جستجوی مقالات مرتبط با کلیدواژه "enzyme activity" در نشریات گروه "آب و خاک"

Enzyme activity measurement is one of the significant methods in the bioremediation of soils contaminated with petroleum compounds. Biostimulation, bioaugmentation and their integration are among the types of bioremediation methods used in this experiment. For this purpose, to reduce light naphtha pollution (1%) in a sandy loam soil, a variety of bioremediation treatments, including providing NP elements, adding cow manure and Tween 80 surfactant, bioaugmentation, and integrated treatment were used. This experiment was carried out in a pot (containing 3 kg soil) based on split plot factorial design (pollution factor, bioremediation factor and time) with 3 replications, at room temperature, for 120 days. On days 0, 5, 10, 15, 30, 45, 60, 90 and 120, subsamples were taken from each pot to measure the activity of dehydrogenase and lipase enzymes. The results of the experiment showed that bioremediation treatments led to the reduction of oil pollutants. Likewise, dehydrogenase activity had a completely downward trend from the beginning of the experiment, and the changes of lipase activity in contaminated soil increased until day 10, decreased slightly from day 10 to 15, then, progressed with slight fluctuations until day 60 and decreased again from day 60 onward. Dehydrogenase activity changes in cow manure treatment during the experiment was from 3.39 to 0.35 (μg TPF g-1 h-1), and lipase activity in integrated treatment dropped from 57 to 33.56 (mU g-1). In addition to increasing the active microbial population involved in the decomposition of petroleum compounds and providing optimal conditions for their activity, the use of integrated treatments and cow manure is a suitable method to reduce the concentration of light naphtha.

Soil hydrocarbons can affect the physical, chemical and biological characteristics. Soil samples were prepared from the oil-rich area of Kermanshah province, which have been under oil pollution for a long time. 120 soil samples were collected from a depth of 0-15 cm with three pollution levels of low (L), moderate (M) and high (H) and the physicochemical characteristics were measured. Then bacteria were counted in NA and CFMM media and a positive and significant correlation was observed between bacterial population and oil concentration. The mean of oil measured by Soxhlet method was 4.03%, 9.95% and 22.50% for L, M and H levels, respectively. With the increase of oil in soil samples, ACP and ALP increased. In all samples, ACP was lower than ALP. The highest ACP and ALP were obtained 45.78 and 84.90 (gPNP.g-1.h-1µ) respectively in soil with high pollution level. Regression analysis showed that the oil percentage, sand percentage and EC with an regression coefficient of 0.71 were effective variables on the ACP, and the oil and sand percentage were also effective variables on the activity of ALP with an regression coefficient of 0.43. PCA analysis was also performed and the results showed that the first two components explained 68% of the variance between the samples. Based on the results, it was observed that natural and long-term oil pollution, with the passage of time led to the adaptation of microbial communities resistant to pollution and the number of these microorganisms and the activity of phosphatase enzyme increased.

Oil contamination affects the biological, physical, and chemical properties of soil. The abundance and diversity of soil microbial communities can significantly be influenced by petroleum hydrocarbons. Soil biological indicators including microbial population and enzyme activity, are highly sensitive to environmental stresses and respond to them quickly. Measuring the microbial population is one of the most common biological indicators which is used to study the quality and health of the soil. Also, measuring the activity of enzymes such as urease is one of the most sensitive indicators of oil-contaminated soils. There are some studies on the effects of oil contamination on microbial population and soil enzyme activity. Most of the studies have tested non-natural and short-term oil pollution and reported the adverse effects of oil hydrocarbons on microbial activities in soil. While the soil sample used in this research had natural and long-term contamination and the microorganisms are compatible with polluted conditions. The aim of this study was to investigate changes in the microbial population and urease activity in the presence of different levels of oil contamination, and how petroleum hydrocarbons can affect them. Petroleum hydrocarbons are toxic and persistent in soil, so it is necessary to study the pattern of changes in soil biological characteristics in effective soil management.

In this study, 120 samples of oil-contaminated soils were collected from the oil-rich area of Naft-Shahr (located in the west of Kermanshah province) which had natural and long-term oil pollution. A nested design was used to analysis data in this research. The test factors included locations (4 locations) and 3 different levels of oil pollution: low (L), moderate (M), and high (H). Also, 10 replications were considered in the three levels of oil contamination. The collected soils were analyzed for physico-chemical (pH, EC, Ɵm, CCE, OC, soil texture) and biological properties (including urease activity, BR and SIR) using standard methods, and the concentration of oil pollutants was determined by the Soxhlet extractor. To determine the abundance of the culturable microbial population, bacterial counting was performed using nutrient agar (NA) and carbon-free minimal medium (CFMM) supplemented with crude oil as the media. Urease activity was measured by the indophenol blue method and finally, the results of measuring chemical, physical and biological properties were analyzed using principal component analysis (PCA).

 The average percentage of oil measured by Soxhlet method was 4.03%, 9.95% and 22.50% respectively for L, M and H levels. The results showed that the microbial population increased with the increase of contamination intensity. The highest microbial population counted in NA culture medium was 9.54 ×105 CFU/g in H soils and the lowest population was 3.25 × 105 CFU/g in L soils. In the CFMM culture medium, the highest population in H soils was 11.3 × 105 CFU/g and the lowest population in L soils was 11.8 × 104 CFU/g. For both NA and CFMM mediums, location 1 had the highest population and location 4 had the lowest microbial population. Oil contamination of soil samples led to a decrease in urease activity in such a way that the highest enzyme activity in soils was obtained with low contamination (594.90 µgNH4/g.h) and the lowest activity in heavily contaminated soils (176.11 µgNH4/g.h). Also, the lowest urease activity was observed in location 1 and the highest in location 4. Principal components analysis (PCA) was also performed and 71% of the variance of the samples could be explained by the first two components (biochemical component and physical component). The results of this research indicated an increase in the microbial population with an increasing of the intensity of oil pollution. It seems that the results obtained from the studies conducted on man-made pollution and natural pollution have differences in terms of the type of biological responses. Aged, long-term and natural oil pollution has caused the selection of oil-resistant microbial community, and therefore we see their positive response to the presence of oil compounds. Conversely, urease enzyme activity was found to be higher in soils with low pollution. This suggests that microbial activity, while influential, is not the sole determinant of urease activity, and various factors contribute to Soil Enzyme Activity (SEA). The type of petroleum pollutant, the direct effect of petroleum compounds on urease-producing microorganisms, as well as the non-microbial origin of urease in soil can be possible reasons for reducing urease activity in contaminated soils.

In areas where petroleum pollutants are naturally and long-term present in the soil, some oil-decomposing microbial groups use petroleum hydrocarbons as a source of carbon for their nutrition, so the abundance of oil-decomposing communities increases. The results showed an increase in the microbial population with an increase in the intensity of oil pollution. On the other hand, the activity of urease enzyme measured in soils with low pollution was higher because non-microbial factors may affect the activity of this enzyme and the increase in the microbial population is not related to the increase in the population of urease-producing microbes.

Soil, as habitat substrate, helps to regulate important ecosystem processes, including nutrient absorption, organic matter decomposition. Water availability and the well-being of humanity are directly linked to soil functions. On the other hand, vegetation with different species and ages have significant effects on the status of the surface soil layer through the creation of diverse environmental conditions and the production of different organic substances. However, few studies have been conducted in relation to the effect of the age of afforestation and the type of vegetation on the soil status. Considering that a practical, complete and effective assessment of soil condition should be the result of simultaneous measurement of physical, chemical and biological indicators, hereupon, the present study aimed to investigate the effect of 20-year old poplar stand, 20-year old maple stand, 10-year old poplar stand, 10-year old maple stand and rangeland cover, in plot 3 of Delak-Khil series of wood and paper forests in Mazandaran province, on the organic layer properties and physical, chemical and biological (including microbial activities, enzyme activity, earthworm population and biomass, the number of soil nematodes and root biomass) properties of the surface soil layer.  

For this purpose, some parts of the study area were selected which are continuous with each other and have minimum height difference from the sea level, minimum change in percentage and direction of slope. Then, in order to take samples from the organic and surface layer of the soil, three one-hectare plots with distances of at least 600 meters were selected in each study habitats. From each of the one-hectare plots, 5 leaf litter samples and 5 soil samples (30 cm × 30 cm by 10 cm depth) were taken to the laboratory for analysis . In total, 15 litter samples and 15 soil samples were collected from each of the habitats under study. One part of the soil samples was passed through a 2 mm sieve after air-drying to perform physical and chemical tests, and the second part of the samples was kept at 4 °C for biological tests. One-way analysis of variance tests was used to compare the characteristics of organic layer and soil between the studied habitats. In the following, Duncan's test (P>0.05) was used to compare the average parameters that had significant differences among different habitats.

The results of this research showed that afforested stands with different ages and pasture cover had a significant effect on the characteristics of the organic and surface soil layers. The results indicated the improvement of most of the characteristics of the organic and surface soil layer in the afforested stands, especially the 20-year old afforestation compared to the rangeland cover. The organic matter produced in 20-year old afforestation, especially with poplar species, had a higher quality (high nitrogen and carbon content and low carbon-to-nitrogen ratio) compared to organic matter produced in 10-year old afforestation and pasture cover. Most of the physicochemical characteristics of the soil under 20-year old afforestation were in a better condition than the other studied habitats. Also, according to the results of this research, the highest values of biological characteristics such as microbial activity, enzyme activity, and the population of earthworms and nematodes were observed in the subsoil of 20-year old afforestation especially with poplar species. Based on the results obtained from the principal component analysis, the higher values of nitrogen, phosphorus, calcium, magnesium and potassium content of the organic layer led to the improvement of soil fertility characteristics, microbial activities, enzyme activity, earthworm population, the number of soil nematodes and root biomass, respectively, under poplar and maple plantation for 20 years, meanwhile, 10-year old plantation, especially with maple species, and rangeland with the production of organic materials with high carbon content and carbon to nitrogen ratio, resulted in the reduction of organic matter decomposition (greater thickness of organic layer), and consequently the reduction of the mentioned properties of the surface soil layer. 

According to the findings of this research, it can be concluded that plantation with poplar species, especially after 20 years, had a higher ability to improve the soil condition compared to maple, which can be considered by managers in future afforestation. Also, with the passage of time, the presence of tree covers (poplar and maple) had a higher priority than rangeland cover in improving the fertility status and suitable edaphological conditions of the soil.

The maintenance of planted forests in arid and semi-arid lands is important. Soil formation in forest ecosystems is different with different tree species. Tree species have a direct and indirect effect on soil organisms. Forest ecosystems change their species composition and abundance of microorganisms, and consequently their biogeochemical cycles. The accumulation of vegetation biomass and the improvement of soil fertility can play a significant role in soil restoration.

In order to investigate the biological characteristics of the soil from 5 treatments, including agricultural (dry farming and relatively poor lands that are usually cultivated barley and wheat and have low productivity), pasture (pastures with minimal vegetation and high slopes that are affected by overgrazing have been changed to barren lands), forest with Acacia type (under and outside the crown), forest with the Cupressus arizonica type (under and outside the crown) and forest with the Pinus brutia type (under and outside the crown) randomly. Sampling was done in 3 repetitions from the 0 to 5 cm layer. The statistical sampling design of this research was completely random, in which, according to the type of afforested species, two types of coniferous forest stands (including Cupressus arizonica and Pinus brutia) and one broadleaf stand (Acacia species) were selected. Also, the area under the crown trees and outside the crown trees was also investigated. Soil samples were sampled with sterile equipment and crushed through a 4-mm sieve. Fresh and moist soil was kept at 4 °C temperature for soil biological tests. Microbial biomass carbon, soil basal respiration (197 days), substrate-induced respiration, and metabolic quotient were measured. Streptomycin sulfate was used to measure fungal respiration and cycloheximide was used to measure bacterial respiration. The activities of urease, acid, and alkaline phosphatase enzymes were determined. After measuring the biological properties of the soil, the normality of the data was checked by the Anderson–Darling test, and the homogeneity of the variance of the treatments was checked by using Levene's test. Analysis of data variance was done using One-Way ANOVA and average data comparison was done using Duncan's test at 5 and 1% probability levels (SAS 9.4 and SPSS 26).

The results of soil biological characteristics analysis showed that the highest values of soil respiration and amount of consumed organic matter, substrate-induced respiration, microbial biomass carbon, enzyme activities, and fungal respiration were measured in conifers. Although the amount of these features was also significant in broadleaf trees, they had significant differences. In this study, the high soil respiration rate in coniferous covers compared to broadleaf can be due to the high organic carbon content of the soil in this cover. According to the results of substrate-induced respiration in different coatings, likely the activity of microorganisms involved in the decomposition of organic matter in the studied habitats had a significant difference; Therefore, different coatings can affect the population of soil microorganisms as the main source of decomposition and emission of carbon dioxide by changing the quantity and quality of organic matter and other factors. Also, the highest values of metabolic quotient and bacterial respiration were observed in agricultural and pasture covers. A higher metabolic quotient in these covers indicates a decrease in the efficiency of the use of leaf litter by the soil microbial community. In general, the metabolic quotient in the bacterial community is higher than the fungal community; Therefore, it seems that the predominance of the bacterial population in agricultural and pasture cover has caused this index to increase, although plowing and cultivation, and disturbance of these covers have caused stress to this bacterial community and as a result increased the metabolic quotient deficit in these covers.

The results of this research showed that the type of planted tree species causes significant changes in the biological characteristics of the soil. The current research shows that the forest, whether coniferous or broadleaf, had the highest values of enzyme activities, basal respiration, substrate-induced respiration, microbial biomass carbon, and the lowest values of metabolic quotient compared to agricultural and pasture covers. Afforestation increases biological activity and possibly the number and diversity of microorganisms, and improves soil characteristics in the long term. In agriculture and pasture land, due to the destruction of soil and aggregates by agricultural activities such as plowing or excessive livestock grazing, the amount of organic carbon and the activity of microorganisms decreases, and with the decrease of other soil characteristics, the quality of the soil decreases over time. From this research, it can be concluded that the planting of forest species in the soils of degraded areas in the long term can increase soil organic carbon due to high-quality leaf litter, and as a result, increase permeability and soil moisture. Increasing soil organic carbon increases the activity of microorganisms, and in the long term, it will improve various soil characteristics. Planting forest plants in the natural areas of the country, which were destroyed due to the change of use to agriculture and indiscriminate cultivation and finally abandoned, can improve the characteristics of the soil and, as a result, establish the native vegetation of the region, and increase the permeability of water in the soil, the risk of soil erosion, floods, etc. reduce.

Chitosan is a natural and destructive polymer that consists of glucosamine units, which, due to reactive groups, can reduce the availability of heavy metals and change soil enzyme activities which is an indicator of soil quality. However, little information is available on simultaneous effect of chitosan and heavy metals on soil enzymes activities. In this study, the interaction of chitosan at three levels of control, low molecular weight (LMC), and high molecular weight (HMC) with Pb at three levels of 0, 50 and 500 mg/kg on available soil lead (Pb) investigated on activity of acid and alkaline phosphatase, L-glutaminase and fluorcine diacetate hydrolysis enzymes in two different soils, Lavark and Langroud. The results were statistically compared. Both chitosan types significantly reduced available Pb concentration in two soils, but HMC was more effective. In Lavark soil, LMC and HMC application to Pb treatments significantly increased the activity of acid and alkaline phosphatase, L-glutaminease and fluorcine diacetate hydrolysis compared to control treatments. In Langroud soil, LMC application to Pb treatments significantly increased L-glutaminease activity, but did not affect the activity of other enzymes. The HMC application in Langroud soil also did not significantly affect activity of any enzymes compared to control. Level of 50 mg/kg Pb in the presence of chitosan significantly decreased acid phosphatase activity in Lavark soil and hydrolysis of fluorcine diacetate hydrolysis in Langroud soil compared to control, but had a positive effect on the activity of other enzymes. Level of 500 mg/kg Pb in the presence of chitosan also reduced acid and alkaline phosphatase activity in Lavark soil and hydrolysis of fluorcine diacetate in Langroud soil, but significantly increased the activity of other enzymes. Generally, increasing or decreasing enzyme activity due to the simultaneous presence of chitosan and Pb depended on soil, enzyme, Pb concentration, and chitosan type.

Biochar application to soil improve organic carbon and soil quality. The objective of this study was to investigate the effect of biochar and sulfur modified biochar (prepared from sugarcane bagasse and corn residue) on changes in organic carbon and biochemical and microbiological characteristics of a calcareous soil under corn cultivation. This study was conducted in a completely randomized design with five treatments and four replications. Corn residue and sugarcane bagasse biochar and their modified biochar were mixed at 1% (w/w) with the soil sample, and corn was grown in 5 kg pots. The results indicated that the application of biochar and biochar modified with sulfur caused a significant increase in total (56.7-115.4%) and dissolved organic carbon (24.3-60.9%) of the soil, microbial basal respiration (43.8-85.8%), substrate-induced respiration (44.5-98.9%), microbial biomass carbon (54.8-93.4%), dehydrogenase (108.0-114.7) and catalase (105.4-151.6%) activity. Comparison between the two feedstock has revealed that corn residue biochar was more effective in improving total and dissolved organic carbon and soil biochemical attributes than sugarcane bagasse biochar. The positive impact of sulfur-modified biochar on dissolved organic carbon, microbial biomass carbon and catalase activity was significantly greater than the raw biochar. The greatest value of dissolved organic carbon, microbial basal respiration, and substrate induced respiration as well as dehydrogenase, and catalase activity, were related to the biochar treatment of modified corn residue. In general, the results of this study demonstrated that biochar derived from corn residue and sugarcane bagasse could be a suitable organic amendment to improve soil organic matter and soil biochemical properties. In addition, modification of biochar with sulfur and production of acidic biochar can increase its efficiency in improving soil microbial activity.

Soil, as an important component of terrestrial ecosystems, plant growth media, and a habitat of diverse living organisms commonly encounters a variety of abiotic stresses. Soil microorganisms play an important role in maintaining soil quality and functioning, since they are responsible for the decomposition of dead organic material, nutrient cycling and degradation of hazardous organic pollutants. Metal toxicity and salinity are the major abiotic stresses affecting soil microbial activity and community structure in many areas of the world, in particular arid regions. Salinity may prompt the negative influences of soil pollution on soil microbial activity. On the other hands, application of organic amendments to saline soils or toxic metal-polluted soils may alleviate the negative consequences of these two abiotic stresses on soil microbial activity and population.

This study was conducted under controlled laboratory conditions at Shahrekord University. The main aim of this study was to investigate the effects of salinity and plant residue as an organic amendment on concentrations of soluble elements, enzyme activity and substrate-induced respirations (SIR) in a calcareous soil polluted with cadmium (Cd) over a three-month incubation experiment. A factorial experiment with two levels of cadmium (0 and 30 mg kg-1), three levels of salinity (1.35, 7.5 and 15 dS m-1) and plant residue treatments (with and without alfalfa residue) was conducted using a completely randomized design with four replications. Using cadmium chloride salt, the soil was contaminated, and subsequently amended with alfalfa residue (1%, w/w). After thorough mixing of soil and plant residue, salinity treatments were applied using NaCl salt. To reactivate the microbial population and for the aging effect, soil moisture was set at 70% of field capacity, and containers were pre-incubated at room temperature for 4 weeks. The samples were then incubated at 25±1 oC for 98 days.

Increasing salinity levels resulted in an increase in soluble Na concentration, a reduction in soil enzyme activity and SIR, and a decline in the concentrations of soluble Ca, Mg and K. The harmful impact of soil salinity on microbial properties was much greater in Cd-polluted soils than unpolluted soils.

Results indicated that addition of plant residue reduced the negative impacts of salinity and Cd pollution stresses on soil microbial and enzyme activity, and that resulted in increases in the concentrations of water soluble elements.The findings of the current study confirmed that application of adequate organic amendments can decrease Cd toxicity, enhance substrate availability and maintain soil microbial and enzyme activity in saline and polluted soils with substrate limitation.

Abiotic stresses such as salinity and contamination individually have a negative effect on the soil enzyme activities, whereas addition of organic matter to soil can alleviate the negative impacts of stresses on the enzyme activity. However, the combined effects of these stresses (multiple stresses) on soil biochemical conditions and the role of organic matter addition in these interactions are largely unknown. The objective of this research was to explore the interaction effect of NaCl salinity and cadmium (Cd)-pollution on the activities of catalase, alkaline phosphatase, arylsulfatase and fluorescein diacetate hydrolysis in a Cd-contaminated calcareous soil treated with alfalfa residue over 3 months of incubation. A factorial experiment with 2 levels of Cd, 3 levels of salinity and 2 plant residue treatments was conducted using a completely randomized design with 4 replications. The results indicated that salinity increased the Cd availability in both uncontaminated and contaminated soils and reduced the soil enzymatic activity. Nevertheless, addition of alfalfa residue reduced the detrimental effects of salinity and Cd-pollution on the soil enzyme activities. This indicated that in saline Cd-contaminated soils with low organic matter, adding plant residues could lower the concentration of available Cd and the effect of soil salinity with a concomitant increase of enzyme activities. So, this study showed that the joint effect of NaCl salt and Cd on enzyme activity was mostly synergistic in plant residue-untreated soils, but it was antagonistic in the plant residue-treated soils.

Assessing biological indicators of soil quality is crucial to evaluation of ecological sustainability of agroecosystem. This study aimed at assessing the effects of four years of different tillage practices (no tillage, minimum tillage and conventional tillage) with and without canola cover crop on selected biological indicators of soil quality and sunflower yield in Dastjerd, Hamedan; A randomized complete block design with factorial arrangement and three replications was conducted. All the measured properties, including soil organic carbon, available P, basal microbial respiration, protease and phosphatase activity and sunflower seed yield were significantly (P

Biochar is a carbon-rich material that is obtained by heating organic feedstock in a limited or absence of oxygen. In general, biochar stimulates soil microbial activity by improvements in soil physiochemical properties such as increasing cation exchange capacity, altering soil pH and direct addition of nutrients, porosity and water holding capacity. Pyrolysis temperature and soil texture are the significant factors affecting soil responses to biochar application. However, there are very limited studies on biochar impact on chemical and microbiological properties of calcareous soils. The aim of this study was to evaluate the effect of corn biochars obtained at different temperatures on the chemical and microbiological characteristics of two calcareous soils with sandy and clayey texture.
The soils used in this study were sampled from the surface layer at two different sites around Karaj city, Alborz province, Iran. Corn raw material and biochars produced at 200, 400 and 600˚C were mixed at 0.5 and 1% (w/w) with the soils and incubated for 90 days. Soil chemical parameters such as pH and electrical conductivity, organic matter, inorganic nitrogen, available K and P; microbiological characteristics including substrate-induced respiration, microbial biomass carbon and enzyme activities (protease, saccharase, catalase and fluorescein diacetate hydrolysis) were measured.
The results showed that with increasing pyrolysis temperature, biochar pH (10-97%), ash content (75-378%), specific surface area (214-1472%), carbon content (19-54%) and carbon enrichment factor (20-54%) were increased, while the cation exchange capacity (12-45%), concentration of hydrogen (76-9%) and volatile matter (16-70%) were reduced. Biochar application increased soil pH (2-5%), electrical conductivity (8-66%), organic matter (36-161%), ammonium-nitrogen (6-28%), available potassium (12-40%), substrate-induced respiration (50-216%), catalase activity (34-320%), saccharase (26-476%), protease (3-186%) and hydrolysis of fluorescein diacetate (27-280%) relative to the control, whereas nitrate-nitrogen (10-77%) and available phosphorus (23-86%) tended to decrease with biochar addition. Increasing pyrolysis temperature increased soil pH (1-11%), electrical conductivity (1-38%), organic matter (18-179%), available phosphorus (2-150%), available potassium (5-25%) when compared with the raw corn residues, while decreased ammonium-nitrogen (7-43%), nitrate-nitrogen (10-77%), microbial biomass carbon (4-27%), substrate-induced respiration (2-39%), catalase activity (21-54%), saccharase (3.7-62%), protease (0-54%) and fluorescein diacetate hydrolysis (21-60%).
Discussion and The findings demonstrated that the positive effect of biochar application on soil chemical and microbiological properties depends upon its application rate, soil texture and the soil attributes involved. The most desirable effect of corn biochars on soil chemical and microbiological properties was observed at 1% application rate in sandy soil. Of the evaluated soil variables, enzyme activity showed the greatest response to biochar application. In brief, biochar is a valuable soil amendment with a positive effect on soil quality in arid and semi-arid environments. Therefore, biochar application is recommended for increasing soil organic matter pool, and consequently improving chemical and microbiological conditions of calcareous soils in Iran.

Rapid development of industrialization, heavy metal and radionuclide contaminants from industrial activities have posed a major threat to the environment owing to their toxicity, non-biodegradability and persistent accumulation. So various ecosystems are continuously contaminated with high levels of high-risk chemicals with different structures and levels of toxicity. Cadmium is one of the high-risk elements that enters the environment and can accumulate in the body of fish and other aquatic organisms, plants and livestock and be transferred to the human body. Therefore, the remediation of contaminated soils with cadmium in order to protect human health is very important. One method for remediation of pollutants is immobilization of them in the soil by adsorbents. Among the absorbents, bentonite has been identified for its unique properties, including high surface area and cation exchange capacity and adsorptive affinity for organic and inorganic ions, low cost and ease of access. If the physical and chemical properties of natural bentonites are improved by a special modification process, the adequate supplies for environmental purposes can be obtained. Among the biosorbents, rice husk has also been reported to be suitable for adsorption of cadmium and other heavy metals. This research was designed with the aim of decreasing the amount of cadmium in the soluble and exchangeable phase of a polluted soil under laboratory conditions in the presence of bentonite and rice husk. Considering that biological properties of the soil are an indicator of soil health and quality, so, after application of adsorbents, biological properties and some soil ecophysiological indices were also investigated. The experiment was done with 13 treatments and 3 replications in a completely randomized design. Treatments were bentonite (B) and modified bentonite with iron (B-Fe), manganese (B-Mn), iron and manganese together (B-Fe-Mn), rice husk (RH), modified rice husk with phosphoric acid (RH-P) in two levels (2 and 5%) and control treatment (without adding adsorbent). Modification of bentonite was done with iron chloride (FeCl3.6H2O), manganese chloride (MnCl2.6H2O) and a mixture of FeCl3.6H2O and MnCl2.6H2O. Some of the characteristics of bentonite and rice husk adsorbents including pH, electrical conductivity, cation exchange capacity and organic carbon were measured. The contaminated soil with CdCl2 was treated with adsorbents and incubated for 2 months under constant lab conditions. After the incubation time, soil biological properties such as basal respiration, substrate-induced respiration (SIR), microbial biomass carbon (MBC), activity of some enzymes and also some ecophysiological indexes were measured. The results showed that the basal respiration, SIR, MCB, activity of phosphatase, dehydrogenase and urease were less in the control treatment. The basal respiration and phosphatase activity in RH-P 5% treatment were 2.6 and 2.25 times more than those in the control, respectively. SIR and urease activity were highest in RH-P 5% treatment. The application of adsorbents to contaminated soil reduced soluble and exchangeable cadmium fraction. The lowest amount of soluble and exchangeable fraction of cadmium was in RH-P 5% treatment that showed 2.5 times reduction in comparison to control. In other words, immobilization of cadmium from these fractions improved soil conditions and caused increasing of biological soil properties and activity of microorganisms. The metabolic quotient was higher in the control treatment, probably due to lower microbial content, and decreased by adding adsorbents. Microbial quotient in control treatment was lower than other treatments which prove again the lower biomass carbon of control treatment. Carbon availability that is the ratio of basal respiration to SID, also was more in control in comparison to other treatments, perhaps due to the suppress or inhibition of dormant or zymogenous microbes by cadmium in the control treatment which can be stimulated to growth in the SIR experiment. The results of this study revealed that cadmium with concentration of 30 mg kg-1has a toxic and inhibitory effect on the microbial activity of the soil. The addition of bentonite and rice husk adsorbents in particular modified form reduced mobility of cadmium and thus improved the biological properties of the soil and also had a positive effect on ecophysiological indexes.
The use of these adsorbents can be a cost effective, succeeded, and operative management strategy for immobilization of cadmium in contaminated soils that reducing the risk of plant reclamation, washing and entry into groundwater and food cycle.

Application of EDTA may increase the heavy metal availability and phytoextraction efficiency in contaminated soils. In spite of that, it might also have some adverse effects on soil biological properties. Metals as freeions are considered to be severely toxic, whereas the complexed form of these metalswith organic compounds or Fe/Mn oxides may be less available to soil microbes. However, apart from this fact, some of these compounds like EDTA and EDTA-metal complexes have low bio- chemo- and photo-degradablity and high solubility in their own characteristics andable to cause toxicity in soil environment. So more attentions have been paid to use of low molecular weight organic acids (LMWOAs) such as Citric acid because of having less unfavorable effects to the environment. Citric acid increases heavy metals solubility in soils and it also improves soil microbial activity indirectly. Soil enzymes activity is a good indicator of soil quality, and it is more suitable for monitoring the soil quality compared to physical or chemical indicators. The aims of this research were to evaluate the changes of dehydrogenase, urease and alkaline phosphomonoesterase activities, substrate-induced respiration (SIR) and Pb availability after EDTA and citric acid addition into a contaminated soil with PbCl2.
An experiment was conducted in a completely randomized design with factorial arrangement and three replications in greenhouse condition. The soil samples collected from surface horizon (0-20 cm) of the Typic haplocalsids, located in Mashhad, Iran. Soil samples were artificially contaminated with PbCl2 (500 mg Pb per kg of soil) and incubated for one months in 70 % of water holding capacity at room temperature. The experimental treatments included control, 3 and 5 mmol EDTA (EDTA3 and EDTA5) and Citric acid (CA3 and CA5) per kg of soil. Soil enzymes activity, substrate-induced respiration and Pb availability of soil samples were determined by standard methods after 7, 14, 21 and 28 days of chelates addition.
The soil texture was loam and the indigenous Pb content was 25.55 mg kg-1. The soil pH was 7.4 and electrical conductivity of saturated extraction measured 2.5 dS m-1. The soil carbonate calcium was 14% and the content of organic carbon and essential nutrients were low. The results showed that EDTA3 and EDTA5 treatments increased Pb availability by 2.17% and 10% compared to control treatment but CA3 and CA5 treatments decreased it by 3.8% and 15.7% respectively. The Pb availability in control and EDTA5 treatments did not change during the incubation time. The available Pb concentration dropped sharply during the incubation time in EDTA3, CA3 and CA5 treatments. The reduction rates in CA3 and CA5 treatments were more than EDTA3 treatment. This may be due to the high stability and low biodegradability of EDTA than biodegradable chelators and low molecular weight organic acids. The results showed that urease and dehydrogenase activities were significantly reduced in EDTA3 and EDTA5 treatments compared to control treatment. Urease and dehydrogenase activities were decreased with the increase of EDTA concentration. Alkaline phosphomonoesterase activity was not affected by the EDTA3 and EDTA5 treatments. In CA3 and CA5 treatments, dehydrogenase and alkaline phosphomonoesterase activities significantly increased with increasing the concentration of citric acid. CA5 treatment showed a prominent effect on urease activity compare to CA3 treatment. The soil enzyme activities increased with incubation time. It seems that reduction in Pb availability causes an increase of soil enzymes activities. Significant negative relationships were found between soil enzymes activities and available Pb concentration (dehydrogenase activity (r=-0.906, P

Soil enzyme activities are considered as one of the most important biological indicators and reflect the soil quality and fertility. Current study was conducted to investigate the relationship between Urease, Invertase, Alkaline phosphatase and Aryl sulphatase activities of two Histosols (located in Kerman and Shahrekord provence) and some of the soil chemical and biological properties. Soil samples were collected from 3 soil profiles (0-120 cm, at each 20 cm layer). The enzyme activities were determined as described in standard methods. Results of Pearson correlation coefficients showed that organic carbon (r > 0.86**), total nitrogen (r > 0.88**), phosphorus (r > 0.77**), carbohydrates (r > 0.86**), microbial respiration (r > 0.94**) and microbial biomass carbon (r > 0.87**) had a positive and significant effect (p< 0.01) on the enzymatic activities of two studied soils. In addition, stepwise regression model was used to evaluate the relative importance of soil properties in conjunction with enzyme activities. The results showed that microbial biomass carbon and phosphorus had negative effects on the activity of some enzymes, while organic carbon, total nitrogen, carbohydrates and microbial respiration had a positive effect on enzyme activities. A significant correlation values, up to 99%, was found among enzymes and they were responding similar to the environmental systems.

Soil is a vital component of environment which its quality and health maintenance should be considered as an important factor. Land use changes mainly affect soil quality and health. Soil microorganisms respond to these changes and have special capability to assay these criteria. This research was carried out as factorial on the basis of randomized complete block design with two factors in 200 ha of Mirabad region, Suldoz plain in West Azerbaijan of Iran. Three types of land uses (pasture, crops and apple orchards) and two soil depths including 0-30 and 30-60 cm were considered in this experiment as main factors. Soil enzyme activity including dehydrogenase (DHA), cellulase (CA), urease (UA), acid and alkaline phosphatases (ACP and ALP) activities were measured as biological indices. Some important soil physical and chemical properties such as organic carbon, pH, EC, calcium carbonate equivalent (CCE), soil texture and water aggregate stability (WAS) were also determined. Results showed that soil quality and health indices were significantly decreased in apple orchard and crop production fields compared to the intact grassland. Decline of urease activity in orchards and crop fields at 0-30 cm depth were 65.5 and 72.7% and in grassland with increasing soil depth (30-60 cm) were 77.5, respectively. Soil enzyme activities were significantly decreased in apple orchard and crop production fields compared to the intact grassland.

The application of herbicides as organic chemical compounds to control pest and weeds may affect the population and activity of microorganisms, and this may have an influence on biochemical processes that are important for soil fertility and plant growth. The primary objective of this study was to evaluate different loading rates of eradican (EPTC) on soil microbial biomass C and N, microbial biomass C/N ratio and the activities of urease and arylsulphatase under field conditions. In this experiment, loading rates of 6 and 9 L ha-1 eradican were applied to a calcareous soil cultivated with corn (Zea mays L.) and left uncultivated using split-plots arranged in a completely randomized block design with three replications. The experiment was conducted in the Kabootarabad’s Agricultural Research Center, Isfahan. Soil microbial biomass C and N were determined at 30th and 90th days after the onset of experiment and the activities of urease and arylsulphatase were assayed at 30th, 60th and 90th days. Results showed that in soils cultivated with corn microbial biomass C increased with increasing eradican levels; and in both cultivated and uncultivated soils microbial biomass N and microbial biomass C/N ratios were increased over the control. At 30th day, urease activity at 6 L ha-1 level reduced, while at 9 L ha-1 level it increased compared with the control soils. At 60 day, there was no significant difference in the urease activity between the treatments. At 90th day, the activity of urease showed slight fluctuations. There was a reduction in arylsulphatase activity of the cultivated soils by increasing the loading rates of eradican during the experiment, and in uncultivated soils no trend was observed. Briefly, the use of eradican can cause either reduced or increased microbial biomass sizes and enzyme activities in calcareous soils These changes, however, depend largely upon the application rate of eradican, time elapsed since eradican application (i.e., sampling date) and the presence or absence of plant