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1.
Soil respiration and photosynthesis are the two largest carbon dioxide (CO2) fluxes between terrestrial ecosystems and the atmosphere and, therefore, the dominant processes influencing the oxygen isotopic composition of atmospheric CO2. The characterization of temporal and spatial variations of plant and soil‐related fluxes of different oxygen isotopologues of CO2 (12C16O2; 12C16O18O) is relevant to constraining the global carbon budget. The oxygen isotopic composition of soil‐respired CO2 is controlled by its release rate, the degree of isotopic equilibrium with soil water and the diffusional transport of CO2. The hypothesis of this study was that, as well as soil moisture, the soil particle size, the presence of an organic litter layer and the enzyme carbonic anhydrase (CA) would have a significant impact on the oxygen isotopic composition of soil‐released CO2. We tested this hypothesis with soil microcosm experiments on columns of medium and fine sand. Soil water content and soil texture influenced the isotopic composition of soil‐released CO2 significantly. A litter layer had a significant effect on the isotopic composition of water vapour but not on CO2 released from soil. In the absence of CA, oxygen isotope equilibration between the CO2 invasion flux and soil water was insignificant, whereas in the presence of CA about 55% of the CO2 invading the soil exchanged oxygen isotopes with soil water. Our findings highlight the importance of small‐scale variability of soil attributes for the oxygen isotopic composition of soil‐released CO2 as well as the strong impact of CA activity in soils.  相似文献   

2.
The humus status and CO2 production have been assessed in soils of natural and anthropogenic landscapes in southern regions of the Far East with different types of redox conditions. A higher production of CO2 is typical of burozems and soddy-eluvial-metamorphic soils with oxidative and contrast redox conditions. These are soils with medium or high humus content, high potential humification capacity, and medium enrichment with catalase. A decrease in the content of humus in the plow horizons of soils in agrogenic landscapes is revealed compared to their natural analogues. The studied soils mainly have humus of the fulvate–humate type. The fractions strongly bound to the mineral soil component prevail in humic acids. In waterlogged mucky-humus gley soils, the anaerobic conditions hamper the biological activity and transformation of organic matter, which favors its accumulation. A low production of CO2 is observed in soils with reducing conditions. To determine the differences between the CO2 emission parameters in soils of agrogenic and natural landscapes, monitoring studies should be extended.  相似文献   

3.
This paper questions whether the presence of biosolids amendment in metal‐spiked soils alters the outcome of soil‐based assays of metal bioavailability. The effects of biosolids amendment on the efficacies of six soil metal bioavailability assays (total recoverable, EDTA, Ca(NO3)2, soil solution, diffusive gradient in thin films and free ion activity) were assessed against metal concentrations in wheat shoots (Triticum aestivum) germinated in three contrasting soils, each previously incubated for either 2 weeks or 6 months following treatment with Cd, Cu, Ni and Zn +/? biosolids amendment. Overall, Ca(NO3)2 was the most accurate method to predict Cd (r2 = 0.62), Ni (r2 = 0.73) and Zn (r2 = 0.55) bioavailability in soils and therefore was used to compare variations in responses between biosolids and nonbiosolids‐amended soils. Comparisons between these two groups revealed no significant differences in linear relationships for all four metals and soil types assessed. These findings not only support Ca(NO3)2 as a robust and valid method for determining soil metal bioavailability across metal matrices and soil types, but also that the presence of biosolids does not compromise the predictive power of this assay or any of the others examined.  相似文献   

4.
Water solutions of fluorine and sulfur-containing salts of sodium—NaF, Na2SO3, and NaF + Na2SO3 (30, 150, and 300 MPC, respectively)—and salts of heavy metals—(Cu(NO3)2 · 3H2O, NiSO4, and Pb(NO3)2 (10, 25, and 50 MPC, respectively)—were applied as pollutants to dark gray forest soils of experimental plots (1 m2) in Siberian larch (Larix sibirica Ledeb.) plantations once per growing period. The soil samples for the determination of the microbial biomass, respiration, and enzymatic activity (urease, protease, invertase, and catalase) were taken from the mineral soil layer (0–5 cm) at the beginning of the growing seasons before the application of the pollutants then in 14- to 18-day intervals every month. The fluorine and sulfur-containing compounds applied activated the respiration, lowered the enzymatic activity of the microorganisms, and decreased the microbial biomass by 1.3–2.2 times in the soils of the test plots as compared to the control one. The single application of Cu, Ni, and Pb increased the microbial biomass, while the changes in the basal respiration were compatible with its natural variability. Two months after the beginning of the experiment, all the parameters characterizing the functioning of the soil microbocenoses were restored.  相似文献   

5.
Siderite (FeCO3) is an iron carbonate mineral commonly found in sediments and soils. Similarly to other carbonates, such as calcite or dolomite, it may substantially affect the quantification of organic carbon (C) as well as determination of C isotope ratio of soil organic matter. Both analyses require effective removal of siderite by pretreatment with acid. However, little is known about the siderite removal efficiency of the acid pretreatment methods which have been previously proposed in the literature. In our study, we tested three previously proposed carbonate removal methods for siderite removal in siderite‐containing soils. Furthermore, we tested whether siderite C content in a soil sample can be detected as CO2 evolved after H3PO4 addition which would allow organic C determination from the difference between total and inorganic C. None of the three tested pretreatment methods led to sufficient removal of siderite C when applied on siderite alone. Therefore, we developed a new protocol for a 4‐day treatment with 10% HCl at 25°C. At siderite content of up to 10 wt.%, the removal efficiency of our method (99–100%) was sufficient both for organic C as well as for C isotope analyses. This was further confirmed with tests on siderite‐containing soils. These showed that the method of Larson et al. ( 2008 ) developed for sediments is also suitable. However, the new protocol provides advantage in terms of less microplate manipulation, capsule overflow and oven use. We found that CO2 is not evolved 2 minutes after H3PO4 addition from siderite in contrast to calcite and dolomite. This fact can be used for separate quantification of inorganic C from calcite/dolomite and siderite, e.g., in studies of their different role in soil development. We showed that siderite‐containing soils require special pretreatment procedure before organic C and 13C/12C analyses. We recommend using our protocol if techniques such as XRD or SEM‐EDS indicate the presence of siderite in soil.  相似文献   

6.
A new method to estimate the rate of denitrification in soil was developed, and two different activities were measured: (1) the initial (or true) denitrifying activity of the soil under prevailing conditions; (2) the potential denitrifying activity induced by the addition of N2O. Less than 50 g of soil, saturated with water, were incubated anaerobically at 37°C, with a known amount of N2O, and the disappearance of N2O was followed by gas chromatography. In 25 paddy soils of Senegal, a highly positive rank correlation was found to exist between the denitrifying activity measured by chromatographic and respirometric methods, under the same conditions of incubation with either N2O or NO3? as the hydrogen acceptor. By the N2O reduction method, it was found that there was no initial denitrifying activity in the rhizosphere of 3-week-old rice.  相似文献   

7.
Histochemical and biochemical approaches were used to investigate the phytotoxicity induced by microcystin-LR (MC-LR) in the shoots of Brassica rapa seedlings. MC-LR exposure was able to induce oxidative stress by triggering the over-generation of reactive oxygen species (ROS) including superoxide anion radical (O2 ?? ? ) and hydrogen peroxide (H2O2) in the shoots of B. rapa. MC-LR exposure led to the significant increase in the concentration of endogenous nitric oxide (NO) in B. rapa. However, such increase was completely suppressed by the treatment with nitrate reductase (NR) inhibitor NaN3, while l-NMMA, a NO synthase (NOS) inhibitor, had only slight effect on the content of endogenous NO in MC-LR-treated plant. These data suggested that NR-dependent pathway was the main source for endogenous NO generation under MC-LR stress. Afterwards, treatment with NaN3 reduced the ROS generation, lipid peroxidation, and loss of membrane integrity in MC-LR-treated plant. MC-LR stress induced the increase in the expression of superoxide dismutase, ascorbate peroxidase, and catalase. However, such an effect could be reversed by the treatment with NaN3. These results indicate that NR-dependent NO production mediates MC-LR-induced oxidative stress by triggering the over-generation of ROS in B. rapa.  相似文献   

8.
The oxygen status in soils is fundamental to a number of earth-science processes including biological, physical and chemical interactions. Since oxygen is time consuming and often difficult to measure in soils, this research explores the use of zero-valent iron rods as a means of estimating oxygen content in soils. Zero-valent iron rods (polished nails) were placed in three soil toposequences and the surface coatings formed by oxidation were compared to measured oxygen concentrations taken every three weeks for one year. When water was present in the soils, the oxygen was measured as dissolved oxygen and in drained conditions it was reported as percent. Coatings on iron metal rods inserted in the soil appear to correlate well with specific oxygen ranges. Rods in soils with O2 concentrations below about 2 mg l− 1 do not develop bright (7.5YR 4/4 to 5/8) oxide/oxyhydroxide coatings, but instead formed black (10YR 2/1–2) coatings. Rods in soils with O2 concentrations between about 2% to 5% develop variegated bright (7.5YR 4/4 to 5/8) oxide/oxyhydroxide coatings indicating soil drainage and microsite differences in O2 concentrations. Rods in soils with O2 concentrations above about 5% with adequate moisture are almost completely coated with bright (7.5YR 4/4 to 5/8) iron oxide/oxyhydroxides. Mineralogy of oxide/oxyhydroxide coatings could not be established by XRD presumably due to the short-range order crystal structure of the metal oxide/oxyhydroxides. This method provides a simple and inexpensive means to qualitatively estimate the ranges of O2 status in soils. This research may have implications in hydric soil determination, horticultural and agricultural applications, as well as, remediation techniques.  相似文献   

9.

Purpose

Two plant species (tall fescue and alfalfa) grown alone and in combination was investigated to evaluate phytoremediation of polychlorinated biphenyl (PCB)-contaminated soil and the impact on the catabolic genes and soil enzyme activities in the rhizosphere.

Materials and methods

Surface soil was collected from Xiaoshan (a PCB-containing capacitors and transformers storage site). The phytoremediation experiment was carried out in an agricultural greenhouse experiment station at Huajiachi campus, Zhejiang University. Soil dressing method and fertilizers were applied to improve soil quality for the pot experiment. Soil dehydrogenase activity was measured spectrophotometrically by the reduction of 2, 3, 5-triphenylterazolium chloride (TTC) to triphenyl formazane (TPF) and catalase activity was determined by back-titrating residual H2O2 with KMnO4. Quantitative real-time PCR using SYBR green I was employed with the individual primer sets to determine the relative abundance of the biphenyl dioxygenase genes. Total bacterial numbers were determined by CFU counting and amplification of 16S rDNA.

Results and discussion

Planting treatment significantly enhanced bacterial numbers and PCB removal. The copy numbers of the bphA, bphD.1.B, bphD.2.A, and bphD.2.A/B genes, total bacteria counts, and dehydrogenase activity were the highest in mixed cropping soil, which indicated that tall fescue (forage grass) and alfalfa (legume) mixed cropping was most beneficial to soil bacteria, the potential PCB degraders, and enzyme activity. However, the highest removal of PCBs was found in tall fescue single plant cultivation, followed by combined plant cultivation, probably because tall fescue had greater biomass and could extract more PCBs from soil. Compared with nutrients amended unplanted control, the removals of tri-, tetra-, and penta-CBs in tall fescue single-planted and tri-CBs in combined planted soils were significantly enhanced (p?<?0.01).

Conclusions

The presence of vegetation significantly promoted the dissipation of PCBs and growth of total bacteria and the potential PCBs degraders in soils. Tall fescue and alfalfa mixed cropping was most beneficial to soil bacteria and enzyme activity. Tall fescue showed highest ability for remediation of PCBs in a poor quality soil.  相似文献   

10.

Purpose

The impacts of different land use practices on soil quality were assessed by measuring soil attributes and using factor analysis in coastal tidal lands. The study provided relevant references for coastal exploitation, land management and related researches in other countries and regions.

Materials and methods

Measured soil attributes include physical indicators [bulk density (ρ b), total porosity (? t) and water-holding capacity (WHC)], chemical indicators [pH, electrical conductivity (EC), total nitrogen (TN), soil organic matter (SOM), available N, available P and available K] and biological indicators (urease activity, catalase activity and phosphatase activity), and 60 soil samples were collected within five land use types [(1) intertidal soils, (2) reclaimed tidal flat soils, (3) farmland soils, (4) suburban vegetable soils, (5) industrial area soils) in Jianggang village of Dongtai county, Jiangsu province of China.

Results and discussion

The results from the investigation indicated that selected soil properties reduced to three factors for 0–20-cm soil depth; “Soil fertility status” (factor 1), “Soil physical status” (factor 2) and “Soil salinity status” (factor 3). For the first factor, the measured soil attributes with higher loadings were TN and SOM, which represented soil fertility feature, and for the second and third factors, the measured soil attributes with higher loadings were ρ b and available K as well as EC, which reflected soil physical properties and soil salinity feature, respectively.

Conclusions

Changes in different land use types due to plants (corn, wheat and green vegetable) and application of fertilizers were characterized by promoted soil quality, including improvements in chemical properties (increasing SOM concentration, TN and nutrient available to plants; decreasing EC), improvements in soil physical properties (decreasing ρ b; increasing ? t and WHC) and enhancements in soil enzyme activities. Judging from the soil quality indices, the soil quality was affected by different land use practices and decreased in sequence of suburban vegetable soils, farmland soils, industrial area soils, reclaimed tidal flat soils and intertidal soils in the study area.  相似文献   

11.
Dissimilatory nitrate reductase in soils is the enzyme that catalyzes the reduction of NO33− to NO2− under anaerobic conditions. The detection of this enzyme in soils is reported, and a simple, sensitive and precise method to assay its activity is described. The method involves determination of the NO2−-N produced when soil. 2,4-dinitrophenol (DNP), and KNO3 are incubated under waterlogged conditions at 25°C for 24 h. At a certain concentration, depending on the soil type, DNP inhibits nitrite reductase but not nitrate reductase. The DNP concentration required for optimum NO2− production in five soils ranged from 5 to 300 μg DNP g−1 soil. The nitrate reductase activity of six soils studied ranged from 18 to 80 μg NO2−-N produced g−1 soil 24 h−1. Optimum activity was found at 5 mM KNO3 and nitrate reductase was inhibited at >5 mM KNO3. Nitrate reductase activity in soils is inactivated at temperatures above 40°C and is completely destroyed by steam sterilization. The relationship between duration of incubation and the amount of NO2−-N produced showed a lag of about 10 h, but in general, thereafter, this relationship was linear for a certain period of incubation, which varied among the soils studied. The duration of the lag was reduced, but not completely eliminated, either by previous incubation for 10 h or by bubbling N2 gas in the soil-water mixture for 3 min to remove the dissolved O2 in the soil-water mixture before addition of NO3−. The relationship between the amount of soil used and the NO2−-N produced was linear unless the substrate concentration was limiting the reaction rate. Application of the Lineweaver-Burk transformation of the Michaelis-Menten equation indicated that the Km values for nitrate reductase in Ames and Okoboji soils were 3.7 and 2.9, respectively, and the Vmax values were 122 and 126μg NO2−-N produced g− soil 24 h−.  相似文献   

12.
Summary Nitrification activity (formation of NO 2 – + NO 3 – per unit soil weight) was measured in the surface layer of 15 presubmerged soils incubated in petri dishes under flooded but aerobic conditions. soils with pH above 5 nitrified quickly, whereas soils with pH below this level did not nitrify or nitrified slowly. The pH values between 7 and 8.5 were optimal for nitrification. Organic-matter levels in the 15 soils of our study did not influence their nitrification activities. In a follow-up greenhouse pot study, after a period of 3 weeks, 15N-balance measurements showed that the loss of N through apparent denitrification did not follow the nitrification patterns of the soils observed in the petri dishes. Apparent denitrification accounted for 16.8% and 18.9% loss of 15N from a soil with insignificant nitrification activity and a soil with high nitrification activity, respectively. These results, thus, indicate a lack of correspondence between the nitrification activities of soil and the denitrification loss of N when the former was measured in the dark and the latter was estimated in the light. Soils that nitrified in the darkness of the incubator did not nitrify in the daylight in the greenhouse.  相似文献   

13.
Soil irrigation with wastewater (WW) gives the opportunity to solve the problems of its disposal, final purification or reuse. Many studies have examined mineral soils upon continued WW application. The aim of this paper was to examine the properties of organic soils 3 years after WW application was discontinued. Peat‐muck soil planted with Populus spp. or Salix spp., and mineral‐muck soil under grasses were irrigated for 4 years with municipal WW at a low (comparable with intensive NPK fertilization) and high WW rate (600 and 1200 mm yearly, respectively). Soils were analysed for organic matter (OM), pH, bulk density (BD), water holding capacity (WHC), P2O5, Fe2O3, Al2O3, MnO, Zn, Pb, Cu, Cr, magnetic susceptibility (MS) and dehydrogenase and catalase activities. The results were compared with control soils which have never received WW. The study showed that only P2O5, MnO and catalase activity (CA) were significantly affected by former WW application. On average, P2O5 increased by 30 per cent, whereas MnO decreased by 35 per cent with no differences between the two WW rates. CA decreased by 18 per cent at the high WW rate. Most of tested characteristics were determined by soil type. The peat‐muck soil showed higher OM, WHC, P2O5, MnO, Pb and CA than mineral‐muck soil and lower BD, MS, Fe2O3, Al2O3 and Cr. Soil depth influenced Fe2O3, MnO, Zn, MS and enzyme activities, while basic soil properties (OM, pH, BD, WHC and P2O5) were not changed by soil depth. Heavy metals (Zn, Cr, Cu and Pb) were below upper permissible limits. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

14.

Purpose

Biochar can be used to reduce the bioavailability and leachability of heavy metals, as well as organic pollutants in soils through adsorption and other physicochemical reactions. The objective of the study was to determine the response of microbial communities to biochar amendment and its influence on heavy metal mobility and PCBs (PCB52, 44, 101, 149, 118, 153, 138, 180, 170, and 194) concentration in application of biochar as soil amendment.

Materials and methods

A pot (macrocosm) incubation experiment was carried out with different biochar amendment (0, 3, and 6 % w/w) for 112 days. The CaCl2-extractable concentration of metals, microbial activities, and bacterial community were evaluated during the incubation period.

Results and discussion

The concentrations of 0.01 M CaCl2-extractable metals decreased (p?>?0.05) by 12.7 and 20.5 % for Cu, 5.0 and 15.6 % for Zn, 0.2 and 0.5 % for Pb, and 1.1 and 8.9 % for Cd, in the presence of 3 and 6 % of biochar, respectively, following 1 day of incubation. Meanwhile, the total PCB concentrations decreased from 1.23 mg kg?1 at 1 day to 0.24 mg kg?1 at 112 days after 6 % biochar addition, representing a more than 60 % decrease relative to untreated soil. It was also found out that biochar addition increased the biological activities of catalase, phosphatase, and urease activity as compared with the controls at the same time point. Importantly, the Shannon diversity index of bacteria in control soils was 3.41, whereas it was 3.69 and 3.88 in soils treated with 3 and 6 % biochar soil. In particular, an increase in the number of populations with the putative ability to absorb PCB was noted in the biochar-amended soils.

Conclusions

The application of biochar to contaminated soils decreased the concentrations of heavy metals and PCBs. Application of biochar stimulated Proteobacteria and Bacteroides, which may function to absorb soil PCB and alleviate their toxicity.
  相似文献   

15.
On the determination of exchangeable cations in acid forest soils Different samples from acid forest soils were percolated with large amounts of H2O. Significant amounts of anions, especially sulfate, were found in the percolates mainly accompanied by Na. K, Ca and Mg (Mb-cations). The dissolution of Al-Sulfates and subsequent exchange of Mb-cations by Al as dominant mechanism is proposed. Thus the common method for determination of the cation exchange capacity (CEC) of acid forest soils, the percolation with NH4Cl may overestimate the CEC. The overestimation may be related to the sulfate content of the soil and also influences the calculation of relative CEC proportions of individual cations.  相似文献   

16.
Exudates are part of the total rhizodeposition released by plant roots to soil and are considered as a substantial input of soil organic matter. Exact quantitative data concerning the contribution of exudates to soil C pools are still missing. This study was conducted to reveal effects of 13C‐labeled exudate (artificial mixture) which was regularly applied to upper soil material from two agricultural soils. The contribution of exudate C to water‐extractable organic C (WEOC), microbial biomass C (MBC), and CO2‐C evolution was investigated during a 74 d incubation. The WEOC, MBC, and CO2‐C concentrations and the respective δ13C values were determined regularly. In both soils, significant incorporation of artificial‐exudate‐derived C was observed in the WEOC and MBC pool and in CO2‐C. Up to approx. 50% of the exudate‐C amounts added were recovered in the order WEOC << MBC < CO2‐C in both soils at the end of the incubation. Newly built microbial biomass consisted mainly of exudates, which substituted soil‐derived C. Correspondingly, the CO2‐C evolved from exudate‐treated soils relative to the controls was dominated by exudate C, showing a preferential mineralization of this substrate. Our results suggest that the remaining 50% of the exudate C added became stabilized in non‐water‐extractable organic fractions. This assumption was supported by the determination of the total organic C in the soils on the second‐last sampling towards the end of the incubation. In the exudate‐treated soils, significantly more soil‐derived C compared to the controls was found in the WEOC on almost all samplings and in the MBC on the first sampling. This material might have derived from exchange processes between the added exudate and the soil matrix. This study showed that easily available substrates can be stabilized in soil at least in the short term.  相似文献   

17.
The decomposition of atmospheric hydrogen in different types of soil was measured. The decomposition of H2 was apparently a first-order reaction. H2 decomposition activity was proportional to the amount of soil with maximum activities at soil water contents of approx. 6–11% (w/w). The activity was lower under anaerobic conditions, but was constant between 1–20% O2. It was destroyed by autoclaving and was partially inactivated by fumigation with NH3, CHC13 or acetone, by u.v. irradiation and by treatment with NaCN or NaN3, indicating that biological processes in the soil were responsible for the observed H2 decomposition. Treatment of soil with toluene or CHCl3 caused only a partial inactivation. Incubation of soil in the presence of streptomycin or actidione reduced H2 decomposition by less than 50%, whereas CO consumption was abolished. The H2 decomposition rates showed H2 saturation curves with apparent Michaelis-Menten kinetics. Cooperative effects were not observed. Vmax was reached at approx. 200 μl1?1. The Km values for H2 were in the range of 30μl 1?1, but increased to higher values, when the soil had been pretreated with high H2 mixing ratios. Apparently, the observed H2 decomposition by soil is not only due to the activity of viable microorganisms, but soil enzymes as well.  相似文献   

18.
The isotopically exchangeable metal pool (E‐value) of zinc (Zn), cadmium (Cd) and lead (Pb) were simultaneously measured, using stable isotope dilution, in soils contaminated by Pb/Zn mining activities and varying in properties likely to affect metal reactivity, including pH, organic matter content, metal concentration and land use. E‐values were compared with single and sequential extraction schemes. Results showed a wide range of metal reactivity (approximately 1–100% of total) depending on the extent of contamination and on the prevailing soil conditions. Across the range of soils, the E‐values showed no consistent correspondence to any single chemical extraction procedure (EDTA, DTPA and HNO3) although there was reasonable agreement with the extractants 0.05 m EDTA and 0.43 m HNO3 in acidic organic soils. Extraction with 0.005 m DTPA substantially under‐estimated the isotopically exchangeable metal content. E‐values corresponded reasonably well with the exchangeable metal (fraction 1 (F1) of the sequential extraction procedure) in calcareous soils but relatively poorly and inconsistently with F1–F2, F1–F3 or F1–F4 in acidic‐neutral soils. Operational aspects associated with determination of multi‐element E‐values are discussed.  相似文献   

19.
A method to determine oxygen partial pressure and oxygen diffusion in single soil aggregates as a function of soil moisture tension Anaerobic zones occur even in unsaturated soils of silty or clayey texture, that are aerated sufficiently in their macropore system. These zones can be related to the inner parts of soil aggregates. To describe the oxygen balances in soils it is necessary to measure not only in soil profiles but as well in single soil aggregates within a range of soil matrix potentials. Therefore oxygen partial pressure in single soil aggregates of different texture was measured continuously as a function of soil matrix potential. For that purpose we developed an oxygen sensitive microelectrode with a tip diameter of 0.5 mm, that is sturdy enough to measure even in sandy soils. One microtensiometer (diameter of the tip < 0.5 mm) and one oxygen microelectrode were placed in water saturated soil aggregates. Soil water potential and oxygen partial pressure were measured continuously during soil drying. The results show an aeration of primarily anoxic soil aggregates at different soil matrix potentials due to different texture and structure. The clayey polyhedral aggregates of the Vertisol were aerated at significantly lower soil matrix potentials than the loamy prisms of the Fluvisol. These show higher values of oxygen partial pressure even at soil water potentials less than 150 hPa. In the aggregates of the Vertisol, that have a fine texture, values of rel. aparent diffusion Ds/Do were in the range of 1 · 10?3 at soil water potentials < ?  相似文献   

20.
《Soil biology & biochemistry》2001,33(4-5):683-687
Emissions of N2O from acid coniferous forest soils are found to be low and considered to be due to nitrification rather than denitrification. Recently we have demonstrated soil-layer specific denitrification in a Scots pine forest in the Netherlands. N2O production, in the presence of high concentrations of acetylene, was detected in the intact needle fraction but was absent in the fragmentation layer of this forest soil. To identify the factors regulating denitrification activity, in the present study the effects of oxygen, pH and organic carbon were investigated in the needle and fragmentation fraction of acid coniferous forest soils. Under natural circumstances denitrification in the Scots pine needles was higher than in Douglas fir needles and absent in fragmentation material. Under anaerobic conditions comparable N2O production in the two soil types was found in needle suspensions of both forest types, indicating that differences in anaerobic microsites were responsible for different N2O production under aerobic circumstances. Denitrifying capacity was absent in the fragmentation layer; under anaerobic circumstances little N2O was produced. Neither an addition of available carbon (glucose and succinate) nor an increase in pH revealed a denitrifying capacity comparable to that observed in needles. The increase in pH, under anaerobic circumstances, was most effective on N2O production in the fragmentation material. The denitrifying capacity in the fragmentation layer remained low during short-term incubation under optimal conditions. This indicates the presence of a low denitrifying population, most likely due to aerobic conditions, low pH and low available organic carbon. Although the significance of N2O production under natural conditions remains speculative, this study seeks to clarify soil-layer specific denitrifying activity in acid coniferous forest soils.  相似文献   

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