Hydrolases extracted from soil: Kinetic parameters of several enzymes catalysing the same reaction

The kinetic parameters (K_m and V_max) of ureases, phosphatases, casein and benzoylargininae-mide-hydrolysing proteases extracted from two different soils were determined. The Eadie-Scatchard plot, which is the most sensitive graphical technique for detecting deviations from Michaelis-Menten kinetics, was used. In the case of phosphatases extracted from two soils and of the benzoylarginineamide hydrolysing protease extracted from one soil the relationship between V/S and V produced two straight lines. The presence of at least two enzymes (or two forms of the same enzyme) catalysing the same reaction and characterized by markedly different K_m and V_max values, was indicated. A procedure to determine the true constants was reported. The conclusion was that the presence in soil of high and low-affinity enzymes permits an efficient reaction at either low or high substrate concentration.     

Characterization of a metalloproteinase component extracted from soil

Summary A metalloproteinase was found to be the main component of a protease in the extract from an Andosol collected from a tomato field. The protease has a pH optimum of 7 for benzyloxycarbonyl-L-phenylalanyl-L-tyrosyl-L-leucine with tyrosylleucine as the main reaction product. The K_m value for the substrate was 0.4 mM. Activity was inhibited by EDTA but not by pepstatin, p-chloromercuribenzoate and phenylmethanesulfonyl fluoride. After the removal of EDTA from the inactivated enzyme by dialysis and the addition of metal ions (Zn²⁺, Mn²⁺ and Fe³⁺), the enzyme activity could be recovered. The apparent isoelectric points of the metalloproteinase components were estimated to be 4.9, 4.5 and 4.1 by isoelectric focusing. A fraction with an apparent isoelectric point of 4.9 was the main component. The apparent molecular weight of the main protease component was estimated to be 4.7 × 10⁴ by gel filtration of Sephadex G-100. The enzyme hydrolyzed a natural polypeptide, angiotensin I (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu). Main split sites in the peptide were -Tyr⁷-Ile⁵- and -Pro⁷-Phe⁸-. The former was the most sensitive site to the soil metalloproteinase concerned.     

Predicting deep drainage in the soil from soil properties and rainfall

Abstract. Simple predictions of deep drainage in the soil profile are often required for preliminary planning of land management where the cost of direct measurement is not warranted. Soil hydraulic conductivity and drainage of water below the root zone can be related to the salt content at the bottom of the root zone, assuming steady-state balances of water and salt. A physically based empirical model uses readily measured soil properties to predict the quantity of drainage below the root zone under varying regimes of water management and shows a good relationship with ponded infiltration rate.     

New phenolic compounds hydrothermally extracted from the olive oil byproduct alperujo and their antioxidative activities

The application of a novel process based on the hydrothermal treatment of olive oil waste (alperujo) led to a final liquid phase that contained a high concentration of simple phenolic compounds. This study evaluated the effects of time (15-90 min) on the composition of the phenolic compounds isolated at a fixed temperature of 160 °C. Phenolic compounds were extracted with ethyl acetate. Both qualitative and quantitative HPLC analyses of the extracts showed variation of the concentrations of phenolic compounds with time. In addition, new phenols that were not present in the untreated control have been characterized. The antioxidant activities of different phenolic extracts was measured by various assays conducted in vitro: antiradical capacity (using DPPH and ABTS radicals), ferric reducing power (P(R)), inhibition of primary and secondary oxidation in lipid systems, and other tests, such as inhibition of tyrosinase activity. The results show that the phenolic extracts inhibited oxidation in aqueous and lipid systems to a significantly greater extent than the untreated control, and they performed as well as or better than vitamin E in this capacity.     

Effects of soil properties and trace metals on urease activities of calcareous soils

A study was conducted to investigate the relationship between urease activity and some physical, chemical, and microbiological properties of soils from central Iran. Inhibitory effects of Cr, Cd, and Pb on urease activity were also studied. Results indicated that no significant difference was observed between urease activity of field-moist and air-dried soils. Soil organic C and total N correlated highly significantly with urease activity, with r values of 0.899*** and 0.797***, respectively. There was also a significant correlation between urease activity and the number of bacteria grown on urea-agar media, with r value of 0.470*. A significant negative correlation (r =–0.492*) was observed between urease activity and electrical conductivity of saturation paste extracts. There were no significant correlations between urease activity and soil textural properties, pH, calcium carbonate equivalent, cation exchange capacity, and populations of soil bacteria on nutrient agar and population of soil fungi on potato dextrose agar. Both Cd and Pb inhibited urease activity to a similar extent and to a greater extent than did Cr.     

Factors affecting the amount of phosphate extracted from soil by anion exchange resin

In resin—solution systems at equilibrium, solution concentration of phosphate was proportional to the square of the phosphorus sorbed, and inversely proportional to the weight of resin and the volume of solution. The rate of approach to equilibrium was decreased by: enclosing the resin in mesh bags, by increasing the volume of solution, and by decreasing the vigour of shaking.In resin-solution-soil systems, the concentration of phosphate in the solution was important in determining the amount of phosphate extracted from the soil. Consequently, phosphorus extracted increased as volume of water and weight of resin increased, and decreased when the resin was enclosed in mesh bags. Even after long periods of shaking, when the concentration of phosphate in solution had reached low values, appreciable phosphate remained on the soil in equilibrium with this solution phosphate. Equations suggested that, if the solution concentration could be reduced to zero, phosphate sorbed by the resin would be proportional to the phosphorus added to the soil. However, at finite levels of addition of resin, the proportion of added phosphate sorbed by the resin increased as the level of addition of phosphate increased.     

Human activities modify soil properties in urban parks: a case study of Tel Aviv-Jaffa

Purpose

The aim of the present study was to investigate the effects of visitors’ activities on soil properties in parks of Tel Aviv-Jaffa city, Israel.

Materials and methods

The city was divided into three geographical regions: south, central, and north. This division reflects the course of development of the city from south to north and encompasses various socioeconomic levels of residents. In each region, 9–15 parks were randomly chosen and classified into three groups according to their size (in m²): 2?×?10³ to 10?×?10³, 11?×?10³ to 20?×?10³, and 21?×?10³ to 50?×?10³. In each park soil, 0–2 cm of depth layer was sampled in areas under various levels of visitor pressure from July to August 2011, and organic matter, electrical conductivity, and sodium and chlorine contents were determined. Lawns and path and picnic areas represented low and high visitor pressure, respectively. Observations were conducted to characterize the various land uses of the parks and to estimate the numbers of visitors. Also, questionnaires were used at selected parks to assess visitors’ motivations or reasons for visiting the parks.

Results and discussion

Socioeconomic indicators, such as the number of residents, the apartment areas, and the percentages of family households, differed among the regions. Soil properties differed between the areas of high and low visitor pressure: they were influenced by type of human activity, size of the park, and number of visitors.

Conclusions

Soil properties are affected by variations in the intensity of park use by visitors and by the type of activities enjoyed by these visitors, both of which depend on the socioeconomic status of the park area.

     

Enzyme activities in apple orchard agroecosystems: How are they affected by management strategy and soil properties

This study under field experimental conditions in apple orchard agroecosystems investigated the effects of pest management strategies (i.e. none, organic, conventional and integrated) on enzyme activities, in relation to soil properties. Enzyme activities chosen are implicated in the major biogeochemical nutrient cycles such as C (cellulase, fluoresceine diacetate hydrolase, β-galactosidase, β-glucosidase, phenol oxidase), N (arylamidase), P (acid and alkaline phosphomonoesterases, phosphodiesterase and phosphotriesterase) and S (arylsulfatase). Redundancy analyses and decomposition of the variances were performed to clarify how enzyme activities are affected by management strategy and soil properties. Results showed that the effects and their proportion attributable to management strategy and soil properties varied considerably depending on enzyme activity. Phenol oxidase activity was the only case where total variance was principally explained by management strategy (i.e. conventional and integrated) rather than by soil properties, and thus it seems to be an attractive potential indicator to assess soil quality in this agrochemical context.     

Potential soil enzyme activities are decoupled from microbial activity in dry residue-amended soil

Extracellular enzymes play an important role in the microbial acquisition of carbon (C) and organically bound nutrients, such as nitrogen (N). The objective of the present study was to investigate the effect of different soil moisture contents on potential soil enzyme activities (β-glucosidase and protease), microbial biomass and activity. Soil incubations were carried out with gravimetric moisture contents (GMC) ranging from 0.8 (air-dry) to 30%. After 14 days, respiration, net N mineralization and potential enzyme activities were lowest at GMC below 10% in the unamended samples. In the residue-amended soil, however, respiration and net N mineralization were highest at GMC of 20% or more, while potential β-glucosidase and protease activity were highest at GMC of 10% or less. Increasing the moisture content of air-dry soil after 14 days of incubation resulted in significantly reduced β-glucosidase activity, but increased protease activity. With the exception of the high potential β-glucosidase activity in the residue-amended dry soil, enzyme activities were well correlated with microbial biomass and ergosterol, a biomarker for fungal biomass. Therefore, our results suggest that across the different GMC, protease activity was mainly dependent on the continuous production by microorganisms, while β-glucosidase accumulated in the dry soil due to an increased half-life, which was the result of interactions with soil colloids. Shifts in microbial community composition may also have contributed to the observed differences.     

Enzyme activities as affected by soil properties and land use in a tropical watershed

Enzyme activities play key roles in the biochemical functioning of soils, including soil organic matter formation and degradation, nutrient cycling, and decomposition of xenobiotics. Knowledge of enzyme activities can be used to describe changes in soil quality due to land use management and for understanding soil ecosystem functioning. In this study, we report the activities of the glycosidases (β-glucosidase, α-galactosidase, and β-glucosaminidase), acid phosphatase, and arylsulfatase, involved in C (C and N for β-glucosaminidase), P, and S cycling, respectively, as affected by soil order and land use within a watershed in north-central Puerto Rico (Caribbean). Representative surface soil (0–15 cm) samples were taken from 84.6% of the total land area (45,067 ha) of the watershed using a completely randomized design. The activity of α-galactosidase was greater in soils classified as Oxisols than in soils classified as Ultisols and Inceptisols, and it was not affected by land use. The activity of β-glucosidase was greater in Oxisols compared to the Inceptisols and Ultisols, and it showed this response according to land use: pasture > forest > agriculture. The activity of β-glucosaminidase was higher in Oxisols than the other soil orders, and it was higher under pasture compared to forest and agriculture. Acid phosphatase and arylsulfatase activities were greater in Oxisols and Ultisols than in Inceptisols, and they decreased in this order due to land use: forest = pasture > agriculture. As a group, β-glucosaminidase, β-glucosidase, and acid phosphatase activities separated the sites under forest and pasture from those under agriculture in a three-dimensional plot. Thus, enzyme activities in Inceptisols under agriculture could be increased to levels comparable to other soil orders with conservative practices similar to those under pasture and secondary forest growth. Our findings demonstrate that within this watershed, acid and low fertility soils such as Oxisols and Ultisols have in general higher enzyme activities than less weathered tropical soils of the order Inceptisols, probably due to their higher organic matter content and finer texture; and that the activities of these enzymes respond to management with agricultural practices decreasing key soil biochemical reactions of soil functioning.     

Residual metal reactivity of humic acids extracted,from soil amended with sewage sludge

Copper, Fe, and Mn were used as probes to investigate residual metal reactivity for humic acid (HA) samples extracted from a loam soil, either non-amended or amended with anaerobically digested sewage sludge for 4, 5, 6, or 7 yr at 90 t ha^?1. yr^?1. Irrespective of their origin, the HA complexes significant amounts of metal, in forms stable against intense water-leaching, in the order Fe > Cl > Mn. Sludge-amended soil HA adsorbed and retained Fe in amounts greater than HA extracted fron non-amended soil. Metal adsorption occurred mainly by cation-exchange replacement of metals previousl: bound to HA. Water-stable Fe³⁺-HA complexes prepared in the laboratory were partially stable agains H⁺ and metal ion exchange reactions, whereas Cu²⁺ and Mn²⁺ in laboratory-prepared, water-stabl HA complexes were desorbed almost completely by these two reactions. Electron spin resonance spectra indicated that the laboratory-prepared metal-HA complexes had a chemical composition and molecula structure similar to that of indigenous metal-HA complexes, which were stable against all leachin, and cation-exchange treatments. Although the HA samples showed a maximal metal binding (i.e. saturation) as metal loading of the sludge-amended soil increased, they still exhibited a high residua binding capacity for the three metals used as probes.     

Spatial and temporal variations in concentrations of three ions in solutions extracted from a woodland soil

Concentrations of Cl, Mg and K in soil solutions extracted from a gleyic brown earth under mixed oak woodland were measured at weekly intervals over a 1 year period. Spatial variability of ion concentrations was large, with coefficients of variation of 30–90% in a 0.1 ha plot. Seasonal variability in Mg and K was effectively buffered by the soil exchange complex, but Cl displayed a distinct pattern with a maximum concentration in late autumn. Flushing of Cl during soil rewetting is the most probable explanation.     

Spatial and temporal variations in concentrations of three ions in solutions extracted from a woodland soil

Concentrations of Cl, Mg and K in soil solutions extracted from a gleyic brown earth under mixed oak woodland were measured at weekly intervals over a 1 year period. Spatial variability of ion concentrations was large, with coefficients of variation of 30–90% in a 0.1 ha plot. Seasonal variability in Mg and K was effectively buffered by the soil exchange complex, but Cl displayed a distinct pattern with a maximum concentration in late autumn. Flushing of Cl during soil rewetting is the most probable explanation.     

Extraction and properties of phosphodiesterase from a forest soil

Phosphodiesterase together with brown-coloured compounds was extracted from a forest soil using 0.1 M phosphate buffer (pH 7). Use of KCl and EDTA with the buffer facilitated phosphodiesterase extraction. Distilled water extracted little enzyme activity. A curvilinear relationship such as the Langmuir type was found between solution volume and phosphodiesterase activity of the extract. The results implied that the phosphodiesterase extracted was extracellular and was adsorbed on the surface of soil particles by ionic bonding. Brown-coloured compounds in the extract were removed by precipitation with protamine sulfate. The phosphodiesterase activity of the extract treated with protamine sulfate was lost on keeping at 80°C for 10 min and was optimal at pH 5.2–6.0. The extract hydrolyzed either the 3'- or the 5'-phosphodiester bond of deoxythymidine p-nitrophenyl phosphate.     

Earthworm activities and the soil system

Summary Earthworms find in soil the energy, nutrient resources, water and buffered climatic conditions that they need. According to the food resource they exploit and the general environmental conditions, earthworms can be grouped into different functional categories which differ essentially in morphology, size, pigmentation, distribution in the soil profile, ability to dig galleries and produce surface casts, demographic profiles and relationships with the soil microflora. Soil characteristics are both the determinant and the consequence of earthworm activities, since these animals greatly influence the functioning of the soil system. When present, they build and maintain the soil structure and take an active part in energy and nutrient cycling through the selective activation of both mineralization and humification processes. By their physical activities and resultant chemical effects, earthworms promote short and rapid cycles of nutrients and assimilable carbohydrates. Thus earthworms represent a key component in the biological strategies of nutrient cycling in soils and the structure of their communities gives a clear indication of the type of soil system that they inhabit.     

Calculations of ion activities in soil solutions from humic horizons

Concentrations of the main components and activities of Ca²⁺, Na⁺, Cl^?, and NO₃^? were determined in soil solutions displaced from chernozem samples (A₁ horizon). To calculate ion activity in these solutions, it was necessary to consider formation of Ca²⁺, Mg² and Na⁺ complexes with organic anions. If 1 : 1-composition of these complexes was assumed, dependence of their stability constants on the ionic strengths was found; this allowed a 17% average error for Ca²⁺ activity and 8% for Na⁺ activity in the calculations. As followed from the computations, 68–80% of the Ca²⁺ and Mg²⁺ were included in ion pairs and complexes with 91–97% of these amounts bound with organic anions. The values for the calcite solubility product were close to those for pure saltwater systems.     

Ammonia volatilization from urea-treated pasture and tillage soils: effects of soil properties

Mean NH₃ losses after nine days incubation at 18°C and 60% FC were 3.1±2.9% and 7.6±6.0% of applied urea-N from the pasture and tillage counterparts of 10 soil series. These losses were highly correlated with buffered CEC and maximal pH values (pH_m) generated three days after urea application. NH₃ volatilization was apparently controlled by buffered CEC and initial pH (R²= 72–87%) and was related to variations in soil organic matter and texture (R²= 77–81%). Losses in the acid pasture soils were attributed largely to initial pH differences, and in the tillage soils to buffered CEC only. Evolution was greater from the tillage than from the pasture equivalent in eight series. This was attributed to differences in CEC, including buffered CEC and pH-dependent charge, caused by differences in OM content primarily but also in texture between the two soil groups. Differences in NH₃ evolution from urea in pasture and tillage soils, in general, are not related to pH differences.     

Rock fragments IL Their impact on soil physical properties and biomass production under Mediterranean conditions

Abstract. The effects of rock fragments on soil temperature, soil moisture conservation, night time water vapour absorption and wheat biomass production were investigated. Under conditions of moderate water stress, water conservation was generally greater in the stony soils. Under conditions of pronounced drought the opposite occurred, with stony soils conserving less water than soils free of stones, though soils with large cobbles on the surface conserved the most water.
Stony soils were generally warmer during daytime and cooler at night than soils free of rock fragments. In the warmest month (July) the diurnal amplitude reached 14.3 °C in the control soil and 24.1 °C in the stony soils. Night time absorption of water vapour in the upper 15–20 cm was less for the stony soil (17.8% cobble cover), than for the stone-free soil. Cobbles on the soil surface increased biomass production by increasing moisture conservation. After removing all the stones from the surface of 16 plots, total dry matter yield of rainfed wheat was on average 20% less than from plots with stones on the surface.     

Natural abundance δN and δC of DNA extracted from soil

We report the first simultaneous measurements of δ¹⁵N and δ¹³C of DNA extracted from surface soils. The isotopic composition of DNA differed significantly among nine different soils. The δ¹³C and δ¹⁵N of DNA was correlated with δ¹³C and δ¹⁵N of soil, respectively, suggesting that the isotopic composition of DNA is strongly influenced by the isotopic composition of soil organic matter. However, in all samples DNA was enriched in ¹³C relative to soil, indicating microorganisms fractionated C during assimilation or preferentially used ¹³C enriched substrates. Enrichment of DNA in ¹⁵N relative to soil was not consistently observed, but there were significant differences between δ¹⁵N of DNA and δ¹⁵N of soil for three different sites, suggesting microorganisms are fractionating N or preferentially using N substrates at different rates across these contrasting ecosystems. There was a strong linear correlation between δ¹⁵N of DNA and δ¹⁵N of the microbial biomass, which indicated DNA was depleted in ¹⁵N relative to the microbial biomass by approximately 3.4‰. Our results show that accurate and precise isotopic measurements of C and N in DNA extracted from the soil are feasible, and that these analyses may provide powerful tools for elucidating C and N cycling processes through soil microorganisms.     

Manganese extracted from different chemical fractions of bulk and rhizosphere soil as affected by method of sample preparation

Abstract

Rhizosphere soils had higher amounts of ‘readily soluble’, ‘weakly adsorbed’, ‘carbonate bound’ and ‘specifically adsorbed’ Mn, but had lower amounts of ‘oxide‐Mn’, than did bulk soils. This observation was true regardless of whether the comparison was based on values within moist or air‐dried treatments. Observed trends in Mn distribution between different soil fractions were qualitatively similar regardless of method of sample preparation. However, there were substantial quantitative differences depending on the method of sample preparation. Air‐dried samples increased significantly in the ‘oxide‐Mn’ fraction and decreased in its soluble and adsorbed fractions relative to moist soil samples. There was a significant effect of method of air‐drying on the distribution of Mn in rhizosphere samples. Samples that were extracted moist at first and then air‐dried accumulated more adsorbed Mn and were depleted in ‘oxide‐Mn’ relative to samples that were air‐dried initially. There was a significant rhizosphere x air‐drying interaction. Air‐drying of some rhizosphere samples resulted in a significant underestimation of the ‘readily soluble’, ‘specifically adsorbed’, and ‘oxide‐Mn’ fractions beyond the overall effect of air‐drying. The results of this study suggested that soil samples used for Mn analyses be extracted immediately in a moist condition rather than air‐dried, particularly for analyses of rhizosphere soil samples.