Effects of butachlor on microbial populations and enzyme activities in paddy soil

This paper reports the influences of the herbicide butachlor (n-butoxymethlchloro -2', 6'-diethylacetnilide) on microbial populations, respiration, nitrogen fixation and nitrification, and on the activities of dehydrogenase and hydrogen peroxidase in paddy soil. The results showed that the number of actinomycetes declined significantly after the application of butachlor at different concentrations ranging from 5.5 microg g(-1) to 22.0 microg g(-1) dried soil, while that of bacteria and fungi increased. Fungi were easily affected by butachlor compared to the bacteria. The growth of fungi was retarded by butachlor at higher concentrations. Butachlor however, stimulated the growth of anaerobic hydrolytic fermentative bacteria, sulfate-reducing bacteria (SRB) and denitrifying bacteria. The increased concentration of butachlor applied resulted in the higher number of SRB. Butachlor inhibited the growth of hydrogen-producing acetogenic bacteria. The effect of butachlor varied on methane-producing bacteria (MPB) at different concentrations. Butachlor at the concentration of 1.0 microg g(-1) dried soil or less than this concentration accelerated the growth of MPB, while at 22.0 microg g(-1) dried soil showed an inhibition. Butachlor enhanced the activity of dehydrogenase at increasing concentrations. The soil dehydrogenase showed the highest activity on the 16th day after application of 22.0 microg g(-1) dried soil of butachlor. The hydrogen peroxidase could be stimulated by butachlor. The soil respiration was depressed during the period from several days to more than 20 days, depending on concentrations of butachlor applied. Both the nitrogen fixation and nitrification were stimulated in the beginning but reduced greatly afterwards in paddy soil.     

四溴双酚A对土壤酶活性的影响

采用室内模拟试验方法,研究了四溴双酚A对土壤多酚氧化酶、过氧化氢酶和脱氢酶活性的影响.结果表明,四溴双酚A对土壤多酚氧化酶和过氧化氢酶有一定的激活效应,这可能是土壤微生物在受到外源四溴双酚A胁迫时产生了应激反应,通过增加多酚氧化酶和过氧化氢酶的产生量来降低四溴双酚A及其代谢、中间产物对其产生的危害;同时,四溴双酚A对土壤脱氢酶产生一定的抑制效应,表明其对土壤微生物活性具有一定的抑制作用,但在试验设置的四溴双酚A浓度范围内基本未达到显著水平(P>0.05).     

Effects of some insecticides on microbial activities in sandy soil

Abstract

Laboratory tests were conducted with 14 insecticides applied to a sandy loam to determine whether these materials caused any effects on microbial activities related to soil fertility. The ammonification of soil native organic nitrogen was not inhibited by any of the insecticide treatments. Some insecticides showed an effect on nitrification during the second week of incubation which subsequently recovered to levels similar to those obtained in the controls. There was a significant effect on denitrification in a number of treated samples. However, recovery of denitrifying capacity was rapid. This recovery indicated that the indigenous soil microorganisms can tolerate the chemicals used for control of insect pests. No significant inhibition of sulfur oxidation was observed. Results indicated that the insecticide treatments at the level tested were not drastic enough to be considered deleterious to soil microbial activities important to soil fertility.     

Effects of trifluralin on soil microbial populations and the nitrogen fixation activities

Effects of trifluralin on soil microbial populations and the nitrogen fixation activity of nitrogen-fixing bacteria Azotobacter chroococcum and Bradyrhizobium japonicum and the decomposition of trifluralin by soil microorganisms were studied. Trifluralin at lower concentrations from 0.5 mg microg(-1) dry soil to lower than 10.0 mg microg(-1) dry soil appeared to stimulate the growth of soil bacteria, actinomycetes, mould, and the pure cultures of Br. japonicum and A. chroococcum. Not only the colony amounts of these two species of nitrogen-fixing bacteria increased, grown on agar medium containing lower concentrations of trifluralin, but also these colonies also enlarged in size and appeared obviously in shorter formation time. However, trifluralin at higher concentrations would inhibit the development of microbial colonies both in amount and size. Trifluralin inhibited the activity of acetylene reduction of A. chroococcum when it was added at the same time of inoculation with A. chroococcum, but it showed a noteworthy stimulation to nitrogen fixation of A.chroococcum when it was put into culture after the cells of the nitrogen-fixing bacterium had grown well. The observation that soil microorganisms could use trifluralin as sole carbon and nitrogen resources for their growth, indicated that microorganisms could decompose trifluralin well.     

Effects of Cd and Pb on soil microbial community structure and activities

Background, aim, and scope  

Soil contamination with heavy metals occurs as a result of both anthropogenic and natural activities. Heavy metals could have long-term hazardous impacts on the health of soil ecosystems and adverse influences on soil biological processes. Soil enzymatic activities are recognized as sensors towards any natural and anthropogenic disturbance occurring in the soil ecosystem. Similarly, microbial biomass carbon (MBC) is also considered as one of the important soil biological activities frequently influenced by heavy metal contamination. The polymerase chain reaction–denaturing gradient gel electrophoresis (DGGE) has recently been used to investigate changes in soil microbial community composition in response to environmental stresses. Soil microbial community structure and activities are difficult to elucidate using single monitoring approach; therefore, for a better insight and complete depiction of the soil microbial situation, different approaches need to be used. This study was conducted in a greenhouse for a period of 12 weeks to evaluate the changes in indigenous microbial community structure and activities in the soil amended with different application rates of Cd, Pb, and Cd/Pb mix. In a field environment, soil is contaminated with single or mixed heavy metals; so that, in this research, we used the selected metals in both single and mixed forms at different application rates and investigated their toxic effects on microbial community structure and activities, using soil enzyme assays, plate counting, and advanced molecular DGGE technique. Soil microbial activities, including acid phosphatase (ACP), urease (URE), and MBC, and microbial community structure were studied.     

Rapid degradation of butachlor in wheat rhizosphere soil

The degradative characteristics of butachlor in non-rhizosphere, wheat rhizosphere, and inoculated rhizosphere soils were measured. The rate constants for the degradation of butachlor in non-rhizosphere, rhizosphere, and inoculated rhizosphere soils were measured to be 0.0385, 0.0902, 0.1091 at 1 mg/kg, 0.0348, 0.0629, 0.2355 at 10 mg/kg, and 0.0299, 0.0386, 0.0642 at 100 mg/kg, respectively. The corresponding half-lives for butachlor in the soils were calculated to be 18.0, 7.7, 6.3 days at 1 mg/kg, 19.9, 11.0, 2.9 days at 10 mg/kg, and 23.2, 18.0, 10.8 days at 100 mg/kg, respectively. The experimental results show that the degradation of butachlor can be enhanced greatly in wheat rhizosphere, and especially in the rhizosphere inoculated with the bacterial community designated HD which is capable of degrading butachlor. It could be concluded that rhizosphere soil inoculated with microorganisms-degrading target herbicides is a useful pathway to achieve rapid degradation of the herbicides in soil.     

Assessment of natural sepiolite on cadmium stabilization, microbial communities, and enzyme activities in acidic soil

A pot trial was conducted to assess the efficiency of sepiolite-induced cadmium (Cd) immobilization in ultisoils. Under Cd concentrations of 1.25, 2.5, and 5 mg?kg^?1, the available Cd in the soil after the application of 1–10 % sepiolite decreased by a maximum of 44.4, 23.0, and 17.0 %, respectively, compared with no sepiolite treatments. The increase in the values of soil enzyme activities and microbial number proved that a certain metabolic recovery occurred after sepiolite treatment. The dry biomass of spinach (Spinacia oleracea) increased with increasing sepiolite concentration in the soil. However, the concentration (dry weight) of Cd in the spinach shoots decreased with the increase in sepiolite dose, with maximum reduction of 92.2, 90.0, and 84.9 %, respectively, compared with that of unamended soils. Under a Cd level of 1.25 mg?kg^?1, the Cd concentration in the edible parts of spinach at 1 % sepiolite amendment was lower than 0.2 mg?kg^?1 fresh weight, the maximum permissible concentration (MPC) of Cd in vegetable. Even at higher Cd concentrations (2.5 and 5 mg?kg^?1), safe spinach was produced when the sepiolite treatment was up to 5 %. The results showed that sepiolite-assisted remediation could potentially succeed on a field scale by decreasing Cd entry into the food chain.     

Effects of six selected antibiotics on plant growth and soil microbial and enzymatic activities

The potential impact of six antibiotics (chlortetracycline, tetracycline and tylosin; sulfamethoxazole, sulfamethazine and trimethoprim) on plant growth and soil quality was studied by using seed germination test on filter paper and plant growth test in soil, soil respiration and phosphatase activity tests. The phytotoxic effects varied between the antibiotics and between plant species (sweet oat, rice and cucumber). Rice was most sensitive to sulfamethoxazole with the EC10 value of 0.1 mg/L. The antibiotics tested inhibited soil phosphatase activity during the 22 days' incubation. Significant effects on soil respiration were found for the two sulfonamides (sulfamethoxazole and sulfamethazine) and trimethoprim, whereas little effects were observed for the two tetracyclines and tylosin. The effective concentrations (EC10 values) for soil respiration in the first 2 days were 7 mg/kg for sulfamethoxazole, 13 mg/kg for sulfamethazine and 20 mg/kg for trimethoprim. Antibiotic residues in manure and soils may affect soil microbial and enzyme activities.     

连作芋艿套作对土壤养分及酶活性的影响

针对芋艿连作障碍造成土壤环境破坏的问题,进行玉米、毛豆与芋艿套作的田间试验,通过对土壤养分、土壤酶活以及芋艿产量、品质的分析,探讨套作减缓芋艿连作障碍的可行性。试验共设置4个处理:连作芋艿、非连作芋艿、套作玉米和套作毛豆。结果表明:(1)套作可以均衡连作土壤的养分含量,套作处理平均可以比连作提升速效氮9.88%、速效钾58.21%、有机质70.36%,降低速效磷64.08%。(2)套作可以提升连作土壤酶活性,套作处理平均可以比连作提高过氧化氢酶活性23.75%、脲酶活性38.15%、蔗糖酶活性129.60%。(3)在套作土壤中,过氧化氢酶活性与速效磷、速效钾显著正相关,脲酶活性与pH、速效氮显著正相关,蔗糖酶活性与有机质、速效氮显著正相关,套作使连作土壤酶活性的影响因子向非连作土壤转化。     

Interactions between plant and rhizosphere microbial communities in a metalliferous soil

In the present work, the relationships between plant consortia, consisting of 1-4 metallicolous pseudometallophytes with different metal-tolerance strategies (Thlaspi caerulescens: hyperaccumulator; Jasione montana: accumulator; Rumex acetosa: indicator; Festuca rubra: excluder), and their rhizosphere microbial communities were studied in a mine soil polluted with high levels of Cd, Pb and Zn. Physiological response and phytoremediation potential of the studied pseudometallophytes were also investigated. The studied metallicolous populations are tolerant to metal pollution and offer potential for the development of phytoextraction and phytostabilization technologies. T. caerulescens appears very tolerant to metal stress and most suitable for metal phytoextraction; the other three species enhance soil functionality. Soil microbial properties had a stronger effect on plant biomass rather than the other way around (35.2% versus 14.9%). An ecological understanding of how contaminants, ecosystem functions and biological communities interact in the long-term is needed for proper management of these fragile metalliferous ecosystems.     

Ozone exposure of field-grown winter wheat affects soil mesofauna in the rhizosphere

A 2-year open-top chamber experiment with field-grown winter wheat (Triticum aestivum L. cv. Astron) was conducted to examine the effects of ozone on plant growth and selected groups of soil mesofauna in the rhizosphere. From May through June in each year, plants were exposed to two levels of O₃: non-filtered (NF) ambient air or NF+ 40 ppb O₃ (NF+). During O₃ exposure, soil sampling was performed at two dates according to different plant growth stages. O₃ exposure reduced above- and below-ground plant biomass in the first year, but had little effect in the second year. The individual density of enchytraeids, collembolans and soil mites decreased significantly in the rhizosphere of plants exposed to NF+ in both years. Differences were highest around anthesis, i.e. when plants are physiologically most active. The results suggest that elevated O₃ concentrations may influence the dynamic of decomposition processes and the turnover of nutrients.     

Influence of tetracycline exposure on the growth of wheat seedlings and the rhizosphere microbial community structure in hydroponic culture

In this study, the effects of tetracycline exposure on wheat growth and the microbial community structure in the rhizosphere were investigated under hydroponic culture conditions. Exposure to various concentrations of tetracycline resulted in significant suppression of the growth of wheat roots and shoots, with minimum doses of 0.8 mg L^?1 and 4 mg L^?1 resulting in inhibition rates of 32% and 15.4%, respectively. Complete inhibition of the growth of these two parts of wheat plants was observed in response to treatment with tetracycline at 20 mg L^?1 and 100 mg L^?1, respectively. However, the germination of wheat seeds was not sensitive to exposure to tetracycline. The effects of tetracycline exposure on the microbial community in the wheat rhizosphere were evaluated through traditional cultivation and molecular biological analyses. The cultivation results indicated that bacteria were the dominant population, being present in concentrations of 1× 10⁸–2.45× 10⁹CFUs mL^?1, although 39% to 87% inhibition occurred in response to tetracycline. The concentration of fungi increased in all tetracycline treated samples to 2.5 to 15.8 times that of the control. The highest concentration of fungi (4.27× 10⁸ CFU mL^?1) was observed in response to 60 mg L^?1 tetracycline after 15 days of cultivation. In this stage, a large amount of fungal colonies was observed on the surface of the culture solution, the wheat roots became rotted and the plants became atrophic or even died. Molecular biological analysis indicated that the bacterial community structure was significantly different in samples that were exposed to high levels of tetracycline (over 20 mg L^?1) than in samples that were exposed to lower concentrations. As the concentration of tetracycline increased, the diversity of the bacteria decreased. Additionally, several dominant sensitive species such as Sphingobacterium multivorum were suppressed by tetracycline, while some resistant species such as Acinetobacter sp. appeared or were conserved. The bacteria population tended to stabilize when the drug concentration exceeded 40 mg L^?1.     

Effects of alkaline dust deposits from phosphate fertilizer production on microbial biomass and enzyme activities in grassland soils

Microbial biomass carbon (Cmic) and soil enzyme activities were measured at 12 sites along a gradient of former emissions of phosphate fertilizer production. Seven years after close down of operation, still moderate to high total concentrations of the dust constituents cadmium (up to 33 mg kg-1 dw), fluoride (5300 mg kg-1 dw) and phosphorous (120,000 mg kg-1 dw) were found in topsoils of contaminated sites. Accumulation of partially decomposed plant matter, soil respiration and dehydrogenase activity paralleled the increase of dust deposits, whereas microbial biomass decreased along the gradient. A significant negative correlation was obtained between the Cmic-to-Corg-ratio and the concentration of contaminants. In contrast, the Cmic-specific respiration (qCO2) and the dehydrogenase activity-to-Cmic-ratio were positively correlated. The low Cmic-values and the enhanced activities in the contaminated soils are suggested as a response of microbial communities to environmental stress or ecosystem disturbances. The apparently missing detrimental effects of the alkaline deposits on soil microbial activities are probably due to the low bioavailability of contaminants in the calcareous soil.     

Effect of some technical and formulated insecticides on microbial activities in soil

Abstract

The influence of 11 formulated and technical insecticides at 10 μg/g soil on growth and activities of microorganisms was determined. The populations of bacteria and fungi initially decreased with some pesticide treatments but recovered rapidly to levels similar to or greater than those of controls after three weeks. Both formulated and technical chlordane, chlorpyrifos and cypermethrin stimulated fungal growth. No inhibition on nitrification after two wks and sulfur oxidation after three wks was observed in treatments with either grade of insecticide. The effect of different treatments on respiration was equal to or greater than that of control sample. Less effect was observed with technical insecticides than the formulated ones on microbial populations and activities in the soil.     

Fungal degradation of metsulfuron-methyl in pure cultures and soil

A fungal strain capable of utilizing metsulfuron-methyl as sole carbon and energy sources was isolated from a metsulfuron-methyl treated soil. The degradation characteristics of metsulfuron-methyl by this fungal strain were investigated in liquid culture and soil. More than 79% of metsulfuron-methyl at concentrations of 0.10 mgl(-1), 1.0 mgl(-1) and 10.0 mgl(-1) in pure culture was degraded by strain MD after incubation for 7 days, whereas only 5.6%, 8.6% and 13.1% of metsulfuron-methyl were degraded at levels of 0.10 mgl(-1), 1.0mgl(-1) and 10.0 mgl(-1) in the controls, respectively. The incorporation of strain MD into soil was found to substantially increase the degradation of metsulfuron-methyl. Degradation was 7.5 and 3.8 times faster in strain MD amended soils than in sterilized and fresh soils. The results show that addition of the isolated strain MD enhances degradation of metsulfuron-methyl in water and soil.     

Effect of five insecticides on microbial and enzymatic activities in sandy soil

Abstract

A laboratory study was conducted to examine the effects of five insecticides on microbial and enzymatic activities important to fertility in sandy soil. Cyfluthrin significantly increased bacterial populations after 2 wks. Imidacloprid showed an inhibitory effect on fungal numbers after 2 wks incubation while the others did not affect fungal population. No inhibitory effect was observed on nitrification of soil indigenous nitrogen. All treatments stimulated S‐oxidation after 4 wks. With the exception of cyfluthrin and imidacloprid after 2 wks, denitrification in sandy soil indicated that all treatment inhibited denitrification throughout the experiment. No inhibitory effects on biomass‐c were observed during 2‐wk periods. An inhibitory effect was observed on amylase after 1 wk while significant recovery was observed after 3 wks. With the exception of HgCl₂, no effect was observed on reducing sugar formation for 2 wks with all treatments. Formazan formation resulting from dehydrogenase activity was significantly greater with tebupirimphos and Aztec for 1 wk. All treatments supressed phosphatase activity for 1 wk, while none of the treatments suppressed phosphatase activity after 2 wks. Amitraz, tebupirimphos and Aztec inhibited urease activity for 1 wk. With the exception of tebupirimphos, no treatments affected N₂‐fixation in soil. Although short‐lived inhibitory effects on activities of microbes and enzymes were caused by the insecticides, the soil indigenous microbes can tolerate the chemicals used for control of soil pests.     

Effect of bound residues of metsulfuron-methyl in soil on rice growth

A pot experiment was conducted to appraise the hazards of bound residues of metsulfuron-methyl in soil at six levels (0, 0.050, 0.089, 0.158, 0.281, and 0.500 mg kg(-1)) to the growth of four rice varieties (Xiushui 63, Eryou 810, Liangyoupeijiu, and Zhenong 952). The morphological characteristics of rice roots like root number, total length, surface area of rice roots, and rice biomass were determined. The results showed that the bound residues of metsulfuron-methyl in soil impacted the growth of rice. Root number, total length of roots, surface area of roots, and biomass were restrained by bound residues of metsulfuron-methyl in soil. The inhibition rate of root growth increased from 69.46-81.32% to 85.18-95.97% with the increasing of levels of bound residues of metsulfuron-methyl from 0.05 mg kg(-1) to 0.50 mg kg(-1). The number of rice roots could be taken as a sensitive index to screen the rice varieties endurable to bound residues of metsulfuron-methyl in soil and to predict the potential hazards of bound residues of metsulfuron-methyl in soil to rice. The level of bound residues of metsulfuron-methyl in soil causing the root numbers decreased by 50% (IC50) followed the order of Xiushui 63 < Eryou 810 < Liangyoupeijiu < Zhenong 952.     

Effects of sulfonamide and tetracycline antibiotics on soil microbial activity and microbial biomass

Increasingly often soil residual concentrations of pharmaceutical antibiotics are detected, while their ecotoxic relevance is scarcely known. Thus, dose related effects of two antibiotics, sulfapyridine and oxytetracycline, on microorganisms of two different topsoils were investigated. The fumigation-extracted microbial C (E(C)) and ergosterol were determined to indicate soil microbial and fungal biomass, respectively. Microbial activity was tested as basal respiration (BR), dehydrogenase activity (DHA), substrate-induced respiration (SIR), and Fe(III) reduction. The BR and DHA were uninfluenced even at antibiotic concentrations of 1000 microg g(-1). This revealed that an activation of microbial growth through nutrient substrate addition is required to test possible effects of the bacteriostatic antibiotics. In addition, the effects of both antibiotics were time dependent, showing that short-term tests were not suitable. Clear dose-response relations were determined with SIR when the short-term incubation of 4h was extended into the growth phase of the microorganisms (24 and 48 h). The Fe(III) reduction test, with a 7-d incubation, was also found to be suitable for toxicity testing of antibiotics in soils. Effective doses inhibiting the microbial activity by 10% (ED(10)) ranged from total antibiotic concentrations of 0.003-7.35 microg g(-1), depending on the antibiotic compound and its soil adsorption. Effective solution concentrations (EC(10)), calculated from distribution coefficients, ranged from 0.2 to 160 ng g(-1). The antibiotics significantly (p<0.05) reduced numbers of soil bacteria, resulting in dose related shifts in the fungal:bacterial ratio, which increased during 14 d, as determined from analysis of ergosterol and E(C). It was concluded that pharmaceutical antibiotics can exert a temporary selective pressure on soil microorganisms even at environmentally relevant concentrations.     

Causes of phytotoxicity of metsulfuron-methyl bound residues in soil

The bioavailability and phytotoxicity of bound residues of metsulfuron-methyl were studied using 14C-labeling and bioassay with oil rape (Brassica napus L.). Soil bound residues at the concentration of 0.27 and 0.53 nmol g(-1) resulted in significant inhibition of oil rape seedling growth. The biologically active component of the bound residues was identified to be metsulfuron-methyl parent compound. Other metabolites, including the hydrolysis product 2-methylformate-benzenesulfonamide, showed no toxicity to the test species. This study suggests that residues of metsulfuron-methyl bound previously to the soil matrix could be again released upon planting. The phytotoxicity of metsulfuron-methyl bound residues was mainly caused by the metsulfuron-methyl parent compound that became available during plant growth.     

Alterations of microbial populations and composition in the rhizosphere and bulk soil as affected by residual acetochlor

Acetochlor is a widely used herbicide in maize fields; however, the ecological risk of its residue in the soil–plant system remains unknown. We investigated the dissipation dynamics of field dose acetochlor and clarified its impact on microbial biomass and community structure both in the rhizosphere and bulk soil over 1 month after its application. Soil microbial parameters such as quantities of culturable bacteria and fungi represented by colony-forming units, soil microbial biomass carbon (SMB_C), and phospholipid fatty acids (PLFAs) were determined across different sampling times. The results showed that the dissipation half-lives of acetochlor were, respectively, 2.8 and 3.4 days in the rhizosphere and bulk soil, and 0.02–0.07 μg/g residual acetochlor could be detected in the soil 40 days after its application. Compared to the bulk soil, microbial communities in the rhizosphere soil were inclined to be affected by the application of acetochlor: SMB_C content and bacterial growth were most likely to be increased; however, fungal growth was prone to be inhibited. The principal component analysis of PLFAs, as well as the comparisons of fungi/bacteria and cy17:0/C16:1ω9c ratios between different treatments over sampling time, revealed that the soil microbial community composition was significantly affected by acetochlor at its early application stage (at day 15); thereafter, the effects of acetochlor were attenuated or even could not be detected. Our results suggested that residual acetochlor did not confer a long-term impairment on viable bacterial groups in the rhizosphere and bulk soil.