A method for measuring adenosine triphosphate in soil

A method was devised for the extraction and measurement of adenosine 5'-triphosphate (ATP) in soil that minimizes sorption of ATP on the soil colloids. Soil was ultrasonified for 1 min with a solution containing trichloracetic acid (0.5 m). disodium hydrogen orthophosphate (0.25 m) and paraquat dichloride (0.1 m). The ATP content of the filtered extract was determined without further treatment in a scintillation spectrometer by the firefly luciferin-luciferase system. Recovery of added ATP was greater using the extratant containing trichloracetic acid, orthophosphate and paraquat than with trichloracetic acid alone or with a sulphuric acid extradant. Recoveries of added ATP ranged from 45% to 84% in thirteen different soils; ATP contents from 0.64 to 9.03 μg g^?1 soil.     

The adenylate energy charge of the soil microbial biomass

A method was developed for measuring adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphate (ADP) and adenosine 5'-monophosphate (AMP) in soil. All three adenine nucleotides were extracted from soil with a solution of trichloroacetic acid, paraquat and phosphate. ATP was measured in the neutralised (pH 7.4) soil extracts by the fire-fly luciferin-luciferase system. ADP was measured as ATP after incubating the neutralised extracts with pyruvate kinase (PK) and phosphoenolpyruvate (PEP) to convert ADP to ATP. AMP was converted to ATP by incubation with the coupled PK-PEP-myokinase system and measured as ATP. The quantities of nucleotides present in the extracts were corrected for incomplete extraction from soil by measuring the percentage recovery of added ATP, ADP and AMP. The adenylate energy charge (AEC) was calculated from the formula AEC = [[ATP] + 0.5[ADP]]/[[ATP] + [ADP] + [AMP]]. Measurements were made on (1) fresh soil, extracted as soon as possible after field sampling (2) soil stored air-dry at 5°C for 18 days and (3) soil stored air-dry at 5°C for 57 days and then rewetted to the original field moisture content and incubated aerobically for 2.5 h at 10°C before extraction.In moist soil the biomass maintains both ATP and AEC at levels close to those of activity growing cells, even though little of the biomass in soil can be in active growth at any given time. ATP accounted for 77% of the total adenine nucleotides (A_T) in the fresh soil, with an AEC of 0.85 (a value comparable to that found in microorganisms undergoing active growth in vitro. In contrast, ATP only accounted for 28% of A_T in the air-dried soil, with an AEC of 0.46. When the air-dried soil was rewetted, ATP increased to 66% of A_T and the AEC increased to 0.76. However, A_T in the air-dried soil (7.65 nmol g^?1 soil) was of the same order as that in rewetted soil (6.70 nmol g^?1) even though the AEC's were very different.These results show that the soil microbial biomass does not maintain a high AEC when air-dried. Once remoistened, the population tends to restore its AEC to the original value. This restoration occurs so rapidly that it cannot be due to the formation of a new biomass.     

Adenosine triphosphate and microbial biomass in soil

Two methods for measuring adenosine 5'-triphosphate (ATP) in soil were compared, one based on extraction with NaHCO₃-CHCl₃ and thel other on extraction by a trichloracetic acid-phosphate-paraquat reagent. Recoveries of added ATP were greater with the NaHCO₃-CHCl₃ reagent but the extraction of “native” soil ATP by NaHCO₃-CHCl₃ was only about a third of that by TCA-phosphate-paraquat.Microbial biomass C and ATP were measured in 8 contrasting English soils, using the fumigation method to measure biomass C and the TCA-phosphate-paraquat method to measure ATP. Except in one acid woodland soil, the ratio (ATP content of the soil)/(biomass C content of the soil) was relatively constant, with a mean of 7.3 mg ATP g^?1 biomass C for the different soils. This value is very similar to that obtained earlier in a range of 11 grassland and arable soils from Australia. Taking the English and Australian grassland and arable soils together, there is a close (r = 0.975) linear relationship between ATP and microbial biomass C that holds over a wide range of soils and climates. From this relationship, the soil biomass contains 7.25 mg ATP g^?1 biomass C, equivalent to an ATP-to-C ratio of 138, or to 6.04 μmoles ATP g^?1 dry biomass.The acid woodland soil (pH 3.9) contained much less biomass C, as measured by the fumigation method, than would have been expected from this relationship. This, and other evidence, suggests that the fumigation method for measuring microbial biomass C breaks down in strongly acid soils.The ATP content of the biomass did not depend on the P status of the soil, as indicated by NaHCO₃-extractable P.     

Adenylate energy charge measurements in soil

Adenosine 5'-triphosphate (ATP), adenosine 5'-diphosphatc (ADP) and adenosine 5'-monophosphate (AMP) were extracted from soil with either a solution of trichloroacetic acid, paraquat and phosphate (TCA reagent) or a mixture of chloroform, sodium hydrogen carbonate, phosphate and adenosine (NaHCO₃ reagent). Standard enzymic procedures were used to convert ADP and AMP to ATP, which was measured by the fire-fly luciferin-luciferase system. The measured quantities of nucleotides were corrected for incomplete extraction using the percentage recoveries of added ATP, ADP and AMP. The adenylate energy charge ratio (AEC) was calculated from the formula AEC = ([ATP] + 0.5 [ADP])/([ATP] + [ADP] + [AMP]).Measurements were made on a grassland soil, following a conditioning incubation at 15°C and 50% WHC for 7 days. Additional measurements were made on the same soil after a further 50- or 100-day incubation at 25°C and 50% WHC, with or without an amendment of 1100 μg ryegrass Cg⁻¹ soil, added at the end of the conditioning incubation. Biomass-ATP concentration, measured in TCA extracts, changed little, even on prolonged incubation, and was maintained at a level comparable to that observed in earlier work (about 10 p mol ATP g⁻¹ biomass C). AEC values in TCA soil extracts were high (0.8–0.9) for all soil treatments and independent of substrate addition or length of incubation.In contrast, AEC was low (0.4) in fresh soil extracted with NaHCO₃ reagent, but increased to 0.6 when ryegrass was incubated with the soil for 50 days. Although the total adenine nucleotide pool (i.e. [ATP] + [ADP] + [AMP]) was similar as measured in NaHCO₃ and in TCA soil extracts, both energy charge and ATP content were lower in the NaHCO₃ extracts. It was therefore concluded that the main reason for the lower AECs observed with the NaHCO₃ reagent was that microbial ATPases were still active during extraction and caused appreciable hydrolysis of microbial ATP to ADP and AMP. In contrast, the TCA reagent rapidly inactivates ATPases and is therefore preferable for extracting adenine nucleotides from soil.The results indicate that the soil microbial biomass, although a mainly dormant population, maintains both AEC and ATP at levels characteristic of exponentially growing organisms in vitro, even during prolonged incubation without fresh substrate. It was also concluded that roots make a negligible contribution to total ATP extracted from fresh sieved soil.     

Modification and application of a soil ATP determination method

Accurate estimation of microbial adenosine 5′-triphosphate (ATP) is a pre-requisite to quantify the impact of varying environments on microbial activity of soil. We investigated the effectiveness of a high efficiency soil ATP determination method (PA) [Webster, J.J., Hampton, G.J., Leach, F.R., 1984. ATP in soil: a new extractant and extraction procedure. Soil Biology & Biochemistry 4, 335-342] in 10 Ontario (Canada) soils collected along a 100 m transect and spanning a textural class gradient ranging from a sandy loam to clay loam with increasing organic matter. Modifications of the method involved using an extract of autoclaved soil to make the standard curve, as it was found that the light emitted by ATP luciferin-luciferase bioluminescence reaction in the pure extractant was different from that in the extracts. Replacing Tricine with Tris buffer in the assay significantly improved the light emission. On an average, the internal standard calibration method (ISM) measured a smaller amount of extracted ATP (1199 ng ATP g⁻¹ soil) and a lower recovery of ATP spike (82.4±7.2%) than did the standard curve method (SCM) (1246 ng ATP g⁻¹ soil and 91.2±4.5%, respectively) (P<0.05 for both comparisons). However, the average total estimated ATP was higher with ISM (1474±102 ng ATP g⁻¹ soil) than with SCM (1373±88 ng ATP g⁻¹ soil) (P<0.07). While the recovery rates determined using SCM were consistent among the soils tested, the rates measured using ISM was negatively correlated with soil clay and organic matter content, implying that the latter assay was affected by the soil properties. Our results confirmed that the recovery rates obtained by the PA method were the highest among those reported, when only SCM was used.     

Influence of pH,dispersion methods,and different compounds on adenosine triphosphate recovery from soil

We studied the recovery of ATP from soil. A soil-water suspension was prepared by two different methods (simple stirring or ballottini mill treatment) at different pH levels and in the presence of different chemicals [Na₂SO₄, Na₃PO₄, Na₅P₃O₁₀, adenosine, ethylenediaminetetra-acetic acid (EDTA), TRIS]. The ATP recovery was evaluated by adding [³H]-8 ATP to the solution and comparing the values obtained by radioactivity measurements with those obtained by an enzymatic assay. Strongly acidic (pH lower than 1.0) or alkaline (pH 10.0) extractions yielded the best ATP recoveries compared with intermediate pH values. At pH 10.0, the addition of Na₃PO₄ or Na₅P₃O₁₀ gave a high level of ATP recovery, 68 and 96%, respectively. No ATP hydrolysis occurred under alkaline extraction conditions. Under acidic extraction conditions, the addition of adenosine, EDTA, Na₂SO₄, or Na₅P₃O₁₀ improved ATP recovery but it was never higher than 34%. The results were discussed in terms of the effects of different physical and chemical conditions on cell disruption, ATP stability, ATP interactions with soil components, and ATP solubilization.     

Acid deposition: Effects of sulphuric acid at pH 3 on chemical and biochemical properties of bracken litter

The effects of increased acid deposition on some biochemical and chemical properties of bracken litter overlying a podzolic soil contained in monolith lysimeters were investigated. Pairs of lysimeters each received 1500 mm yr^?1 of “rain” consisting either of distilled water or pH 3.0 sulphuric acid applied evenly over a 5-yr period. The acid-treatment resulted in a marked acidification of the litter, associated with accelerated leaching of Ca²⁺, Mg²⁺, K⁺ and Mn²⁺. Acid treatment also increased the concentration of extractable Al³⁺ in the litter. The biochemical changes observed in the litter as a consequence of acidification included decreases of 33% in ATP content and 54% in respiration rate. Significant reductions in the mineralization rates of urea, glucose and acetate, and in the activities of 4-nitrophenylphosphatase, $\text{β-N-}\text{acetyl-}\text{d}\text{-glucosaminidase}$, exo-1,4,β-d-xylosidase and peroxidase were also observed in the acid-treated litter. The acid-treated litter also contained slightly less total N, ammonium-N and total P, and slightly more residual hexose carbohydrate than the control litter. The effects observed were consistent with a decrease in microbial activity associated with litter acidification and were reflected in a small (5.5%) but significant (P < 0.05) decrease in litter decomposition. Acid treatment decreased the ATP content of the mineral soil by about 13% in the 3 cm immediately beneath the litter, but below this depth no significant difference was observed.     

Microbial responses of forest soil to moderate anthropogenic air pollution

There is a need to introduce soil microbiological methods into long term ecological monitoring programs. For this purpose we studied the impact of moderate anthropogenic air pollution in polluted and less polluted area districts, forest site types Calluna (CT), Vaccinium (VT) and Myrtillus (MT) and the amount of organic matter, measured as carbon content on the soil respiration activity and the ATP content. The main sources of local air pollutants (SO₂ and NO_x) in the polluted area district were from the capital' region and an oil refinery. Humus (F/H-layer) and the underlying 0 to 5 cm mineral soil samples were collected from 193 study plots located in the 5300 km² study area. We found that the soil respiration rate in humus layer samples was lower in the polluted area district compared to the less polluted one (16.0 and 19.5 μL CO₂ h^?1g^?1 dw, respectively), but the difference occurred only in the dry, coarse-textured CT forest site type. The mineral soil respiration rate and the mineral soil and humus layer ATP content were not affected, by the air pollution. Most of the variations of the biological variables were explained primarily by the soil carbon content, secondly by the forest site type and thirdly by the area division.     

Microbial biomass estimations in soils from tussock grasslands by three biochemical procedures

Microbial biomass was determined by three biochemical procedures in nine topsoils from a climosequence in tussock grasslands. The pH values of the samples ranged from 4.4 to 6.2 and organic C contents from 2.5 to 20.0%. When determined by a chloroform-fumigation procedure, contents of biomass C and mineral-N (Min-N) flush ranged from 530–2780 and 59–167 μgg^?1 dry soil respectively. Adenosine 5'-triphosphate (ATP) content ranged from 2.2 to 10.7 μg g^?1 dry soil. All three estimates were significantly correlated with each other and with several soil properties, including organic C and total N contents and CO₂ production. They were not significantly correlated with any climatic factor.In spite of these significant correlations, the ratios of the biomass estimates varied appreciably in the different soils. The ratios of biomass C/Min-N flush ranged from 7.8 to 22.8 (average 12.5), biomass C/ATP from 163 to 423 (average 248) and Min-N flush/ATP from 12 to 35 (average 22). These ratios were mostly higher than those found elsewhere for Australian and English soils. The high biomass C/ATP and Min-N flush/ATP ratios did not appear to originate from inefficient extraction of “native” ATP or from the soils' P status. Based on these results, care in the use of factors for obtaining soil microbial biomass content from Min-N flush or ATP values is indicated.     

Estimation of the adenylate energy charge in unamended and amended agricultural soils

To determine relatively low concentrations of adenine nucleotides in agricultural soils a NaHCO₃-based extradant was developed and compared with the trichloroacetic acid-paraquat-phosphate extradant. The new medium, consisting of chloroform, sodium bicarbonate, phosphate and adenosine (pH 8.0) gave soil extracts which could be investigated without further neutralization and dilution. ATP was measured directly in the soil extracts by the luciferin-luciferase system. ADP and AMP were estimated after their enzymatic conversion to ATP by standard methods. The quantities of nucleotides corrected for recovery of standards were used to calculate the adenylate energy charge (AEC) from the formula AEC = [ATP] + 1/2[ADP]/[ATP] + [ADP] + [AMP], The AEC was estimated in six unplanted soils from agricultural fields. A very similar energy charge of 0.3-0.4 was found in all soils sampled which indicates a low metabolic activity of the soil population. Two other soils with a pronounced difference in biomass-C content were used to investigate the influence of different amendments on the AEC. In an experiment with low glucose supplements up to 500 μg C g^?1 soil, the soil with the low biomass-C (a cambisol) showed a distinct increase of the AEC from 0.34 to 0.50, whereas the soil with the high biomass-C content (a phaeozem) increased its AEC only slightly from 0.32 to 0.37. In another experiment with high glucose supplements the phaeozem reached its maximum AEC value of 0.56 after the addition of 4000 μg Cg^?1 soil. An amendment with 8000 μg C g^?1 soil gave no further increase. In the combisol the addition of 1000 μg C g^?1 soil increased the AEC to 0.61. Higher supplements gave only a slight further increase to a maximum value of 0.67 after the addition of 8000 μg C g^?1 soil. The same AEC value was reached when the cambisol was amended with a mixture of organic substrates at a concentration of 10,000 μg C g^?1 soil.     

Fraction Distributions of Lead,Cadmium, Copper,and Zinc in Metal‐Contaminated Soil before and after Extraction with Disodium Ethylenediaminetetraacetic Acid

Abstract: The fraction distributions of heavy metals have attracted more attention because of the relationship between the toxicity and their speciation. Heavy‐metal fraction distributions in soil contaminated with mine tailings (soil A) and in soil irrigated with mine wastewater (soil B), before and after treatment with disodium ethylenediaminetetraacetic acid (EDTA), were analyzed with Tessier's sequential extraction procedures. The total contents of lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) exceeded the maximum permissible levels by 5.1, 33.3, 3.1, and 8.0 times in soil A and by 2.6, 12.0, 0.2, and 1.9 times in soil B, respectively. The results showed that both soils had high levels of heavy‐metal pollution. Although the fractions were found in different distribution before extraction, the residual fraction was found to be the predominant fraction of the four heavy metals. There was a small amount of exchangeable fraction of heavy metals in both contaminated soils. Furthermore, in this study, the extraction efficiencies of Pb, Cd, and Cu were higher than those of Zn. After extraction, the concentrations of exchangeable Pb, Cd, Cu, and Zn increased 84.7 mg·kg^?1, 0.3 mg·kg^?1, 4.1 mg·kg^?1, and 39.9 mg·kg^?1 in soil A and 48.7 mg·kg^?1, 0.6 mg·kg^?1, 2.7 mg·kg^?1, and 44.1 mg·kg^?1 in soil B, respectively. The concentrations of carbonate, iron and manganese oxides, organic matter, and residue of heavy metals decreased. This implies that EDTA increased metal mobility and bioavailability and may lead to groundwater contamination.     

Development of an express method for measuring soil nitrate,phosphate, potassium,and pH for future in-field application

Background

In practical farming, there is often a need for short-term availability of information on the soil nutrient status.

Aims

To develop a new express method for the extraction of major plant-available nutrients and measurement of soil nutrients. In future, this method shall serve for in-field measurements of soil samples with an ion-sensitive field-effect transistor (ISFET).

Methods

Various extraction conditions such as type of extractant, soil-to-solution ratio, time, and intensity were investigated on a broad selection of dried soil samples in the laboratory. Based on 83 field-moist soil samples with varying clay contents, these conditions were compared to standard laboratory methods.

Results

With increasing extraction time, the nutrient concentrations increased. When the soil-to-solution ratio was reduced, a greater share of nutrients was extracted, independent of soil type. H₂O and 0.01 M CaCl₂ and standard calcium-acetate-lactate (CAL) solution proved to be too weak in the short period to reach the ISFET sensor measurement range. Higher concentrated CAL solutions performed much better. Finally, a 5-min CaCl₂ extraction followed by the removal of an aliquot for the determination of soil pH and NO₃⁻ was found to be effective. The remaining solution was then mixed with 0.20 M CAL solution for the analysis of H₂PO₄⁻ and K⁺ at 10 min of extra extraction time. This extraction method showed very good correlations with the values based on the German laboratory reference methods for pH (R² = 0.91) and for nitrate (R² = 0.95). For phosphorus and potassium, we obtained an R² of 0.70 and 0.81, respectively, for all soils. When soils were grouped according to clay content higher correlations were found.

Conclusions

A new express method based on a wet-chemical approach with a soil preparation procedure was successfully developed and validated. This seems to be a valuable basis for future in-field measurements via ISFET.     

A simple method for quantitative determination of ATP in soil

A simple method to measure soil ATP by the luciferin-luciferase system is described. The ATP is extracted from the soil by vigorous shaking with a sulfuric acid-phosphate solution for 15 min. An aliquot of the soil suspension is neutralized with a Tris-EDTA solution and mixed with a special ATP releasing reagent (NRB). ATP is measured after a 10 s exposure to the NRB reagent, followed by addition of luciferin-luciferase and integration over 10 s in a Lumacounter M 2080. The ATP content in soils which had been stored at 5°C for 90 days and then incubated at 25°C for 5 days, ranged from 0.37 to 7.52 μg ATP g^?1 dry wt, with standard deviations less than 10%. There was a close (r = 0.96) linear relationship between ATP content and biomass C determinated by fumigation for this group of soils. The soil biomass contained 4.2–7.1 μg ATP mg^?1 biomass C. The ATP content of the biomass declined during storage at 5°C for 210 days.     

Adenylates as an estimate of microbial biomass C in different soil groups

Adenylate (i.e. adenosine tri- (ATP), di- (ADP) and monophosphates (AMP)) and microbial biomass C data were collected over a wide range of sites including forest floor layers and forest, grassland and arable soils. Microbial biomass C was measured by fumigation extraction and adenylates after alkaline Na₃PO₄/DMSO/EDTA extraction and HPLC detection. Our aims were (1) to test whether the sum of adenylates is a better estimate for microbial biomass than the determination of ATP, (2) to compare our conversion values with those proposed by others, and (3) to analyse whether soil properties or land use form affect the relationships between ATP, adenylates and microbial biomass C. A close relationship was found between microbial biomass C and ATP (r=0.96), but also with the sum of adenylates (r=0.96) within all appropriately conditioned soil samples (n=112). In the mineral soil (n=98), the geometric means of the ATP-to-microbial biomass C ratio and the adenylates-to-microbial biomass C ratio were 7.4 and 11.4 μmol g⁻¹, respectively. The mean ratios did not differ significantly between the different texture classes and land use forms. In the forest floor, the ATP-to-microbial biomass C ratio and the adenylates-to-microbial biomass C ratio were both roughly two-thirds of those of the mineral soil. The average adenylate energy charge (AEC) of all soil samples was 0.79 and showed a strong negative relationship with the soil pH (r=−0.69). However, the AEC is presumably only indirectly affected by the soil pH.     

Influence of polychlorinated biphenyls on microbial biomass and its activity in grassland soil

Microbial biomass content, soil respiration and biomass specific respiration rate were measured in two parts of an area polluted by a municipal waste incinerator [polychlorinated biphenyls (PCBs) from combustion processes]. The soils in the studied parts differed significantly only in their levels of PCBs. The concentration of PCBs found in a control plot (4.4 ng g^-1 soil) can be regarded as a background value while the polluted plot contained an increased amount of PCBs (14.0 ng g^-1 soil). A significantly lower microbial biomass (decreased by 23%, based on the chloroform-fumigation extraction technique) and a lower specific respiration rate (decreased by 14%) were observed in the polluted plot in comparison with the control plot at the end of experimental period (1992–1994). Furthermore, a lower ability of microorganisms in the polluted plot to convert available C_org into new biomass was found in laboratory incubations with glucose-amended samples.     

Distribution of anthropogenic lead estimated by Pb isotopic composition in the upper layers of soil from a mixed forest at Dinghushan, southern China

Purpose

The heavy metal lead (Pb) is toxic to living organisms. Forest soils are important sinks for heavy metals generated by human activities. The forest at Dinghushan of southern China has experienced long-term exposure to atmospheric pollutants from the Pearl River Delta (PRD). The objectives of this research were (a) to determine the vertical and temporal distribution of Pb in the forest soil at Dinghushan, (b) to determine whether dilute acid extraction could be used to identify anthropogenic sources of Pb in forest soil, and (c) to determine the main anthropogenic contributors to soil Pb.

Materials and methods

Lead concentrations and isotopes were measured in two sets of forest soil samples. One set consisted of archived samples from 0 to 20 cm depth collected annually from 1997 to 2010. The other set was collected throughout three profiles sampled at 5-cm intervals to the bedrock (85 cm depth) in 2011. The soil samples were air-dried, ground, and passed through a 100-mesh polyethylene sieve. Lead in the samples was digested with concentrated acid (HNO₃?+?HClO₄, 4:1?v/v) or extracted with dilute acid (1 M HCl with a soil/solution ratio of 1:10) and was measured with an inductively coupled plasma mass spectrometer.

Results and discussion

Concentrations of Pb obtained both by total digestion and dilute acid extraction decreased with soil depth in the profile samples and increased over time in the archived ones. Soils at 0–20 cm depth had Pb concentrations of more than twice of the local soil background value. In all soil samples, the ^206/207Pb ratios was lower and the ^206/204Pb, ^207/204Pb, and ^208/204Pb ratios were higher with the dilute acid extraction than with the strong-acid digestion, indicating that dilute acid extraction could be used to distinguish between anthropogenic and geogenic Pb. Comparison of the Pb isotope ratios in the samples with those in the main pollutants from the PRD indicated that coal combustion and industrial emission were the main contributors to the forest soil Pb at Dinghushan.

Conclusions

The forest soil (0–20 cm depth) at Dinghushan was contaminated by Pb. Dilute acid extraction could be used to identify anthropogenic Pb sources. From 1997 to 2010, the main contributors of anthropogenic Pb to the forest soil at Dinghushan were coal combustion and industrial emission. Measures that control Pb emission from coal combustion and industrial activity, changes in coal consumption, and re-adjustments of industry development in the PRD should reduce Pb contamination of forest soil.     

Molybdenum fractions and mobilization kinetics in acid forest soils

We extracted molybdenum (Mo) from eight acid forest soils (19 A, E, and B horizons) in NE-Bavaria and from one site in the Ore Mountains, using (1) anion exchange-resin, (2) 0.2 M ammonium oxalate, and (3) ascorbic acid/ammonium oxalate. The Mo concentrations in the anion exchange-resin fraction varied between 5 and 28 μg kg^-1. Oxalate-extractable Mo ranged from 44 to 407 μg kg^-1 and after reduction of iron (Fe) with ascorbic acid, 135 to 1071 μg Mo kg^-1 were extracted. The lowest concentrations of Mo were measured in acid and sesquioxide impoverished E horizons. The total concentrations of Mo in spruce needles correlated with ion exchange resin extractable Mo, indicating that this fraction represents Mo readily available to plants. The Mo and Fe dissolution kinetics during oxalate extraction were studied on 8 of the soil samples to obtain further information on Mo mobilization. Oxalate extractable iron (Fe_o) was mobilized within a few hours. A first order equation was applicable to the Fe dissolution kinetics with the rate constants ranging between 0.9 and 9.0 h^-1. The mobilization of Mo occurred in two distinct stages. An initially rapid dissolution was followed by a further increase in extractable Mo but with slower kinetics. A combined first order-diffusion equation was found to be appropriate for modelling the results. The first order rate constants for Mo mobilization ranged from 0.6 to 11.4 h^-1. However, correlations between the rates of reaction of Mo and Fe could not be established, indicating that Mo is either not distributed equally along Fe minerals or that there is another pool, possibly the organic substance of the soil, from which Mo is extractable by oxalate.     

不同浸提剂处理森林土壤溶解性有机碳含量比较

为了解亚热带森林土壤溶解性有机碳(DOC)的特征规律,采用培养离心的方法获取土壤溶液测得DOC含量,对比传统水溶性有机碳(WSOC)提取法间的差异。选取湖南大山冲森林公园保存完好的3种亚热带典型次生林地,按10cm一层采集剖面土壤,采用不同方法提取测定土壤DOC和WSOC含量,分析与土壤理化指标的相关性及方法间的显著性关系。结果表明:①典型森林土壤DOC或WSOC含量随土壤剖面深度的增加,呈显著下降趋势。培养离心提取测得的土壤DOC含量明显较低,仅0.82～9.52 mg/kg,超纯水浸提的风干土WSOC含量达10.56～249.19 mg/kg,而0.5 mol/L K₂SO₄提取的鲜土WSOC含量达155.70～576.94 mg/kg,0.5mol/L K₂SO₄浸提的干土WSOC含量最高,达158.94～797.56 mg/kg,含量表现为:DOC<干土超纯水浸提WSOC<鲜土K₂SO₄浸提WSOC<干土K₂...     

几种土壤交换性酸测定方法的效果比较

为真实地反映酸性土壤交换性酸含量水平,探讨了KCl淋溶法、BaCl_2淋溶法、NaAc淋溶法、KCl-三乙醇胺(Triethanolamine,TEA)提取法和BaCl_2-TEA提取法对紫色土、黄壤、红壤和砖红壤4种土壤的交换性酸测定效果。结果表明:5种方法测得的土壤交换性酸大小关系为:BaCl_2-TEA提取法KCl-TEA提取法NaAc淋溶法BaCl_2淋溶法KCl淋溶法。BaCl_2淋溶法能较为真实地反映出土壤交换性酸水平,其次为KCl淋溶法。受土壤有机酸和铝氧化物的影响,NaAc淋溶法、KCl-TEA提取法和BaCl_2-TEA提取法测得的土壤交换性酸含量偏高。但由于尚无标准方法对测定结果进行验证,因此,还需进一步对土壤交换性酸测定方法及其影响因素开展研究。     

Speciation of copper in soils and relation with its concentration in fruits

Abstract

Different extraction reagents were studied in soils and the results obtained were compared with copper (Cu) contents of seven type fruits grown in these soils. For fruits, wet and dry ashing methods were applied and acceptable results were obtained by using dry ashing. The speciation is based on the dissolution of the soil samples in HNO₃/H₂O₂, oxalic acid, acetic acid, EDTA and citric acid as extraction reagents at hot and cold conditions. Mean total Cu concentrations for all fruits studied were (mg kg^‐1) in the range of 3.0–7.0 (dried weight basis). Significant positive correlations have been found between Cu contents of various fruits and different extractants studied. Flame atomic absorption spectrometry was used for determination of Cu in digestions. Probable chemical forms of Cu in soils were evaluated.