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1.
The occurrence and characterization of N2-fixing azospirilla in some Egyptian soils has been investigated. Seven soils, representing a wide range in texture and properties were selected from different localities in Egypt. The highest nitrogenase activity reported for soil samples under investigation were related to numbers of N2-fixing microorganisms (Azotobacter spp., Azospirillum spp., and Clostridium spp.). Seven strains of azospirilla were isolated and purified. Based on morphological characteristics, three types of cell morphology were distinguished. Cultural and physiological characteristics as well as nitrogenase activity of representative isolates in presence of different concentrations of NaCl were determined. According to the physiological properties studied, all isolates were classified as members of Azospirillum brasilense.  相似文献   

2.
The paper summarizes the results of a series of experiments on enumeration of N2-fixing bacteria (diazotrophs) and hormonal effects of Azospirillum on root development. Numbers of N2-fixing and N-heterotrophic bacteria were determined on the root (rhizoplane plus “inner” root surface) and in the rhizosphere soil (0–3 mm from the root surface) of Arrhenatherum elatius, other forage grasses and some herbaceous plant species. Pot experiments involved freshly collected soil from an unfertilized grassland area containing its natural population of N2-fixing bacteria. The MPN (most probable number) of diazotrophs in relation to the MPN of the total bacterial population was always lower on the root than in the rhizosphere soil, suggesting that diazotrophs were not selectively advantaged at the root surface. Supply of mineral nitrogen (NH4NO3) decreased the proportion of N2-fixing bacteria at the rhizoplane as well as in the rhizosphere soil. Similar results were obtained when N was supplied via the leaves. The data suggest that N2-fixing bacteria in the rhizosphere are poor competitors once they loose their competitive advantage of binding dinitrogen. Correspondingly, the increase in the MPN of the diazotrophs found during plant development was interpreted as a result of decreased available combined N in the rhizosphere. The proportion of N2-fixing bacteria relative to the total number of bacteria was generally below 1%. Considering the potential amount of substrate released from the roots and the substrate requirement of the bacterial population, N2-fixation was considered insignificant for plant growth under the given conditions. For the investigations on possible beneficial effects on plant development by bacterial hormones, Azospirillum brasilense was chosen because evidence suggests that amongst the soil bacteria releasing hormones, especially IAA, certain strains of this species are more important than other bacteria. Application of A. brasilense Cd (ATCC 29710) onto the roots of young wheat plants grown in soil increased the number of lateral roots, the total root length and the number of root hairs. Similar results were obtained after application of IAA. This suggests that IAA is an important factor responsible for the effects observed after inoculation with A. brasilense. The increase in root surface may improve acquisition of nutrients and enhance growth of plants. Another hormonal effect of A. brasilense was an increase in nodulation of Medicago sativa grown on agar. Again pure IAA resulted in a similar increase in nodule number. Increases in nodule number were only in part associated with a change in root morphology. Therefore an effect of IAA on the plant immanent regulation system for nodulation is likely.  相似文献   

3.
Summary The present status and merits of inoculating rice with N2-fixing bacteria are discussed in the light of recent advances. Bacterial inoculation improves plant growth and rice yield but not uniformly. The yield response to inoculation is more pronounced in the presence of moderate levels of fertilizer N. Evidence for the establishment and activity of the inoculated bacteria is limited, and the poor survival of the inoculum under field conditions further complicates the effects of inoculation. There is no clear evidence that improved growth and mineral content following inoculation are due to increased N2 fixation. Beneficial effects of the inoculum on rice, such as plant growth promotion, N2 fixation and antagonism effects against pathogens need to be further investigated under laboratory and field conditions. Improved management practices, such as organic amendments, suitable water and soil management, selection of efficient microbial strains, selection of effective breeding lines with high associative nitrogen fixation, and better management of agrochemicals are some of the measures suggested for deriving benefits from bacterial associations with rice.  相似文献   

4.
Several important features of the N. fixation in paddy fields which were reported previously were confirmed and some new additional results regarding the evaluation of the N2 fixation in the rhizosphere were obtained by reinvestigation in the fields. In addition, rice plants were cultivated in the submerged soil in pots and various parts of the soil were analyzed for the N2-fixing activity as well as several other properties. The results of the pot experiments were found to be fairly similar to those observed in the field investigations, indicating the validity of the submerged soil in a pot as a rather simulated model for the actual paddy field. By using this model system, the following facts were ascertained: (1) Water-percolation had almost no effect on the N2-fixing activities of both the rhizosphere and the non-rhizosphere soils. (2) Suppressing effect of washing the root of rice plant on the N2-fixing activity was slight in the seedling stage and marked in the tillering and flowering stages. (3) The N2-fixing activity of a single rice root varied from tip to base.  相似文献   

5.
《Soil biology & biochemistry》2001,33(12-13):1859-1868
The non-nodulating phenophase of a legume tree was tested as a non-N2-fixing reference in application of the 15N natural abundance method for estimating the N2 fixation. We applied this method to study the effects of three pruning intensities, complete pruning every 6 months (T-6), ca. 50% pruning every 3 months (P-3) and intact control (C), on N2 fixation in Erythrina lanceolata (Papilionaceae) planted as shade and support trees for vanilla (Vanilla planifolia) in a subhumid tropical site in Quepos, Costa Rica. We measured nodulation and N2 fixation for 12 months. The trees under the C regime nodulated abundantly during the rainy season vegetative growth but did not nodulate during the dry season and flowering. A linear regression (r2=0.76) was observed between the nodule biomass and δ15N values under the C regime, suggesting quite a stable specific N2 fixation rate. The stable δ15N values throughout the year in the non-N2-fixing Morus nigra (Moraceae) growing on the same soil indicated that the temporal variation in the plant available soil 15N was low. We used the intercept term of the regression (δ15N=3.5 when nodule biomass was 0) as the non-N2-fixing δ15N value when estimating the percentage of N fixed from atmosphere out of tree total N. The percentage varied from 0 during the driest period to 53% during rainy season. Pruning reduced rainy season nodulation under the T-6 and P-3 regimes almost to nil, and the δ15N values were high. Our results suggest that the conditions for using the non-nodulating phenophase as the non-N2-fixing reference required in the 15N natural abundance method were fulfilled. The C trees showed a clear phenological cycle in N2 fixation, while pruning severely disturbed the N2 fixation under the T-6 and P-3 regimes, indicating that E. lanceolata is better suited for agroforestry systems in which the trees are not managed by periodic prunings.  相似文献   

6.
Bacteria associated with roots of grasses from Florida, Ecuador and Venezuela were isolated and their N2-fixing ability was demonstrated by C2H2 reduction assay. The bacterial isolates have been classified as Azospirillum brasilense (formerly Spirillum lipoferum). These N2-fixing isolates have been compared with several Brazilian strains. Fluorescent antibody (FA) techniques were used to assist identifying isolates of N2-fixing bacteria from grass roots. Tests with antisera prepared against four strains of Azospirillum were used to define serological groups. Antigen-antibody specificity was demonstrated using both Azotobacter and Azospirillum antisera against known species of other soil microorganisms and numerous unidentified soil bacteria. Several applications of the FA technique are suggested to identify N2-fixing bacteria associated with grass roots.  相似文献   

7.
Acetyle reduction and 15N studies showed that the addition of sulfate to flooded soil with rice straw enhanced N2 fixation. The extent of the enhancement was dependent on the sulfate concentration. Sulfate also increased the population of SO42? reducing bacteria and was completely reduced to sulfide by those microorganisms. Purified cultures of soil isolates were capable of C2H2 reduction. Based on this evidence, SO42? reducing bacteria were considered responsible for the increase in N2 fixation but only 1–2 mg N2 were fixed g1? SO42? reduced. We conclude that the contribution of SO42? reducing bacteria to the total N2 fixation in flooded soil is unimportant.  相似文献   

8.
The influence of soil pH, redox potential and added organic matter on N2-fixation by Azospirillum was studied. Application of rice straw to alluvial, laterite and acid-sulphate Pokkali soils under submerged conditions enhanced the population of N2-fixing Azospirillum spp. An acid-sulphate saline soil of extremely low pH (3.2) harboured Azospirillum spp with appreciable N2-fixing activity. Enrichment cultures originating from soils with low pH (<4.0) possessed lower N2-fixing activity compared to cultures from soils with higher pH values (upto 6.6). Azospirillum cultures from soils that had undergone prolonged waterlogging showed lower N2-fixing activity than cultures isolated from soils submerged for a few days. A relationship was shown between the in vitro N2-fixing activity of Azospirillum cultures and the redox status of the soil samples; activity was high when the soil redox potential was between ?50 to ?150mV. The results show that the N2-fixing activity of Azospirillum cultures is governed by fluctuations in soil redox potential, pH and organic matter.  相似文献   

9.
Soil heterotrophic respiration during decomposition of carbon (C)-rich organic matter plays a vital role in sustaining soil fertility. However, it remains poorly understood whether dinitrogen (N2) fixation occurs in support of soil heterotrophic respiration. In this study, 15N2-tracing indicated that strong N2 fixation occurred during heterotrophic respiration of carbon-rich glucose. Soil organic 15N increased from 0.37 atom% to 2.50 atom% under aerobic conditions and to 4.23 atom% under anaerobic conditions, while the concomitant CO2 flux increased by 12.0-fold under aerobic conditions and 5.18-fold under anaerobic conditions. Soil N2 fixation was completely absent in soils replete with inorganic N, although soil N bioavailability did not alter soil respiration. High-throughput sequencing of the 16S rRNA gene further indicated that: i) under aerobic conditions, only 15.2% of soil microbiome responded positively to glucose addition, and these responses were significantly associated with soil respiration and N2 fixation and ii) under anaerobic conditions, the percentage of responses was even lower at 5.70%. Intriguingly, more than 95% of these responses were originally rare with < 0.5% relative abundance in background soils, including typical N2-fixing heterotrophs such as Azotobacter and Clostridium and well-recognized non-N2-fixing heterotrophs such as Sporosarcina, Agromyces, and Sedimentibacter. These results suggest that only a small portion of the soil microbiome could respond quickly to the amendment of readily accessible organic C in a fluvo-aquic soil and highlighted that rare phylotypes might have played more important roles than previously appreciated in catalyzing soil C and nitrogen turnovers. Our study indicates that N2 fixation could be closely associated with microbial turnover of soil organic C when available in excess.  相似文献   

10.
This study identified microbial functional groups like total culturable bacteria, potential N2-fixing free living bacteria, N2-fixing hydrocarbonoclastic bacteria, N-assimilating hydrocarbonoclastic bacteria, total fungi, actinobacteria, P-solubilizers, lipolytic microorganisms, and starch, cellulose, pectin and protein degrading microorganisms, isolated from the rhizosphere of four species of mangroves (Red, Black, White, and Button) from the natural protected area at the Terminos Lagoon, Campeche, México. Overall, microbial populations showed significant differences (P < 0.05) among the four mangrove species. The rhizosphere of White mangrove showed better chemical and textural soil properties, and harbored the highest microbial populations when compared to the remaining mangrove species. The principal component analysis indicated that two components accounted the 85.3% of the total variation. The most significant textural and chemical soil properties were the major components, CP1 (organic matter and total organic carbon) and CP2 (sand and clay). Microbial populations correlated (P < 0.05, Pearson coefficient) with sand and clay particles, and with some soil chemical properties such as organic matter. The total nitrogen and organic carbon significantly correlated with cellulose degraders, while phosphorus with N2-fixing bacteria, total fungi, and with pectin and starch degraders.  相似文献   

11.
Summary N2 fixation (acetylene reduction assay) by phylloplane microorganisms was measured in dominant and co-dominant plant species growing in a tropical rain forest. No significant acetylene reduction was recorded with intact leaf samples. Azotobacter sp., Beijerinckia sp., Derxia sp., and Klebsiella pneumoniae were isolated as phylloplane N2-fixing bacteria. Azospirillum lipoferum was only isolated from soil samples containing the roots of Poaceae. Nitrogenase activity was recorded in culture derived from the roots and rhizosphere soil samples, although low acetylene reduction activity indicates that these associations did not provide large amounts of N to the systems studied.  相似文献   

12.
The 4 long-term experimental plots (Umbric haplaquept) with different fertilizer treatment at Cent. Agric. Exp. Sta. in Konosu City, Saitama Prefecture, were used for the sites of investigation. The 4 plots were NF (applied with no fertilizer), IF (applied with inorganic fertilizers), GM (applied with green manure and CaCO2), and OM (applied with manure and inorganic fertilizers). Flooded water, floating weed, upper (0-2cm) and lower (2-10cm) parts of Apg horizon and rhizosphere were collected from each plot before flooding, during flooding, and after drainage. These samples were analyzed for N2-fixing activity by acetylene reduction method, pH, Eh, and contents of Fe2+, NH4 +, chlorophyll-type compounds, and water-soluble carbohydrates.

The N2-fixing activity of all samples showed almost the same pattern of change with time: very low before flooding, rapidly increased after flooding, the maximum value at the maximum tillering stage of rice plant, declined afterwards and reached a very low value after drainage.

Rough estimation of the “N2-fixing capacity” of each part of the paddy field revealed that the most important site of the N2 fixation was the reduced Apg horizon, that the importance of flooded water and/or the oxidized layer in the N2 fixation was rather low except in infertile soil, and that the role of rhizosphere in the N2 fixation could not be neglected also in Japan.

Reduced condition and content of easily decomposable organic substances were judged to be main factors which control the N2-fixing activity in the flooded soil on the basis of correlations between the Nt-fixing activity and several analytical data of the paddy soils.  相似文献   

13.
 In the central highlands of Mexico, heavily eroded soils are often colonized by catclaw (Mimosa buincifiera): an N2-fixing shrub. An experiment was carried out to investigate how this shrub affected characteristics of the soil and its biological functioning. Soil was sampled from outside and under the canopy of catclaw at three sites characterized by different degrees of erosion and an increase in plant density. The soil microbial biomass C, total amounts of bacteria, fungi, actinomycetes and free-living N2-fixing micro-organisms were measured, while production of CO2 and dynamics of nitrate (NO3 –), nitrite (NO2 –) and ammonium (NH4 +) were monitored in an aerobic incubation at 22±1  °C for 35 days. The C content was 1.6 times greater in the area with the largest density of plants and the least erosion (RECUP) compared with the site with the lowest density and greatest erosion (DEGR), while it was 1.2 times greater under the canopy of the catclaw than outside it (average of the three sites). The incorporation of N into the soil organic matter was greater under the canopy of the catclaw than outside it as the C:N ratio was on average 8.4 and 9. 1, respectively. The microbial biomass C, as a percentage of soil organic matter, was 1.5 times greater in the RECUP than in the DEGR site. Greatest total number of colony-forming bacteria and fungi (mean of organisms found under and outside the canopy) were found in the RECUP treatment and lowest in the DEGR treatment. Free-living N2-fixing organisms and actinomycetes showed opposite trends. Greater total numbers of colony-forming bacteria, fungi, actinomycetes and free-living N2-fixing organisms (mean of the three treatments) were found under the canopy of catclaw than outside of it, Production of CO2 was 1.8 times greater in the RECUP than in the DEGR and 1.6 times greater under the canopy of catclaw than outside. Production of NO3 – was 1.3 times greater in the RECUP than in the DEGR and 3.5 times greater under the canopy of catclaw than outside. There was no significant effect of location or canopy on NO2 – and NH4 + concentrations. It is concluded that the natural vegetation of catclaw increased microbial biomass and soil organic matter content under, but also outside its canopy, and preserved N better, releasing greater amounts of inorganic N upon mineralization. Catclaw can serve as a first colonizer of heavily eroded soil and be replaced by other vegetation, natural or crops, when fertility is restored. Received: 4 November 1999  相似文献   

14.
Sustainable cropping systems rely on a minimum of external inputs. In these systems N is largely acquired in animal manures and leguminous green manures. Little is known of how these organic forms of N fertilizer influence the presence and activity of free-living N2-fixing bacteria. High concentrations of inorganic N in soil inhibit N2-fixation in cyanobacteria and Azotobacter spp. It is likely that manure and fertilizer applications would result in concentrations of inorganic N capable of inhibiting N2 fixation and, ultimately, the presence of these organisms. We investigated the effect of synthetic and organic N fertilizer sources on the populations and N2-fixation potential of free-living N2-fixing bacteria in the Farming Systems Trial at the Rodale Research Institute. Field plots received the following N treatments prior to corn (Zea mays L.) production: (1) Legume rotations and green manures supplying about 165 kg N ha-1; (2) beef cattle manure applied at a rate of 220 kg N ha-1 (plus 60 kg N ha-1 from 1994 hay plow-down); or (3) fertilizer N (urea and NH4NO3) applied at a rate of 145 kg N ha-1. Soil samples were collected at two depths from corn plots four times during the growing season, and analyzed for soil moisture, soil pH, numbers of N2-fixing cyanobacteria and Azotobacter spp., extractable NH inf4 sup+ and NO inf3 sup- , and potentially mineralizable N. Soil samples collected in mid-July were analyzed for nitrogenase activity (by C2H2 reduction) and total C and N. Populations of Azotobacter spp. and cyanobacteria were influenced only slightly by treatment; however, cyanobacteria species composition was notably influenced by treatment. Nitrogenase activity in surface soils was greatest in legume-N plots and in subsurface plots levels were greatest in fertilizer-N plots. Populations and activity of free-living N-fixing bacteria appeared to be somewhat reduced in all plots as a result of low soil pH levels and high concentrations of inorganic N across all treatments. Annual applications of N to all plots resulted in high levels of potentially mineralizable N that in turn may have reduced non-symbiotic N2-fixation in all plots.  相似文献   

15.
土壤N2固定细菌和CO2固定细菌是土壤碳氮循环重要的微生物群落,不同施肥下土壤有机碳积累与这两类微生物群落结构及活性的关系有助于了解施肥对农田碳氮循环的影响特点.本文研究了太湖地区自1987年开始的水稻土长期施肥试验,选取不施肥(NF)、氮磷钾(NPK)肥(CF)、NPK肥与猪粪配施(CFM)和NPK肥与秸秆还田配施(CFS)小区,采集(0-20 cm)表层样本,以nifH和cbbLR基因分别作为N2和CO2固定细菌的指示基因,用PCR-DGGE和荧光定量PCR的方法研究二者的群落结构,并用平板菌落计数法测定土壤自生固氮细菌数量和用乙炔还原法测定土壤固氮酶活性.结果表明,与CF处理相比,CF、CFM和CFS处理下的自生固氮细菌数量分别提高了58％、66％和106％;CF、CFM和CFS处理下的nifH基因丰度分别提高了213％、1079％和344％.CF与CFM处理的土壤固氮酶活性显著高于NF和CFS处理.因此,施肥提高了cbbLR基因的多样性.与NF处理相比,CF、CFM和CFS处理下的cbbLR基因丰度分别提高了465％、1827％和758％.相关性分析表明,土壤自生固氮菌数量与土壤有机碳含量呈显著正相关,cbbLR和nifH基因丰度均与归一化的土壤养分呈极其显著正相关.研究表明,有机/无机肥配施下土壤养分平衡对维持N2和CO2固定细菌较高的丰度具有重要的作用.  相似文献   

16.
The effect of three pesticides, benomyl, carbofuran and gamm-BHC at 5 parts 106, rates equivalent to recommended field levels, on the heterotrophic N2 fixation in five air-dried, cellulose-amended, submerged tropical soils was invevstigated employing 15N tracer technique under laboratory conditions. Addition of benomyl, a carbamate fungicide, to alluvial, laterite and two acid sulphate soils resulted in significant increases in N2 fixation, while carbofuran, a methylcarbamate insecticide, exerted a stimulatory effect on N2 fixation in alluvial, alterite and acid saline soils. Gamma-BHC, a chlorinated hydrocarbon insecticide, stimulated N2 fixation in alluvial and acid sulphate pokkali solis, while considerable inhibition of N2 fixation was evident inother soils. Results showed differential responses of specific groups of N2-fixing organisms to the pesticides depending ont he soil type.  相似文献   

17.
Abstract

A series of experiments has been conducted on the N2 fixation in the paddy soils by the authors (1–4). The amount of organic substrates for microorganisms and the degree of reduction of the soil are found to be two major factors affecting the N2-fixing activity of the heterotrophic microorganisms in the submerged soil. Organic debris, rice root and their neighboring soils are identified to be the important micro-sites for the heterotrophic N2 fixers. The organic debris and the rice root are considered to play dual roles by supplying the organic substances; (1) increase of the population of the heterotrophic N2 fixers—the amount of nitrogenase, (2) preparation of the reduced conditions favorable for the nitrogenase activity.

However, it is not yet clearly known which of these two roles of the organic substrates is more essential to the N2-fixing activity in the paddy soil. In addition, it is expected that there must be some differences between the organic debris and rice root in their contribution to the N2 fixation in the paddy soil.

An experiment was carried out to clarify these problems. Moist soil sample was collected from the plough layer of the paddy field at Central Agric. Exp. Sta. in Konosu City, Saitama Pref., passed through a 5 mm sieve and placed in pots (3 kg moist soil/pot). Ammonium sulfate, calcium superphosphate, and potassium chloride at the rate of 0.4-0.4-0.4 (N-P2O5-K20) g/pot were incorporated into the soil 7 days before transplanting. Split application of ammonium sulfate at the rates of 0.2 and 0.4 g N/pot were also incorporated at 30 and 41 days after transplanting respectively. These pots were divided into three series; planted (P-series), non-planted (N-series), and non-planted and applied with organic manure (O-series). In case of O-series, 60 g of fairly rotted organic manure was applied to each pot. Each pot of P-series was planted with two 4O-day-old seedlings of rice plant at 7 days after submergence. The Nseries was regarded as a control. Each series was not replicated in this preliminary experiment.  相似文献   

18.
The composition of the microflora, N2-fixing bacteria particularly, in different soils cultivated with wheat in Egypt was investigated in some samples collected from the fields after applying the agricultural practices recommended for wheat cultivation and just before sowing. The influence of carbon sources, mineral nitrogen and water regimes on potential dinitrogen fixation (acetylene reduction assay) in soils was investigated. The bacterial population densities including-N2-fixing organisms were related to a number of environmental factors such as organic matter content. Among diazotrophs, Azotobacter spp. and Azospirillum spp. were encountered in higher densities in comparison with clostridia. Unamended soils showed a lower acetylene-reducing activity (0.5–61.5 nmoles C2H4 g?1 h?1). Addition of glucose (1% w/w) greatly enhanced such activity being the highest (86.9–2846.5 nmoles C2H4 g?1 h?1) in the clay soil with the highest organic carbon content (1.42%). Glucose amendment had no significant influence on acetylene reduction in the saline soil. N2-fixation in barley straw-amended (1%) soils was not much higher than in unamended soils. Concentrations of up to 70 ppm ammonium-nitrogen depressed N2-fixation in soils that received barley straw. Acetylene reduction in submerged soil increased after addition of cellulose. Non-flooded conditions favoured N2-fixation in the fertile clay soil amended with sucrose.  相似文献   

19.
Summary Acetylene reduction activity by Azospirillum brasilense, either free-living in soils or associated with wheat roots, was determined in a sterilised root environment at controlled levels of O2 tension and with different concentrations of mineral N. In an unplanted, inoculated soil nitrogenase activity remained low, at approximately 40 nmol C2H4 h-1 per 2kg fresh soil, increasing to 300 nmol C2H4 h-1 when malic acid was added as a C source via a dialyse tubing system. The N2 fixation by A. brasilense in the rhizosphere of an actively growing plant was much less sensitive to the repressing influence of free O2 than the free-living bacteria were. An optimum nitrogenase activity was observed at 10 kPa O2, with a relatively high level of activity remaining even at an O2 concentration of 20 kPa. Both NO inf3 sup- and NH inf4 sup+ repressed nitrogenase activity, which was less pronounced in the presence than in the absence of plants. The highest survival rates of inoculated A. brasilense and the highest rates of acetylene reduction were found in plants treated with azospirilli immediately after seedling emergence. Plants inoculated at a later stage of growth showed a lower bacterial density in the rhizosphere and, as a consequence, a lower N2-fixing potential. Subsequent inoculations with A. brasilense during plant development did not increase root colonisation and did not stimulate the associated acetylene reduction. By using the 15N dilution method, the affect of inoculation with A. brasilense in terms of plant N was calculated as 0.067 mg N2 fixed per plant, i.e., 3.3% of the N in the root and 1.6% in the plant shoot were of atmospheric origin. This 15N dilution was comparable to that seen in plants inoculated with non-N2-fixing Psudomonas fluorescens.  相似文献   

20.
Summary We studied the effects of the organophosphorus insecticide methidathion, at concentrations of 10, 50, 100, 200 and 300 g g-1 in an agricultural soil, on fungi, total bacterial populations, aerobic N2-fixing bacteria, denitrifying bacteria, nitrifying bacteria (phases I and II), and nitrogenase activity (acetylene reduction assay). The presence of 10–300 g g-1 of methidathion significantly increased fungal populations (colony-forming units). Denitrifying bacteria, aerobic N2-fixing bacteria and N2 fixation were significantly increased at concentrations of 50–300 g g-1. The total number of bacteria increased significantly at concentrations of 100–300 g g-1. Nitrifying bacteria decreased initially at concentrations of 300 g g-1, but recovered rapidly to levels similar to those in the control soil without the insecticide.  相似文献   

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