Effect of long-term organic and mineral fertilization strategies on rhizosphere microbiota assemblage and performance of lettuce

Long-term agricultural fertilization strategies gradually change soil properties including the associated microbial communities. Cultivated crops recruit beneficial microbes from the surrounding soil environment via root exudates. In this study, we aimed to investigate the effects of long-term fertilization strategies across field sites on the rhizosphere prokaryotic (Bacteria and Archaea) community composition and plant performance. We conducted growth chamber experiments with lettuce (Lactuca sativa L.) cultivated in soils from two long-term field experiments, each of which compared organic versus mineral fertilization strategies. 16S rRNA gene amplicon sequencing revealed the assemblage of a rhizosphere core microbiota shared in all lettuce plants across soils, going beyond differences in community composition depending on field site and fertilization strategies. The enhanced expression of several plant genes with roles in oxidative and biotic stress signalling pathways in lettuce grown in soils with organic indicates an induced physiological status in plants. Lettuce plants grown in soils with different fertilization histories were visibly free of stress symptoms and achieved comparable biomass. This suggests a positive aboveground plant response to belowground plant–microbe interactions in the rhizosphere. Besides effects of fertilization strategy and field site, our results demonstrate the crucial role of the plant in driving rhizosphere microbiota assemblage.     

Disruption of Firmicutes and Actinobacteria abundance in tomato rhizosphere causes the incidence of bacterial wilt disease

Enrichment of protective microbiota in the rhizosphere facilitates disease suppression. However, how the disruption of protective rhizobacteria affects disease suppression is largely unknown. Here, we analyzed the rhizosphere microbial community of a healthy and diseased tomato plant grown <30-cm apart in a greenhouse at three different locations in South Korea. The abundance of Gram-positive Actinobacteria and Firmicutes phyla was lower in diseased rhizosphere soil (DRS) than in healthy rhizosphere soil (HRS) without changes in the causative Ralstonia solanacearum population. Artificial disruption of Gram-positive bacteria in HRS using 500-μg/mL vancomycin increased bacterial wilt occurrence in tomato. To identify HRS-specific and plant-protective Gram-positive bacteria species, Brevibacterium frigoritolerans HRS1, Bacillus niacini HRS2, Solibacillus silvestris HRS3, and Bacillus luciferensis HRS4 were selected from among 326 heat-stable culturable bacteria isolates. These four strains did not directly antagonize R. solanacearum but activated plant immunity. A synthetic community comprising these four strains displayed greater immune activation against R. solanacearum and extended plant protection by 4 more days in comparison with each individual strain. Overall, our results demonstrate for the first time that dysbiosis of the protective Gram-positive bacterial community in DRS promotes the incidence of disease.Subject terms: Plant sciences, Microbiome     

Effect of the aerenchymatous helophyte Glyceria maxima on the sulfate-reducing communities in two contrasting riparian grassland soils

Aims

The research aimed at studying the effect of flooding with sulfate-rich water on the activity, abundance and diversity of sulfate-reducing micro-organisms present in the root zone of an oxygen-releasing plant growing on two riparian grassland soils with contrasting amounts of iron.

Methods

A series of microcosms was used to investigate the effects. Plants were grown under controlled conditions in microcosms containing a rhizosphere and bulk soil compartment for a period of 12 weeks in the presence of sulfate-rich flood water. Molybdate-treated systems served as non-sulfate-reducing controls.

Results

At harvest, activity and numbers of sulfate-reducing micro-organisms were higher in the absence of molybdate, but a rhizosphere effect and an impact of the presence of high levels of iron were not observed on activity and numbers. Both soils had in common a diverse community of sulfate-reducing micro-organisms covering all major cultured bacterial taxa. The appearance of members of the Desulfovibrionaceae exclusively in the rhizosphere of G. maxima was the only unambiguous indication of a plant effect.

Conclusion

The presence of sulfate-rich flood water stimulated the activity and growth of a part of the sulfate-reducing community leading to a change in community composition. The proximity of aerenchymatous plant roots and the abundance of iron in the soil had a negligible effect on the sulfate-reducing community.     

Comparison of Rhizosphere Bacterial Communities in Arabidopsis thaliana Mutants for Systemic Acquired Resistance

Systemic acquired resistance (SAR) is an inducible systemic plant defense against a broad spectrum of plant pathogens, with the potential to secrete antimicrobial compounds into the soil. However, its impact on rhizosphere bacteria is not known. In this study, we examined fingerprints of bacterial communities in the rhizosphere of the model plant Arabidopsis thaliana to determine the effect of SAR on bacterial community structure and diversity. We compared Arabidopsis mutants that are constitutive and non-inducible for SAR and verified SAR activation by measuring pathogenesis-related protein activity via a β-glucoronidase (GUS) reporter construct driven by the β-1-3 glucanase promoter. We used terminal restriction fragment length polymorphism (T-RFLP) analysis of MspI- and HaeIII-digested 16S rDNA to estimate bacterial rhizosphere community diversity, with Lactobacillus sp. added as internal controls. T-RFLP analysis showed a clear rhizosphere effect on community structure, and diversity analysis of both rhizosphere and bulk soil operational taxonomic units (as defined by terminal restriction fragments) using richness, Shannon–Weiner, and Simpson’s diversity indices and evenness confirmed that the presence of Arabidopsis roots significantly altered bacterial communities. This effect of altered soil microbial community structure by plants was also seen upon multivariate cluster analysis of the terminal restriction fragments. We also found visible differences in the rhizosphere community fingerprints of different Arabidopsis SAR mutants; however, there was no clear decrease of rhizosphere diversity because of constitutive SAR expression. Our study suggests that SAR can alter rhizosphere bacterial communities, opening the door to further understanding and application of inducible plant defense as a driving force in structuring soil bacterial assemblages.     

Plant age and genotype impact the progression of bacterial community succession in the Arabidopsis rhizosphere

The rhizosphere is strongly influenced by plant-derived phytochemicals exuded by roots and plant species exert a major selective force for bacteria colonizing the root-soil interface. We have previously shown that rhizobacterial recruitment is tightly regulated by plant genetics, by showing that natural variants of Arabidopsis thaliana support genotype-specific rhizobacterial communities while also releasing a unique blend of exudates at six weeks post-germination. To further understand how exudate release is controlled by plants, changes in rhizobacterial assemblages of two Arabidopsis accessions, Cvi and Ler where monitored throughout the plants'' life cycle. Denaturing gradient gel electrophoresis (DGGE) fingerprints revealed that bacterial communities respond to plant derived factors immediately upon germination in an accession-specific manner. Rhizobacterial succession progresses differently in the two accessions in a reproducible manner. However, as plants age, rhizobacterial and control bulk soil communities converge, indicative of an attenuated rhizosphere effect, which coincides with the expected slow down in the active release of root exudates as plants reach the end of their life cycle. These data strongly suggest that exudation changes during plant development are highly genotype-specific, possibly reflecting the unique, local co-evolutionary communication processes that developed between Arabidopsis accessions and their indigenous microbiota.Key words: rhizobacterial succession, rhizobacterial communities, natural variation, root exudates, Arabidopsis accessions     

Impact of Plant Functional Group, Plant Species, and Sampling Time on the Composition of nirK-Type Denitrifier Communities in Soil

We studied the influence of eight nonleguminous grassland plant species belonging to two functional groups (grasses and forbs) on the composition of soil denitrifier communities in experimental microcosms over two consecutive years. Denitrifier community composition was analyzed by terminal restriction fragment length polymorphism (T-RFLP) of PCR-amplified nirK gene fragments coding for the copper-containing nitrite reductase. The impact of experimental factors (plant functional group, plant species, sampling time, and interactions between them) on the structure of soil denitrifier communities (i.e., T-RFLP patterns) was analyzed by canonical correspondence analysis. While the functional group of a plant did not affect nirK-type denitrifier communities, plant species identity did influence their composition. This effect changed with sampling time, indicating community changes due to seasonal conditions and a development of the plants in the microcosms. Differences in total soil nitrogen and carbon, soil pH, and root biomass were observed at the end of the experiment. However, statistical analysis revealed that the plants affected the nirK-type denitrifier community composition directly, e.g., through root exudates. Assignment of abundant T-RFs to cloned nirK sequences from the soil and subsequent phylogenetic analysis indicated a dominance of yet-unknown nirK genotypes and of genes related to nirK from denitrifiers of the order Rhizobiales. In conclusion, individual species of nonleguminous plants directly influenced the composition of denitrifier communities in soil, but environmental conditions had additional significant effects.     

Effect of Bacillus mesonae H20-5 Treatment on Rhizospheric Bacterial Community of Tomato Plants under Salinity Stress

Plant growth-promoting bacteria improve plant growth under abiotic stress conditions. However, their effects on microbial succession in the rhizosphere are poorly understood. In this study, the inoculants of Bacillus mesonae strain H20-5 were administered to tomato plants grown in soils with different salinity levels (EC of 2, 4, and 6 dS/m). The bacterial communities in the bulk and rhizosphere soils were examined 14 days after H20-5 treatment using Illumina MiSeq sequencing of the bacterial 16S rRNA gene. Although the abundance of H20-5 rapidly decreased in the bulk and rhizosphere soils, a shift in the bacterial community was observed following H20-5 treatment. The variation in bacterial communities due to H20-5 treatment was higher in the rhizosphere than in the bulk soils. Additionally, the bacterial species richness and diversity were greater in the H20-5 treated rhizosphere than in the control. The composition and structure of the bacterial communities varied with soil salinity levels, and those in the H20-5 treated rhizosphere soil were clustered. The members of Actinobacteria genera, including Kineosporia, Virgisporangium, Actinoplanes, Gaiella, Blastococcus, and Solirubrobacter, were enriched in the H20-5 treated rhizosphere soils. The microbial co-occurrence network of the bacterial community in the H20-5 treated rhizosphere soils had more modules and keystone taxa compared to the control. These findings revealed that the strain H20-5 induced systemic tolerance in tomato plants and influenced the diversity, composition, structure, and network of bacterial communities. The bacterial community in the H20-5 treated rhizosphere soils also appeared to be relatively stable to soil salinity changes.     

荒漠孑遗植物四合木对土壤古菌群落的影响

土壤是植物定居的场所,也是植物-微生物互作的重要界面。古菌是土壤微生物重要组份,在碳、氮、硫、铁等元素的生物地球化学循环和植物的生长发育、适应生境中发挥重要作用。植物定居对土壤古菌群落的影响研究鲜有开展,孑遗植物在研究植物-微生物-环境互作中具有独特的优势。采用扩增子高通量测序技术,研究以荒漠孑遗植物四合木为建群种或优势种的四合木-红砂-珍珠-针茅群落、四合木-针茅群落和四合木群落等三种荒漠植物群落类型中,四合木根区土壤和光板地土体土壤古菌群落特征,揭示四合木定居对土壤古菌物种数量、多样性、群落组成及功能的影响。结果表明,荒漠孑遗植物四合木定居不仅增加了根区土壤古菌的物种数量,提高了根区土壤古菌群落多样性,而且改变了土壤古菌群落组成,减少了奇古菌门Nitrososphaeraceae科未分类的属氨氧化古菌（unclassified_f_Nitrososphaeraceae）和暂定Nitrososphaera属氨氧化古菌（Candidatus Nitrososphaera）相对丰度,增加了Nitrososphaeraceae科暂定Nitrocosmicus属氨氧化古菌（Candidatus Nitrocosmicus）和广古菌门海洋古菌类群Ⅱ中未分类的属（norank_o_Marine_Group_II）相对丰度,广古菌门热原体纲未分类的属（unclassified_c__Thermoplasmata）相对丰度变化显著。植物群落演替对四合木根区土壤和光板地土体土壤古菌群落均无显著影响。Nitrososphaeraceae科氨氧化古菌是三种不同荒漠植物群落类型中土壤古菌的核心微生物组。四合木定居也显著改变土壤古菌群落的功能,减弱了高丰度功能,增强了低丰度功能,对有氧呼吸、核苷酸合成、氨基酸合成等途径影响显著。荒漠孑遗植物四合木定居改变了土壤古菌群落物种数量、多样性、组成、功能等特征。     

Influence of Soil Type,Cultivar and Verticillium dahliae on the Structure of the Root and Rhizosphere Soil Fungal Microbiome of Strawberry

Sustainable management of crop productivity and health necessitates improved understanding of the ways in which rhizosphere microbial populations interact with each other, with plant roots and their abiotic environment. In this study we examined the effects of different soils and cultivars, and the presence of a soil-borne fungal pathogen, Verticillium dahliae, on the fungal microbiome of the rhizosphere soil and roots of strawberry plants, using high-throughput pyrosequencing. Fungal communities of the roots of two cultivars, Honeoye and Florence, were statistically distinct from those in the rhizosphere soil of the same plants, with little overlap. Roots of plants growing in two contrasting field soils had high relative abundance of Leptodontidium sp. C2 BESC 319 g whereas rhizosphere soil was characterised by high relative abundance of Trichosporon dulcitum or Cryptococcus terreus, depending upon the soil type. Differences between different cultivars were not as clear. Inoculation with the pathogen V. dahliae had a significant influence on community structure, generally decreasing the number of rhizosphere soil- and root-inhabiting fungi. Leptodontidium sp. C2 BESC 319 g was the dominant fungus responding positively to inoculation with V. dahliae. The results suggest that 1) plant roots select microorganisms from the wider rhizosphere pool, 2) that both rhizosphere soil and root inhabiting fungal communities are influenced by V. dahliae and 3) that soil type has a stronger influence on both of these communities than cultivar.     

Simultaneous assessment of the effects of an herbicide on the triad: rhizobacterial community, an herbicide degrading soil bacterium and their plant host

Aims

This work addresses the relevant effects that one single compound, used as model herbicide, provokes on the activity/survival of a suitable herbicide degrading model bacterium and on a plant that hosts this bacterium and its bacterial rhizospheric community.

Methods

The effects of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), on Acacia caven hosting the 2,4-D degrading bacterium Cupriavidus pinatubonensis JMP134, and its rhizospheric microbiota, were simultaneously addressed in plant soil microcosms, and followed by culture dependent and independent procedures, herbicide removal tests, bioprotection assays and use of encapsulated bacterial cells.

Results

The herbicide provokes deleterious effects on the plant, which are significantly diminished by the presence of the plant associated C. pinatubonensis, especially with encapsulated cells. This improvement correlated with increased 2,4-D degradation rates. The herbicide significantly changes the structure of the A. caven bacterial rhizospheric community; and it also diminishes the preference of C. pinatubonensis for the A. caven rhizosphere compared with the surrounding bulk soil.

Conclusions

The addition of an herbicide to soil triggers a complex, although more or less predictable, suite of effects on rhizobacterial communities, herbicide degrading bacteria and their plant hosts that should be taken into account in fundamental studies and design of bio(phyto)remediation procedures.     

Antifungal Rhizosphere Bacteria Can increase as Response to the Presence of Saprotrophic Fungi

Knowledge on the factors that determine the composition of bacterial communities in the vicinity of roots (rhizosphere) is essential to understand plant-soil interactions. Plant species identity, plant growth stage and soil properties have been indicated as major determinants of rhizosphere bacterial community composition. Here we show that the presence of saprotrophic fungi can be an additional factor steering rhizosphere bacterial community composition and functioning. We studied the impact of presence of two common fungal rhizosphere inhabitants (Mucor hiemalis and Trichoderma harzianum) on the composition of cultivable bacterial communities developing in the rhizosphere of Carex arenaria (sand sedge) in sand microcosms. Identification and phenotypic characterization of bacterial isolates revealed clear shifts in the rhizosphere bacterial community composition by the presence of two fungal strains (M. hiemalis BHB1 and T. harzianum PvdG2), whereas another M. hiemalis strain did not show this effect. Presence of both M. hiemalis BHB1 and T. harzianum PvdG2 resulted in a significant increase of chitinolytic and (in vitro) antifungal bacteria. The latter was most pronounced for M. hiemalis BHB1, an isolate from Carex roots, which stimulated the development of the bacterial genera Achromobacter and Stenotrophomonas. In vitro tests showed that these genera were strongly antagonistic against M. hiemalis but also against the plant-pathogenic fungus Rhizoctonia solani. The most likely explanation for fungal-induced shifts in the composition of rhizosphere bacteria is that bacteria are being selected which are successful in competing with fungi for root exudates. Based on the results we propose that measures increasing saprotrophic fungi in agricultural soils should be explored as an alternative approach to enhance natural biocontrol against soil-borne plant-pathogenic fungi, namely by stimulating indigenous antifungal rhizosphere bacteria.     

Illumina Amplicon Sequencing of 16S rRNA Tag Reveals Bacterial Community Development in the Rhizosphere of Apple Nurseries at a Replant Disease Site and a New Planting Site

We used a next-generation, Illumina-based sequencing approach to characterize the bacterial community development of apple rhizosphere soil in a replant site (RePlant) and a new planting site (NewPlant) in Beijing. Dwarfing apple nurseries of ‘Fuji’/SH6/Pingyitiancha trees were planted in the spring of 2013. Before planting, soil from the apple rhizosphere of the replant site (ReSoil) and from the new planting site (NewSoil) was sampled for analysis on the Illumina MiSeq platform. In late September, the rhizosphere soil from both sites was resampled (RePlant and NewPlant). More than 16,000 valid reads were obtained for each replicate, and the community was composed of five dominant groups (Proteobacteria, Acidobacteria, Bacteroidetes, Gemmatimonadetes and Actinobacteria). The bacterial diversity decreased after apple planting. Principal component analyses revealed that the rhizosphere samples were significantly different among treatments. Apple nursery planting showed a large impact on the soil bacterial community, and the community development was significantly different between the replanted and newly planted soils. Verrucomicrobia were less abundant in RePlant soil, while Pseudomonas and Lysobacter were increased in RePlant compared with ReSoil and NewPlant. Both RePlant and ReSoil showed relatively higher invertase and cellulase activities than NewPlant and NewSoil, but only NewPlant soil showed higher urease activity, and this soil also had the higher plant growth. Our experimental results suggest that planting apple nurseries has a significant impact on soil bacterial community development at both replant and new planting sites, and planting on new site resulted in significantly higher soil urease activity and a different bacterial community composition.     

Development of specific rhizosphere bacterial communities in relation to plant species, nutrition and soil type

Rhizosphere microbial communities are important for plant nutrition and plant health. Using the culture-independent method of PCR-DGGE of 16S rDNA for community analyses, we conducted several experiments to investigate the importance of pH, soil type, soil amendment, nutritional status of the plant, plant species and plant age on the structure of the bacterial community in the rhizosphere. At the same time, we assessed the spatial variability of bacterial communities in different root zone locations. Our results showed that the bacterial community structure is influenced by soil pH and type of P fertilization. In a short-term experiment (15–22 days) with cucumber and barley growing in a N deficient or a P deficient soil, the bacterial community structure in the rhizosphere was affected by soil type and fertilization but not by plant species. In a 7.5-week experiment with three plant species (chickpea, canola, Sudan grass) growing in three different soils (a sand, a loam and a clay), the complex interactions between soil and plant effects on the rhizosphere community were apparent. In the sand and the loam, the three plant species had distinct rhizosphere communities while in the clay soil the rhizosphere community structures of canola and Sudan grass were similar and differed from those of chickpea. In all soils, the rhizosphere community structures of the root tip were different from those in the mature root zone. In white lupin, the bacterial community structure of the non-cluster roots differed from those of the cluster roots. As plants matured, different cluster root age classes (young, mature, old) had distinct rhizosphere communities. We conclude that many different factors will contribute to shaping the species composition in the rhizosphere, but that the plant itself exerts a highly selective effect that is at least as great as that of the soil. Root exudate amount and composition are the key drivers for the differences in community structure observed in this study.     

Specificity in Arabidopsis thaliana recruitment of root fungal communities from soil and rhizosphere

Biotic and abiotic conditions in soil pose major constraints on growth and reproductive success of plants. Fungi are important agents in plant soil interactions but the belowground mycobiota associated with plants remains poorly understood. We grew one genotype each from Sweden and Italy of the widely-studied plant model Arabidopsis thaliana. Plants were grown under controlled conditions in organic topsoil local to the Swedish genotype, and harvested after ten weeks. Total DNA was extracted from three belowground compartments: endosphere (sonicated roots), rhizosphere and bulk soil, and fungal communities were characterized from each by amplification and sequencing of the fungal barcode region ITS2. Fungal species diversity was found to decrease from bulk soil to rhizosphere to endosphere. A significant effect of plant genotype on fungal community composition was detected only in the endosphere compartment. Despite A. thaliana being a non-mycorrhizal plant, it hosts a number of known mycorrhiza fungi in its endosphere compartment, which is also colonized by endophytic, pathogenic and saprotrophic fungi. Species in the Archaeorhizomycetes were most abundant in rhizosphere samples suggesting an adaptation to environments with high nutrient turnover for some of these species. We conclude that A. thaliana endosphere fungal communities represent a selected subset of fungi recruited from soil and that plant genotype has small but significant quantitative and qualitative effects on these communities.     

Control of Late Blight (Phytophthora capsici ) in Pepper Plant with a Compost Containing Multitude of Chitinase-producing Bacteria

Compost sustaining a multitude of chitinase-producing bacteria was evaluated in a greenhouse study as a soil amendment for the control of late blight (Phytophthora capsici L.) in pepper (Capsicum annuum L.). Microbial population and exogenous enzyme activity were measured in the rhizosphere and correlated to the growth and health of pepper plant. Rice straw was composted with and without a chitin source, after having been inoculated with an aliquot of coastal area soil containing a known titer of chitinase-producing bacteria. P. capsici inoculated plants cultivated in chitin compost-amended soil exhibited significantly higher root and shoot weights and lower root mortality than plants grown in pathogen-inoculated control compost. Chitinase and β-1,3-glucanase activities in rhizosphere of plants grown in chitin compost-amended soil were twice that seen in soil amended with control compost. Colony forming units of chitinase-producing bacteria isolated from rhizosphere of plants grown in chitin compost-amended soil were 10³ times as prevalent as bacteria in control compost. These results indicate that increasing the population of chitinase-producing bacteria and soil enzyme activities in rhizosphere by compost amendment could alleviate pathogenic effects of P. capsici.     

Short-term plant species impact on microbial community structure in soils with long-term agricultural history

The goal of our study was to capture the short-term effects of individual plant species on an established microbial community in a soil with a well-defined agricultural history. Using biochemical and molecular techniques we quantified the effects of plant species on changes in the soil microbial community over an 8-week time-course. We conducted a greenhouse experiment using field soil from a site that was managed as a Zea mays monoculture for over 50 years. The conditioned soil provided a baseline from which changes in microbial community composition through the effects of newly introduced plants could be determined. Within a short time frame (8 weeks), introduced plants influenced the soil microbial community in ways unique to each plant. Some species (Fagopyrm esculentum and xTriticosecale spp.) resulted in an increase of total microbial community richness, diversity and the stimulation of new microbial species not associated with the legacy vegetation. Other plants (Vicia villosa and Lolium multiflorum) tended to reduce community diversity. We suggest root surface area is good general predictor of rhizosphere microbial community diversity, but in some cases other plant traits may have dominant influence on plant-induced changes in microbial community composition.     

一株柠条内生解磷菌的分离鉴定及实时荧光定量PCR检测

结合形态观察与16S rDNA序列测定对柠条根系内分离筛选得到的解磷细菌C9进行鉴定,Blast比对结果表明C9为泛菌(Pantoea vagans).在无机磷液体培养基培养条件下,用钼锑抗比色法研究它的解磷能力.结果表明,随着时间的延长,培养液中速效磷含量逐渐增加到4.45mg/L,溶液pH可降至4.2.进一步利用实时荧光定量PCR检测柠条根系中、柠条根际土壤与柠条根围土壤中该细菌存在的相对基因拷贝数,结果发现该基因在3种样品中的数量为:柠条根系＞柠条根际土壤＞柠条根围土壤,表明泛菌解磷细菌能聚集生长在柠条根系内,随着与根系接触距离的增加而呈逐级递减趋势.     

外来植物紫茎泽兰入侵对土壤理化性质及丛枝菌根真菌(AMF)群落的影响

为了揭示外来植物紫茎泽兰入侵对入侵地土壤丛枝菌根真菌(AMF)群落及相关肥力的影响,比较测定了紫茎泽兰不同入侵程度土壤理化性质、AMF侵染率及AMF群落的差异。结果表明,紫茎泽兰入侵降低了土壤pH,使土壤中有机碳、全氮和速效钾含量分别增加83.0%,106.9%和111.0%;尽管对全磷含量没有显著影响,但有机磷含量呈升高的趋势,而速效磷呈降低的趋势。紫茎泽兰入侵降低了本地植物的AMF侵染率;随着入侵程度的加深,土壤中以膨胀无梗囊霉(Acauospora dilatata)为优势种的AMF群落结构逐渐转变为以近明球囊霉(Glomus claroideum )为优势种的结构,紫茎泽兰可在其根周选择培育近明球囊霉,而对其它AMF种,特别是对膨胀无梗囊霉则存在抑制作用;基于各AMF种多度的聚类分析表明,形成紫茎泽兰单优群落土壤中各AMF种多度与未入侵的本地植物群落及入侵程度较轻的紫茎泽兰与本地植物群落之间存在明显分歧。综合分析推断认为,紫茎法兰入侵改变了入侵地土壤理化性状,抑制AMF对土著植物的侵染,改变AMF群落,并在其根周选择培育近明球囊霉,这可能是紫茎泽兰入侵及扩张的重要途径之一。     

The rhizosphere microbial community response to a bio-organic fertilizer: finding the mechanisms behind the suppression of watermelon <Emphasis Type="Italic">Fusarium</Emphasis> wilt disease

We aimed to evaluate the capability of bio-organic fertilizer suppressing watermelon Fusarium wilt disease, compare the variations of the rhizosphere bacterial and fungal community compositions after treatment with different fertilizers, and explore mechanisms causing disease suppression in rhizosphere microbial community. A rhizobacterium (Bacillus amyloliquefaciens JDF35) was identified to control watermelon Fusarium wilt disease. Bio-organic fertilizer JDF35 (BOF) was generated by inoculating JDF35 into the organic fertilizer (OF) composed of cow and chicken manure compost (1:50 v/w). A three successive growing season pot experiment was designed to evaluate the effects of BOF compared with OF and chemical fertilizer (CF). Next-generation sequencing using the Illumina MiSeq platform was used to investigate the variations in rhizosphere microbial community composition. The growth of the watermelon plants, soil pH, and available N, P and K concentrations were the highest in the BOF treatment. The Fusarium wilt incidence in the BOF treatment was lower than that in the CF and OF treatment, and the differences for disease incidence were significant (P < 0.001). The diversity of the rhizosphere bacterial community was higher, and that of the fungal was lower in the BOF treatment. Most importantly, the BOF treatment had lowest abundances of Fusarium. The application of the BOF altered the composition of rhizosphere microbial community, suppressing Fusarium wilt disease and promoting plant growth.