Population dynamics of amoebae in soils suppressive and non-suppressive to wheat take-all

Populations of soil amoebae were estimated throughout two wheat crops and a fallow from wheat rotations suppressive and non-suppressive to take-all. The suppressive pasture-pasture-wheat plot showed higher rhizosphere populations of mycophagous amoebae and higher associations of mycophagous and other amoebae with wheat roots throughout the crop period than the non-suppressive continuous-wheat plot. Populations of mycophagous amoebae were positively and significantly (P = 0.05) correlated with populations of the take-all fungus in both soils, and with soil moisture in the non-suppressive soil. The possible role of mycophagous amoebae in the wheat rhizosphere in suppressive soil is discussed.     

Grazing of a common species of soil protozoa (Acanthamoeba castellanii) affects rhizosphere bacterial community composition and root architecture of rice (Oryza sativa L.)

We performed a controlled experiment with rice seedlings (Oryza sativa L.) growing in Petri dishes on homogeneous nutrient agar containing a simple rhizosphere food web consisting of a diverse bacterial community and a common soil protozoa, Acanthamoeba castellanii, as bacterial grazer. Presence of amoebae increased bacterial activity and significantly changed the community composition and spatial distribution of bacteria in the rhizosphere. In particular, Betaproteobacteria did benefit from protozoan grazing. We hypothesize that the changes in bacterial community composition affected the root architecture of rice plants. These effects on root architecture affect a fundamental aspect of plant productivity. Root systems in presence of protozoa were characterized by high numbers of elongated (L-type) laterals, those laterals that are a prerequisite for the construction of branched root systems. This was in sharp contrast to root system development in absence of protozoa, where high numbers of lateral root primordia and short (S-type) laterals occurred which did not grow out of the rhizosphere region of the axile root. As a consequence of nutrient release from grazed bacteria and changes in root architecture, the nitrogen content of rice shoots increased by 45% in presence of protozoa. Our study illustrates that interactions over three trophic levels, i.e. between plants, bacteria and protozoa significantly modify root architecture and nutrient uptake by plants.     

Protease and deaminase activities in wheat rhizosphere and their relation to bacterial and protozoan populations

Protease and deaminase activities and population dynamics of bacteria and protozoa were measured in the rhizosphere of wheat to study their interactions with the mineralization of nitrogen. The experimental design allowed the separation of roots and soil material by means of a gauze. The most pronounced rhizosphere effect was detected for all the measured variables in the soil closest to the gauze. The number of bacteria was significantly higher in the presence than in the absence of plants up to 4 mm away from the soil-root interface and the closer to this interface the higher the number. Protozoan and bacterial population dynamics were positively correlated; generally, populations of flagellates and amoebae were comparable and their sum accounted for the population of total protozoa. For both enzyme activities the rhizosphere effect extended up to 2 mm away from the soil-root interface. The histidinase activity was of bacterial origin, while it is likely that bacteria, protozoa and root hair all contributed to the overall caseinase activity. Decomposition of root exudates and native organic matter in the rhizosphere, reflected by a growing microbial population, is associated with nitrogen mineralization through increases in caseinhydrolysing and L-histidine-deaminating activities. The adopted soil-plant microcosm is suitable for the study of the rhizosphere effect over time of incubation and distance gradient from the soil-root interface.     

Förderung des Wachstums und der Nährstoffaufnahme bei kruziferen Ölund Zwischenfrüchten durch inokulierte Rhizosphärenmikroorganismen

Promotion of plant growth and nutrient uptake of cruciferous oil- and intercrops by inoculated rhizosphere microorganisms The vegetative growth of rape, oil radish and mustard was repeatedly stimulated by isolates of Pseudomonas fluorescens (PsIA12), P. putida (A1 A2), Stenotrophomonas maltophilia (PsIB2, Psl2), Agrobacterium rhizogenes (A1A4) and Rhizobium trifolii (R39) by improved root development and nutrient uptake (N. P. K. Mg) in pot and field experiments on loamy sand and sandy loam at different yield levels. The seed yield of rape could be increased only by 2 isolates (PsIA12, PsIB2). The growth stimulating bacteria produced phytohormones (auxins and partly cytokinins). No direct relations between plant growth stimulation and the potential microbial metabolic activities nitrogenase, nitrate reductase, P-mobilization, pectinase, cellulase could be found. Effective bacteria are in close association with the plants and can survive in the rhizosphere.     

Interactions between arbuscular mycorrhizal fungi (Glomus intraradices,Glomeromycota) and amoebae (Acanthamoeba castellanii,Protozoa) in the rhizosphere of rice (Oryza sativa)

Rice plants (Oryza sativa L.) were grown in microcosms containing soil with a diverse bacterial community (control) and inoculated either with an axenic arbuscular mycorrhizal fungus (Glomus intraradices) or an axenic inoculum of protozoan grazers of bacteria (Acanthamoeba castellanii), or both, in a factorial design.Amoebae and mycorrhiza affected the root architecture of rice in opposite directions, with mycorrhiza reducing and protozoa increasing early root growth. Rice biomass did not increase in presence of mycorrhiza (×1.08), but strongly increased in presence of Acanthamoebae (×1.29). The positive effects of amoebae were always reduced when plants were also infected with mycorrhiza. Microbial biomass increased (×1.4) and microbial growth was less limited by phosphorus in presence of mycorrhiza. However, plant phosphorus uptake did not increase, rather, plant concentrations of carbon and nutrients decreased in presence of mycorrhiza, suggesting a sequestration of resources during the establishment of a mycorrhizal network. Amoebae strongly interacted with, and partly compensated for, the effects of mycorrhiza, demonstrating that interactions between AM fungi and the microbial food web in the rhizosphere significantly feed back on early plant performance.     

Differential interaction between two Glomus intraradices strains and a phosphate solubilizing bacterium in maize rhizosphere

Arbuscular mycorrhizal (AM) fungi and phosphate solubilizing bacteria (PSB) have a positive effect on plant productivity primarily through increasing phosphate availability. In order to study the interaction between AM fungi and PSB, we used Bacillus megaterium, a PSB isolated from the sterilized surface of AM germinated spores, and two strains of the AM fungus Glomus intraradices with different mycelial architecture. A greenhouse experiment was designed with maize as host plant with the addition of tribasic calcium phosphate. We tested the hypothesis that PSB, intimately linked with AM fungi, could interact differentially with the two AM strains. We concluded that inoculation with the PSB positively affected maize mycorrhization. Insoluble phosphate alone did not influence the AM extraradical mycelium (ERM) length and maize mycorrhization when bacteria were not inoculated. The results provide evidence that the adverse effect on infectivity for some AM strains might be caused by solubilized phosphorus release to the rhizosphere by PSB. Differences related to the mycelium architecture of each AM strain were observed: the density of PSB in rhizosphere soil was significantly higher only with the GA8 strain coinciding with the highest values of maize biomass. The density of bacteria associated with GA8 mycelium could be the result of the transfer of photosynthates through the rhizosphere; this close contact would favor the persistence of the intimate relationship between PSB and AM hyphae. In the bacteria-free treatments, soil adherence was not significantly altered. Although the highest development of ERM occurred with GA5, plants inoculated with GA8 showed the highest values for soil adherence. This may be due to the AM mycelium which modifies bacterial persistence in the rhizosphere and consequently soil adherence. Our results show that for potential applications, some characteristics of the AM strains are key in the selection of the AM fungi–PSB combinations. These include the tolerance to soluble phosphorus, the rate of root colonization, and ERM development that favors the persistence of bacteria in rhizosphere soil.     

Rhizosphere effects on soil bacterial abundance and diversity in the Yellow River Deltaic ecosystem as influenced by petroleum contamination and soil salinization

In this study, we compared the differences of bacterial abundance and diversity between rhizosphere and surrounding bulk soils under soil salinization and petroleum contamination in the Yellow River Delta on a 110-km-distance scale. In comparison with bulk soils, rhizosphere soils were mainly characterized by lower salinity and higher water content in saline soils. For bacterial abundance, the numbers of total bacteria and hydrocarbon degraders were significantly higher in rhizosphere soils than those in bulk soils. Although there was no significant difference in total petroleum hydrocarbon (TPH) concentration between the two types of soils, TPH had distinctly different effects on bacterial abundance in rhizosphere and bulk soils. TPH concentration was the major determinant of total bacterial abundance and had positive effects on abundances of hydrocarbon degraders. However, the abundances of total bacteria and hydrocarbon degraders in bulk soils were primarily determined by soil salinity and water content. Great abundance of rhizosphere bacteria suggested that plant roots could alleviate the stresses from soil salinization and provide more favorable microhabitats for bacterial growth. TPH had positive effects on bacterial diversity of both rhizosphere and bulk soils. Our results support the view that petroleum in the environments functions as both toxic chemicals and carbon sources to soil bacteria. Great abundance and diversity of total bacteria in plant rhizospheres would potentially improve the roles of bacteria in maintaining ecosystem functioning in the degraded ecosystems. Our results would improve our understanding of the relationships between rhizosphere effects and multiple environmental stresses that control the development of bacterial community in fragile anthropologically-affected ecosystems.     

连作土壤盆栽大豆的根际酸度和微生物数量变化

连作土壤条件下，不同抗性品种的根际微生物变化不同。盆栽试验结果表明，连作条件下，抗病品种绥农10号和抗线2号根际环境pH中性偏碱，不利病原真菌生长；感病品种合丰25号根际则处于偏酸环境，使作物易于感染根腐病。抗性大豆品种绥农10号和抗线2号的根际细菌数量增加，真菌数量减少；感病品种合丰25号的细菌和真菌数量变化不显著。     

苹果树根际促生细菌种群分析

利用选择性培养基, 对多年生苹果树根际与连作幼树根际促生细菌进行了分离和测数, 并采用BOX-PCR技术进行聚类分析。结果表明: 多年生苹果树根际细菌总量及固氮细菌、解磷细菌、硅酸盐细菌、拮抗细菌4类根际促生细菌的数量均高于连作幼树根际。在多年生苹果树根际, 硅酸盐细菌的数量最大, 解磷细菌和固氮细菌的数量次之, 拮抗细菌的数量最小; 在连作幼树根际, 解磷细菌的数量最大, 硅酸盐细菌和固氮细菌的数量次之, 拮抗细菌的数量最小。从两种土壤中获得的促生细菌分离株的BOX-PCR图谱最大的相异百分数都在1.25以上, 说明这些细菌分离株的遗传进化距离比较接近。在细菌BOX-PCR图谱相异百分数为0.25的水平上, 多年生苹果树根际促生细菌分为79个聚类群, 其中固氮细菌18个聚类群, 解磷细菌29个聚类群, 硅酸盐细菌19个聚类群, 拮抗细菌18个聚类群; 连作幼树根际促生细菌分为46个聚类群, 其中固氮细菌15个聚类群, 解磷细菌19个聚类群, 硅酸盐细菌8个聚类群, 拮抗细菌9个聚类群。多年生苹果树4类根际促生细菌的多样性、丰富度和均匀度指数均高于连作幼树根际, 而优势度指数低于连作幼树根际。与连作幼树相比, 多年生苹果树根际促生细菌具有丰富的种属多样性。     

The influence of nitrogen fertilisation on bacterial activity in the rhizosphere of barley

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.     

黑麦草（Lolium perenne）根际细菌多样性对Ni污染沉积物修复效果的响应

应用黑麦草（Lolium perenne）对某滨海城市南排污河的重金属污染沉积物——底泥进行植物修复,并结合变性梯度凝胶电泳（DGGE）分析了黑麦草根际土壤的重金属Ni含量和细菌多样性的关系。结果表明,黑麦草对Ni的修复效果较好,种植黑麦草后根际土壤Ni浓度降低了11.8%。根际土壤中Ni有效态含量与根际土壤pH值的变化呈较好的正相关关系,相关系数为0.968 8。对根际土壤细菌多样性进行分析,重金属Ni含量变化能够影响土壤细菌的多样性,根际土壤细菌多样性随黑麦草的生长而不断演变,且与根际土壤中Ni浓度变化有密切联系。对DGGE电泳后回收的部分片段进行测序并建立了进化树,结果表明,测序片段与非培养方法得到的菌种的同源性较高,且其均在土壤或河道底泥的相关研究中被发现。不同时期细菌群体组成和Shannon指数随着修复时间而变化,并与细菌总数有正相关关系。     

Rhizosphere microbial communities and organic acids secreted by aluminum-tolerant and aluminum-sensitive soybean in acid soil

This study aimed to investigate the correlation between organic acids secreted by two soybeans genotypes, BX10 [aluminum (Al) tolerant] and BD2 (Al sensitive) and rhizosphere microbial communities in acid soil. The organic acids secreted by BX10 and BD2 were significantly different at each growth stage. Both fungi/bacteria and gram-negative bacteria/gram-positive bacteria ratio values were affected by the two soybean genotypes at different growth periods. Compared with BD2, phospholipid fatty acid of BX10 showed higher Shannon diversity at the seedling and flowering stages, but had lower Shannon diversity at the pod-setting stage. Redundancy analysis and canonical correspondence analysis revealed that the organic acids including tartaric acid, lactic acid, and citric acid significantly affected rhizosphere bacterial communities. Sequence analysis indicated that uncultured Acidobacterium, Chloroflexi, and actinomycete enriched in BD2, whereas some uncultured bacteria enriched in BX10. The two soybean genotypes exhibit distinct rhizosphere microbial communities; root organic acid exudates may affect composition of microbial communities of rhizosphere soil: tartaric acid may negatively affect rhizosphere bacteria at the seedling stage, lactic acid may positively affect rhizosphere actinomycetes at the flowering stage, and succinic acid may stimulate fungi at the pod-setting stage.     

崇明西红花根际土壤和球茎微生物多样性分析

为研究崇明西红花栽培地根际土壤和球茎中微生物多样性,采用Illumina MiSeq高通量测序技术对其微生物群落组成进行了比对分析。结果表明,西红花根际土壤和球茎中细菌和真菌在门类水平上菌群类别差异不显著,但在丰富度和多样性方面根际土壤明显高于球茎;在属和种水平上差异显著;在种水平上,根际土壤或球茎均有各自特有的细菌或真菌,且具有较高的相对丰度。西红花致病真菌瓶霉(Phialophora)和背芽突霉(Cadophora)在崇明西红花球茎大量存在。因此,推测西红花病害发生,除与土壤菌群相关外,与其内生细菌和真菌也紧密相关。本研究结果初步分析了崇明栽培地西红花根际土壤和球茎中微生物多样性及群落结构组成,为进一步筛选合适的崇明西红花栽培地土壤和种球杀菌剂提供了理论依据。     

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.     

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 6-methoxy-benzoxazolin-2-one (MBOA) levels in the wheat rhizosphere and their effect on the soil microbial community structure

Despite increasing knowledge of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 6-methoxy-benzoxazolin-2-one (MBOA) as allelochemicals involved in the defense of wheat against pests, relatively little is known about their levels in the rhizosphere and interactions with the soil microbial community. This study quantified DIMBOA and MBOA in the wheat rhizosphere and analyzed the soil microbial community structure. MBOA rather than DIMBAO was found in the wheat rhizosphere, and its concentration varied with cultivars, plant densities, and growth conditions. Wheat could detect the presence of competing weeds and respond by increased MBOA in the rhizosphere. There was a linear positive relationship between the MBOA level in the wheat rhizosphere and soil fungi/bacteria. When DIMBOA was applied to soil, yielding MBOA increased soil fungi. There were different phospholipid fatty acid (PLFA) patterns in soil incubated with DIMBOA and MBOA. These results suggested that DIMBOA and MBOA could affect the soil microbial community structure to their advantage through the change in fungi populations.     

铝胁迫对大豆根际土壤微生物区系的影响

通过盆栽试验研究了不同浓度外源铝对大豆根际土壤微生物区系的影响。结果表明:在低浓度下,铝对土壤细菌、放线菌具有刺激作用,在高浓度下,表现为抑制作用。铝对真菌的生长具有明显的刺激作用。在高浓度下,铝对土壤硝化细菌、反硝化细菌、自生固氮菌均产生强烈的抑制作用,最大抑制率分别为96%、98%和89%。土壤硝化细菌、反硝化细菌可以作为铝污染土壤生态环境的指示菌。铝对两个大豆品种根际土壤微生物区系组成的影响不一致,揭示铝胁迫的生物效应还与植物生长、植物根际效应有关。     

3种西兰花种植方式对根际土壤细菌群落结构和多样性的影响研究

为明确不同种植方式减缓西兰花的连作障碍,本研究采用Illumina Miseq高通量测序技术,分析和比较了浙江省台州湾滨海滩涂地西兰花种植区单季稻-西兰花水旱轮作、南瓜-西兰花旱旱轮作和西兰花连作3种种植方式对西兰花根际土壤细菌群落结构和多样性的影响。结果表明,3种种植方式西兰花根际土壤共获得28门、92纲、167目、301科、691属土壤细菌。变形菌门、酸杆菌门、放线菌门、芽单胞菌门、拟杆菌门、绿湾菌门、蓝细菌门、厚壁菌门、硝化螺旋菌门、疣微菌门是台州湾滩涂围垦地西兰花根际土壤细菌相对丰度较高的优势菌群。水旱轮作能提高西兰花根际土壤细菌变形菌门、酸杆菌门和绿湾菌门的相对丰度,但降低了西兰花根际土壤细菌放线菌门、芽单胞菌门、拟杆菌门和蓝细菌门的相对丰度。多样性指数和丰富度指数均以水旱轮作为最高,其次是旱旱轮作,以西兰花连作的土壤多样性指数和丰富度指数最低。因此,与西兰花长期连作相比,水旱轮作和旱旱轮作均能改善台州湾滨海滩涂地区西兰花根际土壤细菌群落结构。水稻-西兰花水旱轮作更能增加西兰花根际土壤细菌有益菌丰度,提高其根际土壤细菌多样性指数,以改良西兰花根际生态环境。本研究结果为实现该区域西兰花优质高产栽培提供了理论和实践依据。     

黄河三角洲刺槐根际与非根际细菌结构及多样性

为精确分析黄河三角洲刺槐根际与非根际土壤细菌群落定殖情况,本研究采用高通量测序方法对刺槐根际与非根际土壤细菌结构及多样性进行了研究。研究表明,根际土壤细菌共有36门214属,非根际土壤细菌共有33门153属。变形菌门(Proteobacteria)、放线菌门(Actinobacteria)、酸杆菌门(Acidobacteria)细菌丰度超过15%,是根际与非根际土壤中的优势菌落。根际与非根际土壤中酸杆菌门、硝化螺旋菌门(Nitrospirae)丰度差异显著。根际土壤中红游动菌属(Rhodoplanes)、溶杆菌属(Lysobacter)、热单胞菌属(Thermomonas)、链霉菌属(Streptomyces)及非根际土壤中红游动菌属、溶杆菌属、链霉菌属、Kaistobacter细菌丰度超过4%。根际土壤中固氮菌丰度显著高于非根际土壤,解磷、解钾细菌丰度差异不显著。根际与非根际土壤细菌Chao丰富度分别为2 054、2 376,差异显著。根际与非根际土壤细菌之间的权重(Weighted Unifrac)距离在0.12~0.25之间。综上所述,黄河三角洲刺槐根际与非根际土壤细菌结构具有一定差异,多样性差异显著。     

健康与罹患青枯病的番茄土壤细菌群落特征比较

应用实时荧光定量PCR及MiSeq高通量测序技术,全面地研究了连作番茄田块中健康与感染青枯病植株周围土体及根际土壤细菌群落结构和组成.结果表明:健康番茄土体土壤的pH及全碳含量显著高于感病番茄土体土壤;土体及根际土壤的细菌群落结构和组成明显不同于感病番茄土体及根际土壤细菌群落.与感病番茄根际相比,健康番茄根际细菌的数量...     

水稻根际反硝化细菌生态分布的研究

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