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PubMed1994

Effect of mineral and organic soil constituents on microbial mineralization of organic compounds in a natural soil.

This research addressed the effect of mineral and organic soil constituents on the fate of organic compounds in soils. Specifically, it sought to determine how the associations between organic chemicals and different soil constituents affect their subsequent biodegradation in soil. Four C-labeled surfactants were aseptically adsorbed to montmorillonite, kaolinite, illite, sand, and humic acids. These complexes were mixed with a woodlot soil, and CO(2) production was measured over time. The mineralization data were fitted to various production models by nonlinear regression, and a mixed (3/2)-order model was found to most accurately describe the mineralization patterns. Different mineralization patterns were observed as a function of the chemical and soil constituents. Surfactants that had been preadsorbed to sand or kaolinite usually showed similar mineralization kinetics to the control treatments, in which the surfactants were added to the soil as an aqueous solution. Surfactants that had been bound to illite or montmorillonite were typically degraded to lesser extents than the other forms, while surfactant-humic acid complexes were degraded more slowly than the other forms. The desorption coefficients (K(d)) of the soil constituent-bound surfactants were negatively correlated with the initial rates of degradation (k(1)) and estimates of CO(2) yield (P(o)) as well as actual total yields of CO(2). However, there was no relationship between K(d) and second-stage zero-order rates of mineralization (k(o)). Microbial community characteristics (biomass and activity) were not correlated with any of the mineralization kinetic parameters. Overall, this study showed that environmental form had a profound effect on the ultimate fate of biodegradable chemicals in soil. This form is defined by the physicochemical characteristics of the chemical, the composition and mineralogy of the soil, and the mode of entry of the chemical into the soil environment.

Journal Article↗
PubMed1998

Comparison of paenibacillus azotofixans strains isolated from rhizoplane, rhizosphere, and non-root-associated soil from maize planted in two different brazilian soils

Paenibacillus azotofixans is a nitrogen-fixing bacterium often found in soil and in the rhizospheres of different grasses. In this study, two Brazilian clay soils were planted with cross-hybrid maize (BR-201) and four stages of plant growth were analyzed to characterize the P. azotofixans populations present in the rhizoplanes, rhizospheres, and non-root-associated soils (herein called nonrhizospheres). A total of 106 strains were isolated and identified as P. azotofixans with an API 50CH kit, by classical biochemical tests, and via the use of specific primers based on the 16S rRNA gene in PCRs. To compare the isolated strains, phenotypic characteristics were determined and three different probes were used in hybridization experiments: two nif probes and one probe comprising a 0.58-kb fragment cloned from the P. azotofixans C3L4 genome. These results were used to construct a dendrogram, in which two main clusters could be observed. One cluster contained exclusively strains from Varzea soil, and the other contained the majority of strains from Cerrado soil. The 60 strains from Varzea soil and the 46 strains from Cerrado soil were further analyzed with REP and BOX primers, respectively. Based on the patterns obtained, it was possible to identify 21 different groups among strains from Varzea soil and 4 different groups among strains from Cerrado soil. These different patterns were tested by multivariate analysis of variance, and differences in the populations of P. azotofixans during the four stages of plant growth were demonstrated. Moreover, strains isolated from the rhizoplanes, rhizospheres, and nonrhizospheres of maize planted in Cerrado and Varzea soils were shown to be statistically different; the diversity of P. azotofixans strains was affected by the soil type.

Journal Article↗
PubMed1977

[Investigations about cause of specific replant disease of fruit trees. VI. Proof of actinomycetes in feeder roots of apple seedlings in soils with different digrees of soil sickness (author's transl)].

Microscopic analysis of longitudinal sections of feeder roots of apple seedlings from soil with experimentally prepared different degrees of soil sickness led to the following results: 1. A colonization of root-barks by actinomycetes could be pointed out in injured and in macroscopic not visible injured feeder roots of apple seedlings from sick soil. 2. The frequency of the colonization of root-pieces of the two highest root classes was in the sick soil at 47.3% and in the two soils with a less degree of soil sickness at 32.4%. In the non-sick soil the root were at a frequency of 0.3% nearly free from actinomycetes. 3. Feeder roots colonizated by actinomycetes showed injuries in the cell-bandage. Increasing injuries of the roots were obtained with increasing intensity of colonization by actinomycetes. In heavy injured feeder roots the proof of actinomycetes was difficult or no more possible. As the share of heavy injured roots was increasing with increasing degree of soil sickness can be supposed that the real frequency of root colonization by actinomycetes is substantially higher than it was observed in roots seeming to be healthy macroscopically. 4. The results obtained support our hypothesis that soil sickness of apple trees is caused by actinomycetes. The injuries of the roots appearing as a consequence of the colonization may explain both, the soil sickness in the case of replanting and the development of soil sickness in growing apple plantations. 5. Since until now there is no proof that actinomycetes cause injuries in roots of fruit-trees further examinations have to be aspired to confirm our results.

Actinomycetales↗
PubMedDate not supplied

Assessment of the ecotoxic potential of soil contaminants by using a soil-algae test.

To assess the ecotoxic potential of soil contaminants, a test with the soil alga Chlorococcum infusionum has been developed, enabling investigations of soil pollutions with soluble and fairly soluble chemicals. Three soil types artificially contaminated with Sb compounds and five soils from a historical mining area, which were highly polluted with Sb, As, Hg, and Cu, were used as test soils. For antimony, EC50 values from 125 mg/kg up to > 1000 mg/kg, depending on soil type, were determined. Two of five soils from the mining area caused toxic effects. Additionally, aqueous extracts of all soils were exposed in established tests (daphnid, alga, bacterium). In contrast with the soil-algae test, no toxic effects were found. Aquatic tests with SbO/K tartrate were performed to point out the toxicity of antimony. The following EC50 values in milligrams of Sb per liter were determined: Scenedesmus subspicatus, 59 mg/liter; Chlorococcum infusionum, 43 mg/liter; Daphnia magna, 8 mg/liter; and Vibrio fisheri, 7 mg/liter.

Animals↗
PubMed1976

Microbial degradation of the thiolcarbamate herbicide, diallate, in soils and by pure cultures of soil microorganisms.

The disappearance of the herbicide, Avadex (40% diallate), from five agricultural soils (differing in either pH, carbon content, or nitrogen content), incubated under sterile and non-sterile conditions, was followed for a period of 20 weeks. Avadex was rapidly lost from microbiologically active soils, with over 50% of the applied (2.5 ppm) dosage disappearing within four weeks; losses from sterile soils were much slower with recoveries of over 50% after 20 weeks. Incubation of soil with Avadex to which 14C-labeled diallate had been added resulted in rapid formation of 14CO2 from microbiologically active samples and only very slow 14CO2 formation from sterile samples. Substantial quantities of radioactivity were retained as unextractable residues in both sterile and non-sterile soils after senven days incubation. From these data it was concluded that the disappearance of the herbicide from non-sterile soils was mainly due to microbial degradation and to binding of diallate or its metabolites as residues to undefined soil components. Losses from sterile soils were attributed to both binding of residues and to a slow chemical degradation. Avadex degradation by pure cultures was studied using representative fungi isolated from the five soils. Of the fungi tested, Phoma eupyrena, Penicillium janthinellum, and Trichoderma harzianium coudl degrade at least 20% of the applied (2.5 ppm) herbicide after ten days incubation. Degradation of Avadex in soil cultures of T. harzianum was found to be slower than degradation in liquid nutrient cultures.

Biodegradation, Environmental↗
PubMed2004

Procedures for determining the pesticide sensitivity of indigenous soil algae: a possible bioindicator of soil contamination?

Soil algae are present in all kinds of soils, both arable and virgin, in large amounts and in great diversity. These photosynthetic microorganisms, which are concentrated in the top few centimeters of the soil profile, are organized in a community structure that varies depending on soil type, farming method and pesticide application. We first tested several extraction and conservation methods for soil algae, and a 14C incorporation procedure to evaluate the photosynthetic activity of these micro-organisms. In a second study, we assessed the sensitivity to atrazine of soil microalgae from two corn fields managed by different agricultural practices (conventional vs. organic). Changes in indigenous diatom communities were monitored, together with photosynthetic tests performed on the whole algal community. Comparison of the data for the treated field with those for the reference, untreated organic cornfield showed that previous atrazine application in the conventional cornfield had changed the species composition of the soil diatom communities. Short-term ecotoxicological tests, using photosynthetic activity as endpoint, also showed that the communities that had developed under pesticide stress were more tolerant to further atrazine application than the control communities. The stress caused by major environmental disturbances, such as ground dressing, was not sufficient to mask the difference between the two crops, suggesting that telluric microalgae could be used as indicators of xenobiotic contamination in soils. These initial findings about using soil microalgal communities as bioindicators are promising. In addition, their photosynthetic activity, which reflects their sensitivity to xenobiotic compounds, seems to be a relevant bioindicator of soil contamination.

Biomarkers↗
PubMed2003

Bioremediation of soil degraded by sewage sludge: effects on soil properties and erosion losses.

Soils in the Mediterranean area are very prone to erosion due to the loss of organic matter and the consequent lack of protective vegetation. In this experiment a Mediterranean degraded soil with a 15% slope was amended at a rate of 250 t ha(-1) wet weight with sewage sludge and with a mixture of sewage sludge and barley straw (70% carbon from sewage sludge and 30% from the straw) in order to study their influence on soil structure recovery and hence the soils's resistance to erosion processes. Both types of organic amendment led to an improvement in several soil properties (physical, biological, and microbiological) as a result of the spontaneous growth plant covering that became evident three months after amendment. This vegetation remained throughout the two years of the experiment and prevented the water erosion processes that normally precede soil degradation. Amendment by sewage sludge alone reduced soil loss by 80% compared with the control soil, while the mixture that included both sewage sludge and barley straw reduced losses by 84%, both reducing runoff by 57%. The amended soils showed increases in the percentage of stable aggregates, the levels of the total and water-soluble C fractions, microbial biomass C, basal respiration, and the activity of the different enzymes involved in the biogeochemical cycles of C, N, and P. The results confirm the usefulness of sewage sludge as an organic amendment for recovering damaged soils.

Biodegradation, Environmental↗
PubMed2005

Pulse additions of soil carbon and nitrogen affect soil nitrogen dynamics in an arid Colorado Plateau shrubland.

Biogeochemical cycles in arid and semi-arid ecosystems depend upon the ability of soil microbes to use pulses of resources. Brief periods of high activity generally occur after precipitation events that provide access to energy and nutrients (carbon and nitrogen) for soil organisms. To better understand pulse-driven dynamics of microbial soil nitrogen (N) cycling in an arid Colorado Plateau ecosystem, we simulated a pulsed addition of labile carbon (C) and N in the field under the canopies of the major plant species in plant interspaces. Soil microbial activity and N cycling responded positively to added C while NH (4) (+) -N additions resulted in an accumulation of soil NO (3) (-) . Increases in microbial activity were reflected in higher rates of respiration and N immobilization with C addition. When both C and N were added to soils, N losses via NH(3) volatilization decreased. There was no effect of soil C or N availability on microbial biomass N suggesting that the level of microbial activity (respiration) may be more important than population size (biomass) in controlling short-term dynamics of inorganic and labile organic N. The effects of C and N pulses on soil microbial function and pools of NH (4) (+) -N and labile organic N were observed to last only for the duration of the moisture pulse created by treatment addition, while the effect on the NO (3) (-) -N pool persisted after soils dried to pre-pulse moisture levels. We observed that increases in available C lead to greater ecosystem immobilization and retention of N in soil microbial biomass and also lowered rates of gaseous N loss. With the exception of trace gas N losses, the lack of interaction between available C and N on controlling N dynamics, and the subsequent reduction in plant available N with C addition has implications for the competitive relationships between plants species, plants and microbes, or both.

Bacterial Physiological Phenomena↗
PubMed2005

Mycotrophy of crops in rotation and soil amendment with peat influence the abundance and effectiveness of indigenous arbuscular mycorrhizal fungi in field soil.

Mycotrophy of previous crops has been shown to have an impact on arbuscular mycorrhizal fungi (AMF), and the growth and productivity of succeeding crops. We studied the impact of 3 years of cultivation of eight crops with different degrees of mycotrophy, including mycorrhizal (strawberry, rye, timothy, onion, caraway) and non-mycorrhizal (turnip rape, buckwheat, fiddleneck) hosts, as well as the impact of peat amendment, on the effectiveness, amount and diversity of indigenous AMF. A field experiment having a split-plot design with peat amendment as the main plot, crop cultivation as a sub-plot and three replications, was carried out on silt clay mineral soil in 1999-2001. A well-humified dark peat was applied immediately before establishment of the field experiment. Each year, the relative mycorrhizal effectiveness of soil collected in September, in terms of shoot dry weight (RME(DW)), was determined in a bioassay. In the 3rd year of the experiment, AMF spores were also extracted and identified from the field soil. Expressed as the mean of 3 years of cropping in unamended soil, the mycorrhizal crops strawberry and caraway maintained RME(DW) most effectively, while the values were lower in the non-host crops buckwheat, turnip rape and fiddleneck. In addition, the numbers of AM spores detected in soil were considerably greater during 3 years of strawberry cultivation. In soil under caraway, there were high numbers of AM spores compared to the other crops. In soil amended with peat, the situation was in some cases opposite of that of unamended soil; RME(DW) was highest in rye and onion and lowest in strawberry and caraway. The reasons behind the negative impact of peat on mycorrhizal effectiveness in strawberry soil may be due to the microbiological properties of peat. The importance of including mycotrophic species in crop rotations for maintaining high soil quality and for increasing yields of subsequent crops is discussed.

Agriculture↗
PubMed2004

Contrasting effects of manure and compost on soil pH, heavy metal availability and growth of Chenopodium album L. in a soil contaminated by pyritic mine waste.

Chenopodium album L. was found to be one of the initial plant species colonising a heavy metal-contaminated site, polluted by pyritic (sulphide-rich) waste from the Aznalcóllar mine spill (South-western Spain). This indicates its importance in the re-vegetation of this soil. In a pot experiment, C. album was sown in soil collected from the contaminated site, either non-amended or amended with cow manure or compost produced from olive leaves and olive mill wastewater, in order to study the effect on heavy metal bioavailability and soil pH. In non-amended and compost-amended soils, soil acidification, probably resulting from oxidation and hydrolysis of sulphide, led to increases in the concentrations of soluble sulphate and plant-available Cu, Zn and Mn in the soil (extractable with 0.1 M CaCl(2)). Under these conditions, shoot growth of C. album was negligible and shoot concentrations of Zn (2,420-5,585 microg g(-1)) and Mn (5,513-8,994 microg g(-1)) were phytotoxic. Manure application greatly increased shoot growth and reduced the shoot concentrations of Cu, Zn, and Mn, and their plant-available concentrations in the soil. These effects appeared to be related to an increase of soil pH, due to an inhibition of sulphide oxidation/hydrolysis, relative to the non-amended soil. For metal sulphides-contaminated soil, liable to acidification, manure application appears to be able to enhance the initial stages of re-vegetation, by species such as C. album.

Analysis of Variance↗
PubMed2006

Sequential soil washing techniques using hydrochloric acid and sodium hydroxide for remediating arsenic-contaminated soils in abandoned iron-ore mines.

Sequential washing techniques using single or dual agents [sodium hydroxide (NaOH) and hydrochloric acid (HCl) solutions] were applied to arsenic-contaminated soils in an abandoned iron-ore mine area. We investigated the best remediation strategies to maximize arsenic removal efficiency for both soils and arsenic-containing washing solution through conducting a series of batch experiments. Based on the results of a sequential extraction procedure, most arsenic prevails in Fe-As precipitates or coprecipitates, and iron exists mostly in the crystalline forms of iron oxide. Soil washing by use of a single agent was not effective in remediating arsenic-contaminated soils because arsenic extractions determined by the Korean standard test (KST) methods for washed soils were not lower than 6mg kg(-1) in all experimental conditions. The results of X-ray diffraction (XRD) indicated that iron-ore fines produced mobile colloids through coagulation and flocculation in water contacting the soils, containing dissolved arsenic and fine particles of ferric arsenate-coprecipitated silicate. The first washing step using 0.2M HCl was mostly effective in increasing the cationic hydrolysis of amorphous ferrihydrite, inducing high removal of arsenic. Thus, the removal step of arsenic-containing flocs can lower arsenic extractions (KST methods) of washed soils. Among several washing trials, alternative sequential washing using 0.2M HCl followed by 1M HCl (second step) and 1M NaOH solution (third step) showed reliable and lower values of arsenic extractions (KST methods) of washed soils. This washing method can satisfy the arsenic regulation of washed soil for reuse or safe disposal application. The kinetic data of washing tests revealed that dissolved arsenic was easily readsorbed into remaining soils at a low pH. This result might have occurred due to dominant species of positively charged crystalline iron oxides characterized through the sequential extraction procedure. However, alkaline extraction using NaOH was effective in removing arsenic readsorbed onto the surface of crystalline minerals. This is because of the ligand displacement reaction of hydroxyl ions with arsenic species and high pH conditions that can prevent readsorption of arsenic.

Arsenic↗
PubMed2026

Urban soil multifunctionality and seasonal variability of carbon-linked soil traits.

Urban soils can play a significant role in climate change mitigation due to their capacity to store carbon (C) and support microbial biodiversity. In this context, this study evaluated the effects of different fertilization strategies on soil quality, greenhouse gas emissions, and microbial communities in two urban green areas located in the Campania region (Southern Italy) over a three-year period. Mineral fertilization (MIN), micronized vermicompost (CMP), micronized biochar (BCH), vermicompost plus biochar (CMP + BCH) were compared to an unfertilized control (CNT). The results showed that soil physicochemical properties were mainly influenced by site-specific conditions and temporal variability, whereas cation exchange capacity was the soil parameter most responsive to fertilization treatments. The QBS-ar index, used as an indicator of soil biological quality based on soil arthropods, was primarily affected by seasonality, with higher values recorded during spring-summer and no significant effects attributable to fertilization treatments. Vermicompost, BCH, and their combination were associated with lower net soil-vegetation CO2 fluxes and smaller temporal increases in the measured flux compared with the control and mineral fertilization treatments. All treatments exhibited a negative estimated annualized net C balance, indicating that, under the adopted temporal upscaling procedure, the estimated gaseous exchanges exceeded the annual increase in soil organic carbon stocks. Nevertheless, BCH showed the least negative estimated annualized balance. Analyses of microbial diversity revealed that bacterial and fungal communities were mainly shaped by temporal and seasonal factors, while fertilization treatments had limited effects on microbial diversity and community composition. Overall, the findings indicate that biochar showed the most favorable estimated carbon balance and the lowest measured net CO2 fluxes under the conditions investigated. However, its effects on soil biological and microbial properties were limited in the short term, and none of the tested treatments achieved net carbon sequestration. These results suggest that biochar may contribute to climate change mitigation as part of long-term, site-specific management strategies rather than as a standalone solution for improving soil multifunctionality.

Biochar↗
PubMed2005

The influence of soil characteristics on the extractability of Cd, Pb and Zn in upland and moorland soils.

A study was undertaken to investigate the feasibility of using existing data sets of total soil metal concentrations and soil parameters, such as pH, to predict available metal concentrations on a regional or national basis. The attraction of such an approach is that it would provide valuable data for initiatives requiring information on the availability and mobility of metals in soils without the need for costly soil sampling and analysis. Ninety-seven topsoil and subsoil samples were collected from 6 soil series in a catenary sequence in north Wales to provide data for the development of an empirical model. These were analysed for total, 0.01 M CaCl2-extractable and porewater metal concentrations and for a range of soil properties including pH, solid and dissolved organic matter and cation exchange capacity. Regression analysis showed that, of the soil parameters measured, pH was the most important predictor variable for the estimation of CaCl2-extractable Cd, Pb and Zn. pH accounted for up to 86% of the variance in the proportion of 'total' metals which were extracted by CaCl2, a reagent that is commonly used to estimate plant uptake of elements. However, the relationships recorded between soil parameters and Kd (total metal/porewater metal) were much weaker, indicating that porewater metal concentrations can less readily be predicted from total soil metal concentrations and soil properties.

Cadmium↗
PubMed2001

Changes in soil solution Zn and pH and uptake of Zn by arbuscular mycorrhizal red clover in Zn-contaminated soil.

Red clover plants inoculated with Glomus mosseae were grown in a sterile pasture soil containing 50 mg Zn kg(-1) in 'Plexiglas' (acrylic) containers with nylon net partitions (30 microm mesh) designed to separate the soil into a central root zone and two outer zones for hyphal growth with no root penetration. Two porous plastic soil moisture samplers were installed in each pot, one in the root compartment and the other in one of the hyphal compartments. The soil in the outer compartments was amended with one of the four application rates of Zn (as ZnSO4) ranging from 0 to 1000 mg kg(-1). Non-mycorrhizal controls were included, and there were five replicates of each treatment in a randomised block in a glasshouse. Uninoculated plants received supplementary P to avoid yield limitation due to low soil P status. Plants grew in the central compartment for nine weeks. Soil moisture samples were collected 4, 24 and 62 days after sowing to monitor changes in the Zn concentration and pH of the soil solution. At harvest, the mean mycorrhizal infection rate of inoculated plants ranged from 29% to 34% of total root length and was little affected by Zn application. Root and shoot yields were not affected by mycorrhizal infection. Plant Zn concentration and uptake were lower in mycorrhizal plants than non-mycorrhizal controls, and this effect was more pronounced with increasing Zn application rate to the soil. Soil solution Zn concentrations were lower and pH values were higher in mycorrhizal treatments than non-mycorrhizal controls and the mycorrhiza effect was more pronounced at higher Zn application rates. The protective effect of mycorrhiza against plant Zn uptake may have been associated with changes in Zn solubility mediated by changes in the soil solution pH, or by immobilisation of Zn in the extraradical mycelium.

Fabaceae↗
PubMed2003

Physicochemical soil parameters affecting sequestration and mycobacterial biodegradation of polycyclic aromatic hydrocarbons in soil.

Six soils, obtained from grasslands and wooded areas in Northeastern Illinois, were physicochemically characterized. Measured parameters included total organic carbon (TOC) content, contents of humic acid, fulvic acid and humin, pore volume and pore size distribution, and chemical makeup of soil organic matter (determined using solid-state 13C-NMR). Moistened, gamma-sterilized soils were spiked with 200 ppm of either phenanthrene or pyrene (including 14C label); following 0, 40, or 120 days of aging, the contaminant-spiked soils were then inoculated with Mycobacterium austroafricanum strain GTI-23, and evolution of 14CO2 was assessed over a 28-day period. Results for both phenanthrene and pyrene indicated that increased contact time led to increased sequestration and reduced biodegradation, and that TOC content was the most important parameter governing these processes. One soil, although only tested with phenanthrene, showed significantly lower-than-expected sequestration (higher-than-expected mineralization) after 40 days of aging, despite a very high TOC value (>24%). Because the level of sequestration in this soil was proportional to the others after 120 days of aging, this implies some difference in the temporal progression of sequestration in this soil, although not in its final result. The primary distinguishing feature of this soil was its considerably elevated fulvic acid content. Further experiments showed that addition of exogenous fulvic acid to a soil with very low endogenous humic acids/fulvic acids content greatly enhanced pyrene mineralization by M. austroafricanum. Extractabilities of 13 three- to six-ring coal tar PAHs in n-butanol from the six soils after 120 days of sequestration were strongly TOC-dependent; however, there was no discernible correlation between n-butanol extractability and mycobacterial PAH mineralization.

1-Butanol↗
PubMed2001

Ecotoxicity of zinc in spiked artificial soils versus contaminated field soils.

Metal bioavailability is influenced by soil characteristics and aging period. In the present study, both factors were modeled by comparing metal bioavailability in spiked artificial soil and historically contaminated field soils. The chronic toxicity of zinc to Folsomia candida in spiked artificial soils could be predicted with a model based on pH, cation exchange capacity, and total zinc concentration. However, this model could not adequately predict chronic zinc toxicity in contaminated field soils. Porewater concentration and water- and calcium chloride-extracted zinc fractions of the contaminated field soils were lower than those predicted using models developed for spiked artificial soils, indicating that the effect of aging on metal bioavailability should be taken into account. The reproduction of F. candida in contaminated field soils was lower than predicted with models developed using zinc concentration in the porewater and the water- and calcium chloride-extracted fractions in spiked artificial soils. This suggests that these fractions are not the only bioavailable zinc fractions and that dietary metal exposure might also be an important route of uptake under environmentally relevant conditions. Aging and dietary uptake should be studied urgently in order to be able to perform effect-based risk assessments of metal contaminated soils.

Animals↗
PubMed2001

Microcosm enrichment of 1,3-dichloropropene-degrading soil microbial communities in a compost-amended soil.

AIMS: A microcosm-enrichment approach was used to investigate bacterial populations that may represent 1,3-dichloropropene (1,3-D)-degrading micro-organisms in compost-amended soil. METHODS AND RESULTS: After 8 weeks of incubation, with repeated application of 1,3-D, volatilization fluxes were much lower for compost-amended soil (CM) than with the unamended soils, indicating accelerated degradation due to addition of compost, or development of new microbial populations with enhanced degradation capacity. Denaturing gradient gel electrophoresis (DGGE) profiles of the PCR-amplified region of 16S rDNA genes were used to identify dominant bacterial populations in the fumigant-degrading soil. The DGGE results indicated that specific bacterial types had been enriched, and a more diverse fingerprint was observed in the community derived from the compost-amended soil compared with the unamended soil. Fragments from 16 different DGGE bands were cloned, sequenced and compared with published 16S rDNA sequences. Two clones, designated E1 and E4, were unique to all soils to which compost was added, and corresponded to strains of Pseudomonas and Actinomadura, respectively. CONCLUSIONS: The results show that the addition of compost to soil increases specific microbial populations and results in the accelerated degradation of fumigants. SIGNIFICANCE AND IMPACT OF THE STUDY: Application of compost manure to soil can help degrade soil fumigants at a faster rate.

Allyl Compounds↗
PubMed2003

Extractable soil lipids and microbial activity as affected by Bt and non Bt maize grown on a silty clay loam soil.

Pyrolysis-gas (Py-GC) chromatography was used to characterize extractable lipids from Bt and non-Bt maize shoots and soils collected at time of harvesting. Py-GC-MS (mass spectrometry) showed that the concentrations of total alkenes identified in non-Bt shoots and soils were 47.9 and 21.3% higher than in Bt maize shoots and soils, respectively. N-alkanes identified were of similar orders of magnitude in Bt and non-Bt maize shoots, but were 28.6% higher in Bt than in non-Bt soils. Bt maize shoots contained 29.7% more n-fatty acids than non-Bt maize shoots, whereas the concentrations of n-fatty acids in Bt soils were twice as high as those in non-Bt soils. Concentrations of unsaturated fatty acids in Bt maize shoots were 22.1% higher than those in non-Bt maize shoots, while concentrations of unsaturated fatty acids were 22.5% higher in non-Bt than in Bt soils. The cumulative CO2-C evolved from soils under Bt and non-Bt crops was 30.5% lower under Bt as compared to non-Bt crops, whereas when maize shoots were added to Bt and non-Bt soils, the decrease in CO2-C evolved were 16.5 and 23.6%, respectively. Our data showed that the cultivation of Bt maize significantly increased the saturated to unsaturated lipid ratios in soils which appeared to negatively affect microbial activity.

Bacillus thuringiensis↗