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1.
In forest soils where a large fraction of total phosphorus (P) is in organic forms, soil micro-organisms play a major role in the P cycle and plant availability since they mediate organic P transformations. However, the correct assessment of organic P mineralization is usually a challenging task because mineralized P is rapidly sorbed and most mineralization fluxes are very weak. The objectives of the present work were to quantify in five forest Spodosols at soil depths of 0-15 cm net mineralization of total organic P and the resulting increase in plant available inorganic P and to verify whether net or gross P mineralization could be estimated using the C or N mineralization rates. Net mineralization of total organic P was derived from the net changes in microbial P and gross mineralization of P in dead soil organic matter. We studied very low P-sorbing soils enabling us to use lower extractants to assess the change in total inorganic P as a result of gross mineralization of P in dead soil organic matter. In addition, to enable detection of gross mineralization of P in dead soil organic matter, a long-term incubation (517 days) experiment was carried out. At the beginning of the experiment, total P contents of the soils were very low (19-51 μg g−1) and were essentially present as organic P (17-44 μg g−1, 85-91%) or microbial P (6-14 μg g−1; 24-39%). Conversely, the initial contents of inorganic P were low (2-7 μg g−1; 9-15%). The net changes in the pool size of microbial P during the 517 days of incubation (4-8 μg g−1) and the amounts of P resulting from gross mineralization of dead soil organic matter (0.001-0.018 μg g−1 day−1; 0.4-9.5 μg g−1 for the entire incubation period) were considerable compared to the initial amounts of organic P and also when compared to the initial diffusive iP fraction (<0.3 μg g−1). Diffusive iP corresponds to the phosphate ions that can be transferred from the solid constituents to the soil solution under a gradient of concentration. Net mineralization of organic P induced an important increase in iP in soil solution (0.6-10 μg g−1; 600-5000% increase) and lower increases in diffusive iP fractions (0.3-5 μg g−1; 300-2000% increase), soil solid constituents having an extremely low reactivity relative to iP. Therefore, soil micro-organisms and organic P transformations play a major role in the bioavailability of P in these forest soils. In our study, the dead soil organic matter was defined as a recalcitrant organic fraction. Probably because gross mineralization of P from this recalcitrant organic fraction was mainly driven by the micro-organisms’ needs for energy, the rates of gross mineralization of C, N and P in the recalcitrant organic fraction were similar. Indirect estimation of gross mineralization of P in dead soil organic matter using the gross C mineralization rate seems thus an alternative method for the studied soils. However, additional studies are needed to verify this alternative method in other soils. No relationships were found between microbial P release and microbial C and N releases.  相似文献   

2.
The effect of increasing concentrations of Cd and Zn in a sandy soil on spring wheat (Triticum vulgare L.) yields and the metal contents of the plants was examined in a pot experiment to establish critical levels of these metals in soil. The metals were added (individually and jointly) to the soil as sulfates in the following doses (in μg g?1, dry wt.): Cd — 2, 3, 5,10, 15, 25, and 50; Zn ?200, 300, 500, 1000, 1500, 2500, and 5000. Cadmium added to soil did not affect yields of wheat. The Zn dose of 1000 μg g?1 strongly reduced crop yields; at 1500 μg g? Zn dose wheat did not produce grain. The metal contents of wheat increased with increasing concentrations of Cd and Zn in soil up to 10.3 and 1587 μ g? of Cd and Zn in straw, respectively. The concentrations of both metals were higher in straw than in grain by factors of 3–7 and 1.5–2 for Zn and Cd, respectively. The relationships between Cd and Zn contents of the plants and soils were best expressed by exponential equations. High concentrations of Zn in soils (1042 and 1542 μg g?1) enhanced uptake of Cd by plants. The tested threshold concentrations of the metals in soils (3 μg g?1 for Cd and 200–300 μg g?1 for Zn) are safe for Zn but are too high for Cd in terms of protecting plants from excessive metal uptake. The critical Cd content of sandy soil should not exceed 1.5 μg g?.  相似文献   

3.
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   

4.
《Soil biology & biochemistry》2001,33(7-8):913-919
A reliable and simple technique for estimating soil microbial biomass (SMB) is essential if the role of microbes in many soil processes is to be quantified. Conventional techniques are notoriously time-consuming and unreproducible. A technique was investigated that uses the UV absorbance at 280 nm of 0.5 M K2SO4 extracts of fumigated and unfumigated soils to estimate the concentrations of carbon, nitrogen and phosphorus in the SMB. The procedure is based on the fact that compounds released after chloroform fumigation from lysed microbial cells absorb in the near UV region. Using 29 UK permanent grassland soils, with a wide range of organic matter (2.9–8.0%) and clay contents (22–68%), it was demonstrated that the increase in UV absorbance at 280 nm after soil fumigation was strongly correlated with the SMB C (r=0.92), SMB N (r=0.90) and SMB P (r=0.89), as determined by conventional methods. The soils contained a wide range of SMB C (412–3412 μg g−1 dry soil), N (57–346 μg g−1 dry soil) and P (31–239 μg g−1 dry soil) concentrations. It was thus confirmed that the UV absorbance technique described was a rapid, simple, precise and relatively inexpensive method of estimating soil microbial biomass.  相似文献   

5.
Nitrogen (N) is an essential element associated with crop yield and its availability is largely controlled by microbially-mediated processes. The abundance of microbial functional genes (MFG) involved in N transformations can be influenced by agricultural practices and soil amendments. Biochar may alter microbial functional gene abundances through changing soil properties, thereby affecting N cycling and its availability to crops. The objective of this study was to assess the effects of wood biochar application on N retention and MFG under field settings. This was achieved by characterising soil labile N and their stable isotope compositions and by quantifying the gene abundance of nifH (nitrogen fixation), narG (nitrate reduction), nirS, nirK (nitrite reduction), nosZ (nitrous oxide reduction), and bacterial and archeal amoA (ammonia oxidation). A wood-based biochar was applied to a macadamia orchard soil at rates of 10 t ha−1 (B10) and 30 t ha−1 (B30). The soil was sampled after 6 and 12 months. The abundance of narG in both B10 and B30 was lower than that of control at both sampling months. Canonical Correspondence Analysis showed that soil variables (including dissolved organic C, NO3−–N and NH4+–N) and sampling time influenced MFG, but biochar did not directly impact on MFG. Twelve months after biochar application, NH4+–N concentrations had significantly decreased in both B10 (4.74 μg g−1) and B30 (5.49 μg g−1) compared to C10 (13.9 μg g−1) and C30 (17.9 μg g−1), whereas NO3−–N concentrations increased significantly in B30 (24.7 μg g−1) compared to B10 (12.7 μg g−1) and control plots (6.18 μg g−1 and 7.97 μg g−1 in C10 and C30 respectively). At month 12, significant δ15N of NO3−–N depletion observed in B30 may have been caused by a marked increase in NO3−–N availability and retention in those plots. Hence, it is probable that the N retention in high rate biochar plots was mediated primarily by abiotic factors.  相似文献   

6.
To investigate the uptake by the microbial community of easily decomposable exogenous organic C and the proportion of this organic C remaining in soils under long-term fertilization schemes, 13C-glucose was supplied to arable soils (aquic inceptisol) following a 20-year (1989–2009) application of compost (CM) or inorganic NPK (NPK), along with a control (no fertilizer). Phospholipid fatty acids (PLFAs) were used as biomarkers for actinobacteria, bacteria and fungi. Gas chromatography–combustion–stable isotope ratio mass spectrometry (GC–C–IRMS) was used to determine the incorporation of 13C into individual PLFAs. The concentrations of soil microbial PLFAs significantly (P < 0.05) increased in all three soils after the addition of 13C-glucose. Over a 30-day incubation period, the highest PLFA concentrations were on day 7 (control) or day 15 (NPK and CM) for bacteria, and on day 30 for both fungi and actinobacteria. The added 13C-glucose was incorporated into bacterial PLFAs first, whilst an increase of 13C in fungal and actinobacterial PLFAs was measured on day 7 and 15, respectively. The mean amounts of 13C in bacterial, actinobacterial and fungal PLFAs in CM-treated soil during the 30-day incubation period were 0.589, 0.030 and 0.056 μg g−1 soil, respectively, which were significantly (P < 0.05) higher than levels measured in the NPK and control soils. Among the bacterial groups, the amount of 13C in Gram-positive (G+) bacteria over the entire incubation ranged from 0.326 to 0.440 μg g−1 soil in the CM scheme, which was significantly (P < 0.05) higher than levels detected in the NPK and control regimes. In contrast, 13C concentrations in monounsaturated PLFAs (aerobic microorganisms) in the CM-treated soil were 0.030–0.045 μg g−1 soil, which was significantly (P < 0.05) lower than in the NPK schemes. The proportion of glucose-derived 13C remaining in soils was ranked as follows: CM (53%) > NPK (41%) > control (28%) after 30 days of incubation. Easily decomposable exogenous organic C was thus more effectively maintained under the CM regime, primarily because, after 20 years, CM had altered the microbial community by reducing the ratio of aerobic to anaerobic microorganisms whilst increasing levels of G+ bacteria in soil compared to the control and NPK soils. This study aids our understanding of the transformation and maintenance of easily decomposable organic C in soil over long-term fertilization regimes.  相似文献   

7.
The addition of small or trace amounts of carbon to soils can result in the release of 2-5 times more C as CO2 than was added in the original solution. The identity of the microorganisms responsible for these so-called trigger effects remains largely unknown. This paper reports on the response of individual bacterial taxa to the addition of a range of 14C-glucose concentrations (150, 50 and 15 and 0 μg C g−1 soil) similar to the low levels of labile C found in soil. Taxon-specific responses were identified using a modification of the stable isotope probing (SIP) protocol and the recovery of [14C] labelled ribosomal RNA using equilibrium density gradient centrifugation. This provided good resolution of the ‘heavy’ fractions ([14C] labelled RNA) from the ‘light’ fractions ([12C] unlabelled RNA). The extent of the separation was verified using autoradiography. The addition of [14C] glucose at all concentrations was characterised by changes in the relative intensity of particular bands. Canonical correspondence analysis (CCA) showed that the rRNA response in both the ‘heavy’ and ‘light’ fractions differed according to the concentration of glucose added but was most pronounced in soils amended with 150 μg C g−1 soil. In the ‘heavy RNA’ fractions there was a clear separation between soils amended with 150 μg C g−1 soil and those receiving 50 and 15 μg C g−1 soil indicating that at low C inputs the microbial community response is quite distinct from that seen at higher concentrations. To investigate these differences further, bands that changed in relative intensity following amendment were excised from the DGGE gels, reamplified and sequenced. Sequence analysis identified 8 taxa that responded to glucose amendment (Bacillus, Pseudomonas, Burkholderia, Bradyrhizobium, Actinobacteria, Nitrosomonas, Acidobacteria and an uncultured β-proteobacteria). These results show that radioisotope probing (RNA-RIP) can be used successfully to study the fate of labile C substrates, such as glucose, in soil.  相似文献   

8.
The benzoxazinoid 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) is produced by rye (Secale cereale) and may contribute to plant-parasitic nematode suppression when rye plants are incorporated as a green manure. We investigated the fate of DIBOA in soil and DIBOA's effects on nematode reproduction. Soil in plastic bags was treated with DIBOA at concentrations ranging from 1.1 to 18 μg g−1 dry soil, and with the root-knot nematode Meloidogyne incognita. Control soils were treated with water or with 0.31% methanol, with or without nematodes. DIBOA concentrations extracted from the soil were measured at selected times for 5 consecutive days. The soil from each bag was then placed into a pot in the greenhouse, and a cucumber seedling was transplanted into each pot. Five weeks later, only the highest DIBOA concentration, 18 μg g−1 soil, reduced nematode egg numbers. At 0 h, DIBOA measured in soil ranged from 19.68 to 35.51% of the initial DIBOA concentration, and was dependent on the concentration added to the soil. DIBOA half-life was from 18 to 22 h, and very little DIBOA was present in soil after 120 h. Identified breakdown products accounted for only 4% at maximum of the initially added DIBOA. The results of our study demonstrate that high soil concentrations of DIBOA are necessary to suppress M. incognita; DIBOA may not be a major factor in nematode suppression by a rye cover crop.  相似文献   

9.
2,4-Dichlorophenoxyacetic acid butyl ester (2,4-D butyl ester) is extensively applied for weed control in cultivation fields in China, but its effect on soil microbial community remains obscure. This study investigated the microbial response to 2,4-D butyl ester application at different concentrations (CK, 10, 100 and 1000 μg g?1) in the soils with two fertility levels, using soil dilution plate method and phospholipid fatty acid (PLFA) analysis. Culturable microorganisms were affected by the herbicide in both soils, particularly at the higher concentration. After treating soil with 100 μg g?1 herbicide, culturable bacteria and actinomycetes were significantly higher, compared to other treatments. Treatment of soil with 1000 μg g?1 2,4-D butyl ester caused a decline in culturable microbial counts, with the exception of fungal numbers, which increased over the incubation time. PLFA profiles showed that fatty acids for Gram-negative (GN) bacteria, Gram-positive (GP) bacteria, total bacteria and total fungi, as well as total PLFAs, varied with herbicide concentration for both soil samples. As herbicide concentration increased, the GN/GP ratio decreased dramatically in the two soils. The higher stress level was in the treatments with high concentrations of herbicide (1000 μg g?1) for both soils. Principal component analysis of PLFAs showed that the addition of 2,4-D butyl ester significantly shifted the microbial community structure in the two soils. These results showed that the herbicide 2,4-D butyl ester might have substantial effects on microbial population and microbial community structure in agricultural soils. In particular, the effects of 2,4-D butyl ester were greater in soil with low organic matter and fertility level than in soil with high organic matter and fertility level.  相似文献   

10.
Soil microbial biomass P is usually determined through fumigation-extraction (FE), in which partially extractable P from lysed biomass is converted to biomass P using a conversion factor (Kp). Estimation of Kp has been usually based on cultured microorganisms, which may not adequately represent the soil microbial community in either nutrient-poor or in altered carbon and nutrient conditions following fertilisation. We report an alternative approach in which changes in microbial P storage are determined as the residual in a mass balance of extractable P before and after incubation. This approach was applied in three low-fertility sandy soils of southwestern Australia, to determine microbial P immobilisation during 5-day incubations in response to the amendment by 2.323 mg C g−1, 100 μg N g−1 and 20 μg P g−1. The net P immobilisation during the amended incubations determined to be 18.1, 14.1 and 16.3 μg P g−1 in the three soils, accounting for 70.6-90.5% of P added through amendment. Such estimates do not rely on fumigation and Kp values, but for comparison with the FE method we estimated ‘nominal’ Kp values to be 0.20-0.31 for the soils under the amended conditions. Our results showed that microbial P immobilisation was a dominant process regulating P concentration in soil water following the CNP amendment. The mass-balance approach provides information not only about changes in the microbial P compartment, but also about other major P-pools and their fluxes in regulating soil-water P concentrations under substrate- and nutrient-amended conditions.  相似文献   

11.
A high level of biological degradation is usually observed in soils under semiarid climate where the low inputs of vegetal debris constraint the development of microbiota. Among vegetal inputs, cellulose and lignin are dominant substrates but their assimilation by the microbial community of semiarid soils is yet not understood. In the present study, 13C-labeled cellulose and 13C-labeled lignin (75 μg 13C g−1 soil) were added to two semiarid soils with different properties and degradation level. Abanilla soil is a bare, highly degraded soil without plant cover growing on it and a total organic C content of 5.0 g kg−1; Santomera soil is covered by plants (20% coverage) based on xerophytic shrubs and has a total organic C content of 12.0 g kg−1. The fate of added carbon was evaluated by analysis of the carbon isotope signature of bulk soil-derived carbon and extractable carbon fractions (water and sodium-pyrophosphate extracts). At long-term (120 days), we observed that the stability of cellulose- and lignin-derived carbon was dependent on their chemical nature. The contribution of lignin-derived carbon to the pool of humic substances was higher than that of cellulose. However, at short-term (30 days), the mineralization of the added substrates was more related to the degradation level of soils (i.e. microbial biomass). Stable isotope probing (SIP) of phospholipid fatty acids (PLFA-SIP) analysis revealed that just a minor part of the microbial community assimilated the carbon derived from cellulose and lignin. Moreover, the relative contribution of each microbial group to the assimilation of lignin-derived carbon was different in each soil.  相似文献   

12.
Biological control agents like Bacillus subtilis offer an alternative and supplement to synthetic pesticides. Antibiotic production by biocontrol strains of B. subtilis can play a major role in plant disease suppression. Our current understanding of B. subtilis antibiosis comes from culture media measurements of antibiotic production and in vitro suppression of pathogens. Quantifying the antibiotic metabolite chemistry of B. subtilis biofilms growing on root surfaces provides a more accurate understanding of in vivo antibiotic production. An analytical method based on solid-phase extraction (SPE) with high-performance liquid chromatography (HPLC) and mass spectroscopy (MS) has been developed to quantify antibiotics produced by B. subtilis growing on plant roots. Cucumber (Cucumis sativus) was grown in composted soil and potting media inoculated with B. subtilis strain QST 713 (AgraQuest, USA). Two important B. subtilis antibiotics, surfactin and iturin A, were extracted from root and rhizosphere soil using acidified organic solvents followed by cleaning and concentration using SPE. HPLC and HPLC-MS were used to measure surfactin and iturin A. Rhizosphere concentrations of both antibiotics increased with plant age. For plants grown in peat-based potting media, surfactin concentrations increased from 9 μg g−1 root fresh weight (RFW) at 15 d to 30 μg g−1 RFW at 43 d. Iturin concentrations were 7 μg g−1 RFW at 15 d and 180 μg g−1 RFW at 43 d. In an initial field trial in a composted fine sandy loam, we demonstrated rhizosphere production of surfactin and iturin under competition and predation by the myriad macro- and microfauna existing in a fertile high-organic soil, with mature B. subtilis-inoculated cucumber roots yielding 33 μg g−1 RFW surfactin and 630 μg g−1 RFW iturin at 78 d.  相似文献   

13.
A study was carried out in order to establish the relationship between the water extractable organic carbon (WEOC) content of soils and soil microbial activity, and to determine how variations in the extraction procedure might influence the quantity of WEOC recovered. Concentrations of WEOC were determined in soils taken from 12 different sites in the south east of Scotland, using a procedure in which samples were shaken with distilled water, centrifuged at 5000g and then filtered through 0.45 μm Millipore filters. Filtration resulted in between 30 and 400 μg C g−1 being extracted using this procedure and the concentration of WEOC in the resultant extracts correlated with soil microbial production of CO2 and dehydrogenase activity (P<0.001). Without filtration, although more WEOC was extracted (between 31 and 716 μg C g−1), there was no significant correlation with biological activity. There was also no correlation between WEOC and nitrous oxide release during the incubations. Centrifugation at 20,000g for at least 10 min prior to filtration was required to remove particulate organic materials. Storage of samples at 4 °C or for up to 1 week or freezing for up to 3 months was not found to have a large influence on the concentration of WEOC in extracts, although amounts increased with soil:extractant ratio and increasing extraction time (from 15 to 60 min).  相似文献   

14.
Phosphomonoesterase (PMEase) activity plays a key role in nutrient cycling and is a potential indicator of soil condition and ecosystem stress. We compared para-nitrophenyl phosphate (pNPP) and 4-methylumbelliferyl phosphate (MUP) as substrate analogues for PMEase in 7 natural ecosystem soils and 8 agricultural top soils with contrasting C contents (8.0-414 g kg−1 C) and pH (3.0-7.5). PMEase activities obtained with pNPP (0.05-5 μmol g−1 h−1) were significantly less than activities obtained with MUP (0.9-13 μmol g−1 h−1), especially in soils with a high organic matter content (>130 g kg−1). Only PMEase activities assayed with MUP correlated significantly with total C and total N (r=0.7, P<0.01 all), and pH (r=−0.71, P<0.01). PMEase activities obtained with the two substrate analogues were correlated when expressed on a C-content basis (r=0.8, P<0.001), but not when expressed on an oven-dry soil weight basis. This indicated that interference by organic matter is related to the quantity rather than to the quality of organic matter. Overall, assaying with MUP was more sensitive compared to assaying with pNPP, particularly in the case of high organic and acid soils.  相似文献   

15.
High Cd and Ni concentrations in sandy soils were built up in a field experiment, receiving an unusually metal-polluted sewage sludge between 1976 and 1980, at Bordeaux, France. The study evaluates the availability of metals and their after effects on maize at one point in time, the 8th year following termination of sludge application (1988). Plant parts (leaves, stalks, roots, grains) and soil samples were collected from plots which received 0 (Control), 50 (S1) and 300 Mg sludge DW ha?1 (S2) as cumulative inputs. Dry-matter yield, plant metal concentrations, total, and extractable metals in soils were determined. Metal inputs resulted in a marked increase in total and extractable metals in soils, except for extractable Mn and Cu with either 0.1 N Ca(NO3)2 or 0.1 N CaCl2. Total metal contents in the metal-loaded topsoils (0–20 cm depth) were very often lower, especially for Cd, Zn, and Ni, than the expected values. Explanation was partly given by the increases of metal contents below the plow layer, particularly for Cd at the low metal loading rate, and for Cd, Ni, and Cu at the high one (Gomez et al., 1992). In a control plot beside a highly metal- polluted plot, Cd, Zn, and Ni concentration in soil increased whereas the concentration of other metals was unchanged; lateral movement, especially with soil water, is plausible. Yield of leaves for plants from the S2 plot was reduced by 27%, but no toxicity symptoms developed on shoots. Yields of stalks for plants in both sludge-treated plots numerically were less than the controls but the decrease was not statistically significant. Cd and Ni concentrations increased in all plant parts with metal loading rate while Mn concentrations decreased. Leaf Cd concentration in plants from sludge-treated plots (i.e. 44 and 69 mg Cd kg?1 DM for S1 and S2) was above its upper critical level (i.e. dry matter yield reduced by 10%: 25μg Cd g?1 DM in corn leaves, Macnicol and Beckett, 1985). Yield reduction at the high metal-loading rate was probably due to 3 main factors: Mn deficiency in leaves, the accumulation of Ni especially in roots, and the increase of Cd in leaves. The amount of metal taken up by plants from the control plot ranked in the following order (mole ha?1): Fe(22)? Mn(7)>Zn (5.6)?Cu (0.7), Ni (0.6), Cd (0.4). For sludge-treated plots, the order was (values for S1 and S2 in mole ha ?1): Fe (16, 15)>Zn (7.9, 7.7)>Ni (4.3, 4.7)>Cd (1.9, 2.1)>Cu (1.0,1.2), Mn (1.5, 1.1). Zn and Cd had the greatest offtake percent from the soil to the above ground plant parts. Cd or Ni uptake by maize were correlated with extractable metals by unbuffered salts (i.e. 0.1 N Ca(NO3)2 and 0.1 N CaCl2). It is concluded that part of the sludge-borne Cd and Ni can remain bioavailable in this sandy soil for a long period of time (e.g. 8 yr) after the termination of metal-polluted sludge application.  相似文献   

16.
Soil microbial biomass N is commonly determined through fumigation-extraction (FE), and a conversion factor (KEN) is necessary to convert extractable N to actual soil biomass N. Estimation of KEN has been constrained by various uncertainties including potential microbial immobilisation. We developed a mass-balance approach to quantify changes in microbial N storage during nutrient-amended incubation, in which microbial uptake is determined as the residual in a ‘mass-balance’ based on soil-water N before and after amended incubation. The approach was applied to three sandy soils of southwestern Australia, to determine microbial N immobilisation during 5-day incubation in response to supply of 2.323 mg C g−1, 100 μg N g−1 and 20 μg P g−1. The net N immobilisation was estimated to be 95-114 μg N g−1 in the three soils, equivalent to 82.7-85.1% of soil-water N following the amendment. Such estimation for microbial uptake does not depend on fumigation and KEN conversion, but for comparison purposes we estimated ‘nominal’ KEN values (0.11-0.14) for the three soils, which were comparable to previously reported KEN from soils receiving C and N amendment. The accuracy of our approach depends on the mass-balance equation and the integrated measurement errors of the multiple N pools, and was assessed practically through recoveries of added-N when microbial uptake can be minimised. Near-satisfactory recoveries were achieved under such conditions. Our mass-balance approach provides information not only about changes in the microbial biomass nitrogen storage, but also major N-pools and their fluxes in regulating soil N concentrations under substrate and nutrient amended conditions.  相似文献   

17.
Anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) are two recently discovered processes in the nitrogen cycle that are catalysed by anammox bacteria and n-damo bacteria, respectively. Here, the depth-specific distribution and importance of anammox bacteria and n-damo bacteria were studied in an urban wetland, Xixi Wetland, Zhejiang Province (China). Anammox bacteria related to Candidatus Brocadia, Candidatus Kuenenia and Candidatus Anammoxoglobus, and n-damo bacteria related to “Candidatus Methylomirabilis oxyfera” were present in the collected soil samples. The abundance of anammox bacteria (2.6–8.6 × 106 copies g−1 dry soil) in the shallow soils (0–10 cm and 20–30 cm) was higher than that (2.5–9.8 × 105 copies g−1 dry soil) in the deep soils, whereas the abundance of n-damo bacteria (0.6–1.3 × 107 copies g−1 dry soil) in the deep soils (50–60 cm and 90–100 cm) was higher than that (3.4–4.5 × 106 copies g−1 dry soil) in the shallow soils. Anammox activity was detected at all depths, and higher potential rates (12.1–21.4 nmol N2 g−1 dry soil d−1) were observed at depths of 0–10 cm and 20–30 cm compared with the rates (3.5–8.7 nmol N2 g−1 dry soil d−1) measured at depths of 50–60 and 90–100 cm. In contrast, n-damo was mainly occurred at depths of 50–60 cm and 90–100 cm with potential rates of 0.7–5.0 nmol CO2 g−1 dry soil d−1. This study suggested the niche segregation of the anammox bacteria and n-damo bacteria in wetland soils, with anammox bacteria being active primarily in deep soils and n-damo bacteria being active primarily in shallow soils.  相似文献   

18.
Organic carbon (OC) is generally low in Alabama (U.S.A.) soils and varies considerably with cropping systems. Information on decomposition rates of the added C is a prerequisite to designing strategies that improve C sequestration in farming systems. Different models including exponential models have been used to describe OC mineralization in soils as well as to describe its potential as CO2 to be released into the environment. We investigated the decomposition of broiler litter added to ten non-calcareous soils (Appling, Troup, Cecil, Decatur, Sucarnoochee, Linker, Hartsells, Dothan, Maytag, and Colbert soils). A non-linear regression approach for N mineralization was used to estimate the potentially mineralizable OC pools (Co) and the first-order rate constant (k) in the soil samples. Results showed that the non-amended soils have distinct differences in their ability to release their native OC as CO2 and can be divided into four groups depending on their potentially mineralizable C (Co) and their ability to protect stable organic matter. Sucarnoochee soil represents the first group and contains a moderate amount of OC (11.4 g C kg−1) but had the highest Co (7.30 g C kg−1 soil). The second distinct group of soils has Co varying between 5.50 and 5.00 g C kg−1 soil (Decatur, Hartsells, Dothan, and Maytag). The third group has Co between 5.00 and 4.00 (Appling, Cecil, and Linker). The fourth group has Co less than 4.00 g C kg−1 soil (Troup and Colbert). Half-life of C remaining in non-amended soils varied from 26 days in Maytag soil to 139 days in Cecil soil. The OC in these non-amended soils represents a very stable form of organic C and thus, not easily decomposed by soil microorganisms. In the broiler litter-amended soils, the Co varied from 3.82 g C kg−1 in Appling soil amended with broiler litter 1-7.04 g C kg−1 soil in Maytag amended with broiler litter 2. Decomposition of the added OC proceeded in two phases with less than 31% decomposed in 43 days. Potentially mineralizable organic C (Co) was related to soil organic C (r = 0.661**) and soil C/N ratio (r = 0.819*).  相似文献   

19.
There is conflicting evidence, and therefore continuing concern, as to whether metals in sewage sludge are deleterious to soil microbial processes and long-term agricultural productivity. Nine field experiments with sewage sludge cakes, three with metal-amended liquid sludges and three with inorganic metal salts were set up across Britain in 1994 to give individual metal dose–response treatments to try to answer this question. This study reports on the effects of Zn, Cu and Cd on the population size of Rhizobium leguminosarum biovar trifolii, a nitrogen fixing symbiont of white clover (Trifolium repens), in soils from these experiments over 11 years. Significant (P < 0.05) reductions in indigenous rhizobial numbers occurred on the Zn metal dose–response treatments at eight of the sludge cake sites in 2005, but few consistent effects were evident on the Cu or Cd metal dose–response treatments during the 11-year monitoring period. The soil total Zn concentrations where effects occurred were near to the UK statutory limit of 300 mg kg?1 for soils receiving sewage sludge. No significant reductions occurred in any treatments on the metal-amended liquid sludge or inorganic metal salt experiments in which the metals would be expected to be in a more bioavailable form, even after 11 years. The effects in the sludge cake experiments were related consistently with soil total Zn, with no recovery to date. The reductions in clover rhizobial numbers in the sludge cake experiments were due to Zn effects on free-living rhizobia in the soil, with gradual die-off over a long time with increasing soil total Zn concentrations. Currently, no consistent adverse effects on rhizobia have been seen at the UK limits for Cu and Cd of 135 and 3 mg kg?1, respectively.  相似文献   

20.
The activity of heterotrophic soil microorganisms is usually limited by the availability and quality of carbon (C). Adding organic substances will thus trigger a microbial response. We studied the response in bacterial growth and respiration after the addition of low amounts of glucose. First we determined if additions of glucose, at concentrations which did not result in an exponential increase in respiration after the lag phase, still stimulated bacterial growth. The second aim was to determine the threshold concentration of glucose needed to induce bacterial growth. Adding glucose-C at 1000 μg g−1 soil resulted in an increased respiration rate, which was stable during 12 h, and then decreased without showing any exponential increase in respiration. Bacterial growth, determined as leucine incorporation, did not change compared to an unamended control during the first 12 h, but then increased to levels 5 times higher than in the control. Thus, after the lag phase, a period with increasing bacterial growth, but at the same time decreasing respiration rates, was found. Similar results, but with a more modest increase in bacterial growth, were found using 500 μg glucose-C g−1 soil. Adding 50–700 μg glucose-C g−1 resulted in increased respiration during 24 h correlating with the addition rate. In contrast, bacterial growth after 24 h was only stimulated by glucose additions >200 μg C g−1 soil. Thus, there was a threshold concentration of added substrate for inducing bacterial growth. Below the threshold concentration growth and respiration appear to be uncoupled.  相似文献   

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