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1.
The incorporation of [14C]-leucine into protein by soil organisms was measured both in soil slurries and for bacteria extracted from soil by homogenization-centrifugation. The result was compared with thymidine incorporation. Using a soil slurry, 9.1×10-10 mol leucine h-1g-1 dry weight of soil was incorporated into protein, with a calculated leucine: thymidine ratio (mol:mol) of about 34. Non-specific labelling of macromolecules other than protein was observed with both the soil slurry and the homogenization-centrifugation method. With the latter, 46.5% of the total incorporation was found in the protein fraction (hot-acid insoluble). The incorporation of leucine was linear with time for at least 4 h for extracted bacteria. Even at 2000 nM, [14C]-leucine did not saturate incorporation into protein. Isotope dilution plots indicated that with 750 nM leucine, the degree of participation of the labelled substance in protein synthesis was 0.59. With this value, the ratio of leucine:thymidine incorporation into total macromolecules was calculated as 41 for extracted bacteria. On the basis of incorporation into protein (leucine) and incorporation into DNA (thymidine) only, the leucine:thymidine ratio was calculated as 117. The mean turnover time of bacteria at 22°C, calculated using conversion factors from published studies and leucine incorporation into protein of extracted bacteria, was 4.3 days.  相似文献   

2.
The effect of nitrogen addition on the activity of rhizosphere bacteria was studied using barley seedlings. Three different nitrogen sources were added to the soil (nitrate, ammonium and ammonium+nitrate) at four different concentrations (0, 100, 300 and 500 mg N kg−1 soil) and the plants were allowed to grow for 6 weeks. The bacterial activity was estimated by measuring thymidine and leucine incorporation into bacteria extracted using homogenisation-centrifugation. Bulk soil bacterial activity was low compared with that of rhizosphere bacteria. Nitrogen addition did not affect the activity of the bulk soil bacteria, indicating that the activity was not nitrogen limited. The thymidine and leucine incorporation rates of rhizosphere bacteria decreased when ammonium or ammonium+nitrate was applied compared with the non-amended controls. No effect on bacterial activity was found following nitrate addition. There was a significant positive correlation between rhizosphere bacterial activity and rhizosphere pH. Shoot length following ammonium treatment was significant lower than in the non-amended control, while nitrate and ammonium+nitrate addition had no effect. This indicates that the varying effects due to nitrogen sources on rhizosphere bacterial activity were not due to effects on plant growth.  相似文献   

3.
The effects of temperature on the growth rate and metal toxicity in soil bacterial communities extracted from unpolluted and polluted soils were investigated using the thymidine and leucine incorporation techniques. An agricultural soil, which was contaminated in the laboratory with Cu, Cd, Zn, Ni or Pb, and an uncontaminated forest soil were used. Measurements were made at 0°C and 20°C. Leucine incorporation was found to be as sensitive to heavy metals as thymidine incorporation in the short-term trial used to indicate heavy metal tolerance. Similar IC50 values (the log of the metal concentration that reduced incorporation to 50%) were also obtained at 0 and 20°C, independently of the technique used. Metal tolerance could thus be measured using both techniques at any temperature in the range 0–20°C. In the long-term experiment different temperature-growth relationships were obtained on the basis of the rate of thymidine or leucine incorporation into bacterial assemblages from unpolluted and polluted soils, as judged from the minimum temperature values. This could not be attributed to the metal addition alone since different patterns were observed when different metals were added to the soil. Thus, the minimum temperature for thymidine incorporation was similar in Cu-polluted and unpolluted soil, while in soils polluted with Cd and Zn the minimum temperature increased by 2°C, and Ni and Pb additions increased the minimum temperature by 4°C compared to the unpolluted soil. This suggested that heavy metal pollution led to bacterial communities showing different temperature characteristics to those in the corresponding unpolluted soil. Similar observations were deduced from the minimum temperatures required for leucine incorporation. Three groups of bacterial communities were distinguished according to the growth response to temperature in polluted soils, one group in Cu-polluted soil, a second group in soil polluted with Zn and Cd, and a third group in soils polluted with Ni and Pb.  相似文献   

4.
The effect of adding easily available and more complex carbon sources, with and without nitrogen, on fungal and bacterial growth and activity in soil were studied in the laboratory. Total microbial activity was estimated by measuring respiration, fungal growth with the acetate-in-ergosterol incorporation technique and bacterial growth with the thymidine and leucine incorporation techniques. The substrate additions consisted of glucose and cellulose, with and without nitrogen (as ammonium nitrate), and gelatine. The microbial development was followed over a 2-month period. The respiration rate increased within a few days after adding glucose, with and without nitrogen, and gelatine, initially by more than 10 times, but after 2 months no differences were seen compared with the control. Bacterial growth estimated with the thymidine and leucine incorporation techniques gave similar results. Adding glucose with nitrogen, or gelatine, increased bacterial growth within a few days up to 10 times, but even after 2 months of incubation bacterial growth rates were still about 5 times higher than in the control. Adding only glucose increased bacterial growth rates by about twice over the whole incubation period. Fungal growth rates especially increased after adding cellulose and nitrogen, although a minor increase was found after adding cellulose alone. Fungal growth rates started to increase after 10 days of incubation with cellulose. There were indications of synergistic effects in that bacterial growth increased after the fungi had started to grow after adding cellulose. Treatments resulting in high bacterial growth rates (adding easily available carbon sources) led to decreased fungal growth rates compared with the control, indicating antagonistic effects of bacteria.  相似文献   

5.
Pollution induced community tolerance (PICT) has been suggested as an end-point measurement less affected by confounding environmental factors compared to standard methods of microbial growth, activity and community composition. We evaluated the use of PICT to determine Cu toxicity in vineyard soils polluted with Cu based fungicides (25-1120 mg Cu kg−1). These soils also varied in pH (4.3-7.3), organic C (0.31-6.91%) and texture (14-56% silt). PICT was estimated as bacterial community tolerance to Cu measured by the [3H]leucine incorporation method. Bacterial tolerance to Cu increased 9 times in the most polluted compared to the unpolluted soils. Cu tolerance was also affected to a minor degree by pH, organic C and soil texture. Lower bacterial tolerance was found in soils with high pH and organic C, probably due to Cu becoming less bioavailable in soils with high pH and organic C content. The silt content appeared to increase bacterial tolerance, probably due to fine soil particles decreasing Cu bioavailability during the PICT detection phase. Despite the effects of other environmental factors, the main determinant of increased bacterial community tolerance to Cu was the pollution level. PICT measured with the leucine incorporation technique thus appears to be a sensitive and stable concept to evaluate toxic impacts, unless soils with very different pH, organic C or texture are studied.  相似文献   

6.
Lack of carbon has been assumed to be the most common limiting factor for bacterial growth in soil, although there are reports of limitation by other nutrients, e.g. nitrogen and phosphorus. We have studied which nutrient(s) limited instantaneous growth rates of bacteria in 28 Swedish soils using the thymidine or leucine incorporation technique to measure increased growth rate after adding different combinations of organic carbon (glucose), nitrogen and phosphorus. The soils ranged in pH between 3.1 and 8.9, in organic matter content between 1% and 91% and in soil C/N ratio between 10 and 28. We also tested the effect of adding different amounts of carbon on the bacterial change in growth rate for two soils with different organic matter content. We found that bacterial growth in most of the 28 soils was limited by a lack of carbon, indicated by an increased bacterial growth rate 48 h after adding glucose. In some soils, adding carbon together with nitrogen increased the bacterial growth rates even further. In three soils no effects were seen upon adding nutrients separately, but adding carbon and nitrogen together increased bacterial growth rates. Nitrogen addition tended to decrease bacterial growth rates, while phosphorus addition had little effect in most soils. No correlations were found between the soil C/N ratio, ammonium or nitrate content in soil and bacterial growth limitation, indicating that even soils with a C/N ratio of 28 could be carbon limited. Although the interpretation of the effects of a single limiting nutrient was in most cases straightforward, an interaction between the amount of carbon added and the organic matter content of the soil confounded the interpretation of the extent of a second limiting nutrient.  相似文献   

7.
Resource availability and limiting factors for bacterial growth during early stages of soil development (8-138 years) were studied along a chronosequence from the glacial forefield of the Damma glacier in the Swiss Alps. We determined bacterial growth (leucine incorporation) and we investigated which resource (C, N or P) limited bacterial growth in soils formed by the retreating glacier. The latter was determined by adding labile sources of C (glucose), N and P to soil samples and then measuring the bacterial growth response after a 40 h incubation period. Bacterial growth increased with increasing soil age in parallel with the build up of organic matter. However, lower bacterial growth, when standardized to the amount of organic C, was found with time since the glacier retreat, indicating decreasing availability of soil organic matter with soil age. Bacterial growth in older soils was limited by the lack of C. The bacteria were never found to be limited by only N, only P, or N + P. In the youngest soils, however, neither the addition of C, N nor P singly increased bacterial growth, while a combination of C and N did. Bacterial growth was relatively more limited by lack of N than P when the C limitation was alleviated, suggesting that N was the secondary limiting resource. The availability of N for bacterial growth increased with time, as seen by an increased bacterial growth response after adding only C in older soils. This study demonstrated that bacterial growth measurements can be used not only to indicate direct growth effects, but also as a rapid method to indicate changes in bacterial availability of nutrients during soil development.  相似文献   

8.
One of the most influential factors determining the growth and composition of soil bacterial communities is pH. However, soil pH is often correlated with many other factors, including nutrient availability and plant community, and causality among factors is not easily determined. If soil pH is directly influencing the bacterial community, this must lead to a bacterial community growth optimised for the in situ pH. Using one set of Iberian soils (46 soils covering pH 4.2-7.3) and one set of UK grassland soils (16 soils covering pH 3.3-7.5) we measured the pH-optima for the growth of bacterial communities. Bacterial growth was estimated by the leucine incorporation method. The pH-optima for bacterial growth were positively correlated with soil pH, demonstrating its direct influence on the soil bacterial community. We found that the pH from a water extraction better matched the bacterial growth optimum compared with salt extractions of soil. Furthermore, we also showed a more subtle pattern between bacterial pH growth optima and soil pH. While closely matched at neutral pHs, pH-optima became higher than the in situ pH in more acid soils, resulting in a difference of about one pH-unit at the low-pH end. We propose that an explanation for the pattern is an interaction between increasing overall bacterial growth with higher pHs and the unimodal pH-response for growth of bacterial communities.  相似文献   

9.
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10.
《Applied soil ecology》2003,22(1):15-28
The effects of two Bacillus strains (Bacillus pumillus and B. licheniformis) on Medicago sativa plants were determined in single or dual inoculation with three arbuscular-mycorrhizal (AM) fungi and compared to P-fertilization. Shoot and root plant biomass, values of thymidine and leucine incorporation as well as ergosterol and chitin in rhizosphere soil were evaluated to estimate metabolic activity and fungal biomass, respectively, according to inoculation treatments. For most of the plant parameters determined, the effectiveness of AM fungal species was influenced by the bacterial strain associated. Dual inoculation of Bacillus spp. and AM fungi did not always significantly increase shoot biomass compared to single AM-colonized plants. The most efficient treatment in terms of dry matter production was the dual Glomus deserticola plus B. pumillus inoculation, which produced similar shoot biomass and longer roots than P-fertilization and a 715% (shoot) and 190% (root length) increase over uninoculated control. The mycorrhizas were more important for N use-efficiency than for P use-efficiency, which suggests a direct mycorrhizal effect on N nutrition not mediated by P uptake. Both chemical and biological treatments affected thymidine and leucine incorporation in the rhizosphere soil differently. Thymidine was greater in inoculated than in control rhizospheres and B. licheniformis was more effective than B. pumillus in increasing thymidine. Non-inoculated rhizospheres showed the lowest thymidine and leucine values, which shows that indigenous rhizosphere bacteria increased with introduced inocula. The highest thymidine and leucine values found in P-fertilized soils indicate that AM plants are better adapted to compete with saprophytic soil bacteria for nutrients than P-amended plants. Chitin was only increased by coinoculation of B. licheniformis and G. intraradices. B. pumillus increased ergosterol (indicative of active saprophyte fungal populations) in the rhizosphere of AM plants and particularly when colonized by G. mosseae. The different AM fungi have different effects on bacterial and/or fungal saprophytic populations and for each AM fungus, this effect was specifically stimulated or reduced by the same bacterium. This is an indication of ecological compatibilities between microorganisms. Particular Glomus–bacterium interactions (in terms of effect on plant growth responses or rhizosphere population) do not seem to be related to the percentage of AM colonization. The effect on plant growth and stimulation of rhizosphere populations, as a consequence of selected microbial groups, may be decisive for the plant establishment under limiting soil conditions.  相似文献   

11.
Abstract

With the aim of understanding how diverse bacteria are distributed within a heterogeneous soil, we compared local bacterial communities on individual soil particles. We picked up 11 coarse sand-sized particles (quartz, whitish feldspar, yellow feldspar or unidentified brown particles) from a sandy soil, extracted DNA from each particle, and carried out partial 16S rDNA polymerase chain reaction denaturing gradient gel electrophoresis analysis. Bacterial communities located on soil particles of the same type were more similar in composition than communities located on particles of the other types. Thus, the local structure of a bacterial community is related to the type of soil particle, which suggests that a high diversity of soil bacteria emerges through a combination of local bacterial communities on different types of soil particles.  相似文献   

12.
The biodegradation of polyaromatic hydrocarbons (PAHs) has been well documented; however, the biodegradation of PAHs in contaminated soil has proved to be problematic. Sorption of PAHs to soil over time can significantly decrease their availability for extraction much less than for biodegradation. In this study the ability of various organic solvents to extract PAHs from coal tar-contaminated soil obtained from former manufactured gas plant (MGP) sites was investigated. Solvents investigated included acetone/hexane, dichloromethane, ethanol, methanol, toluene, and water. The extraction of MGP soils with solvents was investigated using soxhlet extraction, multiple soxhlet extractions, sonication, and brief agitation at ambient temperature with a range of solvent concentrations. Of particular interest was the documentation of the recalcitrance of PAHs in weathered MGP soils to extraction and to bioremediation, as well as to demonstrate the ease with which PAHs extracted from these soils can be biodegraded. The efficiency of extraction of PAHs from MGP soils was found to be more dependent upon the choice of solvent. The environmentally-benign solvent ethanol, was shown to be equal to if not better than acetone/hexane (the EPA recommended solvent) for the extraction of PAHs from MGP soils, brief contact/agitation times (minutes) using small quantities of ethanol (2 volumes or less) can achieve nearly quantitative extraction of PAHs from MGP soils. Moreover aqueous slurries of an MGP soils experienced less than 10% biodegradation of PAHs in 14 days while in the same period about 95% biodegradation was acieved using PAHs extracted from this soil by ethanol and subsequently added to aqueous bacterial suspensions.  相似文献   

13.
中国长江三角洲地区一新石器时代水稻土细菌群落   总被引：1，自引：0，他引：1  
An ancient irrigated paddy soil from the Neolithic age was excavated at Chuodunshan Site in the Yangtze River Delta, close to Suzhou, China. The soil organic matter (SOM) content in the prehistoric rice soil is comparable to the average SOM content of present rice soils in this region, but it is about 5 times higher than that in the parent materials. As possible biomarkers to indicate the presence of the prehistoric paddy soil, the bacterial communities were investigated using the techniques of aerobic and anaerobic oligotrophic bacteria enumeration, Biolog analysis, and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). The results showed that in the buried soil layers, the prehistoric paddy soil had the largest number of aerobic and anaerobic oligotrophic bacteria, up to 6.12 and 5.86 log cfu g-1 dry soil, respectively. The prehistoric paddy soil displayed better carbon utilization potential and higher functional diversity compared to the parent materials and a prehistoric loess layer. The Shannon index and richness based on DGGE profiles of bacterial 16S rRNA genes were higher in prehistoric paddy soil than those in the prehistoric loess soil. It might be concluded that the prehistoric irrigated rice cultivation accumulated the SOM in plowed soil layer, and thus increased soil bacterial populations, metabolic activity, functional diversity and genetic diversity. Bacterial communities might be considered as the sensitive indicators of the presence of the prehistoric paddy soil in China’s Yangtze River Delta.  相似文献   

14.
Nitrification occurs slowly in many acid Scots pine forest soils. We examined if bacterial community structure and interactions between members of the bacterial community in these forest soils prohibit growth of ammonia-oxidising microorganisms and their nitrifying activity. Native and gamma-irradiated Scots pine forest soils known to have low net nitrification rates were augmented with fresh soils or soil slurries from nitrifying Scots pine forest soil, and vice versa. Augmentation of native non-nitrifying soils with nitrifying soils induced net nitrification, although no significant changes in bacterial community structure, as measured by 16S rRNA gene-based denaturing gradient gel electrophoresis (DGGE), were observed. In sterilised soils, the inoculum, i.e. native nitrifying soil or non-nitrifying soil, determined the occurrence of net nitrification and bacterial community structure, and not the origin of the sterilised soils. Our results demonstrate that low net nitrification rates in acid Scots pine forest soils cannot be (solely) explained by unfavourable abiotic soil conditions, but that still uncaptured biotic factors contribute to suppression of nitrification.  相似文献   

15.
The fate of [14C]-amitrole herbicide was studied in eight soils having different capacities for amitrole mineralisation. Laboratory incubations were run combining different experimental conditions: temperature (4, 28 and 50°C), soil moisture (50, 100 and 150% of soil water holding capacity) and microbial activity (sterile and non-sterile conditions). During incubation, samples of the soils were periodically extracted with 0.5 M NH4OH and extracts were analysed by HPLC. The lengths of time needed for 50% dissipation of amitrole (DT50) in soils ranged from less than 1 day to more than 70 days. Amitrole mineralisation occurred only in non-sterile soils, showing that it is a biological process. Mineralisation was lower in soils with a coarse texture than in soils with a fine texture. Soil water content had little influence on the total amount of amitrole mineralised at the end of incubation. Temperature had a greater influence on mineralisation, although rates were still high at low and high temperatures. In non-sterile as in sterile soils, the major product detected in the extracts was amitrole. Additional non-identified radioactivity was occasionally extracted. However, it never represented more than 10% of initially applied amitrole. Non-extractable residues represented less than 15% of applied radioactivity in acidic soils and about 30% of applied radioactivity in alkaline and neutral soils. The amount of non-extractable radioactivity formed was enhanced in sterile as compared to non-sterile soils. Furthermore, in sterile soils, high temperature induced an increase of non-extractable residues, showing that amitrole is chemically quite reactive.  相似文献   

16.
Phosphorus (P) limitation in the coming decades calls for the utilization of alternative fertilizers in agriculture. Struvite is a promising P source, but its potential role as a fertilizer is dependent on different physical, chemical, and biological properties, which are very heterogeneous in soil, complicating the prediction of the best soil conditions for its application. Here, we evaluated the solubility of struvite in soil, its redistribution into P fractions, and its potential abiotic and biotic drivers in 62 globally distributed soils with contrasting properties through an incubation assay. We found that after 40 d, about 35% of struvite P was redistributed into soil fractions more accessible to plants and microbes. Phosphorus redistribution from struvite was driven by a complex suite of soil physical, chemical, and microbial properties as well as environmental factors that varied across soils. Soil texture played a critical role in determining the redistribution of P in struvite-amended soils in soluble (H2O extraction), labile (NaHCO3 extraction), and moderately labile (NaOH extraction) fractions. In addition, the soil solution cation concentration was one of the most important drivers of available struvite-derived P fractions. The great importance of texture and cations in determining struvite-derived P fractions in soil was contrasted with the relatively minor role of pH. At the microbial level, the number of bacterial operational taxonomic units (OTUs) from the unfertilized soils that correlated with struvite-derived P fractions was higher than that of fungi. The number of OTUs that correlated with the struvite-derived soluble P fraction was dominated by fungi, whereas the number of OTUs that correlated with the struvite-derived labile P fraction was dominated by bacteria. Overall, this study provided a predictive framework for the potential use of struvite as a P fertilizer in contrasting soils.  相似文献   

17.
稻秸对土壤细菌群落分子多态性的影响   总被引：8，自引：0，他引：8       下载免费PDF全文
卜元卿  黄为一 《土壤学报》2005,42(2):270-277
模拟稻秸原位还田条件,分别在水稻土和红壤中添加水稻秸秆培养70d ,第0、5、2 5、4 5、70天采集土样。采用非机械破壁法直接提取水稻土和红壤细菌总DNA ,水稻土细菌总DNA经过二次纯化;红壤细菌总DNA经过一次纯化后,PCR扩增其16SrDNAV3可变区,均可获得清晰的目的条带,对扩增产物进行DGGE分析,结果显示:水稻土和红壤样品的DGGE条带增加,说明稻秸能够增加土壤细菌群落分子多态性的丰富度,随着培养期的延长,施有稻秸的处理中土壤细菌群落多态性的变化远远复杂于空白对照土壤中的细菌群落变化;同时发现在稻秸刺激下不同土壤细菌群落多态性高峰期出现时间不同  相似文献   

18.
The intensity of a fire is an important factor determining the recovery of soil microorganisms after a forest fire, since it can alter the quality and quantity of carbon sources. Recovery of the microbial community was studied in a Mediterranean pine forest soil subjected to different temperatures to simulate the short-term effects of fire intensity on bacterial and fungal growth, estimated using leucine incorporation for bacteria and acetate incorporation into ergosterol for fungi. Soil samples were heated for 15 min at 50, 80, 120, 200, 300, 400 and 500 °C. After inoculation with fresh soil, and adding water to achieve 60% WHC, the soils were incubated at 20 °C for 21 days. Bacterial growth was initially inhibited in the samples heated above 50 °C (totally inhibited ≥ 200 °C), but recovered within days to levels much higher than the control, except for the samples heated at 500 °C, where growth remained low throughout the incubation period due to the destruction of most of the organic matter. After the first week of incubation, the bacterial response decreased to values close to, but still above, that of the control. Samples heated at 200 °C showed the highest cumulative bacterial growth. Fungal growth was initially lower than in the control in all the heated samples (totally inhibited ≥ 200 °C). Fungal growth recovered slowly during incubation in soils heated at ≤ 300 °C, but the cumulative growth in heated soils did not exceed that in the control. No fungal growth was observed in samples heated at the two highest temperatures. Soil respiration was initially totally inhibited in soil heated at ≥ 200 °C, but recovered rapidly in all soils; the highest respiration being observed already 1 day after inoculation. This is the first time both fungal and bacterial growth has been directly estimated in heated soils. High soil pH favouring bacteria can explain these results, but the differences in fungal and bacterial responses suggest a competitive interaction between these groups.  相似文献   

19.
红壤坡地利用方式对土壤细菌群落结构的影响   总被引：5，自引：0，他引：5  
利用中国科学院桃源农业生态试验站坡地不同利用方式长期定位观测试验场农田、自然恢复和茶园土壤为研究对象,直接从土壤中抽提总DNA,应用T-RFLP和RT-PCR技术研究红壤坡地利用方式对土壤细菌群落结构的影响。结果表明,红壤坡地三种土地利用方式土壤细菌多样性指数农田>茶园>自然恢复(p<0.05),但土壤细菌数量茶园>自然恢复>农田(p<0.05),茶园土壤细菌数量是农田的8.76倍。基于T-RFLP图谱的样品间相似性指数和主要限制性片段(T-RFs)定性分析均表明,农田与茶园和自然恢复土壤均存在显著的差异(p<0.05),而茶园和自然恢复土壤细菌群落比较相似。不同土地利用方式土壤有机质、有效磷和速效钾均对土壤细菌群落结构产生显著影响(p<0.05)。综合考虑经济效益和保持红壤坡地的可持续利用,茶园将成为中国南方红壤丘陵坡地可持续利用的一种有效方式。  相似文献   

20.
潮土区不同质地土壤的养分动态变化研究   总被引：17，自引：6，他引：17  
对华北平原大兴县 1 982— 2 0 0 0年两个时段大量土壤样本的分析结果表明 ,土壤养分含量与土壤质地表现出明显的一致性 ,体现了土壤质地越重 ,养分含量越高的特点 ;土壤质地对土壤养分含量的影响 ,1 982年的大于 2 0 0 0年的 ;但 2 0年来 ,由于土地利用集约度的增强 ,质地对土壤养分水平的影响渐趋减弱 ,不同质地土壤的养分水平渐趋一致  相似文献   

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