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1.
The effect of liming on microbial biomass C and respiration activity was studied in four liming experiments on young pine plantations. One of the experimental sites had been limed and planted 12 years before, two 5 years before, and one a year before soil sampling. The youngest experimental site was also treated with ash fertilizer. Liming raised the pHKCl of the humus layer by 1.5 units or less. Microbial biomass was measured using the fumigation-extraction and substrate-induced respiration methods. Liming did not significantly affect microbial biomass C, except in the experiment which had been limed 11 years ago, where there was a slight biomass increase. Basal respiration, which was measured by the evolution of CO2, increased in the limed soils, except for the youngest experiment, where there was no effect. Ash fertilization raised the soil pHKCl by about 0.5 unit, but did not influence microbial biomass C or basal respiration. Fumigation-extraction and substrate-induced respiration derived microbial biomass C values were correlated positively with each other (r=0.65), but substrate-induced respiration gave approximately 1.3 times higher results. In addition, the effect of storing the soil samples at +6 and -18°C was evaluated. The effects were variable but, generally, the substrate-induced respiration derived microbial biomass C decreased, and the fumigation-extraction derived microbial biomass C and basal respiration decreased or were not affected by storage.  相似文献   

2.
Bacterial and fungal contributions to microbial respiration in three beechwood soils rich in C (two basalt soils and one limestone soil) were investigated by using streptomycin and cycloheximide to inhibit substrate-induced respiration after glucose (8000 g g-1), N, and P addition to soil samples. The inhibitors were added as solutions (2000, 8000, and 16000 g g-1) and the reduction in substrate-induced respiration after separate and combined inhibitor addition was measured in an automated electrolytic microrespirometer. Bacterial and fungal contributions to microbial respiration were calculated using the interval 6–10 h after inhibitor application. The microbial biomas was smaller in the two basalt soils (Oberhang and Mittelhang) than in the limestone soil (Unterhang). In the presence of both inhibitors, microbial respiration was inhibited by a maximum of 45, 45, and 25% in the two basalt soils and the limestone soil, respectively. Inhibition of microbial respiration was at a maximum at streptomycin and cycloheximide concentrations of 16000 g g-1. The inhibitor additivity ratio approached 1.0 even at high inhibitor concentrations, indicating high inhibitor selectivity. Calculated prokaryote: eukaryote ratios indicated lower bacterial contributions to the microbial biomass in the Mettelhang (0.74) and Unterhang (0.73) than in the Oberhang (0.88) soil.  相似文献   

3.
Contamination of grazed pasture gave 0–5 cm soil contents of 19–835 mg kg-1 Cu, 47–739 mg kg-1 Cr, and 12–790 mg kg-1 As. Soil Cu, Cr, As contents were correlated and declined with depth to 30 cm. In plots with medium and high contamination buried cotton strips retained most of their original tensile strength, indicating repression of decomposition processes.Lumbricus rubellus andAporrectodea rosea were absent in plots with medium and high contamination; there was no evidence of heavy metal accumulation in earthworm tissue; soil bulk density was greater in the absence of lumbricids. Enchytraeids and nematodes were most abundant with low contamination. Nematode diversity was greater with low (0–5 cm) or medium (5–10 cm) contamination than in control plots or those with high contamination; the proportion of predators increased with contamination. Basal soil respiration was less sensitive than substrate-induced respiration to contamination. Although contamination reduced the nitrification rate, all mineral N was found as NO inf3 sup- after 14 days. Sulphatase was the enzyme activity most sensitive to high contamination. Whereas contamination by 100 mg kg-1 of Cu, Cr, and As caused little depression of soil biological activity, there was some supperssion at 400 mg kg-1 and at 800 mg kg-1 normal processes were inhibited and herbage production was negligible. No single measurement adequately indicated the need for site remediation.  相似文献   

4.
Four contrasting soils were amended with glucose at concentrations up to 10 mg g?1 soil. The soils were incubated at 22°C for 14 days and the biomass determined at various times by chloroform fumigation or substrate-induced respiration. The adenosine triphosphate (ATP) content or the amylase and dehydrogenase activities were also determined. The size of the increases in biomass, ATP content and the enzyme activities was generally related to the amount of glucose added. The initially higher ATP levels quickly declined, and apparent substrate conversion figures up to 84% indicated that substrate-induced respiration overestimated the biomass. There were generally no significant correlations between ATP, biomass or enzyme activities.  相似文献   

5.
To determine whether there is a relationship between the composition of soil organic matter and the activity of the soil microbial biomass, the composition of the organic matter in 12 typical arable soils in Northwest Germany was investigated by wet chemical analysis and CPMAS cross polarization magic angle spinning 13C-NMR spectroscopy. The data were correlated with the microbial biomass as estimated by substrate-induced respiration. A strong correlation between the microbial biomass and alkylic C compounds was observed (r=-0.960***). Recalcitrant substances were enriched in this fraction, which were classified as humic acids according to the wet chemical procedure. The microbial decomposition of these humic acids is probably retarded, due to their chemical structure and/or physical bonding, when the soil microbial biomass activity is limited.  相似文献   

6.
Inherent soil properties have an influence on microbial activity. These effects were measured in a field trial at Weihenstephan with 30 agricultural and 2 vineyard soils from different sites in Bavaria which had been kept under bare fallow for 6 years. The soils represented a wide range of arable soils from a temperate climate. Unaffected by recent differences in climatic conditions or cropping managements, they were used to assess the relationship between microbial biomass C and a broad spectrum of soil physical and chemical properties (clay content 5–63%, pH 4.5–7.5, organic C 0.55–2.93%). Microbial C was measured using the substrate-induced respiration method. In addition, soil catalase activity and the abundance and biomass of earthworms were determined. Among the soil properties, microbial C was most strongly correlated with organic C (r=0.86, n=29). In a comparison of linear regressions between microbial biomass C and organic C for different cropping managements, the slope under bare fallow was lowest, followed by monoculture and crop rotation. The microbial: organic C ratio ranged from 1.1 to 4.3% and was significantly correlated with soil pH (r=0.66). A positive relationship between microbial C and the clay content (r=0.66) was significantly improved when soils with more than 25% clay were excluded (r=0.80). Partial correlation analysis indicated that clay had a direct influence, hardly affected by an intercorrelation with organic C. Catalase activity was highly correlated with microbial C (r=0.95) and, because a rapid and sensitive method of determination is available, was considered suitable for estimating relative amounts of active microbial biomass. A positive relationship between microbial C and the abundance of earthworms indicated interactions between microorganisms and mesofauna.  相似文献   

7.
Attempts to determine available carbon in soils   总被引：10，自引：0，他引：10  
Summary The size of the C pool that is readily available to microorganisms affects important N transformations that occur in soils, e.g., denitrification and N immobilization. In the present work, the C content of soil extracts, the C in water displaced from soil and biomass C were compared as indicators of available C. A comparison of C measured by the anthrone method and a total organic-C analysis of extracts indicated that only a small portion of C was in carbohydrates. The substrate-induced respiration method of measuring biomass in conjunction with the Wright-Hobbie model was used as an additional determination of available C. Total organic-C analysis of a 1 N H2SO4 extract gave the highest C values (500–1700 mg C kg-1 soil) and the substrate-induced respiration method gave the lowest (1–5 mg glucose equivalents kg-1 soil). The C values closest to the C turnover measured in long-term incubation studies were obtained by the substrate-induced respiration method using the Wright-Hobbie model.Contribution from the Soil-Microbial Systems Laboratory, NRI, USDA-ARS, Beltsville, MD 20705, USA  相似文献   

8.
The need to identify microbial community parameters that predict microbial activity is becoming more urgent, due to the desire to manage microbial communities for ecosystem services as well as the desire to incorporate microbial community parameters within ecosystem models. In dryland agroecosystems, microbial biomass C (MBC) can be increased by adopting alternative management strategies that increase crop residue retention, nutrient reserves, improve soil structure and result in greater water retention. Changes in MBC could subsequently affect microbial activities related to decomposition, C stabilization and sequestration. We hypothesized that MBC and potential microbial activities that broadly relate to decomposition (basal and substrate-induced respiration, N mineralization, and β-glucosidase and arylsulfatase enzyme activities) would be similarly affected by no-till, dryland winter wheat rotations distributed along a potential evapotranspiration (PET) gradient in eastern Colorado. Microbial biomass was smaller in March 2004 than in November 2003 (417 vs. 231 μg g−1 soil), and consistently smaller in soils from the high PET soil (191 μg g−1) than in the medium and low PET soils (379 and 398 μg g−1, respectively). Among treatments, MBC was largest under perennial grass (398 μg g−1). Potential microbial activities did not consistently follow the same trends as MBC, and the only activities significantly correlated with MBC were β-glucosidase (r = 0.61) and substrate-induced respiration (r = 0.27). In contrast to MBC, specific microbial activities (expressed on a per MBC basis) were greatest in the high PET soils. Specific but not total activities were correlated with microbial community structure, which was determined in a previous study. High specific activity in low biomass, high PET soils may be due to higher microbial maintenance requirements, as well as to the unique microbial community structure (lower bacterial-to-fungal fatty acid ratio and lower 17:0 cy-to-16:1ω7c stress ratio) associated with these soils. In conclusion, microbial biomass should not be utilized as the sole predictor of microbial activity when comparing soils with different community structures and levels of physiological stress, due to the influence of these factors on specific activity.  相似文献   

9.
In studying the basal respiration, microbial biomass (substrate-induced respiration, SIR), and metabolic quotient (qCO2) in western red cedar (Thuja plicata Donn ex D. Don)-western hemlock [(Tsuga heterophylla Raf.) Sarg.] ecosystems (old-growth forests, 3- and 10-year-old plantations) on northern Vancouver Island, British Columbia, Canada, we predicted that (1) soil basal respiration would be reduced by harvesting and burning, reflecting the reduction in microbial biomass and activities; (2) the microbial biomass would be reduced by harvesting and slash-burning, due to the excessive heat of the burning or due to reduced substrate availability; (3) microbial biomass in the plantations would tend to recover to the preharvesting levels with growth of the trees and increased substrate availability; and (4) microbial biomass measured by the SIR method would compare well with that measured by the fumigation-extraction (FE) method. Decaying litter layer (F), woody F (Fw) and humus layer (H) materials were sampled four times in the summer of 1992. The results obtained supported the four predictions. Microbial biomass was reduced in the harvested and slash-burned plots. Both SIR and FE methods provided equally good estimates of microbial biomass in the samples [SIR microbial C (mg g-1)=0.227+0.458 FE microbial C (mg g-1), r=0.63, P=0.0001] and proved suitable for microbial biomass measurements in this strongly acidic soil. Basal respiration was significantly greater in the old-growth forests than in the young plantations (P<0.05) in both F and H layers, but not in the Fw layer. For the 3- and 10-year-old plantations, there was no difference in basal respiration in F, Fw, and H layers. Basal respiration was related to changes in air temperature, precipitation, and the soil moisture contant at the time of sampling. The qCO2 values were higher in the old-growth stands than in the plantations. Clear-cutting followed by prescribed burning did not increase soil microbial respiration, but CO2 released from slash-burning and that contributed from other sources may be of concern to increasing atmospheric CO2 concentrations.  相似文献   

10.
High rates of atmospheric nitrogen (N) deposition have raised questions about shifting patterns of nutrient limitation in northern hardwood forests. Of particular interest is the idea that increased supply of N may induce phosphorus (P) limitation of plant and microbial processes, especially in acid soils where P sorption by Al is high. In this study, we established field plots and plant-free laboratory mesocosms with P and Ca additions to test the hypotheses that 1) microbial biomass and activity are limited by P in the northern hardwood forest soils at the Hubbard Brook Experimental Forest in NH USA; 2) elevated Ca increases inherent P availability and therefore reduces any effects of added P and 3) P effects are more marked in the more carbon (C) rich Oie compared to the Oa horizon. Treatments included P addition (50 kg P ha−1), Ca addition (850 kg Ca ha−1) and Ca + P addition (850 kg Ca ha−1 and 50 kg P ha−1). The P treatments increased resin-available P levels and reduced phosphatase activity, but had no effect on microbial biomass C, microbial respiration, C metabolizing enzymes, potential net N mineralization and nitrification in the Oie or Oa horizon of either field plots or plant free mesocosms, in either the presence or absence of Ca. Total, prokaryote, and eukaryote PLFA were reduced by P addition, possibly due to reductions in mycorrhizal fungal biomass. These results suggest that increased N deposition and acidification have not created P limitation of microbial biomass and activity in these soils.  相似文献   

11.
Estimation of microbial biomass and activity in soil using microcalorimetry   总被引：2，自引：0，他引：2  
Relationships between the rate of heat output from soil, the rate of respiration and the soil microbial biomass were investigated for 25 soils from northern Britain. The rate of heat output, measured in a Calvet microcalorimeter at 22°C, correlated well with the rate of carbon dioxide respiration. The average amount of heat evolved per cm3 of gas respired. 21.1 J cm?3, suggests that the biomass metabolism was largely aerobic. The rate of heat output per unit of total microbial biomass was remarkably uniform over a wide range of soils, but showed differences depending upon whether the soil had been stored or amended. Mineral soils that had been stored at 4°C had the lowest heat output, 12.0 mW g?1 biomass C, compared with a mean of 20.4 mW g?1 biomass C for freshly-collected soils. Amendment with glucose (0.5% w/w) caused an immediate increase in respiration and heat output, up to 59.4 mW g?1 biomass C for stored soils and 188.2 mW g?1 biomass C for freshly collected soils. There was a consistent relationship between the biomass and the rate of heat output from freshly collected and amended mineral and organic soils which gave a linear fit using log transformed data: y= 0.6970+ 1.025x (r= 0.98, P < 0.001) (y=log10 biomass C, μgC g?1; x=log10 rate of heat output at 22°C, μW g?1). The overall relationship between biomass and the rate of heat output for all the amended samples was: 1 g biomass C= 180.05 ± 34.61 mW.  相似文献   

12.
Long-term effects of mineral fertilization on microbial biomass C (MBC), basal respiration (R B), substrate-induced respiration (R S), β-glucosidase activity, and the r–K-growth strategy of soil microflora were investigated using a field trial on grassland established in 1969. The experimental plots were fertilized at three rates of mineral N (0, 80, and 160 kg ha−1 year−1) with 32 kg P ha−1 year−1 and 100 kg K ha−1 year−1. No fertilizer was applied on the control plots (C). The application of a mineral fertilizer led to lower values of the MBC and R B, probably as a result of fast mineralization of available substrate after an input of the mineral fertilizer. The application of mineral N decreased the content of C extracted by 0.5 M K2SO4 (C ex). A positive correlation was found between pH and the proportion of active microflora (R S/MBC). The specific growth rate (μ) of soil heterotrophs was higher in the fertilized than in unfertilized soils, suggesting the stimulation of r-strategists, probably as the result of the presence of available P and rhizodepositions. The cessation of fertilization with 320 kg N ha−1 year−1 (NF) in 1989 also stimulated r-strategists compared to C soil, probably as the result of the higher content of available P in the NF soil than in the C soil.  相似文献   

13.
Heavy metal availability, microbial biomass and respiration, bacterial diversity and enzyme activity were studied in soils from long-term field experiments contaminated with Mn-Zn- or Cd-Ni-rich sludge, incorporated into soils at two different rates. Soils that never received sludge were used as controls. Microbial biomass C content (BC) and soil respiration (CO2-C) were slightly reduced in soils amended with Mn-Zn at the higher incorporation rate whereas in soils receiving Cd-Ni-rich sludge BC and respiration were unaffected. Metabolic quotient values (qCO2) calculated by the BC-to-CO2-C ratio were not significantly different, regardless of the sludge type whereas the microbial biomass C-to-total organic C (BC-to-TOC) ratios were significantly reduced in the soils receiving the higher rates of both sludge types. Phosphomonoesterase, β-glucosidase and arylsulfatase activities and hydrolase-to-BC ratios, were significantly reduced in soils amended with Ni-Cd-sludge at both rates, whereas the Mn-Zn-sludge only reduced the arylsulfatase activity at the higher rate. Protease activity was generally higher in all the sludge-amended soils as compared to control soils whereas urease activity was unaffected by sludge amendments. The structure of the bacterial community, as determined by denaturing gradient gel electrophoresis (DGGE), was different in the sludge-amended soils as compared to the respective controls. The most important changes were observed in the soils amended with high-level Ni-Cd sludge. Because some of the adverse effects were observed at moderate contamination levels, our results indicate that the presence of certain heavy metal combinations can be a serious limitation for sludge disposal.  相似文献   

14.
Soil contamination by heavy metals is a problem in agricultural irrigation systems.To assess the accumulation and sources of heavy metals in the Yongji irrigation district of the Hetao area,Inner Mongolia,China,195 soil samples from 39 sites(0–100 cm)were collected,and Zn,Cu,Pb,Cr,and Cd concentrations were analyzed.The mean concentrations were 107.17,32.48,12.31,53.53,and 0.22 mg kg-1,respectively,with no significant differences between soil depths(P>0.05).Concentrations of Zn,Cu,and Cd were higher than the background levels,with moderate accumulation;the contamination factor(CF)values were 1.9,1.7,and 1.9,respectively,and the geoaccumulation index(Igeo)was>0.Concentrations of Pb and Cr were lower than,or close to,the background levels(CF<1,Igeo<0),indicating that they originated from a natural source.The monomial potential ecological risk index(Eri)for Zn,Cu,Pb,and Cr was low;Eri for Cd was 55.73,implying a moderate risk.The grade of potential ecological risk index of the five heavy metals(RI)was low,declining from south to north.The studied soils were contaminated with Zn,Cu,and Cd;principal component(PC)analysis implicated the enrichment of Cd and partial Cu(high loading in PC 2)was related to agricultural activities;Zn and partial Cu,closely associated with PC 3,may have originated from irrigation water from the Yellow River.Future agricultural development should focus on fertilizer and pesticide application and the quality of irrigation water.  相似文献   

15.
We examined the long-term effects of cattle slurry, applied at high rates, on microbial biomass, respiration, the microbial quotient (qCO2) and various soil enzyme activities. In March, June, July, and October 1991, slurry-amended grassland soils (0–10 cm) contained significantly higher levels of microbial biomass, N mineralization and enzyme activities involved in N, P, and C cycling. With microbial biomass as the relative value, the results revealed that the slurry treatment influenced enzyme production by the microbial biomass. High levels of urease activity were the result not only of a larger microbial biomass, but also of higher levels of enzmye production by this microbial biomass. The ratio of alkaline phosphatase and xylanase to microbial biomass was nearly constant in the different treatments. The metabolic quotient (qCO2) declined with increased levels of slurry application. Therefore it appears that microorganisms in slurry-amended soils require less C and energy if there is no competition for nutrients. The results of this study suggest that urease activity, nitrification, and respiration (metabolic quotient) can be used as indicators of environmental stress, produced by heavy applications of cattle slurry.  相似文献   

16.
《Soil biology & biochemistry》2012,44(12):2441-2449
High rates of atmospheric nitrogen (N) deposition have raised questions about shifting patterns of nutrient limitation in northern hardwood forests. Of particular interest is the idea that increased supply of N may induce phosphorus (P) limitation of plant and microbial processes, especially in acid soils where P sorption by Al is high. In this study, we established field plots and plant-free laboratory mesocosms with P and Ca additions to test the hypotheses that 1) microbial biomass and activity are limited by P in the northern hardwood forest soils at the Hubbard Brook Experimental Forest in NH USA; 2) elevated Ca increases inherent P availability and therefore reduces any effects of added P and 3) P effects are more marked in the more carbon (C) rich Oie compared to the Oa horizon. Treatments included P addition (50 kg P ha−1), Ca addition (850 kg Ca ha−1) and Ca + P addition (850 kg Ca ha−1 and 50 kg P ha−1). The P treatments increased resin-available P levels and reduced phosphatase activity, but had no effect on microbial biomass C, microbial respiration, C metabolizing enzymes, potential net N mineralization and nitrification in the Oie or Oa horizon of either field plots or plant free mesocosms, in either the presence or absence of Ca. Total, prokaryote, and eukaryote PLFA were reduced by P addition, possibly due to reductions in mycorrhizal fungal biomass. These results suggest that increased N deposition and acidification have not created P limitation of microbial biomass and activity in these soils.  相似文献   

17.
We investigated the effects of slug (Arion rufus L.) mucus and cast material on litter decomposition, nutrient mobilization, and microbial activity in two laboratory experiments: (1) Slug mucus and cast material was added to beech leaf litter (Fagus sylvatica L.), and leaching of N and P and CO2 production in microcosm systems were measured during 77 days of incubation; (2) mucus was added to beech leaf litter, and basal respiration, microbial biomass (substrate-induced respiration), specific respiration (qO2), microbial growth ability after C, CN, CP, and CNP amendment, and lag time (time between CNP addition and start of exponential increase in respiration rate) were measured during 120 days of incubation. Leaching of N and P from beech leaf litter was significantly increased in treatments with mucus or faecal material of A. rufus. Following day 3, slug mucus increased nitrification processes. Mucus addition to beech leaf litter also increased basal respiration and microbial biomass significantly. In contrast, specific respiration was not significantly affected by mucus addition, and generally declined until day 60 but then increased until day 120. Nutrient amendments indicated that between days 1 and 30, N was available for microbial growth in litter with mucus but not in control litter. Generally, the lag time in beech leaf litter with added mucus was shorter than in control litter. Lag times generally increased with age, indicating dominance of slow-growing microbial populations at later stages as a consequence of depletion of easily available C resources and nutrients. We conclude that C, N, and P cycling is accelerated by slug activity.  相似文献   

18.
The soil microbial biomass and activity were estimated for seven field (intensive and extensive management), grassland (dry and wet), and forest (beech, dry and wet alder) sites. Three of the sites (wet grassland, dry and wet alder) are located on a lakeshore and are influenced by lake water and groundwater. Four different methods were selected to measure and characterize the microbial biomass. Values of microbial biomass (weight basis) and total microbial biomass per upper horizon and hectare (volume basis) were compared for each site.Fumigation-extraction and substrate-induced respiration results were correlated but dit not give the same absolute values for microbial biomass content. When using the original conversion factors, substrate-induced respiration gave higher values in field and dry grassland soils, and fumigation-extraction higher values in soils with low pH and high water levels (high organic content). Results from dimethylsulfoxide reduction and arginine ammonification, two methods for estimating microbial activity, were not correlated with microbial biomass values determined by fumigation-extraction or substrate-induced respiration in all soils examined. In alder forest soils dimethylsulfoxide reduction and arginine ammonification gave higher values on the wet site than on the dry site, contrary to the values estimated by fumigation-extraction and substrate-induced respiration. These microbial activities were correlated with microbial biomass values only in field and dry grassland soils. Based on soil dry weight, microbial biomass values increased in the order intensive field, beech forest, extensive field, dry grassland, alder forest, wet grassland. However, microbial biomass values per upper horizon and hectare (related to soil volume) increased in agricultural soils in the order intensive field, dry grassland, extensive field, wet grassland and in forest soils in the order beech, wet alder, dry alder. We conclude that use of the original conversion factors with the soils in the present study for fumigation-extraction and substrate-induced respiration measurements does not give the same values for the microbial biomass. Furthermore, dimethylsulfoxide reduction and arginine ammonification principally characterize specific microbial activities and can be correlated with microbial biomass values under specific soil conditions. Further improvements in microbial biomass estimates, particularly in waterlogged soils, may be obtained by direct counts of organisms, ATP estimate, and the use of 14C-labelled organic substrates. From the ecological viewpoint, data should also be expressed per horizon and hectare (related to soil volume) to assist in the comparison of different sites.  相似文献   

19.
A forest ecosystem study was conducted along a deposition gradient of air pollutants in old Scots pine stands located near the industrial belt around the city of Bitterfeld in northeast Germany from 1999 to 2000. In order to estimate the impact of different atmospheric deposition loads on microbial biomass and enzyme activities, samples were taken from the forest floor (L, F, and H horizon) and the mineral topsoil (0–10 cm). The emission-induced increases in ferromagnetic susceptibility, soil pH, concentrations of mobile (NH 4NO 3 extractable) Cr and Ni, effective cation exchange capacity, and base saturation in the humus layer along the 25-km long transect reflected that great portions of the past depositions were characterized by alkaline fly ash. Alkaline depositions significantly ( P <0.05) decreased the microbial biomass C and N contents, microbial biomass C-to-organic C ratios, and microbial respiration rates, but increased the metabolic quotient (qCO 2) of the mineral topsoil and forest floor. Variations in microbial biomass and activity can mainly be predicted ( r 2 =0.60) by the concentrations of Ca, Zn and Cd in these forest soils. The specific activities (activity kg -1 organic C) of l-asparaginase, l-glutaminase, arylsulfatase, and in part, acid phosphatase were significantly ( P <0.05) higher at forest sites receiving higher fly ash loads than those of the other sites, and thus followed the trend of the qCO 2. In contrast, the specific activity of ß-glucosidase was significantly ( P <0.05) decreased at heavily affected sites compared to moderate and less affected sites, suggesting an inhibition of C mineralization in the forest floor of pine stands affected by predominantly alkaline emissions. A great portion ( r 2=0.91) of the variation in the specific enzyme activity data in forest soils in emission areas can be predicted from a linear combination of the variables total organic C and NH 4Cl-extractable Ca, pH and effective cation exchange capacity.  相似文献   

20.
Bader  J. L.  Gonzalez  G.  Goodell  P. C.  Pillai  S. D.  Ali  A. S. 《Water, air, and soil pollution》1999,109(1-4):263-276
Chromium-containing industrial effluents are primarily responsible for environmental contamination by toxic and highly mobile, hexavalent chromium. The dilution plate-count method, using media amended with Cr(VI) at concentrations ranging from 0 to 1000 mg L-1, was used to compare the sizes of Cr(VI)-resistant bacterial populations from a soil contaminated with 25 100 mg kg-1 total Cr [12 400 mg kg-1 Cr(VI)] to those isolated from a slightly contaminated soil (99.6 mg kg-1 total Cr) and two other soils without any history of Cr contamination. Bacterial populations resistant to 500 mg L-1 Cr(VI) were isolated from all soils except the heavily contaminated soil. To determine whether Cr-resistant bacterial populations were indigenous to both the contaminated and the uncontaminated soils, enrichment cultures containing Cr(VI) at concentrations ranging from 0 to 1000 mg L-1 were employed. Bacterial populations, as high as 105 (colony forming units) CFU g-1 soil, tolerant of 500 mg L-1 Cr(VI) were isolated from all soils within 48 h of enrichment suggesting that the presence of aerobic Cr(VI)-resistant bacterial populations is unrelated to contamination levels or contamination history. However, identification of these resistant bacteria using fatty acid profiles was unsuccessful suggesting that these populations may have unique characteristics. Fungal colonies resistant to 1000 mg L-1 Cr(VI) were routinely isolated from both uncontaminated and contaminated soils. The results suggest that Cr-resistant microorganisms may be present in soils, even those with no history of Cr contamination.  相似文献   

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