Bioavailability of the herbicide 2,4-D formulated with organoclays

Research on organoclays as sorbents of pesticides has shown the usefulness of these materials as pesticide supports to prolong the efficacy of soil-applied pesticides and to reduce the large transport losses that usually affect pesticides applied in an immediately available form. Nevertheless, little information exists on the availability of organoclay-formulated pesticides for bacterial degradation. In this work, laboratory experiments were conducted to determine the adsorption-desorption behavior of two hexadecyltrimethylammonium-treated Arizona montmorillonites (SA-HDTMA₅₀ and SA-HDTMA₁₀₀) for the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), and to evaluate the ability of these organoclays to slow the release of the herbicide and to reduce herbicide leaching losses as compared to the free (technical) compound. The kinetics of mineralization of free and formulated 2,4-D by adapted bacteria was also determined. Organoclay-based formulations of 2,4-D displayed slow release properties in water and reduced herbicide leaching through soil columns, while maintained a herbicidal efficacy similar to that of the free (technical) 2,4-D. The total amount of ¹⁴C-2,4-D mineralized at the end of the biodegradation experiment (t=130 h) ranged between 30% and 46% of the formulated herbicide, which represented 53-81% of the amount of free 2,4-D mineralized in the same conditions. The release, leaching, and mineralization patterns of the formulated herbicide were found to depend both on the affinity of the organoclay for the herbicide and on the degree of interaction promoted during the preparation of the herbicide-organoclay complex. This suggests the possibility to select diverse preparations to achieve the desired release, leaching and biodegradation behavior.     

Effect of humic preparation on winter wheat productivity and rhizosphere microbial community under herbicide-induced stress

Purpose

The aim of the present work was to study the effect of humic preparation on the yielding capacity of winter wheat, the dynamics of mineral nutrients in the rhizosphere, and the activity of rhizosphere microbial community, as well as the protective properties of humate treatment under the stress caused by the application of a sulfonylurea herbicide.

Materials and methods

The humic preparation BIO-Don is prepared from vermicompost by alkaline extraction. The effect of humic preparation was estimated in a field experiment. The contents of the mobile ammonium and nitrate, exchangeable potassium, phosphorus, and humus were determined. Sampling and nutrient determination were performed in the tillering, booting, and grain maturing stages. Production experiments on the study of the combined effect of the humic preparation and the sunfonylurea pesticide Granstar Pro were performed in 2015 and 2017. The dynamics of mobile phosphorus in soil was studied. The abundance of culturable bacteria in the rhizosphere and bacterial species with different ecological strategies was determined. The dominant bacterial species were identified by MALDI-TOF mass spectrometry.

Results and discussion

The results of a small-plot experiment showed that at the tillering stage, the use of humic preparation has led to significantly higher supply of soil with mobile phosphorus. The winter wheat yield was 32.0 dt/ha in the control and 39.2 dt/ha with humic preparation or 22.5% gain in yield. The results of production experiment show that the application of sulfonylurea herbicide induced a chemical stress on winter wheat plants, but the use of humic preparation reduced this effect and increased the availability of phosphorus compounds. The treatment of plants with pesticides caused the general decrease in abundance of bacteria in the rhizosphere. The effect on quickly growing bacteria is more pronounced, while slowly growing bacteria and fungi are more resistant to this impact.

Conclusions

The application of humic preparation to winter wheat plantations allows to decrease the toxic effect of sulfonylurea herbicide, improve the supply of soil with mineral nutrients, and increase the crop yield. The favorable effects of humic preparation can be related to the active regulation of phosphorus mobilization by plants through the mechanism of root exudates due to the activation of root microbiota.

     

Laboratory investigations into the effects of the pesticides mancozeb, chlorothalonil, and prosulfuron on nitrous oxide and nitric oxide production in fertilized soil

Independent soil microcosm experiments were used to investigate the effects of the fungicides mancozeb and chlorothalonil, and the herbicide prosulfuron, on N₂O and NO production by nitrifying and denitrifying bacteria in fertilized soil. Soil cores were amended with NH₄NO₃ or NH₄NO₃ and pesticide, and the N₂O and NO concentrations were monitored periodically for approximately 48 h following amendment. Nitrification is the major source of N₂O and NO in these soils at soil moistures relevant to those observed at the field site where the cores were collected. At pesticide concentrations from 0.02 to 10 times that of a standard single application on a corn crop, N₂O and NO production was inhibited by all three pesticides. Generally N₂O production was inhibited by the pesticides from 10 to 62% and 20 to 98% at the lowest and highest dosages, respectively. Nitric oxide production was generally inhibited from about 5 to 47% and by 20 to 97% at the lowest and highest dosages, respectively. Nitrous oxide and nitric oxide production by nitrification was more susceptible to inhibition by these pesticides than denitrification. Production of both N₂O and NO by nitrification was inhibited by as much as 99%, at the highest concentration of pesticide applied. The net production of N₂O increased as soil moisture increased. The rate of NO production was greatest at the intermediate moistures investigated, between 14 and 19% gravimetric soil moisture, suggestive that nitrification is the dominant source of NO.     

Nitrapyrin,terrazole, atrazine,and simazine influence on nitrification and corn growth

Most farming systems involving tilled crops require use of pesticides and nitrogen fertilizers in different combinations although most pesticides effects on soil N transformation are scantly documented. Studies were initiated to compare atrazine and simazine herbicides with two biological nitrification inhibitors (nitrapyrin and terrazole) for their effects on biological nitrification and corn (Zea mays L.) growth. In a laboratory study, inhibition of nitrification was less than 3% in a Tifton loamy sand incubated with 10 μg a.i g^‐1 soil atrazine or simazine but was more than 10% in soil amended with nitrapyrin or terrazole, applied separately or in combinations with either herbicide at the same rate. Similar trends were observed with soil treated with different combinations of 2.5 μg a.i. g^‐1 soil nitrapyrin or terrazole and 1.25 μg a.i. g^‐1 soil atrazine or simazine and incubated with and without corn plants under greenhouse conditions. The combination of either herbicide with nitrapyrin or terrazole significantly reduced the corn dry weights with substantial accumulation of Kjeldahl N and NO₃ ^‐ in tissues of plants, probably due to a concentration effect. However, these chemical combinations, applied at the rate of 1.2 kg a.i. ha^‐1 in conjunction with 35 kg ha^‐1 N as (NH₄)₂SO₄ in split banded applications (at planting and at the 6^th leaf stage), showed a nonsignificant trend towards increased corn ear yields in two‐year field studies. Generally, when atrazine or simazine was part of the chemical treatment, its effects on nitrification, plant growth and total N contents outweighed or masked those of nitrapyrin or terrazole.     

Saprophytic soil microflora in relation to yield reductions in soil repeatedly cropped with barley (Hordeum vulgare L.)

Summary The yield-depressing effect due to repeated cropping (monoculture) of barley reported from long-term field experiments was observed as a reduction in plant growth in short-term pot experiments. The nature of the monoculture effect was investigated by mixing field soils with different cropping histories in different proportions in the greenhouse, while the influence of rhizosphere microflora from the monocultured and crop rotation soils on barley growth was studied in gnotobiotic experiments. Indigenous bacterial populations and the pH of the test soils were also measured. Significantly more bacteria were found in the crop rotation soil compared to the monocultured soil, but the two soils did not differ in pH. Greenhouse experiments showed that in the monocultured soil, seed germination was delayed and plant dry weight reduced, and that these effects had a biological origin. Attempts were also made to induce the monoculture effect in the crop rotation soil by inoculation with known harmful bacteria. The results from the experiments with mixed soils and with soil inoculation indicated that where crop rotation was practised the soil was more sensitive to bacterial effects than the monocultured soil. The rhizosphere microflora from the monocultured soil did not affect plant weights in short-term gnotobiotic experiments, but it significantly stimulated the number of lateral roots compared with the crop rotation microflora. This stimulation could not be related to differences in bacterial counts, pH, or ion concentrations in the plant-growing medium.     

化学农药减量化措施对水稻病虫草害发生及产量的影响

为研究化学农药减量下不同栽培管理措施对水稻田间病虫草害发生及水稻干物质生产及产量的影响,进一步明确减少化学农药施用与水稻产量的关系,采用裂区试验设计,主区因素为2种杂草防治方式[浅旋耕作+常规除草剂用量（浅耕）、深耕耕作+减少30%除草剂用量（深耕）],副区因素为2种病虫防治方式[常规病虫害药剂用量（常规防治）、植物激活蛋白+减少30%病虫害药剂用量（喷施激活蛋白）],副副区因素为秧苗处理方式（未带药移栽、带药移栽）,分析测定了田间病虫草害发生、水稻干物质积累与转运、产量及构成因素等指标。结果表明：深耕下,分蘖期和灌浆期田间杂草株数和鲜重较浅耕显著降低,螟虫引起的植株白穗率也明显较浅耕低。浅耕方式下水稻植株带药移栽或喷施激活蛋白后叶瘟病发生情况明显降低。在水稻干物质生产方面,病虫防治方式和杂草防治方式显著或极显著影响茎鞘干物质积累,且显著或极显著影响茎鞘干物质输出量、输出率和转化率;杂草方式、秧苗处理和病虫防治3种方式的互作显著影响茎鞘干物质输出率和转化率;喷施激活蛋白后,齐穗期水稻植株的茎鞘干物质量增加4.0%~19.4%;深耕下,成熟期水稻植株的茎鞘干物质量平均增加7.1%,但在齐穗至成熟阶段的茎鞘干物质输出和转化相对较小。相关性分析表明水稻产量与分蘖期和灌浆期杂草发生情况和叶瘟发生呈显著或极显著负相关。此外,在深耕、带药移栽或喷施植物激活蛋白方式下,减少30%的病虫草害药剂用量后水稻产量没有显著变化。表明通过深耕、带药移栽或喷施植物激活蛋白等病虫草害防治方式,能有效减少水稻的化学农药用量,实现水稻稳产增效。     

Interaction of the herbicides Bromoxynil and Afalon S with Azospirillum and growth of maize

The possible interaction of herbicides Bromoxynil and Afalon S with Azospirillumspp. and growth of maize was investigated in a greenhouse experiment. Neither inoculation nor herbicide application with or without inoculation had significant effect on the major groups of soil microflora (bacteria, actinomycetes, and fungi). The highest values of nitrogenase as well as dehydrogenase activity were recorded in treatment received only Azospirillum. Incorporation in soil of either Bromoxynil or Afalon S at the recommended field dose seemed to have no significant effect on the enzymatic activities, while application of these herbicides with Azospirillum had stimulatory effects in some cases. The application of either Bromoxynil or Afalon S significantly increased the dry weight of roots and shoots at 45 days period. The effect of herbicide on plant growth was more pronounced when applied with Azospirillum and the highest stimulatory effect was observed when Afalon S was applied with the N₂-fixing microorganism.     

Effects of the pesticides thiotox,dichlorvos and carbofuran on the test fishMystus vittatus

A quantitative index of synergism, antagonism and additivity has been measured experimentally in the fishMystus vittatus for three pesticides viz. Thiotox (Endosulfan) (T), Dichlorvos (D) and Carbofuran (C). For a combination of two pesticides, the dose of the one pesticide of a pair was fixed at the no-effect level while the dose of the second pesticide was increased until the entire dose response curve was obtained. To evaluate interactions of three pesticides, the previous pair of pesticides was kept fixed at their combined TL_O level, and the third pesticide was increased and again a dose-response curve was obtained. From the results obtained, it is shown that a particular combination could be synergistic, antagonistic or additive, depending on the relative doses employed. In the present study (T + D)/C combination was most synergistic (toxic) in nature while D/T and C/T were least toxic or antagonistic in their effects. However, T/D, (C + T)/D, C/D and D/C combinations were additive in nature. (D + T)/C, (D + C)/T, (T + C)/D and (C + D)/T combinations were found less synergistic in nature than (T + D)/C.     

营养和病虫害管理对双季杂交水稻种植系统的土壤生态质量的共同影响

The mineral fertilizers(NPK) and pesticide,including herbicides,insecticides and fungicides,were applied alone or in combination and the soil sampling was done at different growth stages during the crop cycle to study the changes in soil organic matter,microbial biomass and their activity parameters in a paddy soil with different nutrient and pest management practices in a hybrid rice double-cropping system.A consistent increase in the electron transport system(ETS) activity was measured during the different crop growth stages of rice.The use of fertilizers(NPK) alone or with pesticides increased ETS activity,while a decline of ETS activity was noticed with pesticides alone as compared with the control.Nearly an increasing trend in soil phenol content was observed with the progression of crop growthstages,while the usage of pesticides alone caused maximum increments in the soil phenol content.The soil protein content was found nearly stable with fertilizers and/or pesticides application at various growth stages in both crops taken.But notable changes were noticed at different growth stages probable because of fluctuations in moisture and temperature at particular stages,which might have their effects on N mineralization.Marked depletions in the phospholipid content were found with the advancement of crop growth stages,while the incorporation of fertilizers and/or pesticides also produced slight changes,in which a higher decline was noticed with pesticide application alone compared with the control.     

Shifts in rhizosphere microbial communities and enzyme activity of Poa alpina across an alpine chronosequence

This study quantifies the influence of Poa alpina on the soil microbial community in primary succession of alpine ecosystems, and whether these effects are controlled by the successional stage. Four successional sites representative of four stages of grassland development (initial, 4 years (non-vegetated); pioneer, 20 years; transition, 75 years; mature, 9500 years old) on the Rotmoos glacier foreland, Austria, were sampled. The size, composition and activity of the microbial community in the rhizosphere and bulk soil were characterized using the chloroform-fumigation extraction procedure, phospholipid fatty acid (PLFA) analysis and measurements of the enzymes β-glucosidase, β-xylosidase, N-acetyl-β-glucosaminidase, leucine aminopeptidase, acid phosphatase and sulfatase. The interplay between the host plant and the successional stage was quantified using principal component (PCA) and multidimensional scaling analyses. Correlation analyses were applied to evaluate the relationship between soil factors (C_org, N_t, C/N ratio, pH, ammonium, phosphorus, potassium) and microbial properties in the bulk soil. In the pioneer stage microbial colonization of the rhizosphere of P. alpina was dependent on the reservoir of microbial species in the bulk soil. As a consequence, the rhizosphere and bulk soil were similar in microbial biomass (ninhydrin-reactive nitrogen (NHR-N)), community composition (PLFA), and enzyme activity. In the transition and mature grassland stage, more benign soil conditions stimulated microbial growth (NHR-N, total amount of PLFA, bacterial PLFA, Gram-positive bacteria, Gram-negative bacteria), and microbial diversity (Shannon index H) in the rhizosphere either directly or indirectly through enhanced carbon allocation. In the same period, the rhizosphere microflora shifted from a G⁻ to a more G⁺, and from a fungal to a more bacteria-dominated community. Rhizosphere β-xylosidase, N-acetyl-β-glucosaminidase, and sulfatase activity peaked in the mature grassland soil, whereas rhizosphere leucine aminopeptidase, β-glucosidase, and phosphatase activity were highest in the transition stage, probably because of enhanced carbon and nutrient allocation into the rhizosphere due to better growth conditions. Soil organic matter appeared to be the most important driver of microbial colonization in the bulk soil. The decrease in soil pH and soil C/N ratio mediated the shifts in the soil microbial community composition (bacPLFA, bacPLFA/fungPLFA, G⁻, G⁺/G⁻). The activities of β-glucosidase, β-xylosidase and phosphatase were related to soil ammonium and phosphorus, indicating that higher decomposition rates enhanced the nutrient availability in the bulk soil. We conclude that the major determinants of the microflora vary along the successional gradient: in the pioneer stage the rhizosphere microflora was primarily determined by the harsh soil environment; under more favourable environmental conditions, however, the host plant selected for a specific microbial community that was related to the dynamic interplay between soil properties and carbon supply.     

Density,metabolic activity,and identity of cultivable rhizosphere bacteria on Salix viminalis in disturbed arable and landfill soils

The objective of this study was to provide fundamental data for a subsequent selection of willow growth and soil remediation promoting bacterial strains. The rhizosphere of willows (Salix viminalis) was screened for cultivable bacteria with high enzymatic activity (proteolytic, pectolytic, cellulolytic, amylolytic) and production of siderophores at four test sites with broad spectrum of anthropogenic soil disturbance: sewage‐sludge application, impoverishment by unfavorable arable use, ash dumping, and household‐waste depositing. The density of bacteria in the rhizosphere ranged from 7.92 to 8.56 log₁₀ of colony‐forming units per gram dry weight of soil and varied in a site‐ and willow‐clone‐specific manner. Within the 240 bacterial strains, a high diversity of metabolic activities was observed but was rarely combined in one strain (1.2% having six and 5.8% having five out of seven metabolic activities, respectively). The majority of strains (79.2%) revealed just one or two metabolic activities. Most common was a combination of lipolytic, proteolytic activities, and siderophore production as found in 13.8% of the bacterial strains. The 50 strains with the highest metabolic activity belonged predominantly to the Gammaproteobacteria (66%), the others to Flavobacteria (18%), Betaproteobacteria (8%), Actinobacteria (4%), and Bacilli (4%). The highest portion of cultivable strains of rhizosphere bacteria with high metabolic activities belonged to the genera Pseudomonas, Serratia, and Flavobacterium. We hypothesize that these genera include strains that support willow growth and soil remediation. Therefore, the described strain collection from the rhizosphere of S. viminalis provides a valuable basis for a subsequent selection of these candidates for applications in improvement of site adaptation of plants or remediation of soils.     

Rhizosphere micro-organisms of seminal and nodal roots of wheat grown in pots

Wheat grown in Gabalong soil was examined for the microflora of its seminal and nodal root systems of similar age. At all stages of sampling, the seminal roots were found to support a significantly-larger population of bacteria, actinomycetes and fungi in their rhizosphere than the nodal roots. The seminal roots had higher numbers of bacteria and actinomycetes in their residues, but fungal numbers were not significantly different. The “rhizosphere effects” of the two root systems, in the combined analysis, were significantly different only for fungi. An interesting trend on both root systems was that while the numbers of bacteria, actinomycetes and fungi in the rhizosphere decreased with root age, their numbers in the residue increased with age.     

微生物有机肥结合土壤改良剂防治烟草青枯病

盆栽试验设置了五个处理:对照(T1)、施用普通有机肥(T2)、施用SQY-7号微生物有机肥(T3)、石灰处理土壤后施用SQY-7号微生物有机肥(T4)、石灰和碳铵处理土壤后施用SQY-7号微生物有机肥(T5),用DGGE和平板计数法研究了根际土壤微生物群落的多样性,旨在探讨微生物有机肥及微生物有机肥结合土壤改良剂对烟草青枯病的防治效果和对烟草根际土壤细菌群落多样性的影响.结果表明:连作土壤中,施用普通有机肥(T2)不仅不能防治烟草青枯病,还提高了烟草青枯病的病情指数,而施用微生物有机肥处理(T3、T4和T5)对烟草青枯病的防治效果达66.7％～87.9％;施用微生物有机肥可显著改变根际微生物区系结构:T2处理的根际土壤细菌和放线菌数量较T1处理略有增加,真菌数量则较T1处理增加了1.1倍;T3和T4处理的根际土壤细菌分别较T1处理增加了3.5倍和6.1倍,同时,放线菌数量分别增加了3.7倍和3.5倍,而真菌数量分别下降了66.2％和70.1％;T5处理的根际土壤细菌和放线菌数量较T1处理分别增加了13.6倍和5.1倍,真菌数量下降了75.0％;各处理的细菌群落多样性均较T1处理增加.初步研究表明,连作病害土壤用石灰和碳铵预处理后再施用SQY-7号微生物有机肥能有效防控烟草青枯病和减缓连作生物障碍,其作用机制主要通过改变微生物区系和降低病原菌数量实现.     

A simplified procedure for terminal restriction fragment length polymorphism analysis of the soil bacterial community to study the effects of pesticides on the soil microflora using 4,6-dinitroorthocresol as a test case

We have studied the structural effects of application to the soil of a potentially detrimental herbicide, 4,6-dinitroorthocresol (DNOC) by analysing amplified ribosomal DNA restriction analysis (ARDRA) and terminal restriction fragment length polymorphism (T-RFLP) signatures of 16S rDNA fragments of culturable bacterial communities isolated from diluted soil suspensions. This approach has the potential to reveal changes induced by stressing the soil microflora with DNOC. This paper shows that, whereas only few changes of the ARDRA and T-RFLP profiles result from ageing of the soil, treatment of the soil with DNOC induces major modifications of these profiles. Therefore, for the practical purpose of pesticide registration, ARDRA and T-RFLP analysis performed on the dominant culturable fraction of the soil bacteria, implemented using conventional gel electrophoresis, offers the means of a routine, simple and meaningful test for detecting some of the changes affecting the structure of the soil microflora in response to pesticide application.     

Influence of introduced potential biocontrol agents on maize seedling growth and bacterial community structure in the rhizosphere

Two species of Pseudomonas chromosomally tagged with gfp, which had shown antagonistic activity against the tomato pathogen Ralstonia solanacearum in a previous study, were assessed for their impact in the rhizosphere of maize. Plant growth characteristics, numbers of indigenous heterotrophic bacteria, changes in the bacterial community structure according to the r/K strategy concept, and shifts in MIDI-FAME profiles of culturable bacterial fractions as well as total rhizosphere microbial communities were determined in relation to seed and soil treatment with the exogenous pseudomonads. The maize rhizosphere proved to be a suitable habitat for the introduced P. chlororaphis IDV1 and P. putida RA2, which showed good survival after introduction. However, both inoculants showed a small growth-reducing effect towards maize, which might have been caused by the high densities of inoculants used (i.e. competition for nutrients and action of metabolites produced) and/or changes in microbial community structure (both culturable bacterial fraction and the total microflora). Probably, an altered balance among the indigenous maize rhizosphere populations occurred. Thus, the culturable bacteria, as well as the total microflora in the rhizosphere, changed in response to the introduced pseudomonads, and their development was dependent on the growth stage of the plant. The FAME analyses showed that these microbial communities comprised different populations, and were separated according to, first, the method used (direct versus cultivation-based), second, sampling time, and, finally, inoculation level.     

Using the spermosphere model technique to describe the dominant nitrogen-fixing microflora associated with wetland rice in two Egyptian soils

Summary This study is an attempt to describe the dominant N₂-fixing microflora associated with the roots of wetland rice. Rice cultivar Giza 171 was grown in a phytotron on two alluvial Egyptian soils for 8 days, a stage when the nitrogenase activity of undisturbed plants reached a level of 245 × 10^–6 mol C₂H₄ h^–1 g^–1 dry weight of leaf. The roots and rhizosphere soils were then used for counting and isolating dominant diazotrophs. Counts and initial enrichment steps were carried out on a selective medium made of an axenic rice plantlet, the spermosphere model, incubated under 1 % acetylene. The counts were very high, exceeding 10⁸ bacteria g^–1 dry weight of rhizosphere soil. Enterobacteriaceae were dominant; most isolates were Enterobacter cloacae belonging to different biotypes in the two soils. Enterobacter agglomerans, Citrobacter freundii and Klebsiella planticola were also present as members of the dominant microflora. Azospirillum brasilense and Azospirillum lipoferum were present as well, but less abundant.     

Soil Properties and Yield of Groundnut associated with Herbicides,Plant Geometry,and Plastic Mulch

Abstract

Experiments were conducted over 2 years during the dry season of 2002 (June–September) and wet season of 2002–2003 (December–March) at Regional Research Station, Tamil Nadu Agricultural University, Vridhachalam, India, to study the influence of two colors of polyethylene film mulch (black and white polyethylene film mulch), herbicides (Fluchloralin at 1.0 kg/ha and no herbicide application), and three plant geometries [30×10 cm, 20×20 cm (two seeds/hill), and 20×15 cm] on soil properties, growth, and yield of groundnut. Results indicated that the soil physical properties such as rate of water loss/day was highest with white polyethylene film mulch, the hydraulic conductivity of the soil was significantly more with black polyethylene film mulch, and soil bulk density and percentage of pore space did not differ between the two colors of polyethylene films. The rate of water loss was highest with plots with no herbicide, whereas the hydraulic conductivity of the soil was more with herbicide‐applied treatments. However, the bulk density and pore space did not differ significantly. The plant geometry did not have any significant influence on any of the soil physical properties. With regard to soil microorganisms, the bacterial and fungal population was significantly higher in black polyethylene film mulch at all the three stages of observation, whereas no significant difference between the colors of polyethylene film mulch was observed for actinomycetes at all the stages of observations. Interestingly, no variation in the population of soil microflora was observed between the herbicide and no‐herbicide treatments. The soil‐available nitrogen, phosphorus, and potassium (NPK), at harvest, was significantly higher with white polyethylene film mulch, whereas crop NPK uptake was higher with black polyethylene film mulch. The soil‐available NPK and crop uptake was higher with herbicide application. The evolution of carbon dioxide (CO₂; soil respiration) was significantly influenced by polyethylene film mulch and herbicides, and the evolution of CO₂ was altered by the plant geometry. The crop dry‐matter production, pegging percentage, pod setting ratio number of matured pods/plant, and pod yield were significantly higher under black polyethylene mulch. Herbicide application significantly improved the majority of the growth and yield attributes and significantly higher pod yield was obtained with herbicide application. However, most of the yield and growth attributes and pod yield were not significantly influenced by the different plant geometries studied.     

轮作与连作对烟田土壤微生物区系及多样性的影响

为探讨轮作与连作对烟田根际土壤微生物群落的影响,采用实验室微生物培养联合微生物高通量测序技术,分析了玉米-烤烟轮作和烟叶连作对烟株根际土壤微生物数量、群落结构及其多样性的影响。研究结果表明,轮作烟田根际土壤中可培养细菌和放线菌数量均高于连作烟田根际土壤,但真菌数量低于连作烟田。土壤高通量测序结果表明,轮作烟田根际土壤真菌和细菌群落多样性均高于连作烟田;在烟株的生长过程中,轮作和连作烟田在旺长期和成熟期微生物群落相似度降低。相较于黑胫病/根腐病/根结线虫发病率较高(36. 67%)的连作烟田来说,轮作烟田发病率较低(0%),进一步分析真菌和细菌群落结构发现,轮作烟田根际土壤中拮抗菌如Sphingomonas (鞘脂单胞菌属)、Pseudomonas (假单胞菌属)、Aspergillus (曲霉属)等相对丰度均高于连作烟田,而连作烟田根腐病病菌Pythium (腐霉属)丰度较高。     

Studies on the rhizosphere microflora of onion plants in relation to temperature changes

A study was made of the changes in the rhizosphere microflora of onion seedlings grown under controlled conditions at either 25, 18 or 16°C. In plants grown at the lower temperatures there was a very small rhizosphere effect for the bacteria compared with that for plants grown at 25°C. A series of tests on bacteria isolated from both rhizosphere and root-free soil showed the rhizosphere isolates from seedlings grown at 25°C to be more active physiologically than those from seedlings grown at the lower temperatures. In particular, the ammonifying bacteria were greatly increased in the rhizosphere of plants grown at 25°C. Numbers of rhizosphere fungi were also greater at the higher temperature but the rhizosphere effect was not as great as that for bacteria. Contrary to expectation the greatest rhizosphere effect did not occur at the optimum temperature for growth of the onions.     

抗病性不同大豆品种根面及根际微生物区系的变化 Ⅱ.连作大豆(重茬)根面及根际微生物区系的变化

采用平板计数法测定了两个抗根腐病连作大豆品种生育期间根面和根际微生物区系动态变化。结果表明,两个品种大豆根面细菌随生育期增加呈递减趋势,品种间无差异。合丰25(H25)的根际细菌数量随生育期呈递减趋势,绥农10号(S10)根际细菌数量从三叶期到鼓粒初期不断增加,到成熟期又急剧减少。感病品种H25根瘤重明显低于抗病品种S10。H25根面真菌和镰孢霉总数在三叶期和成熟期均高于S10,苗期是根腐病的主要发病期。总之,在连作条件下,无论抗病品种还是感病品种大豆成熟期其根面和根际细菌减少,真菌和主要病原菌(镰孢霉Fusarium)都会大量富集,表明根系分泌物对根面和根际的微生物种群有选择性地促进或抑制作用。