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1.
Copper-based fungicides have been applied in apple orchards for a long time, which has resulted in increasing soil Cu concentration. However, the microbial and enzyme properties of the orchard soils remain poorly understood. This study aimed to evaluate the effect of long-term application of Cu-based fungicides on soil microbial (microbial biomass carbon (Cmic), C mineralization, and specific respiration rate) and enzyme (urease, acid phosphatase, and invertase activities) properties in apple orchards. Soil samples studied were collected from apple orchards 5, 15, 20, 30, and 45 years old, and one adjacent forest soil as for reference. The mean Cu concentrations of orchard soils significantly increased with increasing orchard ages ranging from 21.8 to 141 mg kg−1, and the CaCl2-extractable soil Cu concentrations varied from 0.00 to 4.26 mg kg−1. The soil mean Cmic values varied from 43.6 to 116 mg kg−1 in the orchard soils, and were lower than the value of the reference soil (144 mg kg−1). The ratio of soil Cmic to total organic C (Corg) increased from 8.10 to 18.3 mg Cmic g−1 Corg with decreasing orchard ages, and was 26.1 mg Cmic g−1 Corg for the reference soil. A significant correlation was observed between total- or CaCl2-extractable soil Cu and soil Cmic or Cmic/Corg, suggesting that the soil Cu was responsible for the significant reductions in Cmic and Cmic/Corg. The three enzyme activity assays also showed the similar phenomena, and declined with the increasing orchard ages. The mean soil C mineralization rates were elevated from 110 to 150 mg CO2-C kg−1 soil d−1 compared with the reference soil (80 mg CO2-C kg−1 soil d−1), and the mean specific respiration rate of the reference soil (0.63 mg CO2-C mg−1 biomass C d−1) was significantly smaller than the orchard soils from 1.19 to 3.55 mg CO2-C mg−1 biomass C d−1. The soil C mineralization rate and the specific respiration rate can be well explained by the CaCl2-extractable soil Cu. Thus, the long-term application of copper-based fungicides has shown adverse effects on soil microbial and enzyme properties.  相似文献   

2.
This study sought to assess the influence of compost and earthworms (Dendrobaena veneta) upon the level of hydrocarbon catabolism in petroleum contaminated forecourt soil (extractable petroleum hydrocarbons (EPH) 10 + 1.8 g kg−1 and total 16 United States Environment Protection Agency (USEPA) polycyclic aromatic hydrocarbons (PAH) 1.62 ± 0.5 g kg−1). The catabolic activity of the indigenous microorganisms within uncombined materials (soil and compost) and within the combined treatments (soil plus compost; either with or without earthworms) was assessed by 14C-radiorespirometry (14C-hexadecane, 14C-toluene and 14C-phenanthrene). Maximum levels of catabolic activity were observed (at the end of the incubation period; 84 d) for all three compounds in the combined contaminated soil, compost and earthworm mixtures. Significant (p < 0.05) enhancement factors (relative to the soil only control) in catabolic activity in the combined treatments (soil:compost (1:0.5)) of 3.6 times, 1.5 times and 3.5 times were observed for 14C-hexadecane, 14C-phenanthrene and 14C-toluene, respectively; with maximum levels of catabolic activity for these substrates being 68.6 ± 1.7%, 37.9 ± 5.3% and 85.9 ± 1.3%.  相似文献   

3.
A pot culture experiment was carried out to study the growth of and Cu uptake by maize (Zea mays) inoculated with or without arbuscular mycorrhizal (AM) fungus Acaulospora mellea in sterilized soil with different Cu amounts added (0, 100, 200, 400, 800 mg kg−1). Root colonization rates were significantly lower with the addition of 400 and 800 mg kg−1 Cu. AM inoculation increased shoot dry weights at 200 and 400 mg kg−1 Cu added but showed no effects at other levels, while increased root dry weights at all Cu addition levels except 800 mg kg−1. Compared with the nonmycorrhizal plants, shoot Cu concentrations in mycorrhizal plants were higher when no Cu was added but lower at other levels, while root Cu concentrations were lower at 400 and 800 mg kg−1 Cu added but not affected at other levels. Thus, shoot Cu uptake in mycorrhizal plants increased with no Cu added but decreased at other levels, while mycorrhizal effects on root Cu uptake varied. Compared with nonmycorrhizal controls, Cu uptake efficiency and phytoextraction efficiency in mycorrhizal plants were higher when no Cu was added but lower at other levels, and Cu translocation efficiency was lower at all Cu addition levels. AM inoculation improved shoot and root P nutrition at all Cu addition levels. Soil pH was higher in mycorrhizal treatment than in the control when 200 mg kg−1 or more Cu was added. These results indicate that A. mellea ZZ may be not suitable for Cu phytoextraction by maize, but shows a potential role in phytostabilization of soil moderately polluted by Cu.  相似文献   

4.
To study the feasibility of using magnetic techniques for monitoring soil pollution in Shanghai, magnetic properties and heavy metals in the topsoils in an urban site (Songnan Town) and a less-urbanized agricultural site (Luojing Town) in Baoshan District, Shanghai, were studied. Compared with the background, magnetic signals of the urban topsoils are extremely enhanced with magnetic susceptibility (χlf) from 127.3–1959 × 10− 8 m3 kg− 1; while those of the agricultural topsoils are only slightly increased. However, both the urban and agricultural topsoils contain few pedogenic SP grains, as indicated by their low χfd% (< 3.6%). Ratios of χarm/SIRM, χarm/χlf and SIRM/χlf indicate that the grain size of magnetic minerals in the urban topsoils is significantly coarser than that in the background and the agricultural topsoils. Furthermore, the urban topsoils show low coercivity and magnetic soft behaviors, as indicated by higher SOFT%, lower HARD%, higher IRM300 mT/SIRM (close to 1) and lower IRM− 200 mT/SIRM (close to − 1). It suggests that the urban topsoils have received some coarse ferrimagnetic particles. Heavy metals are highly enriched in the magnetic fractions of the topsoils. Geochemical properties of the magnetic fraction of the urban topsoils are significantly different from those of the agricultural topsoils, further indicating that the extra magnetic minerals accumulated in the urban topsoils are neither inherited from soil parent materials nor from pedogenic processes, but originate from anthropogenic activities. The significant correlations between heavy metals and χlf, χarm, SIRM, SOFT and HIRM of the topsoils in the district indicate that the magnetic techniques can be used for monitoring soil pollution in Shanghai. The soils with χlf from 39–50 × 10− 8 m3 kg− 1 in the district are tentatively defined as “slightly polluted soils”; those with χlf > 50 × 10− 8 m3 kg− 1 are defined as “polluted soils”.  相似文献   

5.
Soil moisture and gaseous N-flux (N2O, N2) dynamics in Costa Rican coffee plantations were successively simulated using a mechanistic model (PASTIS) and two process-based models (NGAS and NOE). Two fertilized (250 kg N ha−1 y−1) coffee plantations were considered, namely a monoculture and a system shaded by the N2 fixing legume species Inga densiflora. In situ N2O fluxes were previously measured in these plantations. NGAS and NOE used specific microbial activities for the soils. To parameterize NGAS, we estimated N mineralization via in situ incubations and the contribution of heterotrophic soil respiration to total soil respiration. Potential denitrification rates and the proportion of denitrified N emitted as N2O were measured in the laboratory to define the values of NOE parameters, as well as nitrification rates and related N2O production rates for parameterizing both models. Soil moisture and both NGAS and NOE N2O fluxes were best modelled on an hourly time step. Soil moisture dynamics were satisfactorily simulated by PASTIS. Simulated N2O fluxes by both NGAS and NOE (3.2 and 2.1 kg N ha−1 y−1 for NGAS; 7.1 and 3.7 kg N ha−1 y−1 for NOE, for the monoculture and shaded plantations respectively) were within a factor of about 2 of the observed annual fluxes (4.3 and 5.8 kg N ha−1 y−1, for the monoculture and shaded plantations respectively). Statistical indicators of association and coincidence between simulated and measured values were satisfactory for both models. Nevertheless, the two models differed greatly in describing the nitrification and denitrification processes. Some of the algorithms in the model NGAS were apparently not applicable to these tropical acidic Andosols. Therefore, more detailed information about microbial processes in different agroecosystems would be needed, notably if process-oriented models were to be used for testing strategies for mitigating N2O emissions.  相似文献   

6.
Global change scenarios predict an increasing frequency and duration of summer drought periods in Central Europe especially for higher elevation areas. Our current knowledge about the effects of soil drought on nitrogen trace gas fluxes from temperate forest soils is scarce. In this study, the effects of experimentally induced drought on soil N2O and NO emissions were investigated in a mature Norway spruce forest in the Fichtelgebirge (northeastern Bavaria, Germany) in two consecutive years. Drought was induced by roof constructions over a period of 46 days. The experiment was run in three replicates and three non-manipulated plots served as controls. Additionally to the N2O and NO flux measurements in weekly to monthly intervals, soil gas samples from six different soil depths were analysed in time series for N2O concentration as well as isotope abundances to investigate N2O dynamics within the soil. N2O fluxes from soil to the atmosphere at the experimental plots decreased gradually during the drought period from 0.2 to −0.0 μmol m−2 h−1, respectively, and mean cumulative N2O emissions from the manipulated plots were reduced by 43% during experimental drought compared to the controls in 2007. N2O concentration as well as isotope abundance analysis along the soil profiles revealed that a major part of the soil acted as a net sink for N2O, even during drought. This N2O sink, together with diminished N2O production in the organic layers, resulted in successively decreased N2O fluxes during drought, and may even turn this forest soil into a net sink of atmospheric N2O as observed in the first year of the experiment. Enhanced N2O fluxes observed after rewetting up to 0.1 μmol m−2 h−1 were not able to compensate for the preceding drought effect. During the experiment in 2006, with soil matric potentials in 20 cm depth down to −630 hPa, cumulative NO emissions from the throughfall exclusion plots were reduced by 69% compared to the controls, whereas cumulative NO emissions from the experimental plots in 2007, with minimum soil matric potentials of −210 hPa, were 180% of those of the controls. Following wetting, the soil of the throughfall exclusion plots showed significantly larger NO fluxes compared to the controls (up to 9 μmol m−2 h−1 versus 2 μmol m−2 h−1). These fluxes were responsible for 44% of the total emission of NO throughout the whole course of the experiment. NO emissions from this forest soil usually exceeded N2O emissions by one order of magnitude or more except during wintertime.  相似文献   

7.
The relationships of soil microbial biomass C (Cmic) or N (Nmic) with mean annual precipitation and temperature were studied along a climatic transect in the Mongolian steppe. Soil organic C (Corg) and total N (Nt), respiration rate, Cmic and Nmic at depths of 0–5 and 5–10 cm decreased with increasing aridity. The contents of Corg and Nt in the 0- to 5-cm soil layers decreased linearly with precipitation reduction along the transect. Cmic and Nmic changes with precipitation were not linear, with higher changes between 330 and 128 mm mean annual precipitation. Cmic/Corg and Nmic/Nt increased with increasing aridity. The metabolic quotient qCO2 of 0- to 5-cm soil layers was low between 330 and 273 mm precipitation. The relationship between the qCO2 of the 0- to 5-cm soil layers and the mean annual precipitation was well fitted with a quadratic function y =0.0006x2 –0.40x +86.0, where y is the qCO2 (µmol CO2-C mmol–1 Cmic) and x is the mean annual precipitation (mm). Corg, Nt, Cmic, Nmic and respiration rate decreased exponentially with increasing mean annual temperature in both the 0- to 5- and 5- to 10-cm soil layers, and change rate was lower when the mean annual temperature was higher than 2.6°C. The close relationships of the mean annual precipitation or temperature with soil Corg, Nt, Cmic, Nmic, Cmic/Corg and qCO2 indicate that each parameter can be calculated by determining the other parameters in this specific climatic range.  相似文献   

8.
Conservation tillage (no-till and reduced tillage) brings many benefits with respect to soil fertility and energy use, but it also has drawbacks regarding the need for synthetic fertilizers and herbicides. Our objective was to adapt reduced tillage to organic farming by quantifying effects of tillage (plough versus chisel), fertilization (slurry versus manure compost) and biodynamic preparations (with versus without) on soil fertility indicators and crop yield. The experiment was initiated in 2002 on a Stagnic Eutric Cambisol (45% clay content) near Frick (Switzerland) where the average annual precipitation is 1000 mm. This report focuses on the conversion period and examines changes as tillage intensity was reduced. Soil samples were taken from the 0–10 and 10–20 cm depths and analysed for soil organic carbon (Corg), microbial biomass (Cmic), dehydrogenase activity (DHA) and earthworm density and biomass. Among the components tested, only tillage had any influence on these soil fertility indicators. Corg in the 0–10 cm soil layer increased by 7.4% (1.5 g Corg kg−1 soil, p < 0.001) with reduced tillage between 2002 and 2005, but remained constant with conventional tillage. Similarly, Cmic was 28% higher and DHA 27% (p < 0.001) higher with reduced than with conventional tillage in the soil layer 0–10 cm. In the 10–20 cm layer, there were no significant differences for these soil parameters between the tillage treatments. Tillage had no significant effect on total earthworm density and biomass. The abundance of endogeic, horizontally burrowing adult earthworms was 70% higher under reduced than conventional tillage but their biomass was 53% lower with reduced tillage. Wheat (Triticum aestivum L.) and spelt (Triticum spelta L.) yield decreased by 14% (p < 0.001) and 8% (p < 0.05), respectively, with reduced tillage, but sunflower (Helianthus annuus L.) yield was slightly higher with reduced tillage. Slurry fertilization enhanced wheat yield by 5% (p < 0.001) compared to compost fertilization. Overall, Corg, Cmic, and DHA improved and yields showed only a small reduction with reduced tillage under organic management, but long-term effects such as weed competition remain unknown.  相似文献   

9.
The toxic effects of single and joint stress of Cd (cadmium) and Phe (phenanthrene) on enchytraeid Fridericia bulbosa were investigated by natural soil tests. Mortality of single and joint stress of Cd and Phe was significant (p < 0.01) except the lowest concentration of single pollutant. There was a positive correlation between mortality and the concentration of pollutant added to soil. Also, the more exposed to single or joint Cd and Phe, the more morality. For joint pollution, Cd was the main contributive factor of toxic effects, the different concentration and interaction of Cd and Phe significantly influenced mortality (p < 0.01). The joint effects of Cd and Phe were additive, after a 14-d exposure. When Phe was 0.1 mg kg−1 and 1.6 mg kg−1, the interactive effects between Cd and Phe were synergistic. When Phe was 25.6 mg kg−1, the interactive effects were antagonistic. It suggested that morality may be considered as a valuable and sensitive biomarker to diagnose adverse effects of Cd or Phe in soil environment.  相似文献   

10.
The purpose of this study was to assess the spatial variability of the activity of three hydrolytic enzymes, i.e. urease activity (UAc), alkaline phosphatase activity (APAc), and arylsulfatase activity (ASAc), in pasture topsoils using geostatistics. Enzyme activities along a transect in a 1.35-ha pasture were determined using 77 soil samples from the upper 20 cm of soil. UAc varied from 101.0 to 182.7 μg N g−1 soil h−1; APAc varied from 1.56 to 3.62 μg p-nitrophenol g−1 soil h−1; and ASAc varied from 1.50 to 3.26 μg p-nitrophenol g−1 soil h−1. The linear models fit the best semivariogram models for UAc, APAc, and ASAc. Semivariograms for enzyme activities exhibited spatial dependence with ranges of influence of approximately 124.7 m.  相似文献   

11.
Salinisation of soil is a problem in many parts of the world especially in agricultural lands that could also be contaminated with metals from pesticide use. This study aimed to derive a quality criterion standard in a defined substrate with the eventual aim of protecting earthworms against salinity, and to assess the influence of salinity on partitioning of, uptake in and toxicity of zinc to earthworms. To achieve this, two experiments were conducted with specimens of Eisenia fetida exposed in the laboratory for 28 days using OECD artificial soil spiked with either NaCl (experiment 1) or combination of Zn and NaCl (experiment 2). In the first experiment, NaCl was added in the following concentrations: 0, 1000, 2000, 4000, 6000 and 8000 mg kg−1 NaCl. Mortality, growth and cocoon production were assessed at day 28. The results showed 28-day LC50 of 5436 mg kg−1 for NaCl. The EC50s for growth and cocoon production were 4985 and 2020 mg kg−1 NaCl, respectively. In the second experiment, Zn, added as ZnCl2 in a range of sub-lethal concentrations (0, 250, 500, 750 mg kg−1 Zn) was combined with 0, 2000 or 4000 mg kg−1 NaCl. The endpoints: mortality, weight change, and the internal zinc concentration were assessed at day 1, 7, 14 and 28 while cocoon production was assessed only at day 28. Apart from the total zinc concentration in the substrates, DTPA and CaCl2 extractable Zn concentrations were also determined at day 1 and 28 to assess how salinity influenced the partitioning of this metal in the substrates. There was a significant increase in CaCl2 and DTPA extractable Zn in the substrates as salinity increased suggesting that salinity influenced the partitioning of Zn in the substrates. Weight and mortality of worms were not significantly affected by NaCl and Zn as individual substances, but in combination both had significant effects on these parameters. In contrast, cocoon production was significantly affected by increased NaCl and Zn administered as individual substances, and the effects were more severe when both substances were present. The apparent synergy between Zn and NaCl could not be fully explained by internal zinc concentrations in the worms. It could, however, be partly explained by Cl− effect from the addition of Zn as ZnCl2. It is concluded that salinity resulting from increased NaCl had an additive to synergistic effect in combination with Zn, in influencing toxicity to these earthworms.  相似文献   

12.
蒙古高原草原土壤微生物量碳氮特征   总被引：48，自引：0，他引：48  
李香真  曲秋皓 《土壤学报》2002,39(1):97-104
沿着水分梯度采集了蒙古高原不同草原类型表层土壤样品 1 44个 ,分析了土壤微生物量C、N含量及其与年平均温度和降雨量的关系。结果表明 :蒙古高原草原土壤微生物量C、N与土壤有机C、全N、降雨量、温度均表现出了很好的相关性。微生物量C变化在5 1 7～ 797mgkg- 1之间 ,微生物量N变化在 1 1 0～ 1 1 8 6mgkg- 1之间。微生物量C∶N比变化在 5～ 9之间。土壤微生物量碳 (Cmic)占土壤有机碳 (Corg)的比例 (Cmic Corg)变化在 1 1 5 %～ 4 1 %之间 ,Cmic Corg与土壤有机C、全N、降雨量均成显著的负相关。土壤呼吸表现为草甸草原土壤 >典型草原 >荒漠草原 ,土壤呼吸与降雨量显著正相关 ,与温度显著负相关。呼吸熵 (QCO2 )与降雨量成二次抛物线关系。放牧对微生物量的影响与不同草原类型和放牧率有关。  相似文献   

13.
Cover crop and tillage effects on soil enzyme activities following tomato   总被引：2，自引：0，他引：2  
Increasing numbers of vegetable growers are adopting conservation tillage practices and including cover crops into crop rotations. The practice helps to increase or maintain an adequate level of soil organic matter and improves vegetable yields. The effects of the practices, however, on enzyme activities in southeastern soils of the United States have not been well documented. Thus, the objectives of the study were to investigate the effects of cover crops and two tillage systems on soil enzyme activity profiles following tomato and to establish relationships between enzyme activities and soil organic carbon (C) and nitrogen (N). The cover crops planted late in fall 2005 included black oat (Avena strigosa), crimson clover (Trifolium incarnatum L.), or crimson clover–black oat mixed. A weed control (no cover crop) was also included. Early in spring 2006, the plots were disk plowed and incorporated into soil (conventional tillage) or mowed and left on the soil surface (no-till). Broiler litter as source of N fertilizer was applied at a rate of 4.6 Mg ha−1, triple super phosphate at 79.0 kg P ha−1, and potassium chloride at 100 kg K ha−1 were also applied according to soil testing recommendations. Tomato seedlings were transplanted and grown for 60 days on a Marvyn sandy loam soil (fine-loamy, kaolinitic, thermic Typic Kanhapludults). Ninety-six core soil samples were collected at incremental depths (0–5, 5–10, and 10–15 cm) and passed through a 2-mm sieve and kept moist to study arylamidase (EC 3.4.11.2), l-asparaginase (EC 3.5.1.1), l-glutaminase (EC 3.5.1.2), and urease (EC 3.5.1.5) activities. Tillage systems affected only l-glutaminase activity in soil while cover crops affected activities of all the enzymes studied with the exception of urease. The research clearly demonstrated that in till and no-till systems, l-asparaginase activity is greater (P ≤ 0.05) in plots preceded by crimson clover than in those preceded by black oat or their mixture. Activity of the enzyme decreased from 11.7 mg NH4+–N kg−1 2 h−1 at 0–5 cm depth to 8.73 mg NH4+–N kg−1 2 h−1 at 5–10 cm and 10–15 cm depths in the no-till crimson clover plots. Arylamidase activity significantly correlated with soil organic C (r = 0.699**) and soil organic N (r = 0.764***). Amidohydrolases activities significantly correlated with soil organic N but only urease significantly correlated with soil organic C (r = 0.481*). These results indicated that incorporation of cover crops into rotations may increase enzyme activities in soils.  相似文献   

14.
Effects of the broad-spectrum insecticide fipronil were investigated on a non-target insect living in the soil, the springtail Folsomia candida Willem. Fipronil induced a significant reduction in juvenile production (PNEC = 250 μg kg−1 dry soil), which seemed to be linked with an impact on the first stages of springtail development: juveniles and 7-day-old adults. These young organisms have a thinner integument, a smaller mass body and a weaker detoxification efficiency and were more sensitive than adults (14 days old) to fipronil and phenylpyrazole derivatives. Contact toxicity for juveniles was measured (LC50(96 h)) giving the following values: fipronil, 450 μg l−1; sulfone-fipronil, 430 μg l−1; sulfide-fipronil, 160 μg l−1. F. candida organisms were able to avoid contaminated food because phenylpyrazoles decreased food appetency. However, F. candida could bioaccumulate fipronil through trans-tegumental penetration (BAF96 h = 160) and its high biotransformation rate inside springtail bodies (1 ng fipronil metabolized day−1 individual−1) was suspected to increase this process. Under natural conditions, phenylpyrazoles risk assessment on springtails seems to be weak due to their capacity of avoiding high contaminated zones and their biochemical tolerance to this class of insecticides.  相似文献   

15.
土法炼锌区大气沉降Pb、Zn、Cd及其对土壤质量的影响   总被引：6，自引：0，他引：6  
Dust emissions from smelters, as a major contributor to heavy metal contamination in soils, could severely influence soil quality. Downwind surface soils within 1.5 km of a zinc smelter, which was active for 10 years but ceased in 2000, in Magu Town, Guizhou Province, China were selected to examine Pb, Zn, and Cd concentrations and their fractionation along a distance gradient from a zinc smelter, and to study the possible effects of Pb, Zn, and Cd accumulation on soil microorganisms by comparing with a reference soil located at a downwind distance of 10 km from the zinc smelter. Soils within 1.5 km of the zinc smelter accumulated high levels of heavy metals Zn (508 mg kg-1), Pb (95.6 mg kg-1), and Cd (5.98 mg kg-1) with low ratios of Zn/Cd (59.1--115) and Pb/Cd (12.4--23.4). Composite pollution indices (CPIs) of surface soils (2.52--15.2) were 3 to 13 times higher than the reference soils. In metal accumulated soils, exchangeable plus carbonate-bound fractions accounted for more than 10% of the total Zn, Pb, and Cd. The saturation degree of metals (SDM) in soils within 1.5 km of the smelter (averaging 1.25) was six times higher than that of the reference soils (0.209). A smaller soil microbial biomass was found more frequently in metal accumulated soils (85.1--438 μg C g-1) than in reference soils (497 μg C g-1), and a negative correlation (P < 0.01) of soil microbial biomass carbon to organic carbon ratio (Cmic/Corg) with SDM was observed. Microbial consumption of carbon sources was more rapid in contaminated soils than in reference soils, and a shift in the substrate utilization pattern was apparent and was negatively correlated with SDM (R = -0.773, P < 0.01). Consequently, dust deposited Pb, Zn, and Cd in soils from zinc smelting were readily mobilized, and weredetrimental to soil quality mainly in respect of microbial biomass.  相似文献   

16.
The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha−1) compared to oak stands (15.7t ha−1). Canopy leaf area was also significantly larger in mixed stands (1.96m2 m−2) than in oak stands (1.73m2 m−2). Soil organic carbon (C org) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (C mic), nitrogen (N mic), and total soil nitrogen (N tot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean C org/N tot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as C mic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.  相似文献   

17.
Methane (CH4) oxidation potential of soils decreases with cultivation, but limited information is available regarding the restoration of that capacity with implementation of reduced tillage practices. A study was conducted to assess the impact of tillage intensity on CH4 oxidation and several C-cycling indices including total and active microbial biomass C (t-MBC, a-MBC), mineralizable C (Cmin) and N (Nmin), and aggregate-protected C. Intact cores and disturbed soil samples (0–5 and 5–15 cm) were collected from a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation under moldboard-plow (MP), chisel-plow (CP) and no-till (NT) for 8 years. An adjacent pasture (<25 years) and secondary growth forest (>60 years) soils were also sampled as references. At all sites, soil was a Kokomo silty clay loam (mesic Typic Argiaquolls). Significant tillage effects on t-MBC and protected C were found in the 0–5 cm depth. Protected C, a measure of C retained within macro-aggregates and defined as the difference in Cmin (CO2 evolved in a 56 days incubation) between intact and sieved (<2 mm) soil samples, amounted to 516, 162 and 121 mg C kg−1 soil in the 0–5 cm layer of the forest, pasture and NT soils, respectively. Protected C was negligible in the CP and MP soils. Methane uptake rate (μg CH4-C kg−1 soil per day, under ambient CH4) was higher in forest (2.70) than in pasture (1.22) and cropland (0.61) soils. No significant tillage effect on CH4 oxidation rate was detected (MP: 0.82; CP: 0.41; NT: 0.61). These results underscore the slow recovery of the CH4 uptake capacity of soils and suggest that, to have an impact, tillage reduction may need to be implemented for several decades.  相似文献   

18.
The rationale of the study was to investigate microbial activity in different soil horizons in European forests. Hence, activities of chitinase and cellulase, microbial biomass carbon (Cmic) and basal respiration were measured in litter, fragmentation, humus and mineral soil layers collected several times from various beech and spruce forests. Sites were selected to form a gradient in N availability. Analyses were also performed on beech litter from a litterbag transplant experiment. Furthermore, microbiological parameters were measured in horizons of beech and spruce chronosequence sites with different stand age in order to investigate the influence of forest rotation, and hence changes in soil organic matter (SOM) dynamics, on microbial activity. Finally in horizons of one beech forest, the seasonal variation of selected microbiological parameters was measured more intensively. β-Glucosaminidase and cellobiohydrolase activities were measured using fluorogenic 4-methylumbelliferyl substrates to estimate chitinase and cellulase activities, respectively. On a spatial scale, chitinase and cellulase activities, Cmic determined by substrate induced respiration, and basal respiration ranged from 144 to 1924 and 6-177 nmol 4-MU g−1 org-C h−1, 8-48 mg C g−1 org-C and 11-149 μg CO2-C g−1 org-C h−1, respectively; in general values were significantly lower in layers of humus and mineral soil than of litter. Chitinase activity, Cmic and basal respiration from humus and mineral soil layers, together, correlated positively, while none correlated with cellulase activity. Similarly in the litter layer, no correlations were found between the microbiological parameters. On a seasonal scale, a time lag between a burst in basal respiration rate and activities of both enzymes were observed. In general, activities of cellulase and chitinase, Cmic and basal respiration, did not change with stand age, except in the humus layer in the spruce chronosequence, where Cmic decreased with stand age. In the litter layer, cellulase activity was significantly and positively related to the C:N ratio, while only a tendency for chitinase activity was shown, indicating that enzyme activities decreased with increasing N availability. In accordance, the enzyme activities and Cmic decreased significantly with increasing chronic N deposition in the humus layer, while basal respiration only tended to decrease with increasing N deposition. In contrast, enzyme activities in beech litter from litterbags after 2 years of incubation were generally higher at sites with higher N deposition. The results show different layer-specific responses of enzyme activities to changes in N availability, indicating different impacts of N availability on decomposition of SOM and stage of litter decomposition.  相似文献   

19.
The use of composts in agricultural soils is a widespread practice and the positive effects on soil and plants are known from numerous studies. However, there have been few attempts to compare the effects of different kinds of composts in one single study. The aim of this paper is to investigate to what extent and to which soil depth four major types of composts would affect the soil and its microbiota.In a crop-rotation field experiment, composts produced from (i) urban organic wastes, (ii) green wastes, (iii) manure and (iv) sewage sludge were applied at a rate equivalent to 175 kg N ha−1 yr−1 for 12 years. General (total organic C (Corg), total N (Nt), microbial biomass C (Cmic), and basal respiration), specific (enzyme activities related to C, N and P cycles), biochemical properties and bacterial genetic diversity (based on DGGE analysis of 16S rDNA) were analyzed at different depths (0-10, 10-20 and 20-30 cm).Compost treatment increased Corg at all depths from 11 g kg−1 for control soil to 16.7 g kg−1 for the case of sewage sludge compost. Total N increased with compost treatment at 0-10 cm and 10-20 cm depths, but not at 20-30 cm. Basal respiration and Cmic declined with depth, and the composts resulted in an increase of Cmic and basal respiration. Enzyme activities were different depend on the enzyme and among compost treatments, but in general, the enzyme activities were higher in the upper layers (0-10 and 10-20 cm) than in the 20-30 cm layer. Diversity of ammonia oxidizers and bacteria was lower in the control than in the compost soils. The type of compost had less influence on the composition of the microbial communities than did soil depth.Some of the properties were sensitive enough to distinguish between different compost, while others were not. This stresses the need of multi-parameter approaches when investigating treatment effects on the soil microbial community. In general, with respect to measures of activity, biomass and community diversity, differences down the soil profile were more pronounced than those due to the compost treatments.  相似文献   

20.
A three-month microcosm study was carried out in order to evaluate: (i) the capacity of sorghum plants to phytoextract Cd (50 mg kg−1) and Zn (1000 mg kg−1) from artificially polluted soil and (ii) the possibility of biomonitoring the efficiency of phytoremediation using parameters related to the size, activity and functional diversity of the soil microbial community. Apart from plant and soil (total and bioavailable) metal concentrations, the following parameters were determined: soil physicochemical properties (pH, OM content, electrical conductivity, total N, and extractable P and K), dehydrogenase activity, basal- and substrate-induced respiration (with glucose and a model rhizodeposit solution, both adjusted to 800 mg C kg−1 DW soil and 45.2 mg N kg−1 DW soil), microbial respiration quotient, functional diversity through community level physiological profiles and, finally, seed germination toxicity tests with Lepidium sativum. Sorghum plants were highly tolerant to metal pollution and capable of reaching high biomass values in the presence of metals. In the first two harvests, values of shoot Cd concentrations were higher than 100 mg Cd kg−1 DW, the threshold value for hyperaccumulators. Nonetheless, in the third harvest, the bioconcentration factor was 1.34 and 0.35 for Cd and Zn, respectively, well below the threshold value of 10 considered for a phytoextraction process to be feasible. In general, microbial parameters showed lower values in metal polluted than in control non-polluted soils, and higher values in planted than in control unplanted pots. As a result of the phytoextraction process, which includes both plant growth and metal phytoextraction, the functioning of the phytoremediated soil, as reflected by the values of the different microbial parameters here determined, was restored. Most importantly, although the phytoextracted soil recovered its function, it was still more phytotoxic than the control non-polluted soil.  相似文献   

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