation. Bacterization of peanut seeds with fluorescent Pseudomonas GRC2 resulted in increased seed germination, early seedling growth, fresh nodule weight, grain yield and reduced charcoal rot disease of peanut in M. phaseolina-infested soil as compared with control. A streptomycin-resistant marker of the bacterium GRC2strep+ was used to monitor root colonization, which positively confirmed the efficient colonization of peanut root. Seed bacterization reduced charcoal rot disease in M. phaseolina-infested soil as compared with the control by 99%, making the organism a potential biocontrol agent against charcoal rot of peanut.  相似文献   

14.
Samples from topsoils (0-10 cm) of 16 Polish arable Cambisols developed from different parent materials (sand, silt, sandy gravel, loess, loam and clay), were incubated under flooded conditions with NO3-. Dehydrogenase activity, redox potential (Eh), and emissions of CO2 and N2O were measured. According to dehydrogenase activity, the soils were divided into two groups: those of low activity (I), where the final dehydrogenase activity was <0.03 nmol triphenylformazan (TPF) g-1 min-1, and those with high final dehydrogenase activity (II), >0.03 nmol TPF g-1 min-1. Generation of CO2 and of N2O under flooded conditions was shown to be significantly related to dehydrogenase activity. Soil dehydrogenase activity increased curvilinearly with organic matter content, showed a maximum at pH 7.1, and decreased curvilinearly with Eh. The final cumulative CO2 production increased linearly with soil organic matter content and curvilinearly with dehydrogenase activity and decreased linearly with Eh. The most significant relationship was found with dehydrogenase activity (R2=0.74, P<0.001). The final cumulative N2O production decreased linearly with Eh and increased curvilinearly with pH and dehydrogenase activity but linearly with organic matter content; the most significant relation being found with dehydrogenase activity (R2=0.69, P<0.001). The CO2:N2O ratio in the gases evolved increased curvilinearly with Eh and decreased with dehydrogenase activity and N2O and CO2 production.  相似文献   

15.
Use of renewable N and C sources such as green manure (GM) and crop residues in rice-wheat cropping systems of South Asia may lead to higher crop productivity and C sequestration. However, information on measurements of gaseous N losses (N2O+N2) via denitrification and environmental problems such as N2O and CO2 production in rice-wheat cropping systems is not available. An acetylene inhibition-intact soil core technique was employed for direct measurement of denitrification losses, N2O and CO2 production, in an irrigated field planted to rice (Oryza sativa L.) and wheat (Triticum aestivum L.) in an annual rotation. The soil was a coarse-textured Tolewal sandy loam soil (Typic Ustochrept) and the site a semi-arid subtropical Punjab region of India. Wheat residue (WR, C:N=94) was incorporated at 6 t ha-1 and sesbania (Sesbania aculeata L.) was grown as GM crop for 60 days during the pre-rice fallow period. Fresh biomass of GM (C:N.=18) at 20 or 40 t ha-1 was incorporated into the soil 2 days before transplanting rice. Results of this study reveal that (1) denitrification is a significant N loss process under wetland rice amounting to 33% of the prescribed dose of 120 kg N ha-1 applied as fertilizer urea-N (FN); (2) integrated management of 6 t WR ha-1 and 20 t GM ha-1 supplying 88 kg N ha-1 and 32 kg FN ha-1 significantly reduced cumulative gaseous N losses to 51.6 kg N ha-1 as compared with 58.2 kg N ha-1 for 120 kg FN ha-1 alone; (3) application of excessive N and C through applying 40 t GM ha-1 (176 kg N ha-1) resulted in the highest gaseous losses of 70 kg N ha-1; (4) the gaseous N losses under wheat were 0.6% to 2% of the applied 120 kg FN ha-1 and were eight- to tenfold lower (5-8 kg N ha-1) than those preceding rice; (5) an interplay between the availability of NO3- and organic C largely controlled denitrification and N2O flux during summer-grown flooded rice whereas temperature and soil aeration status were the primary regulators of the nitrification-denitrification processes and gaseous N losses during winter-grown upland wheat; (6) the irrigated rice-wheat system is a significant source of N2O as it emits around 15 kg N2O-N ha-1 year-1; (7) incorporation of WR in rice and rice residue (C:N=63) in wheat increased soil respiration, and increased CO2 production in WR- and GM-amended soils under anaerobic wetland rice coincided with enhanced rates of denitrification; and (8) with adequate soil moisture, most of the decomposable C fraction of added residues was mineralized within one crop-growing season and application of FN and GM further accelerated this process.  相似文献   

16.
An experiment was conducted in an Andosol paddy field in Shizukuishi (Iwate Prefecture, Japan) to determine the effects of free-air CO2 enrichment (FACE) on biological N2-fixation activity and soil microbial biomass C at three levels of N application. Rice (Oryza sativa L. cv. Akitakomachi) plants were grown under ambient CO2 or FACE (ambient +200 µmol mol-1 CO2) conditions throughout the growing season with each treatment having four replicated plots. Three levels of N fertilizer (high, standard and low; 15, 9 and 4 g N m-2, respectively) were applied to examine the effect of different N availability under both CO2 conditions. Soil samples were collected at four different times from upper and lower soil layers (0-1-cm and 1-10-cm soil depths, respectively) and analysed for biological N2-fixation (BNF) activity and microbial biomass C (MBC) by the acetylene reduction and chloroform fumigation-extraction methods, respectively. The amounts of chlorophyll-type compounds (Chls), an index of algal growth, and soil available C were also determined. Compared to the ambient CO2 treatment, the FACE treatment had significantly higher BNF activity in both the upper and lower soil layers at ripening only in low-N soil and at harvest at all three levels of N fertilization rates. MBC was significantly increased by FACE in both the upper and lower soil layers from the middle to later period of the growing season compared to the ambient CO2 treatment. The FACE treatment increased the Chls in the upper soil layers at ripening only in low-N soil and at harvest at all three levels of N fertilization rates. The amount of soil available C was not significantly different between FACE and ambient CO2 treatments in both the upper and lower soil layers throughout the cropping season. From these results it can be concluded that the FACE treatment had a significantly positive influence on BNF activity, MBC and Chls at different levels of N fertilization rates in paddy field during the cropping season.  相似文献   

17.
Heterotrophic N2-fixing bacteria are a potentially important source of N2 fixation in rice fields due to the moist soil conditions. This study was conducted at eight sites along a geographic gradient of the Yangtze River Plain in central China. A nitrogen-free solid malate-sucrose medium was used to isolate heterotrophic N2-fixing bacteria. Numbers of the culturable N2-fixing bacteria expressed as CFU (colony forming units) ranged between 1.41ǂ.42᎒6 and 1.24ǂ.23᎒8 in the sampled paddy field sites along the plain. Thirty strains with high ARA (acetylene reduction activity) were isolated and purified; ARA of the strains varied from 0.9 to 537.8 nmol C2H4 culture-1 h-1, and amounts of 15N fixed ranged between 0.008 and 0.4866 mg·culture-1·day-1. According to morphological and biochemical characteristics, 14 strains were identified as the genus Bacillus, 2 as Burkholderia, 1 as Agrobacterium, 4 as Pseudomonas, 2 as Derxia, 1 as Alcaligenes, 1 as Aeromonas, 2 as Citrobacter, and 3 strains belonged to the corynebacter-form group.  相似文献   

18.
Cecil sandy loam soils (ultisol) from forest (coniferous and deciduous), pasture, and arable ecosystems were sampled (0-10 cm) in the vicinity of Athens, Georgia, USA. Soil from each site was subdivided into three portions, consisting of untreated soil (control) as well as live and sterile samples treated with the fungicide metalaxyl and the herbicide propachlor at 10 mg kg-1 soil. Pesticide transformation rate, basal respiration (basal) and substrate-induced respiration (SIR) rates, and microbial metabolic quotient (qCO2) were measured for the initial application of metalaxyl [methyl-N-(2,6-dimethylphenyl)-N-(metoxyacetyl)-DL-alaninate] or propachlor (2-chloro-N-isopropyl-acetanilide) at 22°C and 60% water holding capacity. Positive correlations were found for the following: metalaxyl transformation rate constant (Kmet) and basal (r=0.73); Kmet and SIR (r=0.83); propachlor transformation rate constant (Kpr) and basal (r=0.89); and Kpr and SIR (r=0.91). Regression analysis of pesticide transformation rate and soil respiration activity, coupled with specific soil properties (pH, Corg, and clay content), revealed a positive correlation between K and SIR for Corg (r=0.88 and 0.98, for metalaxyl and propachlor, respectively). qCO2s were not significantly different (P=0.05) in propachlor-amended and pesticide-free soils. Metalaxyl amendment resulted in a change in the ecophysiological status of the soil microbial community as expressed by qCO2. The qCO2 values in metalaxyl-amended soils were significantly greater (P=0.05) in pine forest (by 25%) and arable and pasture (by 20%) soils compared to unamended soils. Differences in qCO2 values may represent the magnitude of pesticide-induced disturbance. The duration of this disturbance was greater in the pine forest soil (48 days) compared to arable and pasture soils (21 and 15 days, respectively).  相似文献   

19.
Our objective was to evaluate how increasing levels of N in the medium (0, 4, 8 and 16 mmol N added kg-1 soil) affect the interaction between Sinorhizobium and arbuscular mycorrhiza (AM) fungi in the tripartite symbiosis with Medicago sativa. Growth response, nutrient acquisition, protein content, and nitrate reductase (NR) activity were measured both in plant shoots and roots. Results showed that N levels in soil did not affect mycorrhizal colonization but they strongly influenced nodulation, particularly of mycorrhizal plants. Mycorrhizal colonization was required for a proper nodulation when no N was applied to soil. In contrast, the addition of 4 mmol N kg-1 soil reduced nodulation only in mycorrhizal plants and 8 mmol N added kg-1 soil allowed nodule formation only in non-mycorrhizal plants. Nodulation was totally inhibited in all treatments with the addition of 16 mmol N added kg-1 soil. N addition enhanced NR activity in all the treatments, while AM colonization increased the proportion of NR allocated to roots. This effect was more pronounced under the lowest N levels in the medium. The two AM fungal species showed different distribution pattern of enzymatic activities in plant tissues indicating specific physiological traits. Protein content as well as the relative proportion of protein in roots were greatly increased after mycorrhizal colonization. Glomus intraradices-colonized plants had the highest protein content in shoot and root. Mycorrhizal effects on growth, N acquisition and biochemical variables cannot be interpreted as an indirect P-mediated effect since P content was lower in mycorrhizal plants than in those which were P fertilized. Mycorrhizal colonization increased the N content in plants irrespective of the N level, but the effectiveness of AM fungi on plant N acquisition depended on the AM fungus involved, G. intraradices being the most effective, particularly at the highest N rate. N2 fixation, enhanced by AM colonization, contributed to N acquisition when a moderate N quantity was available in the soil. Nevertheless, under a high N amount the nodulating process and/or fixing capacity by Sinorhizobium was reduced in AM plants. In contrast, the AM fungal mycelium from a particular mycorrhizal fungus may continue to contribute efficiently to the N uptake from the soil even at high N levels. These results demonstrate the particular sensitivity of AM fungal species in terms of their growth and/or function to increasing N amounts in the medium. A selection of AM fungi used to address specific environmental conditions, such as N fertilization regimes comparable to those used in agronomic practices, is required for a better use of N applied to soil.  相似文献   

20.
Seasonal dynamics of in situ gross nitrogen (N) mineralization rates were measured using the 15N-NH4+ isotope dilution method in a Danish soil subjected to four different agricultural practices (set aside, barley, winter wheat and clover). Results were compared to arginine ammonification in the soil samples measured as NH4+ production following addition of excess (1 mM) arginine. In the set aside, barley, winter wheat and clover soils the average annual rates of gross N mineralization (0.29, 0.60, 1.34 and 1.75 µg NH4+-N g-1 day-1, respectively) and arginine ammonification activity (0.21, 0.55, 0.88, and 1.33 µg NH4+-N g-1 h-1, respectively) were well correlated. Furthermore, the seasonal variations of gross N mineralization and arginine ammonification activities were very similar, showing rapid responses to rainfall and generally higher activities in wetted soils. As tested in the laboratory, the arginine ammonification activity correlated well with heterotrophic microbial respiration activity (CO2 production) in soil samples and further displayed a simple, one-component Michaelis-Menten kinetics with a high affinity for arginine (Km value of 48 µM LJ µM) as determined from non-linear parameter estimation. This indicated that arginine ammonification activity was primarily due to microorganisms, and the activity was also shown to be at a minimum in sterile soil samples. All evidence thus supported that our standard assay of arginine ammonification activity provides a good index of gross N mineralization rates by the microorganisms in soil under in situ conditions.  相似文献   

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