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1.
This study was carried out to investigate the long‐term influence of lime application and tillage systems (no‐till, ridge‐till, and chisel plow) on the activities of phosphatases and arylsulfatase in soils at four research sites in Iowa, USA. The activities of the following enzymes were studied: acid and alkaline phosphatases, phosphodiesterase, and arylsulfatase at their optimal pH values. With the exception of acid phosphatase, which was significantly (P < 0.001) but negatively correlated with soil pH (r ranged from –0.65** to –0.98***), the activities of other enzymes were significantly (P < 0.001) and positively correlated with soil pH, with r values ranging from 0.65** to 0.99*** for alkaline phosphatase, from 0.79*** to 0.97*** for phosphodiesterase, and from 0.66*** to 0.97*** for arylsulfatase. The Δ activity/Δ pH values were calculated to determine the sensitivity of each enzyme to changes in soil pH. Acid phosphatase was the most sensitive and arylsulfatase the least sensitive to changes in soil pH. Activities of the enzymes were greater in the 0 – 5 cm depth samples than those in 0 – 15 cm samples under no‐till treatment. With the exception of acid phosphatase, enzyme activities were mostly significantly (P < 0.001) and positively correlated with microbial biomass C (Cmic), with r values ranging from 0.28 (not significant) to 0.83*** and with microbial biomass N (Nmic), with r values ranging from 0.31 (not significant) to 0.94***. Liming and tillage systems significantly affected the activities of some enzymes but not others, as was evident from the specific activity values (g of p‐nitrophenol released kg–1 Corg h–1).  相似文献   

2.
This study was carried out to investigate the effect of tillage and residue management on activities of phosphatases (acid phosphatase, alkaline phosphatase, phosphodiesterase, and inorganic pyrophosphatase) and arylsulfatase. The land treatments included three tillage systems (no-till, chisel plow, and moldboard plow) in combination with corn residue placements in four replications. The activities of these enzymes in no-till/double mulch were significantly greater than those in the other treatments studied, including no-till/bare, no-till/normal, chisel/normal, chisel/mulch, moldboard/normal, and moldboard/mulch. The effect of mulching on activities of phosphatases was not as significant as on activities of arylsulfatase. The lowest enzyme activities were found in soil samples form no-till/bare and moldboard/normal treatments, with the exception of inorganic pyrophosphatase, which showed the lowest activity in no-till/bare only. Among the same residue placements, no-till and chisel plow showed comparable arylsulfatase activity, whereas the use of moldboard plow resulted in much lower arylsulfatase activity. The activities of phosphatases and arylsulfatase were significantly correlated with organic C in the 40 soil samples studies, with r values ranging from 0.71*** to 0.92***. The activities of alkaline phosphatase, phosphodiesterase, and arylsulfatase were significantly correlated with soil pH, with r values of 0.85***, 0.78***, and 0.77***, respectively, in the 28 surface soil samples studied, but acid phosphatase and inorganic pyrophosphatase activities were not significantly correlated with soil pH. The activities of phosphatases and arylsulfatase decreased markedly with increasing soil depth and this decrease was associated with a decrease in organic C content. The activities of these enzymes were also significantly intercorrelated, with r values ranging from 0.50*** to 0.92***. Received: 4 October 1995  相似文献   

3.
 This study was carried out to investigate the effect of very high cadmium concentrations (50 and 500 μg Cd g–1 soil) on some biochemical and microbiological measurements under laboratory conditions involving daily soil samplings. The data for both DTPA- and water-soluble Cd showed two distinctive patterns during soil incubation; from 0 to 4 days, values were about 50–500 and 1–100 μg g–1 dry weight soil, whereas they decreased markedly after 7 days. Both daily respiration and the ATP content but not the microbial biomass C determined by the fumigation–extraction method were lowered by high DTPA- and water-soluble Cd concentrations. Dehydrogenase and phosphatase activities as well as both enzyme activity : microbial biomass ratios were decreased by the high DTPA- and water-soluble Cd concentrations. In the first 2 days of incubation, the metabolic quotient (qCO2) was also decreased by the highest values of available Cd. The early (after 6 h) mineralization of l- but not d-glutamic acid to CO2 was inhibited during the 0–4 day incubation period by the highest Cd concentration. Possibly the l-enantiomer was used by a larger fraction of soil microorganisms than the d-enantiomer or, if they were used by the same fraction of soil microorganisms, the d-enantiomer was mineralized at a lower rate. The l- : d-glutamic acid respiration ratio was decreased by the high available Cd content because under polluted conditions soil microorganisms probably discriminated less between the two stereoisomers of glutamic acid. Received: 13 July 1999  相似文献   

4.
Little information is available on soil microbial and biochemical properties, important for understanding nutrient cycling and organic matter dynamics, as affected by different peanut cropping systems and how they relate to soil functioning. Thus, we studied a Tifton loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) in Georgia, which is first in peanut production in USA, after 5 and 8 years under continuous cotton (Gossypium hirsutum, L) (CtCtCt), cotton–cotton–peanut (CtCtPt), corn (Zea mays L.)–peanut–cotton (CrPtCt), peanut–peanut–cotton (PtPtCt), and continuous peanut (PtPtPt). Soil organic carbon (OC) at 0–20 cm was already higher under PtPtPt (average, 8.7 g C kg−1 soil), PtPtCt (average, 7.7 g C kg−1 soil), and CrPtCt (average, 7.8 g C kg−1 soil) compared with CtCtPt (average, 4.7 g C kg−1 soil) and CtCtCt (average, 3.3 g C kg−1 soil). Similarly, alkaline phosphatase, acid phosphatase, and phosphodiesterase as a group showed higher activities under PtPtPt, PtPtCt, and CrPtCt than under CtCtPt and CtCtCt. The activities of glycosidases (α-galactosidase, β-glucosidase, and β-glucosaminidase) as a group were more sensitive to the cropping systems than phosphastases and showed a distinctive cropping system separation as follows: PtPtPt = CrPtCt > PtPtCt > CtCtPt > CtCtCt. Similar to OC and microbial biomass C trends, distinctive differences were found in the microbial community structure of this sandy soil after 8 years between peanut-based cropping systems (CrPtCt, PtPtCt, and PtPtPt) and cotton-based cropping systems (CtCtCt and CtCtPt) as indicated by the fatty acid methyl esters profiles. Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS.  相似文献   

5.
The aim of this work was to calculate indices of hydrolase production (Pr) and persistence (Pe) through simple arithmetical calculations. Changes in acid and alkaline phosphomonoesterase, phosphodiesterase, urease, protease, and β-glucosidase activities were monitored under controlled conditions in seven soils with a wide range of properties, in which microbial growth was stimulated by adding glucose and nitrogen. Glucose mineralization was monitored by CO2–C evolution, and microbial growth was quantified by determining the soil adenosine triphosphate (ATP) content. Hydrolase Pr and Pe indices were numerically quantified by the following relationships: Pr = H / t H and Pe = (r / H)Δt, respectively, where H indicates the peak value of each measured hydrolase activity, t H is the time of the peak value, r indicates the residual activity value, and Δt is the time interval t r − t H, where t r is the time of the residual activity value. Addition of glucose and N-stimulated soil respiration increased ATP content and stimulated the production of the measured hydrolase activities in all soils; the measured variable reached a maximum value and then decreased, returning to the value of the control soil. Apart from β-glucosidase activity, whose activity was not stimulated by glucose and N addition, the other measured hydrolase activities showed a trend that allowed us to calculate the Pr and Pe indices using the above-mentioned equations. Acid phosphomonoesterase and protease Pr values were significantly higher in soils under forest or set aside management; the alkaline phosphomonoesterase and phosphodiesterase Pr values were generally higher in the neutral and alkaline soils, and the urease Pr values showed no obvious relationships with soil pH or management. Concerning the persistence of enzyme activities, Pe values of the acid phosphomonoesterase activity were significantly higher in the acidic soils, and those of urease activity were higher in acidic soils and the Bordeaux neutral soil. No relationships were observed between Pe values of alkaline phosphomonoesterase, phosphodiesterase, or protease activities and soil pH or management. The different responses of hydrolases were discussed in relation to soil properties, microbial growth, and regulation at the enzyme molecular level.  相似文献   

6.
A study was conducted to investigate the effects of cow manure and sewage sludge application on the activity and kinetics of soil l-glutaminase. Soil samples were collected from a farm experiment in which 0, 25, and 100 Mg ha−1 of either cow manure or sewage sludge had been applied annually for 4 consecutive years to a clay loam soil (Typic Haplargid). A chemical fertilizer treatment had also been applied. Results indicated that the effects of chemical fertilizer and the solid waste application on pH in the 18 surface soil (0–15 cm) samples were not significant. The organic C content, however, was affected significantly by the different treatments, being the greatest in soils treated with 100 Mg ha−1 cow manure, and the least in the control treatment. l-Glutaminase activity was generally greater in solid-waste applied soils and was significantly correlated (r = 0.939, P < 0.001) with organic C content of soils. The values of l-glutaminase maximum velocity (Vmax) ranged from 331 to 1,389 mg NH4 +–N kg−1 2 h−1. Values of the Michaelis constant (K m) ranged from 35.1 to 71.7 mM. Organic C content of the soils were significantly correlated with V max (r = 0.919, P < 0.001) and K m (r = 0.763, P < 0.001) values. These results demonstrate the considerable influence that solid waste application has on this enzymatic reaction involved in N mineralization in soil.  相似文献   

7.
Effects of conventional tillage on biochemical properties of soils   总被引：3，自引：1，他引：3  
Modification of soil environment by different farming practices can significantly affect crop growth. Tillage causes soil disturbance, altering the vertical distribution of soil organic matter and plant nutrient supplies in the soil surface, and it may affect the enzyme activity and microbial biomass which are responsible for transformation and cycling of organic matter and plant nutrients. In this study, the influence of three conventional tillage systems (shallow plowing, deep plowing and scarification) at different depths on the distribution and activity of enzymes, microbial biomass and nucleic acids in a cropped soil was investigated. Analysis of variance for depth and tillage showed the influence of the different tillage practices on the activity of some enzymes and on the nucleic acids. Glucosidase, galactosidase, nitrate reductase and dehydrogenase activity were significantly affected by the three tillage modalities. Activity in the upper layer (0–20 cm) was higher in the plots tilled by shallow plowing and scarification than in those tilled by deep plowing. Positive relationships were observed between the soil enzymes themselves, with the exception of urease and pyrophosphatase activity. Moreover, significant correlations were found between DNA and β-galactosidase, and between RNA and β-glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase. α-Glucosidase, β-galactosidase, alkaline phosphatase and phosphodiesterase were highly correlated with biomass C determined by the fumigation-extraction method. Received: 27 June 1996  相似文献   

8.
There is limited knowledge of biochemical processes in low carbon content soils of semiarid regions under different land use and management. This study investigated several enzyme activities of C, N, P, and S transformations in semiarid soils with different clay (10–21 %) and sand (59–85 %) contents that were under conservation reserve program (CRP), native rangeland (NR), and cropland (CL) under sunflowers (Eriophyllum ambiguum (Gray)), continuous cotton (Gossypium hirsutum L.), or in rotations with wheat (Triticum aestivum L.) or sorghum (Sorghum bicolor L.) in West Texas, USA. Soils under CRP and NR showed higher total C and N contents than cultivated soils under continuous cotton, but soil pH (6.7–8.4) was not affected by the management or land use studied. The activities of β‐glucosidase, β‐glucosaminidase, arylamidase, acid and alkaline phosphatase, phosphodiesterase, and arylsulfatase (mg product (kg soil)–1 h–1) were lower in CL under continuous cotton compared to cotton in rotation with other crops, CRP, and NR. The enzyme activities were also lower when compared to soils from other regions. Linear regression analyses indicated positive correlations between enzyme activities and total C (r values up to 0.96, P < 0.01). There was a positive relationship between enzyme activities and total N, but soil pH showed the opposite trend. Enzyme activities were significantly intercorrelated with r values up to 0.98 (P < 0.001). The specific enzyme activities (mg product (g organic C)–1) were lower in continuous cotton in comparison to the uncultivated soils (i.e., NR and CRP) reflecting differences in organic matter quantity and quality due to cultivation. Among the enzymes studied, the specific activities of β‐glucosidase and arylamidase showed a more pronounced decrease with increasing soil depth. In general, soils under CRP or wheat‐cotton rotations revealed higher enzyme activities than soils under the common agricultural practice for these regions, i.e., continuous cotton under conventional tillage.  相似文献   

9.
自然植物群落对铜尾矿废弃地土壤酶活性的影响   总被引：21，自引：0，他引：21       下载免费PDF全文
在铜陵铜矿区堆存着大量的不同时期弃置的尾矿废弃物,形成大面积铜尾矿废弃地。为了解自然植物群落对铜尾矿废弃地酶活性的影响,对铜陵铜矿区6处不同时期弃置的铜尾矿废弃地进行了调查。结果表明,自然定居在尾矿废弃地上的植物群落类型能够显著影响表层尾矿中(0~5 cm)的脲酶、芳基硫酸酯酶、碱性磷酸酶和脱氢酶的活性。位于木贼-中华结缕草群落和白茅群落下尾矿中的几种土壤酶的活性高于位于狗牙根群落和中华结缕草群落下的尾矿中酶的活性。在所测定的4种土壤酶中,碱性磷酸酶和脱氢酶的活性高于脲酶和芳基硫酸酯酶的活性。相关分析表明,4种土壤酶的活性与表层尾矿中的腐殖质、总氮、有效磷、速效钾含量以及电导率表现出显著正相关,而芳基硫酸酯酶和脱氢酶与pH之间存在着显著负相关。强烈氧化的表层尾矿不仅具有极端贫瘠的养分条件,同时也具有极低的土壤酶活性。  相似文献   

10.
 The impacts of crop rotations and N fertilization on different pools of arylsulfatase activity (total, intracellular, and extracellular) were studied in soils of two long-term field experiments in Iowa to assess the contibution of the microbial biomass to the activity of this enzyme. Surface-soil samples were taken in 1996 and 1997 in corn, soybeans, oats, or meadow (alfalfa) plots that received 0 or 180 kg N ha–1 before corn, and an annual application of 20 kg P ha–1 and 56 kg K ha–1. The arylsulfatase activity in the soils was assayed at optimal pH (acetate buffer, pH 5.8) before and after chloroform fumigation; microbial biomass C (Cmic) and N (Nmic) were determined by chloroform-fumigation methods. All pools of arylsulfatase activity in soils were significantly affected by crop rotation and plant cover at sampling time, but not by N fertilization. Generally, the highest total, intracellular, and extracellular arylsulfatase activities were obtained in soils under cereal-meadow rotations, taken under oats or meadow, and the lowest under continuous cropping systems.Total, intracellular, and extracellular arylsulfatase activities were significantly correlated with Cmic (r>0.41, P<0.01) and Nmic (r>0.38, P<0.01) in soils. The averages of specific activity values, i.e., of arylsulfatase activity of the microbial biomass, expressed per milligram Cmic, ranged from 315 to 407 μg p-nitrophenol h–1. The total arylsulfatase activity was significantly correlated with the intracellular activity, with r values >0.79 (P<0.001). In general, about 45% of the total arylsulfatase activity was extracellular, and 55% was associated with the microbial biomass in soils, indicating the importance of the microflora as an enzyme source in soils. Received: 23 April 1998  相似文献   

11.
 An incubation experiment lasting 120 days was carried out to ascertain the effect on the soil microbial activity and organic matter mineralization of adding a sewage sludge compost contaminated with two different levels of Cd to an arid soil. Two composts, with a low (2 mg kg–1) and high (815 mg kg–1) Cd content, respectively, were used in this experiment. Both composts increased the total organic C, humic substance and water-soluble C contents, the beneficial effects still being noticeable after 120 days of incubation. The most labile C fraction (water-soluble C) was the most sensitive to the high Cd content. The high Cd concentration decreased soil microbial biomass C and stimulated the metabolic activity of the microbial biomass, the metabolic quotient (qCO2) revealing itself to be a very sensitive index of the stress that the incorporation of a Cd-contaminated sewage sludge compost causes in a soil. The effect of Cd contamination on enzyme activities (urease, protease that hydrolyse N-α-benzoil-l-arginamide, phosphatase, and β-glucosidase) depended on the enzyme studied. Received: 10 September 1997  相似文献   

12.
Soil organic matter level, soil microbial biomass C, ninhydrin-N, C mineralization, and dehydrogenase and alkaline phosphatase activity were studied in soils under different crop rotations for 6 years. Inclusion of a green manure crop of Sesbania aculeata in the rotation improved soil organic matter status and led to an increase in soil microbial biomass, soil enzyme activity and soil respiratory activity. Microbial biomass C increased from 192 mg kg–1 soil in a pearl millet-wheat-fallow rotation to 256 mg kg–1 soil in a pearl millet-wheat-green manure rotation. Inclusion of an oilseed crop such as sunflower or mustard led to a decrease in soil microbial biomass, C mineralization and soil enzyme activity. There was a good correlation between microbial biomass C, ninhydrin-N and dehydrogenase activity. The alkaline phosphatase activity of the soil under different crop rotations was little affected. The results indicate the green manuring improved the organic matter status of the soil and soil microbial activity vital for the nutrient turnover and long-term productivity of the soil. Received: 7 January 1996  相似文献   

13.
 Particle-size fractionation of a heavy metal polluted soil was performed to study the influence of environmental pollution on microbial community structure, microbial biomass, microbial residues and enzyme activities in microhabitats of a Calcaric Phaeocem. In 1987, the soil was experimentally contaminated with four heavy metal loads: (1) uncontaminated controls; (2) light (300 ppm Zn, 100 ppm Cu, 50 ppm Ni, 50 ppm V and 3 ppm Cd); (3) medium; and (4) heavy pollution (two- and threefold the light load, respectively). After 10 years of exposure, the highest concentrations of microbial ninhydrin-reactive nitrogen were found in the clay (2–0.1 μm) and silt fractions (63–2 μm), and the lowest were found in the coarse sand fraction (2,000–250 μm). The phospholipid fatty acid analyses (PLFA) and denaturing gradient gel electrophoresis (DGGE) separation of 16S rRNA gene fragments revealed that the microbial biomass within the clay fraction was predominantly due to soil bacteria. In contrast, a high percentage of fungal-derived PLFA 18 : 2ω6 was found in the coarse sand fraction. Bacterial residues such as muramic acid accumulated in the finer fractions in relation to fungal residues. The fractions also differed with respect to substrate utilization: Urease was located mainly in the <2 μm fraction, alkaline phosphatase and arylsulfatase in the 2–63 μm fraction, and xylanase activity was equally distributed in all fractions. Heavy metal pollution significantly decreased the concentration of ninhydrin-reactive nitrogen of soil microorganisms in the silt and clay fraction and thus in the bulk soil. Soil enzyme activity was reduced significantly in all fractions subjected to heavy metal pollution in the order arylsulfatase >phosphatase >urease >xylanase. Heavy metal pollution did not markedly change the similarity pattern of the DGGE profiles and amino sugar concentrations. Therefore, microbial biomass and enzyme activities seem to be more sensitive than 16S rRNA gene fragments and microbial amino-sugar-N to heavy metal treatment. Received: 21 January 2000  相似文献   

14.
The species‐specific microbial root and rhizosphere colonization contributes essentially to the plant nutrient supply. The species number and colonization densities of cultivable saprotrophic microfungi and the activities of nutrient‐releasing soil enzymes (protease, acid and alkaline phosphatase, arylsulfatase) were investigated in the rhizosphere of one low mycorrhizal (Salix viminalis) and one higher mycorrhizal (S. × dasyclados) willow clone at a Eutric Cambisol in N Germany. After soil washing, in total 32 and 28 saprotrophic microfungal species were isolated and identified microscopically from the rhizosphere of S. viminalis and S. × dasyclados, respectively. The fungal species composition changed within the growing season but the species number was always lower under S. × dasyclados than under S. viminalis. Under both willow clones, the fungal colonization density was largest in spring, and the species number was largest in autumn. Acid‐phosphatase activity (p < 0.001) and protease activity (p < 0.003) were significantly affected by the Salix clone, whereas arylsulfatase and alkaline‐phosphatase activities did not show clone‐specific differences. All enzyme activities reached their maxima in the summer sampling. Rhizosphere colonization with Acremonium butyri, Cladosporium herbarum, and Penicillium janthinellum contributed significantly to explain the activities of acid phosphatase. Rhizosphere colonization with Cylindrocarpon destructans, Penicillium spinulosum, Plectosphaerella cucumerina, and Trichoderma polysporum contributed significantly to explain the arylsulfatase activities. Effects of the saprotrophic fungal colonization densities on the protease activities in the rhizosphere were low. Acid‐ and alkaline‐phosphatase and arylsulfatase activities in the rhizosphere soil were stronger affected by the composition of the saprotrophic fungal communities than by the Salix clone itself. In conclusion, the colonization density of some saprotrophic microfungi in the rhizosphere contributed to explain shifts in soil‐enzyme activities of the P and S cycles under different willow clones.  相似文献   

15.
Rice seedling wilt frequently occurs in upland nurseries under well-aerated conditions and causes considerable economic loss. Whether the wilt is pathogenic or edaphic is not known. We hypothesize the use of composts to alleviate seedling wilt. The severity level of upland rice seedling wilt was significantly (p < 0.05) positively correlated with soil pH (r = 0.499; n = 19), but negatively correlated with soil organic matter (r = −0.745), microbial biomass C (r = −0.669), activities of dehydrogenase (r = −0.589), arylsulfatase (r = −0.272), fluorescein diacetate hydrolysis (r = −0.466), and β-glucosidase (r = −0.280). Correlations between severity level and soil inorganic N and exchangeable potassium K were not significant. Contents of Fe, Zn, Cu, and Mn in healthy seedlings were not significantly (p < 0.05) different from those in infected seedlings. These data suggest that seedling wilts are not associated with nutrient constraints. Compost amendment at the rate of 3% or above in pot experiments significantly improved seedling growth and reduced the wilt symptoms. Field trials further showed that aboveground weight of seedlings in compost-amended treatment ranged from 11.5 to 14.9 mg per plant, significantly higher than the range from 6.38 to 12.1 mg per plant in the control treatment; in addition to rice growth compost significantly increased microbial biomass and enzyme activities of soils. Soil fumigation significantly increased rice growth and alleviation symptoms in 11 out of 19 soils, suggesting the involvement of pathogens. It is concluded that upland seedling wilt is a pathogen-associated disease. Probably high soil pH and low soil biochemical activities may favor pathogen activities.  相似文献   

16.
This study investigated the impacts of cropping systems of cotton (Gossypium hirsutum L.; Ct) and peanut (Arachis hypogaea L.; Pt) on a Brownfield fine sandy soil (Loamy, mixed, superactive, thermic Arenic Aridic Paleustalfs) in west Texas, United States. Samples (0–12 cm) were taken 2 and 3 years after establishment of the plots from PtPtPt, CtCtPt and PtCtCt in March, June and September 2002, and in March 2003. Soil total N and aggregate stability were generally not different among the cropping systems. The pH of the soils was >8.0. Continuous peanut increased soil organic C, microbial biomass C (Cmic) and the activities of -glucosidase, -glucosaminidase, acid phosphatase, alkaline phosphatase, phosphodiesterase and arylsulfatase compared to the peanut-cotton rotations. The arylsulfatase activity of the fumigated field-moist soil and that resulting from the difference of the fumigated minus non-fumigated soil were greater in PtPtPt, but arylsulfatase activity of non-fumigated soil was unaffected by the cropping systems. Soil Cmic showed a different seasonal variation to enzyme activities during the study. Enzyme activities:microbial biomass ratios indicated that the microbial biomass may not have produced significant amounts of enzymes or that newly released enzymes did not become stabilized in the soil (i.e., due to its low clay and organic matter contents). Fungal (18:26c and 18:19c) and bacterial (15:0, a15:0, and a17:0) FAMEs were higher in PtPtPt than in CtCtPt or PtCtCt cropping systems. Our results suggest that the quality or quantity of residues returned to the soil under a peanut and cotton rotation did not impact the properties of this sandy soil after the first 3 years of this study.  相似文献   

17.
The short-term effects of wildfire on the characteristics of Mediterranean pine forest soils, exposed to semiarid climatic conditions, were evaluated by measuring different chemical, biochemical and microbiological parameters 9 months after the fire. Soils in which the fire had been intense showed higher electrical conductivity values than unburnt soils. All burnt soils had higher contents of nitrates, exchangeable NH4 + and available P and K while their contents of total organic C, extractable C, humic acids, water-soluble C and total and water-soluble carbohydrates were, in general, lower than those of unburnt soils. Microbial biomass-C in burnt soils represented from 50% to 79% of that of unburnt soils; basal respiration and dehydrogenase activity were also negatively affected by fire. In general, fire decreased urease and N-α-benzoyl-l-argininamide hydrolysing protease activities. Alkaline phosphatase activity in burnt soils was 29–87% that of the respective unburnt control soil. Arylsulphatase activity was also lower in burnt soils as was β-glucosidase activity, although in this case the differences from values of unburnt soils were not always statistically significant. Received: 15 July 1996  相似文献   

18.
Elevated concentration of atmospheric carbon dioxide will affect carbon cycling in terrestrial ecosystems. Possible effects include increased carbon input into the soil through the rhizosphere, altered nutrient concentrations of plant litter and altered soil moisture. Consequently, the ongoing rise in atmospheric carbon dioxide might indirectly influence soil biota, decomposition and nutrient transformations.N-mineralisation and activities of the enzymes invertase, xylanase, urease, protease, arylsulfatase, and alkaline phosphatase were investigated in spring and summer in calcareous grassland, which had been exposed to ambient and elevated CO2 concentrations (365 and 600 μl l−1) for six growing seasons.In spring, N-mineralisation increased significantly by 30% at elevated CO2, while there was no significant difference between treatments in summer (+3%). The response of soil enzymes to CO2 enrichment was also more pronounced in spring, when alkaline phosphatase and urease activities were increased most strongly by 32 and 21%. In summer, differences of activities between CO2 treatments were greatest in the case of urease and protease (+21 and +17% at elevated CO2).The stimulation of N-mineralisation and enzyme activities at elevated CO2 was probably caused by higher soil moisture and/or increased root biomass. We conclude that elevated CO2 will enhance below-ground C- and N-cycling in grasslands.  相似文献   

19.
This study investigated the long-term effect of lime application and tillage systems (no-till, ridge-till and chisel plow) on the activities of arylamidase and amidohydrolases involved in N cycling in soils at four long-term research sites in Iowa, USA. The activities of the following enzymes were assayed: arylamidase, -asparaginase, -glutaminase, amidase, urease, and -aspartase at their optimal pH values. The activities of the enzymes were significantly (P<0.001) and positively correlated with soil pH, with r values ranging from 0.42* to 0.99*** for arylamidase, 0.81*** to 0.97*** for -asparaginase, 0.62*** to 0.97*** for -glutaminase, 0.61*** to 0.98*** for amidase, 0.66** to 0.96*** for urease, and 0.80*** to 0.99*** for -aspartase. The Δactivity/ΔpH values were calculated to assess the sensitivity of the enzymes to changes in soil pH. The order of the sensitivity of enzymes was as follows: -

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-aspartase. The enzyme activities were greater in the samples of the 0–5 cm depth than those of the 0–15 cm samples under no-till treatment. Most of the enzyme activities were significantly (P<0.001) and positively correlated with microbial biomass C (Cmic) and N (Nmic). Lime application significantly affected the specific activities of the six enzymes studied. Results showed that soil management practices, including liming and type of tillage significantly affect soil biological and biochemical properties, which may lead to changes in nitrogen cycling, including N mineralization in soils.  相似文献   

20.
ABSTRACT

This study investigated the relationship between a recently proposed alkaline hydrolysis method for estimating the chemical index of nitrogen (N) mineralization potential of soils and the activities of arylamidase and four amidohydrolases involved in hydrolysis of organic N (ON) in soils. Nitrogen mineralization was studied in 13 soils from uncultivated fields in Iowa, USA, by direct steam distillation of 1 g field-most soil treated with 1 M KOH or 1 M NaOH. The distillate was collected in boric acids, which was changed every 5 min for a total of 40 min. The NH4 +-N in the distillate was determined by titration with 0.005 M H2SO4. The cumulative amounts of N hydrolyzed were fitted to the first-order exponential equation to determine the “potentially hydrolyzable N (Nmax )” for the soils. The activities of arylamidase, L-asparaginase, L-glutaminase, amidase, and L-aspartase were assayed at their optimal pH values. Results showed that estimated Nmax values were strongly correlated with the activities of arylamidase and amidohydrolases. The activities of arylamidase and the amidohydrolases were significantly correlated, indicating that the activities of the two groups of enzymes are coupled in mineralization of ON in soils. Based on the specificity of enzyme reactions and the strong relationship between estimated Nmax values and the activities of arylamidase and amidohydrolases, we concluded that similar amide-N bonds were susceptible to enzymatic and alkaline hydrolysis, and that alkaline hydrolyzable ON can be used as an index of N mineralization in soils.  相似文献   

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