Hydrolase activity, microbial biomass and community structure in long-term Cd-contaminated soils

Long-term effects of high Cd concentrations on enzyme activities, microbial biomass and respiration and bacterial community structure of soils were assessed in sandy soils where Cd was added between 1988 and 1990 as Cd(NO₃)₂ to reach concentrations ranging from 0 to 0.36 mmol Cd kg⁻¹ dry weight soil. Soils were mantained under maize and grass cultivation, or ‘set-aside’ regimes, for 1 year. Solubility of Cd and its bioavailability were measured by chemical extractions or by the BIOMET bacterial biosensor system. Cadmium solubility was very low, and Cd bioavailability was barely detectable even in soils polluted with 0.36 mmol Cd kg⁻¹. Soil microbial biomass carbon (B_C) was slightly decreased and respiration was increased significantly even at the lower Cd concentration and as a consequence the metabolic quotient (qCO₂) was increased, indicating a stressful condition for soil microflora. However, Cd-contaminated soils also had a lower total organic C (TOC) content and thus the microbial biomass C-to-TOC ratio was unaffected by Cd. Alkaline phosphomonoesterase, arylsulphatase and protease activities were significantly reduced in all Cd-contaminated soils whereas acid phosphomonoesterase, β-glucosidase and urease activites were unaffected by Cd. Neither changes in physiological groups of bacteria, nor of Cd resistant bacteria could be detected in numbers of the culturable bacterial community. Denaturing gradient gel electrophoresis analysis of the bacterial community showed slight changes in maize cropped soils containing 0.18 and 0.36 mmol Cd kg⁻¹ soil as compared to the control. It was concluded that high Cd concentrations induced mainly physiological adaptations rather than selection for metal-resistant culturable soil microflora, regardless of Cd concentration, and that some biochemical parameters were more sensitive to stress than others.     

Quantitative assessment of hydrolase production and persistence in soil

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.     

Functional activity and microbial community structure in soils amended with bimetallic sludges

Heavy metal availability, microbial biomass and respiration, bacterial diversity and enzyme activity were studied in soils from long-term field experiments contaminated with Mn-Zn- or Cd-Ni-rich sludge, incorporated into soils at two different rates. Soils that never received sludge were used as controls. Microbial biomass C content (B_C) and soil respiration (CO₂-C) were slightly reduced in soils amended with Mn-Zn at the higher incorporation rate whereas in soils receiving Cd-Ni-rich sludge B_C and respiration were unaffected. Metabolic quotient values (qCO₂) calculated by the B_C-to-CO₂-C ratio were not significantly different, regardless of the sludge type whereas the microbial biomass C-to-total organic C (B_C-to-TOC) ratios were significantly reduced in the soils receiving the higher rates of both sludge types. Phosphomonoesterase, β-glucosidase and arylsulfatase activities and hydrolase-to-B_C ratios, were significantly reduced in soils amended with Ni-Cd-sludge at both rates, whereas the Mn-Zn-sludge only reduced the arylsulfatase activity at the higher rate. Protease activity was generally higher in all the sludge-amended soils as compared to control soils whereas urease activity was unaffected by sludge amendments. The structure of the bacterial community, as determined by denaturing gradient gel electrophoresis (DGGE), was different in the sludge-amended soils as compared to the respective controls. The most important changes were observed in the soils amended with high-level Ni-Cd sludge. Because some of the adverse effects were observed at moderate contamination levels, our results indicate that the presence of certain heavy metal combinations can be a serious limitation for sludge disposal.     

Effects of multiple heavy metal contamination and repeated phytoextraction by Sedum plumbizincicola on soil microbial properties

The threat of heavy metal contamination to food and human health in south and east China has become a public concern as industrial development continues. The aims of this study were to investigate the influence of repeated phytoextraction over a two-year period by successive crops of the Zn and Cd hyperaccumulator Sedum plumbizincicola on multiple metal contaminated soils and to assess recovery of soil quality. Total and NH₄OAc-extractable Zn and Cd concentrations were significantly reduced in planted soils compared to unplanted soils. Microbial biomass C (C_mic), basal respiration and microbial quotient (qM) were significantly and positively correlated and soil metabolic quotient (qCO₂) was negatively correlated with heavy metal concentrations in unplanted soils (P < 0.05). However, C_mic, basal respiration and qM values increased significantly after phytoremediation by five crops over two years compared to unplanted soil. Urease, β-glucosidase, neutral phosphatase and arylsulfatase activities also increased significantly with decreasing heavy metal contents and hydrolase activity was enhanced in planted soil (P < 0.05) compared to the unplanted control. The data indicate the capacity of S. plumbizincicola to extract Zn and Cd from contaminated soil and also that phytoremediation had beneficial effects on soil microbial and hydrolase activities, with the metal phytoextraction procedure restoring soil quality.     

三江平原岗地白浆土水解酶活性和动力学特性对不同连作农作物的响应

作物种植会对农田生态系统产生一定的影响。大田试验条件下,在黑龙江省853农场岗地白浆土上连续6年种植玉米、大豆、小麦、水稻,研究了土壤理化性质以及土壤中与碳、氮、磷、硫元素转化相关的9种水解酶活性和动力学特性的响应;同时研究了不同作物种植对土壤脲酶、磷酸单酯酶、磷酸二酯酶、芳基硫酸酯酶及β-葡糖苷酶动力学特性的影响。结果表明,大豆连作土壤的有效氮、总碳、总氮、总磷和总硫含量都稍高;大豆处理土壤pH值略低,但其它三种作物种植下的土壤均呈微酸性,差异不显著。土壤水解酶动力学参数对种植作物的反应与表观活性的反应不一致。玉米连作土壤蛋白酶和磷酸单酯酶活性高于其它处理;小麦处理的磷酸二酯酶和芳基硫酸酯酶活性最高,水稻连作土壤蛋白酶、磷酸二酯酶和磷酸三酯酶活性最低。连年种植小麦处理的土壤脲酶、磷酸二酯酶以及芳基硫酸酯酶Vmax显著高于其它处理,小麦连作土壤β-葡萄糖苷酶、脲酶、磷酸二酯酶和芳基硫酸酯酶的Vmax/Km值显著高于其它处理,可以看出在此处理下土壤酶具有较强的催化潜势。     

Soil biochemical and microbial indices in wet tropical forests: Effects of deforestation and cultivation

Little information is available about the long‐term effects of deforestation and cultivation on biochemical and microbial properties in wet tropical forest soils. In this study, we evaluated the general and specific biochemical properties of soils under evergreen, semi‐evergreen, and moist deciduous forests and adjacent plantations of coconut, arecanut, and rubber, established by clear felling portions of these forests. We also examined the effects of change in land use on microbial indices and their interrelationships in soils. Significant differences between the sites occurred for the biochemical properties reflecting soil microbial activity. Microbial biomass C, biomass N, soil respiration, N mineralization capacity, ergosterol, levels of adenylates (ATP, AMP, ADP), and activities of dehydrogenase and catalase were, in general, significantly higher under the forests than under the plantations. Likewise, the activities of various hydrolytic enzymes such as acid phosphomonoesterase, phosphodiesterase, casein‐protease, BAA‐protease, β‐glucosidase, CM‐cellulase, invertase, urease, and arylsulfatase were significantly higher in the forest soils which suggested that deforestation and cultivation markedly reduced microbial activity, enzyme synthesis and accumulation due to decreased C turnover and nutrient availability. While the ratios of microbial biomass C : N and microbial biomass C : organic C did not vary significantly between the sites, the ratios of ergosterol : biomass C and ATP : biomass C, qCO2 and AEC (Adenylate Energy Charge) levels were significantly higher in the forest sites indicating high energy requirements of soil microbes at these sites.     

Microbial activities in forest soils exposed to chronic depositions from a lignite power plant

Atmospheric emissions of fly ash and SO₂ from lignite-fired power plants strongly affect large forest areas in Germany. The impact of different deposition loads on the microbial biomass and enzyme activities was studied at three forest sites (Picea abies (L.) Karst.) along an emission gradient of 3, 6, and 15 km downwind of a coal-fired power plant (sites Ia, II, and III, respectively), representing high, moderate and low emission rates. An additional site (site Ib) at a distance of 3 km from the power plant was chosen to study the influence of forest type on microbial parameters in coniferous forest soils under fly ash and SO₂ emissions. Soil microbial biomass C and N, CO₂ evolved and activities of l-asparaginase, l-glutaminase, β -glucosidase, acid phosphatase and arylsulfatase (expressed on dry soil and organic C basis) were determined in the forest floor (L, Of and Oh horizon) and mineral top soil (0-10 cm). The emission-induced increases in ferromagnetic susceptibility, soil pH, concentrations of mobile (NH₄NO₃ extractable) Cd, Cr, and Ni, effective cation exchange capacity and base saturation in the humus layer along the 15 km long transect significantly (P<0.05) reflected the effect of past depositions of alkaline fly ash. Soil microbial and biochemical parameters were significantly (P<0.05) affected by chronic fly ash depositions. The effect of forest type (i.e. comparison of sites Ia and Ib) on the studied parameters was generally dominated by the deposition effect. Alkaline depositions significantly (P<0.05) decreased the microbial biomass C and N, microbial biomass C-to-N ratios and microbial biomass C-to-organic C ratios. Microbial respiration, metabolic quotient (qCO₂) and the activities of l-asparaginase, l-glutaminase, β-glucosidase, acid phosphatase and arylsulfatase were increased by long-term depositions from the power plants. Acid phosphatase had the highest specific (enzyme activities expressed per unit organic C) activity values among the enzymes studied and arylsulfatase the lowest. The responses of the microbial biomass and soil respiration data to different atmospheric deposition loads were mainly controlled by the content of organic C and cation exchange capacity, while those of enzyme activities were governed by the soil pH and concentrations of mobile heavy metals. We concluded that chronic fly ash depositions decrease litter decomposition by influencing specific microbial and enzymatic processes in forest soils.     

Use of organic amendment as a strategy for saline soil remediation: Influence on the physical, chemical and biological properties of soil

The effectiveness of adding two organic wastes (cotton gin crushed compost, CGCC, and poultry manure, PM) to a saline soil (Salorthidic Fluvaquent) in dryland conditions near Seville (Guadalquivir Valley, Andalusia, Spain) was studied during a period of 5 years. Organic wastes were applied at rates of 5 and 10 t organic matter ha⁻¹. One year after the assay began, spontaneous vegetation had appeared in the treated plots, particularly in that receiving a high PM dose. After 5 years the plant cover in this treated plot was around 80% (compared with the 8% of the control soil). The effect on the soils physical and chemical properties, soil microbial biomass, and six soil enzymatic activities (dehydrogenase, urease, protease, β-glucosidase, arylsulfatase, and phosphatase activities) were ascertained. Both added organic wastes had a positive effect on the physical, chemical and biological properties of the soil, although at the end of the experimental period, the soil physical properties, such as bulk density, increased more significantly in the CGCC-amended soils (23%) and the exchangeable sodium percentage (ESP) decreased more significantly in the CGCC-amended soils (50%) compared to the unamended soil. Water soluble carbohydrates and soil biochemical properties were higher in the PM-amended soils compared to the CGCC-amended soils (by 70% for water soluble carbohydrates, and by 34, 18, 37, 39, 40 and 30% for urease, protease, β-glucosidase, phosphatase, arylsulfatase and dehydrogenase activities, respectively). After 5 years, the percentage of plant cover was >50% in all treated plots and 8% in the control soil.     

Responses of soil chemical and microbial indicators to conservational tillage versus traditional tillage in the North China Plain

This study compared the responses of soil chemical and microbial indicators to the conservational tillage (CT) versus traditional tillage (TT) in a Haplic Cambisol in the North China Plain (NCP). These indicators included soil organic C (SOC), soil total N (STN), soil available P (SAP), cation exchange capacity (CEC), exchangeable Ca²⁺ and Mg²⁺, microbial biomass C (MBC), microbial biomass N (MBN), alkaline phosphomonoesterase (AP), β-glucosidase, N-acetyl-β-glucosaminidase (NAG), nitrate reductase (NR), protease, urease and the geometric mean of the assayed enzymes (GMea). Our results showed that almost all investigated parameters, except the contents of CEC, Ca²⁺, Mg²⁺ and the ratios of GMea/MBN and C/N, were significantly higher under the CT (no-till, NT and reduced-till, RT) than those under the TT, whilst the crop yield was not significantly affected by tillage treatments. Principle component analysis (PCA) showed that the first and second component explained 67.2% and 16.6% of the total variation, respectively. The first component was significantly correlated with GMea, MBC, MBN and β-glucosidase, and effectively discriminated soils under the NT or RT from those under the TT. Our results indicated that the 6-year CT improved the quality of the Haplic Cambisol by enhancing its chemical and microbial properties, whilst GMea, MBC, MBN and β-glucosidase were among the most effective indicators for monitoring these improvements.     

Phyllostachys edulis (moso bamboo) rhizosphere increasing soil microbial activity rather than biomass

Purpose

Rhizosphere and fertilization might affect soil microbial activities, biomass, and community. This study aimed to evaluate the impacts of Phyllostachys edulis (moso bamboo) rhizospheres on soil nutrient contents and microbial properties in a moso bamboo forest with different fertilizer applications and to link soil microbial activities with abiotic and biotic factors.

Materials and methods

The experiment included three treatments: (1) application of 45% slag fertilizer (45%-SF); (2) application of special compound fertilizer for bamboos (SCF); and (3) the control without any fertilizer application (CK). Simultaneously, bulk soils and 0.5, 2.5, 4.5, and 6.5-year-old (y) bamboo rhizosphere soils were selected. Soil nutrient contents were analyzed. Microbial activities were evaluated based on the activities of soil enzymes including β-glucosidase, urease, protease, phosphatase, and catalase. The total microbial biomass and community were assessed with the phospholipid fatty acids (PLFAs) method.

Results and discussion

In the CK and SCF treatments, organic matter contents of rhizosphere soils were significantly higher than those of bulk soils. Soil β-glucosidase, urease, protease, phosphatase, and catalase activities in rhizosphere soils were higher than those of bulk soils, with the sole exception of β-glucosidase of 0.5 y rhizosphere soil in the 45%-SF treatment. Compared with the CK treatment, fertilizer applications tended to increase soil total PLFAs contents and changed soil microbial community. Moso bamboo rhizospheres did not significantly increase the total microbial biomass. In the SCF treatment, the Shannon index of bulk soil was significantly lower than those of rhizosphere soils.

Conclusions

Our results suggested that both rhizospheres and fertilizer applications could change the soil microbial community structures and that moso bamboo rhizosphere could increase microbial activity rather than biomass in the forest soils with different fertilizer applications.

     

The ecological dose value (ED50) for assessing Cd toxicity on ATP content and dehydrogenase and urease activities of soil

Two soils of contrasting texture, organic matter content and pH were treated with CdSO₄ solutions to give a Cd concentration range of 0–4000 mg kg⁻¹ soil. The content of ATP and dehydrogenase and urease activities of soils were assayed after 3 h, and 7 and 28 days of Cd contamination. The relative ED₅₀ values were calculated by two kinetic models (model 1 and model 2) used by Speir et al. (1995) and by the sigmoidal dose–response model (model 3) employed by Haanstra et al. (1985). Model 1 was the most successful in calculating the ED₅₀ values for the ATP content, urease and dehydrogenase activities when both soils were contaminated by Cd. Similar ED₅₀ values were predicted by model 1 (describing the full inhibition) and model 3 only when the correlation coefficients r² were higher than 0.9. The ED₅₀ values of ATP calculated by model 1 were markedly higher than those calculated by model 2 (describing partial inhibition) when both models gave correlation coefficients higher than 0.9. This behavior was due to the high asymptote values obtained using model 2. According to model 2, some of the enzyme activities responsible for the ATP synthesis were probably not inhibited at the highest Cd concentrations. The inhibitory effect of Cd on the ATP content and both enzymatic activities was lower in the Castelporziano soil, which had the highest total organic carbon content.     

Long term CO2 enrichment stimulates N-mineralisation and enzyme activities in calcareous grassland

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.     

Enzyme activities in agricultural soils fumigated with methyl bromide alternatives

Pre-plant fumigation of agricultural soils with a combination of methyl bromide (MeBr) and chloropicrin (CP) to control nematodes, soil-borne pathogens and weeds has been a common practice in strawberry (Fragaria X ananassa Duchesne) production since the 1960s. MeBr will be phased out by 2005, but little is known about the impacts of alternative fumigants on soil microbial processes. We investigated the response of microbial biomass and enzyme activities in soils fumigated over two years with MeBr+CP and the alternatives propargyl bromide (PrBr), InLine, Midas and CP. Results were compared to control soils, which were not fumigated for the last 4-5 years for Watsonville and Oxnard, respectively, but had a 10 year history of MeBr+CP fumigation (history soils). Soil samples (0-15 cm) were taken from two sites in the coastal areas of California, USA, in Watsonville and Oxnard, at peak strawberry production after two years of repeated application. In addition to the soil enzymes, the activities of purified reference enzymes of β-glucosidase, acid phosphatase and arylsulfatase were assayed before and after fumigation with MeBr+CP and alternative biocides. At the Oxnard site, microbial respiration significantly decreased in soils fumigated with MeBr+CP (P=0.036), while microbial biomass C and N showed no response to fumigation at both sites. These results may indicate that fumigation promotes the growth of resistant species or that soil microorganisms had recovered at the time of sampling. Repeated soil fumigation with MeBr+CP significantly decreased the activities of β-glucosidase and acid phosphatase at the Watsonville site, and dehydrogenase activity at the Oxnard site. Although, enzyme activities in soils fumigated with PrBr, InLine, Midas and CP were lower compared to the control soil, effects were, in general, not significant. Fumigation with MeBr+CP and alternatives reduced the activities of purified reference enzymes by 13, 76 and 28% for acid phosphatase, β-glucosidase and arylsulfatase, respectively. Mean enzyme protein concentrations in fumigated agricultural soils were 2.93, 0.105, and 2.95 mg protein kg⁻¹ soil for acid phosphatase, β-glucosidase and arylsulfatase, respectively, all lower than in control soils. Organic matter turnover and nutrient cycling, and thus, the long-term productivity of agricultural soils seem unaffected in soils repeatedly fumigated with PrBr, InLine, Midas and CP.     

Effect of organic-complexed superphosphates on microbial biomass and microbial activity of soil

Organic complexed super-phosphates (CSPs) are formed by the complexation of humic acid (HA) with calcium monophosphate. The aim of this study was to determine whether two CSPs, characterized by different HA concentrations, added to a calcareous soil at an agronomic dose, were able to maintain the phosphorus (P) in a soluble form longer than the superphosphate fertilizer. Another important goal was to verify if CSP could positively influence soil microbial biomass and soil microbiological activities. Organic complexed super-phosphates were capable of keeping a large portion of P in a soluble form under different soil water conditions. In particular, the CSP with the highest organic C content was the most effective product, capable of maintaining, in an available form, the 73 % of the initially added P at the end of the experiment. In addition, it was the most effective in increasing C–CO₂ soil emission, microbial biomass carbon (C) and nitrogen (N), fluoresceine diacetate hydrolysis and activities of alkaline phosphomonoesterase, β-glucosidase and urease. The addition of CSPs to soil probably produced a priming effect, increasing several times C–CO₂ release by the treated soil. The significant correlation (p?<?0.05) between C–CO₂ emission and the amount of C added to soil by CSP suggests that the added HA acted as trigger molecules.     

Soil amendments with organic wastes reduce the toxicity of nickel to soil enzyme activities

The effects of adding a crushed cotton gin compost (CCGC) and poultry manure (PM) on the biological properties of a Typic Xerofluvent soil contaminated with Ni were studied in the laboratory. Urease, BBA-protease, alkaline phosphatase, β-glucosidase and arylsulfatase activities were measured in soils containing seven concentrations (100, 250, 500, 1000, 2500, 5000 and 8000 mg kg⁻¹ soil) of Ni after four incubation times (1 day, 7 days, 15 days and 45 days). The resulting inhibition was compared with that of the enzymatic activities in the same soil containing similar concentrations of the Ni but amended with crushed cotton gin compost and poultry manure. The 50% ecological dose (ED₅₀) values were calculated by the two kinetic models used by Speir et al. [T.W. Speir, H.A. Kettles, A. Parshotam, P.L. Searle, L.N.C. Vlaar, A simple kinetic approach to derive the ecological dose value, ED50, for the assessment of Cr(VI) toxicity to soil biological properties, Soil Biol. Biochem. 27 (1995) 801–810] and by the sigmoidal dose–response model used by Haanstra et al. [L. Haanstra, P. Doelman, J.H. Oude Voshaar, The use of sigmoidal dose response curves in soil ecotoxicological research, Plant Soil 84 (1985) 293–297]. The urease, BBA-protease, β-glucosidase, alkaline phosphatase and arylsulfatase activities were higher in the organic amended soils (76%, >99.7%, >95.7%, >27.6% and >87.2%, respectively) than in the control soil. Also, the enzymatic activities were higher in CCGC-amended soils than in the PM-amended soils (51%, 20%, 11.2%, and 11.3% increase for urease, BBA-protease, β-glucosidase and alkaline phosphatase, respectively). For all soil enzymatic activities and at the end of the period of incubation, the ED₅₀ values were lowest in control soil, followed by PM and CGCC-amended soils. This may have been due to the adsorption capacity of Ni being higher in the humic acid (CGCC) than in the fulvic acid-amended soil (PM).     

Microbial activities in soils of a Mediterranean ecosystem in different successional stages

This study reports a comparative analysis of soil enzyme activities (β-glucosidase, protease, urease, arylsulphatase, phosphatase and fluorescein diacetate hydrolase), ATP, total N and organic matter contents in three vegetal successional stages (meadow, low shrubland and high maquis) of a Mediterranean ecosystem in the Natural Reserve of Castel Volturno (Campania, Italy). Because water availability is a major limiting factor of soil microbial activity in Mediterranean ecosystems, the analysis was performed in late spring (May), after the rainy period, and in early autumn (October), after the long dry summer.A significant decrease in protease, arylsulphatase, urease and β-glucosidase activities was observed in meadow soil in the autumn sampling, probably due to the prolonged summer drought. Combining the values measured in the two sampling dates, the high maquis tended to have higher levels of enzymes activities than shrubland and meadow. Notably, high maquis had significantly higher phosphatase and arylsulphatase activities than shrubland and meadow and, in addition, a higher ATP content compared to meadow. Drastic changes were observed in EA/ATP ratios between the sampling periods in the meadow and shrubland, suggesting changes in the efficiency of microbial community more likely linked to climatic fluctuations than to the successional stage. The more stable EA/ATP ratio in the maquis probably reflects a constant contribution of microbial biomass to enzyme secretion.In conclusion, our results point to an increase in soil microbial activity accompanying the succession from meadow to high maquis that probably reflects a parallel increase in soil functions. Nevertheless, spatial heterogeneity and, more important, temporal variations in soil activities often may obscure differences related to the plant cover type.     

Physical,chemical and microbiological soil attributes influence soil greenhouse gases fluxes in Atlantic Forest and pine (Pinus taeda) plantations in Brazil

Forest soils can be sources or sinks of greenhouse gases (GHGs) depending on soil attributes that affect biomass and activity of soil micro-organisms involved in GHGs fluxes. In this work, we tested the hypothesis that soil physical, chemical and microbiological attributes, under different forests ecosystems, affect the soil GHGs [nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄)] fluxes. The study was carried out in two locations in southern Brazil in 2019, with three experimental plots of 900 m² in native forests of the Atlantic Forest biome and in loblolly pine (Pinus taeda) plantations. Air samples released from the soil surface were analysed for concentration and flux of CO₂, N₂O and CH₄. Soil samples were analysed for chemical attributes, density (Ds), soil microporosity (MiPs), soil macroporosity (MaPs), total porosity (TP), water-filled pore space (WFPS), microbial biomass carbon (MB-C), basal respiration (BR), microbial (qMic) and metabolic (qCO₂) quotient and activities of soil urease and β-glucosidase enzymes. The seasons influenced the CO₂ and N₂O emissions, probably because of the changes in seasonal conditions. However, native forests consumed more CH₄ than pine plantations. Meanwhile, the native forests presented soils with lower Ds (average 21.5% lower), more TP (average 12.5% higher) and more moisture (average 33% higher), which improved the microbiological attributes of the soil (20% to 60% more MB-C, 67% higher urease activity and 30% higher β-glucosidase activity) compared with pine plantations. Native forests contributed more intensely to CH₄ consumption than pine plantations because they present better physical, chemical and microbiological soil conditions. Therefore, it is possible that forestry practices that improve soil physical attributes are likely to contribute to increase CH₄ consumption, and to reduce GHGs emissions in forest ecosystems.     

Nine years of enriched CO2 changes the function and structural diversity of soil microorganisms in a grassland

To gain insight into microbial function following increased atmospheric CO₂ concentration, we investigated the influence of 9 years of enriched CO₂ (600 μl litre⁻¹) on the function and structural diversity of soil microorganisms in a grassland ecosystem under free air carbon dioxide enrichment (FACE), as affected by plant species (Trifolium repens L. and Lolium perenne L. in monocultures and mixed culture) and nitrogen (N) supply. We measured biomass and activities of enzymes covering cycles of the most important elements (C, N and P). The microbial community was profiled by molecular techniques of phospholipid fatty acid (PLFA) and denaturing gradient gel electrophoresis (DGGE) analysis. The enrichment in CO₂ increased soil microbial biomass (+48.1%) as well as activities of invertase (+36.2%), xylanase (+22.9%), urease (+23.8%), protease (+40.2%) and alkaline phosphomonoesterase (+54.1%) in spring 2002. In autumn, the stimulation of microbial biomass was 25% less and that of enzymes 3–12% less than in spring. Strong correlations between activities of invertase, protease, urease and alkaline phosphomonoesterase and microbial biomass were found. The stimulation of microbial activity in the enriched atmosphere was probably caused by changes in the quantity and kind of root litter and rhizodeposition. The response of soil microorganisms to enriched CO₂ was most pronounced under Trifolium monoculture and under greater N supply. The PLFA analysis revealed that total PLFA contents were greater by 24.7% on average, whereby the proportion of bioindicators representative of Gram‐negative bacteria increased significantly in the enriched CO₂ under less N‐fertilized Lolium culture. Discriminant analysis showed marked differences between the PLFA profiles of the three plant communities. Shannon diversity indices calculated from DGGE patterns were greater (+12.5%) in the enriched CO₂, indicating increased soil bacterial diversity. We conclude that greater microbial biomass and enzyme activity buffer the potential increase in C sequestration occurring from greater C addition in enriched CO₂ due to greater mineralization of soil organic matter.     

淹水厌氧培养对水稻土中酶活性的影响

An incubation experiment with soil water content treatments of 0.15 （W1）, 0.20 （W2）, and 0.40 （W3） g g^-1 soil was carried out for two months to investigate the activities of important enzymes involved in C, N, P, and S cycling in a paddy soil from the Taihu Lake region, China, under waterlogged and aerobic conditions. Compared with air-dried soil, waterlogging resulted in a significant decrease （P ≤ 0.05） of fluorescein diacetate （FDA） and /3-D-glucosidase activities, and this effect was enhanced with increasing waterlogging time. Waterlogging also significantly inhibited （P ≤ 0.05） arylsulfatase as well as alkaline and acid phosphatase activities, but did not decrease the activities with the increase in waterlogging time. Short-term waterlogging did not affect urease activity, but prolonged waterlogging decreased it markedly. In contrast, the aerobic incubation （W1 and W2 treatments） significantly increased （P ≤ 0.05） FDA, alkaline phosphatase, and /3-D-glucosidase activities. With aerobic treatments the activities of FDA and alkaline phosphatase increased with incubation time, whereas /3-D-glucosidase activity decreased. A significant difference （P ≤ 0.05） was usually observed between the W1 and W2 treatments for the activities of FDA as well as alkaline and acid phosphatase; however,/3-D-glucosidase and urease were usually not significant （P ≤ 0.05）. No activity differences were observed between waterlogging and aerobic incubation for arylsulfatase and urease.     

Effects of a cadmium-contaminated sewage sludge compost on dynamics of organic matter and microbial activity in an arid soil

 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