| 1. |
- Aira, Manuel, et al.
(författare)
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Plant genotype strongly modifies the structure and growth of maize rhizosphere microbial communities
- 2010
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 42:12, s. 2276-2281
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Tidskriftsartikel (refereegranskat)abstract
- We studied the microbial communities in maize (Zea mays) rhizosphere to determine the extent to which their structure, biomass, activity and growth were influenced by plant genotype (su1 and sh2 genes) and the addition of standard and high doses of different types of fertilizer (inorganic, raw manure and vermicompost). For this purpose, we sampled the rhizosphere of maize plants at harvest, and analyzed the microbial community structure (PLFA analysis) and activity (basal respiration and bacterial and fungal growth rates). Discriminant analysis clearly differentiated rhizosphere microbial communities in relation to plant genotype. Although microorganisms clearly responded to dose of fertilization, the three fertilizers also contributed to differentiate rhizosphere microbial communities. Moreover, larger plants did not promoted higher biomass or microbial growth rates suggesting complex interactions between plants and fertilizers, probably as a result of the different performance of plant genotypes within fertilizer treatments, i.e. differences in the quality and/or composition of root exudates. (c) 2010 Elsevier Ltd. All rights reserved.
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| 2. |
- Akerblom, Staffan, et al.
(författare)
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Experimentally induced effects of heavy metal on microbial activity and community structure of forest mor layers
- 2007
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Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 44:1, s. 79-91
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Tidskriftsartikel (refereegranskat)abstract
- This study compared the toxic effects of adding chromium (Cr), zinc (Zn), lead (Pb), molybdenum (Mo), nickel (Ni), and cadmium (Cd) at three dose levels to mor layer samples in laboratory experiments. Microbial activity in the form of soil respiration was monitored for 64 days. At the end of the experimental period, the composition of the soil microbial community structure was analysed by phospholipid fatty acid (PLFA) analysis. The metals added induced changes in the microbial community structure and affected respiration negatively, indicating toxicity. The microbial community structure (principal component analysis of the PLFA pattern) for all metals was significantly related to microbial activity (cumulative respiration), indicating intimate links between microbial community structure and activity. The most striking result in this study was that the shift in the microbial community because of metal stress was similar for all metals. Thus, the PLFA i16:0 increased most in relative abundance in metal-polluted soils, followed by other PLFAs indicative of Gram-positive bacteria (10Me16:0, 10Me17:0, 10Me18:0, a17:0 and br18:0). The PLFA 16:1 omega 5 was consistently negatively affected by metal stress, as were the PLFAs 18:1, 18:1 omega 7 and 19:1a. However, a significant separation between Cr- and Cd-polluted soils was observed in the response of the PLFA cy19:0, which decreased in abundance with Cr stress, and increased with Cd stress. Furthermore, the PLFA 18:2w6, indicating fungi, only increased with Cr and Zn stress. The effective doses of the metals, ranked with regard to background metal concentrations, decreased in the order: Zn > Cr > Pb > Mo > Ni > Cd. We concluded that interpretation of results of microbial activity from experiments of metal toxicity should include microbial structural patterns and background metal concentrations.
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| 3. |
- Aldén, Louise, et al.
(författare)
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Effects of sulfamethoxazole on soil microbial communities after adding substrate
- 2009
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 41:4, s. 840-848
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the antibiotic sulfamethoxazole (SMX) on soil bacteria was studied using two methods (leucine incorporation and Biolog plates) of estimating pollution-induced community tolerance (PICT). SMX was added to an agricultural soil in a microcosm setup. The addition of different substrates (manure and alfalfa), and a non-amended soil, were also studied over 5 weeks. PICT measurements were validated by comparison with other measurements. Community structure was assessed using phospholipid fatty acid (PLFA) analysis and community-level physiological profiling (CLPP), and bacterial growth was estimated using leucine incorporation. Increased PICT was found at SMX concentrations of 20 and 500 mg SMX kg(-1) soil in samples containing manure and alfalfa, and at 500 mg SMX kg(-1) soil in non-amended soil (only concentration tested) using leucine incorporation. No effect was seen at 1 mg SMX kg(-1) soil. It was not necessary to add any substrate to increase the microbial activity in order to detect the effects of a bacteriostatic toxicant such as SMX when using measures based on bacterial growth. Direct inhibition of bacterial growth 2 days after SMX addition was correlated to PICT. No major changes in PICT due to SMX addition were found when using Biolog plates. However, there was a tendency towards increased PICT at the higher SMX concentrations in the manure-amended soil. Thus, different methods of detecting PICT have different sensitivities in detecting the toxic effects of SMX The effects of substrate amendment were reflected by changes in the microbial community, estimated using both PLEA and CLPP SMX was found to have a clear effect at the two highest levels of SMX in the manure- and alfalfa-amended soils, with an increase in fungal and a decrease in bacterial PLFAs. Little difference in the PLFA composition was found in the non-amended soil. CLPP was only affected at the highest SMX concentration. Although different variables showed different sensitivities to the effects of SMX, the results were consistent with an initial decrease in bacterial growth rates of sensitive species, which eventually transformed into more tolerant species, altering the community composition. (C) 2009 Elsevier Ltd. All rights reserved.
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| 4. |
- Aldén, Louise, et al.
(författare)
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No long-term persistence of bacterial pollution-induced community tolerance in tylosin-polluted soil
- 2008
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 1520-5851 .- 0013-936X. ; 42:18, s. 6917-6921
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Tidskriftsartikel (refereegranskat)abstract
- Pollution-induced community tolerance (PICT) of soil bacteria to the antibiotic tylosin was studied over 95 days. Tylosin was added at increasing concentrations, together with different amounts of alfalfa to study the effects of substrate addition on PICT and bacterial growth in soil. The leucine incorporation technique was used to estimate bacterial growth and as a detection method in the PICT concept. Direct inhibition of the bacterial growth rates, resulting in a dose-response curve, was found above 50 mg of tylosin kg(-1) of soil two days after tylosin addition (IC50 value of 960 mg tylosin kg(-1)). After 10 days of exposure to at least 50 mg of tylosin kg(-1), the PICT was observed and correlated to inhibition of bacterial growth by tylosin. A return of the PICT to control levels was found over time, and after 95 days at 1500 mg of tylosin kg(-1), essentially no PICT was found, as compared to the unpolluted control soil. The return of PICT to pre-exposure levels was not totally reflected in the recovery of bacterial growth. Alfalfa addition did not affect the inhibitory effect of tylosin on bacterial growth rates; neither did it alter the PICT. Since tylosin is relatively rapidly degraded in soil, our results indicate that the PICT will return to prepollution levels when the selective pressure of the toxicant is removed and will thus be a useful technique for monitoring remediation measures.
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| 5. |
- Aldén, Louise, et al.
(författare)
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Rapid method of determining factors limiting bacterial growth in soil
- 2001
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 67:4, s. 1830-1838
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Tidskriftsartikel (refereegranskat)abstract
- A technique to determine which nutrients limit bacterial growth in soil was developed. The method was based on measuring the thymidine incorporation rate of bacteria after the addition of C, N, and P in different combinations to soil samples. First, the thymidine incorporation method was tested in two different soils: an agricultural soil and a forest humus soil. Carbon (as glucose) was found to be the limiting substance for bacterial growth in both of these soils. The effect of adding different amounts of nutrients was studied, and tests were performed to determine whether the additions affected the soil pH and subsequent bacterial activity. The incubation time required to detect bacterial growth after adding substrate to the soil was also evaluated. Second, the method was used in experiments in which three different size fractions of straw (1 to 2, 0.25 to 1, and <0.25 mm) were mixed into the agricultural soil in order to induce N limitation for bacterial growth. When the straw fraction was small enough (<0.25 mm), N became the limiting nutrient for bacterial growth after about 3 weeks. After the addition of the larger straw fractions (1 to 2 and 0.25 to 1 mm), the soil bacteria were C limited throughout the incubation period (10 weeks), although an increase in the thymidine incorporation rate after the addition of C and N together compared with adding them separately was seen in the sample containing the size fraction from 0.25 to 1 mm. Third, soils from high-pH, limestone-rich areas were examined. P limitation was observed in one of these soils, while tendencies toward P limitation were seen in some of the other soils.
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| 6. |
- Aldén, Louise, et al.
(författare)
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The use of leucine incorporation to determine the toxicity of phenols to bacterial communities extracted from soil
- 2008
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Ingår i: Applied Soil Ecology. - : Elsevier BV. - 0929-1393. ; 38:1, s. 34-41
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Tidskriftsartikel (refereegranskat)abstract
- The toxicity of different phenols to the soil bacterial community was studied in the laboratory using the leucine incorporation technique. The effects of environmental factors such as pH, temperature and binding strength to soil particles were also assessed in order to deduce confounding effects due to the chemical and physical conditions in the soil from which the bacterial community was extracted. Bacterial growth varied with temperature and pH, the optima being at around 33 degrees C and pH 7 in a soil with a natural pH of 7. The toxicity of different phenols varied less than bacterial growth as a function of temperature and pH, but the toxicity of 2,3,6-trichlorophenol increased at lower temperatures and pH. The pH affected the toxicity in the same way in soils with naturally different pH values and when the pH was changed using buffers, showing that this was a direct effect of pH and was not due to different communities in different soils. The degree to which the bacteria were bound to soil particles had no effect on the toxicity of phenols. Neither did freezing nor thawing the soil have any effect on toxicity, although the bacterial growth was lower in frozen soil than in non-frozen soil. Increasing numbers of substitutes on the phenols increased their toxicity to soil bacteria, and chlorine substitutes were more toxic than the corresponding methyl substitutes. The toxicity of the phenols studied to the whole soil bacterial community was correlated with literature data on the toxicity to the single species Pseudomonas putida. Applying the leucine incorporation technique to the bacterial community extracted from soil was shown to be a rapid and sensitive method of estimating toxicity. The methodology also allowed differentiation between the effects of environmental factors on toxicity to the soil bacterial community and changes in the tolerance of the community. Thus, the development of pollution-induced community tolerance in phenol- and 2-chlorophenol-polluted soils could be shown. (c) 2007 Elsevier B.V. All rights reserved.
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| 7. |
- Aldén, Louise, et al.
(författare)
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Use of pollution-induced community tolerance of the bacterial community to detect phenol toxicity in soil.
- 2008
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Ingår i: Environmental Toxicology and Chemistry. - 0730-7268. ; 27:2, s. 334-340
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Tidskriftsartikel (refereegranskat)abstract
- Pollution-induced community tolerance (PICT) was used to study effects of phenol on soil bacteria. Phenol was added to an agricultural soil in a microcosm experiment. The effects were studied for up to four months. Bacterial growth rates were estimated with the leucine incorporation technique. This technique was also used as detection method for PICT. Changes in community structure were studied using the phospholipid fatty acid (PLFA) pattern. Increased phenol PICT of the bacterial community was found at phenol concentrations above 1 micromol/g wet weight soil. Direct inhibiting effect on bacterial growth rates 1 d after adding phenol was correlated to PICT. Phenol toxicity was reflected by changes in the structure of the bacterial community, although PICT appeared more sensitive than the PLFA method. In soil amended with 1 to 10 micromol phenol/g soil, bacterial growth recovered within one week. In the soil amended with the highest phenol concentration (30 micromol/g soil), bacterial growth rate recovered from total inhibition after 27 d, eventually reaching values six times higher than in the control. However, PICT did not change during the four months the experiment was performed. The specificity of PICT was also studied by examining cotolerance to 2-chlorophenol, 2,4-dichlorophenol, 2,3,6-trichlorophenol, Cu, and Zn. Adding phenol induced cotolerance of the bacterial community to the other phenols, although always at a lover level than to phenol. No cotolerance was found to metals in phenol-polluted soil. We conclude that the PICT concept is a valuable tool in determining phenol toxicity to bacterial communities, especially in situations where bacterial growth has recovered. Cotolerance between different phenols can, however, make interpretations of PICT more complicated.
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| 8. |
- Andréasson, Frida, et al.
(författare)
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Bioavailability of DOC in leachates, soil matrix solutions and soil water extracts from beech forest floors
- 2009
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 41:8, s. 1652-1658
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Tidskriftsartikel (refereegranskat)abstract
- The biodegradability of dissolved organic carbon (DOC) in different fractions from the forest floor was studied. Soil leachate (SI, the soil solution in macropores which is freely drained from forest floor after rainfall), the soil matrix solution (SMS, the soil solution in meso-/micropores of the soil matrix), and soil water extracts (SWE) from two different beech forest floors were compared. Zero-tension and tension lysimeters were used to collect SL and SMS, respectively. Loss of DOC (during 21 days) and respiration of CO2-C (during 7 days) were used as conventional measures of the availability of DOC. Bacterial production, measured using the leucine incorporation technique, and bacterial growth efficiency were also estimated. All methods were used to study differences in biodegradability between plots with and without ground flora (Deschampsia flexuosa or Anemone nemorosa) and different type of forest floor (with an organic (O) horizon or a mull (A) horizon). There were no differences in bioavailability of DOC from soil solutions extracted from plots with and without ground flora. The bioavailability of DOC in the different collected soil solutions varied, however. DOC in SWE was the most available, with a mean of 39% of DOC-loss in 21 days, and 18% of DOC being respired in 7 days. DOC in soil matrix solution was the least available of the soil solutions (7% respired), significantly less than DOC in soil leachate (11% respired). The methods measuring biodegradation of DOC, DOC-loss and CO2-C respiration gave similar results and were comparable to bacterial production and bacterial growth efficiency, with the exception of SWE from the O-horizon at the a flexuosa site, which had low bacterial production and bacterial growth efficiency, indicating a limitation of the bacterial growth. This study is one of the first to use bacterial production and bacterial growth efficiency for measuring bioavailability in terrestrial environments, giving an extra dimension for the process of biodegradation of DOC. (C) 2009 Elsevier Ltd. All rights reserved.
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| 9. |
- Arnebrant, Kristina, et al.
(författare)
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Changes in microfungal community structure after fertilization of Scots pine forest soil with ammonium-nitrate or urea
- 1990
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 22:3, s. 309-312
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Tidskriftsartikel (refereegranskat)abstract
- The microfungal population structure of two Scots pine forest soils in Southern Sweden was studied 8–13 yr after nitrogen fertilization. The different fertilizers used. ammonium nitrate and urea. influenced the species composition in different ways. The main effect of the NH4NO3 treatment was an increased isolation frequency of Penicillium spinulosum and 4Oidiodendron echinulatum, while Penicillium cf. brevi-compactum. Mortierella subgenus Mortierella. Chaunopycnis alba and Oidiodendron griseum were isolated less frequently in ammonium nitrate-amended treatments compared to the non-fertilized control. In the urea-fertilized plots the isolation frequency of P. cf. brevi-compactum increased, while that of C. alba. O. echinulatum, O. griseum and P. spinulosum decreased in comparison with control plots. The changes in species composition were most evident at the highest rate of application, 600 kg N ha−1, especially when NH4NO3 was used as a fertilizer.
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| 10. |
- Arnebrant, Kristina, et al.
(författare)
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Copper Tolerance of Microfungi Isolated from Polluted and Unpolluted Forest Soil
- 1987
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Ingår i: Mycologia. - : Informa UK Limited. - 0027-5514. ; 79:6, s. 890-895
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Tidskriftsartikel (refereegranskat)abstract
- Microfungi were isolated from unpolluted and copper polluted forest soils and their tolerance was tested on agar plates. Species from polluted sites were usually tolerant to Cu. The species were Paecilomyces farinosus, Beauveria bassiana, Verticillium spp. and Penicillium pactum. Sensitive species were found among Mortierella, Oidiodendron and Penicillium. usually rare in polluted sites. Little evidence for adaptation to Cu was found among isolates with short or long history of pollution.
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