Consecutive Monoculture Research Articles

Rhizosphere Fungal Community Dynamics Associated with Rehmannia glutinosa Replant Disease in a Consecutive Monoculture Regime.

Consecutive monoculture of Rehmannia glutinosa in the same field leads to a severe decline in both quality and yield of tuberous roots, the most useful part in traditional Chinese medicine. Fungi are an important and diverse group of microorganisms in the soil ecosystem and play crucial roles in soil health. In this study, high-throughput pyrosequencing of internal transcribed spacer 2 ribosomal DNA amplicons was applied to gain insight into how consecutive monoculture practice influence and stimulate R. glutinosa rhizosphere and bulk soil fungal communities. The results from nonmetric multidimensional scaling ordination and clustering analysis revealed distinctive differences between rhizosphere and bulk soil fungal communities. However, longer-term monocultured bulk soils were more similar to the rhizosphere soils in comparison with the shorter-term monocultured bulk soils. Moreover, consecutive monoculture caused a gradual shift in the composition and structure of the soil fungal community. The cultivation of this plant led to the appearance of some exclusive operational taxonomic units in rhizosphere or bulk soils that were assigned to the genera Fusarium, Rhizoctonia, and so on. Furthermore, the sum of the relative abundance of species of Fusarium, Cylindrocarpon, and Gibberella (belonging to the family Nectriaceae); Rhizoctonia, Thanatephorus, and Ceratobasidium (belonging to the family Ceratobasidiaceae); and Lectera and Plectosporium (belonging to the family Plectosphaerellaceae) was significantly higher in consecutively monocultured (CM) than in newly planted (NP) soil in both rhizosphere and bulk soils. In particular, Fusarium abundance was significantly higher in CM than in NP in the rhizosphere, and higher in rhizosphere soils than in bulk soils for each treatment. A pathogenicity test showed that both Fusarium strains isolated were pathogenic to R. glutinosa seedlings. In addition, the culture filtrate and mycotoxins produced by Fusarium oxysporum significantly repressed the growth of the antagonistic bacterium, Pseudomonas aeruginosa. In conclusion, consecutive monoculture of R. glutinosa restructured the fungal communities in both rhizosphere and bulk soils but bulk effects developed more slowly over time in comparison with rhizosphere effects. Furthermore, microbial interactions might lead to a reduction in the abundance of beneficial microbes.

Rhizosphere responses to environmental conditions in Radix pseudostellariae under continuous monoculture regimes

The root exudates of Radix pseudostellariae, working as a rhizospheric intermediary between plants and microbes, can deteriorate the microbial community in the rhizosphere in a consecutive monoculture system. We assessed the effects of artificially applied R. pseudostellariae root exudates on R. pseudostellariae seedling growth, rhizosphere soil microbial communities, and soil physicochemical properties. We found that phenolic acids and organic acids acted as a driver of changes in the microbial community. High-throughput sequencing and qRT-PCR analysis demonstrated that treatment with phenolic acids significantly decreased the relative abundance of Trichoderma, Penicillium, Pseudomonadales, Xanthomonadales, and Streptomycetales. Organic acids had a significant negative effect on the relative abundance of Pseudomonadales and Streptomycetales and significantly increased the abundance of Fusarium, Xanthomonadales, Micrococcales, and Gemmatimonadales. Analysis based on the noninvasive microtest technique indicated that root exudates increased H+ efflux and plasma membrane H+-ATPase activity in the pathogenic fungi and decreased them in the beneficial fungi. These phenomena created an acidic environment for the inhibition of beneficial bacteria and accumulation of specialized plant pathogens. This study explains the mechanisms underlying the shift in microflora and structural disorder caused by root exudates in continuously monocultured R. pseudostellariae rhizosphere soil through responses to environmental conditions.

Effects of consecutive monoculture of sweet potato on soil bacterial community as determined by pyrosequencing.

Soil bacteria play key roles in determining soil health and plant growth. In this study, four sweet potato fields that had been consecutively monocultured for 1, 2, 3, and 4 years were used to investigate the effect of monoculture on soil physicochemical properties and soil bacterial communities. The results revealed that continuous cropping led to a significant decline in soil pH, soil organic carbon, and soil bacterial abundance. Miseq pyrosequencing analysis of 16S rRNA genes revealed that Proteobacteria and Bacteroidetes were the main phyla in the sweet potato monoculture soils, comprising up to 66.24% of the total sequences. The relative abundances of beneficial bacteria, including Actinobacteria, Gemmatimonadetes, Firmicutes, Xanthomonadaceae, Rhodospirillaceae, and Syntrophobacteraceae, as well as their subgroups at the genus and operational taxonomic unit (OTU) levels, decreased considerably as the number of continuous cropping years increased. In contrast, the number of potentially pathogenic bacteria, such as Acidobacteria, Sphingomonadaceae, and Pedobacter accumulated with increasing years. The results also showed the alterations to the bacterial community in the sweet potato monoculture soils were mainly driven by soil pH and soil organic matter. Overall, the decline in soil quality after successive sweet potato monoculture can be attributed to the imbalance in soil properties and soil microbes, including the decrease in soil pH and soil organic carbon, and the enrichment of pathogenic bacteria at the expense of plant-beneficial bacteria.

Identification of Rehmannia glutinosa L. NB-ARC family proteins and their typical changes under consecutive monoculture stress

NB-ARC proteins are critical to effector-triggered immunity and play important roles in effector recognition and signal transduction in healthy plant growth. However, their primary protein traits, functions and roles remain incompletely understood in Rehmannia glutinosa. Here, we identified 45 NB-ARC protein sequences from the protein sequence sets and transcriptome of R. glutinosa. The CC type was the main one, accounting for 84.44% of these sequences. The most conserved motif was a 288 aa ADP-binding sequence. This motif belongs to the disease-resistance proteins. Differential expression of 36 expressed NB-ARC genes revealed that NB-ARC genes were rarely expressed 30 days after planting and were frequently expressed approximately 60 days after planting. To further understand the function of NB-ARC in replanted R. glutinosa, the genes encoding NB-ARC domains were profiled using qRT-PCR under the different stress states involved in the formation of consecutive monoculture problems. The results showed that NB-ARC genes might play a role in the formation of R. glutinosa consecutive monoculture problems. This study is the first to identify NB-ARC genes in R. glutinosa and to reveal their roles in consecutive monoculture problems in R. glutinosa. These findings provide insights into the mechanism of formation of consecutive monoculture problems.

Barcoded Pyrosequencing Reveals a Shift in the Bacterial Community in the Rhizosphere and Rhizoplane of Rehmannia glutinosa under Consecutive Monoculture

The production and quality of Rehmannia glutinosa can be dramatically reduced by replant disease under consecutive monoculture. The root-associated microbiome, also known as the second genome of the plant, was investigated to understand its impact on plant health. Culture-dependent and culture-independent pyrosequencing analysis was applied to assess the shifts in soil bacterial communities in the rhizosphere and rhizoplane under consecutive monoculture. The results show that the root-associated microbiome (including rhizosphere and rhizoplane microbiomes) was significantly impacted by rhizocompartments and consecutive monoculture. Consecutive monoculture of R. glutinosa led to a significant decline in the relative abundance of the phyla Firmicutes and Actinobacteria in the rhizosphere and rhizoplane. Furthermore, the families Flavobacteriaceae, Sphingomonadaceae, and Xanthomonadaceae enriched while Pseudomonadaceae, Bacillaceae, and Micrococcaceae decreased under consecutive monoculture. At the genus level, Pseudomonas, Bacillus, and Arthrobacter were prevalent in the newly planted soil, which decreased in consecutive monocultured soils. Besides, culture-dependent analysis confirmed the widespread presence of Pseudomonas spp. and Bacillus spp. in newly planted soil and their strong antagonistic activities against fungal pathogens. In conclusion, R. glutinosa monoculture resulted in distinct root-associated microbiome variation with a reduction in the abundance of beneficial microbes, which might contribute to the declined soil suppressiveness to fungal pathogens in the monoculture regime.

The role of soil bacterial community during winter fallow period in the incidence of tobacco bacterial wilt disease.

Bacterial wilt, caused by Ralstonia solanacearum, occurs occasionally during tobacco planting and potentially brings huge economic losses in affected areas. Soil microbes in different management stages play important roles in influencing bacterial wilt incidence. Studies have focused on the impacts of species diversity and composition during cropping periods on disease morbidity; however, the effects of the soil bacterial biomass, species diversity, species succession, and population interactions on morbidity remain unclear during non-cropping periods. In this study, we explored the soil bacterial communities in the non-cropping winter fallow (WF) and cropping late growing (LG) periods under consecutive monoculture systems using 16S ribosomal RNA gene sequencing and qPCR and further analyzed their effects on tobacco bacterial wilt incidence. We found that the bacterial communities in the WF period were significantly different from those in the LG period based on detrended correspondence analysis and dissimilarity tests. Crop morbidity was significantly related to bacterial community structure and to the presence of some genera during WF and LG periods. These genera, such as Arthrobacter, Pseudomonas, Acidobacteria GP6, and Pasteuria, may be potential biological control agents for bacterial wilt. Further analysis indicated that low soil bacterial diversity during the WF period, decrease of bacterial interactions from the WF to LG periods, and low soil biomass during the LG period all have the potential to increase morbidity. In conclusion, an increase of soil bacterial diversity and control of some bacterial abundances in the WF period might be an effective approach in controlling bacterial wilt incidence.

The root transcriptome of Achyranthes bidentata and the identification of the genes involved in the replanting benefit.

The transcriptome profiling in replanting roots revealed that expression pattern changes of key genes promoted important metabolism pathways, antioxidant and pathogen defense systems, adjusted phytohormone signaling and inhibited lignin biosynthesis. The yield of the medicinal plant Achyranthes bidentata could be significantly increased when replanted into a field cultivated previously for the same crop, but the biological basis of this so-called "replanting benefit" is unknown. Here, the RNA-seq technique was used to identify candidate genes responsible for the benefit. The analysis of RNA-seq libraries prepared from mRNA extracted from the roots of first year planting (normal growth, NG) and second year replanting (consecutive monoculture, CM) yielded about 40.22GB sequencing data. After de novo assembly, 87,256 unigenes were generated with an average length of 1060bp. Among these unigenes, 55,604 were annotated with public databases, and 52,346 encoding sequences and 2881 transcription factors were identified. A contrast between the NG and CM libraries resulted in a set of 3899 differentially transcribed genes (DTGs). The DTGs related to the replanting benefit and their expression profiles were further analyzed by bioinformatics and qRT-PCR approaches. The major differences between the NG and CM transcriptomes included genes encoding products involved in glycolysis/gluconeogenesis, glutathione metabolism and antioxidant defense, in aspects of the plant/pathogen interaction, phytohormone signaling and phenylpropanoid biosynthesis. The indication was that replanting material enjoyed a stronger level of defense systems, a balance regulation of hormone signals and a suppression of lignin formation, thereby promoting root growth and development. The study provides considerable significant insights for a better understanding of the molecular mechanism of the replanting benefit and suggests their possible application in developing methods to reinforce the effects in medicinal plants.

Transcriptome analysis of Pseudostellaria heterophylla in response to the infection of pathogenic Fusarium oxysporum

BackgroundPseudostellaria heterophylla (P. heterophylla), a herbaceous perennial, belongs to Caryophyllaceae family and is one of the Chinese herbal medicine with high pharmacodynamic value. It can be used to treat the spleen deficiency, anorexia, weakness after illness and spontaneous perspiration symptoms. Our previous study found that consecutive monoculture of Pseudostellaria heterophylla could lead to the deterioration of the rhizosphere microenvironment. The specialized forms of pathogenic fungus Fusarium oxysporum f.Sp. heterophylla (F. oxysporum) in rhizosphere soils of P. heterophylla plays an important role in the consecutive monoculture of P. heterophylla.ResultsIn this study, F. oxysporum was used to infect the tissue culture plantlets of P. heterophylla to study the responding process at three different infection stages by using RNA-sequencing. We obtained 127,725 transcripts and 47,655 distinct unigenes by de novo assembly and obtained annotated information in details for 25,882 unigenes. The Kyoto Encyclopedia of Genes and Genomes pathway analysis and the real-time quantitative PCR results suggest that the calcium signal system and WRKY transcription factor in the plant-pathogen interaction pathway may play an important role in the response process, and all of the WRKY transcription factor genes were divided into three different types. Moreover, we also found that the stimulation of F. oxysporum may result in the accumulation of some phenolics in the plantlets and the programmed cell death of the plantlets.ConclusionsThis study has partly revealed the possible molecular mechanism of the population explosion of F. oxysporum in rhizosphere soils and signal response process, which can be helpful in unraveling the role of F. oxysporum in consecutive monoculture problems of P. heterophylla.

Assessment of the Diversity of Pseudomonas spp. and Fusarium spp. in Radix pseudostellariae Rhizosphere under Monoculture by Combining DGGE and Quantitative PCR.

Radix pseudostellariae is a perennial tonic medicinal plant, with high medicinal value. However, consecutive monoculture of this plant in the same field results in serious decrease in both yield and quality. In this study, a 3-year field experiment was performed to identify the inhibitory effect of growth caused by prolonged monoculture of R. pseudostellariae. DGGE analysis was used to explore the shifts in the structure and diversity of soil Fusarium and Pseudomonas communities along a 3-year gradient of monoculture. The results demonstrated that extended monoculture significantly boosted the diversity of Fusarium spp., but declined Pseudomonas spp. diversity. Quantitative PCR analysis showed a significant increase in Fusarium oxysporum, but a decline in Pseudomonas spp. Furthermore, abundance of antagonistic Pseudomonas spp. possessing antagonistic ability toward F. oxysporum significantly decreased in consecutively monocultured soils. Phenolic acid mixture at the same ratio as detected in soil could boost mycelial and sporular growth of pathogenic F. oxysporum while inhibit the growth of antagonistic Pseudomonas sp. CJ313. Moreover, plant bioassays showed that Pseudomonas sp. CJ313 had a good performance that protected R. pseudostellariae from infection by F. oxysporum. In conclusion, this study demonstrated that extended monoculture of R. pseudostellariae could alter the Fusarium and Pseudomonas communities in the plant rhizosphere, leading to relatively low level of antagonistic microorganisms, but with relatively high level of pathogenic microorganisms.

Banana Fusarium Wilt Disease Incidence Is Influenced by Shifts of Soil Microbial Communities Under Different Monoculture Spans.

The continuous cropping of banana in the same field may result in a serious soil-borne Fusarium wilt disease and a severe yield decline, a phenomenon known as soil sickness. Although soil microorganisms play key roles in maintaining soil health, the alternations of soil microbial community and relationship between these changes and soil sickness under banana monoculture are still unclear. Bacterial and fungal communities in the soil samples collected from banana fields with different monoculture spans were profiled by sequencing of the 16S rRNA genes and internal transcribed spacer using the MiSeq platform to explore the relationship between banana monoculture and Fusarium wilt disease in the present study. The results showed that successive cropping of banana was significantly correlated with the Fusarium wilt disease incidence. Fungal communities responded more obviously and quickly to banana consecutive monoculture than bacterial community. Moreover, a higher fungal richness significantly correlated to a higher banana Fusarium wilt disease incidence but a lower yield. Banana fungal pathogenic genus of Fusarium and Phyllosticta were closely associated with banana yield depletion and disease aggravation. Potential biocontrol agents, such as Funneliformis, Mortierella, Flavobacterium, and Acidobacteria subgroups, exhibited a significant correlation to lower disease occurrence. Further networks analysis revealed that the number of functionally interrelated modules decreased, the composition shifted from bacteria- to fungi-dominated among these modules, and more resources-competitive interactions within networks were observed after banana long-term monoculture. Our results also showed that bacterial and fungal communities were mainly driven by soil organic matter. Overall, the findings indicated that the bacterial and fungal community structures altered significantly after banana long-term monoculture, and the fungal richness, abundance of Fusarium, interactions between and within bacteria and fungi in ecological networks, and soil organic matter were associated with banana soil-borne Fusarium wilt disease.

Soil microbial community structure and catabolic activity are significantly degenerated in successive rotations of Chinese fir plantations

This study examined the hypotheses that soil microbial community composition and catabolic activity would significantly degenerated by consecutive monoculture in Chinese fir plantations. The phospholipid fatty acids (PLFA) and community level physiological profiles (CLPP) methods were used to assess the variations of soil microbial community among the first rotation Chinese fir plantation (FCP), the second rotation plantation (SCP) and the third rotation plantation (TCP). The total content of PLFA biomarkers was highest in FCP, followed by SCP, and TCP was the least detected. Conversely, the fungi/bacteria ratio significantly increased in the SCP and TCP soils. The average well-color development (AWCD) values significantly decreased (FCP > SCP > TCP). However, the sum of AWCD values of amino acids, carboxylic acids and phenolic compounds were higher significantly in the SCP and TCP soils than FCP soils, suggesting that the microflora feeding on acids gradually became predominant in the continuous monoculture plantation soils. Soil C/N ratio was one of the most important factors to soil microbial diversity. Both the PLFA and CLPP results illustrated the long-term pure plantation pattern exacerbated the microecological imbalance in the rhizospheric soils of Chinese fir, and markedly decreased the soil microbial community diversity and metabolic activity.

Transcriptome analysis reveals metabolic alteration due to consecutive monoculture and abiotic stress stimuli in Rehamannia glutinosa Libosch.

We deeply investigated the mechanism underlying metabolic regulation in response to consecutive monoculture (replanting disease) and different abiotic stresses that unfolded the response mechanism to consecutive monoculture problem through RNA-seq analysis. The consecutive monoculture problem (CMP) resulted of complex environmental stresses mediated by multiple factors. Previous studies have noted that multiple stress factors in consecutive monoculture soils or plants severely limited the interpretation of the critical molecular mechanism, and made a predict that the specifically responding factor was autotoxic allelochemicals. To identify the specifically responding genes, we compared transcriptome changes in roots of Rehamannia glutinosa Libosch using consecutive monoculture, salt, drought, and ferulic acid as stress factors. Comparing with normal growth, 2502, 2672, 2485, and 1956 genes were differentially expressed in R. glutinosa under consecutive monoculture practice, salt, drought, and ferulic acid stress, respectively. In addition, 510 genes were specifically expressed under consecutive monoculture, which were not present under the other stress conditions. Integrating the biological and enrichment analyses of the differentially expressed genes, the result demonstrated that the plants could alter enzyme genes expression to reconstruct the complicated metabolic pathways, which used to tolerate the CMP and abiotic stresses. Furthermore, most of the affected pathway genes were closely related to secondary metabolic processes, and the influence of consecutive monoculture practice on the transcriptome genes expression profile was very similar to the profile under salt stress and then to the profile under drought stress. The outlined schematic diagram unfolded the putative signal regulation mechanism in response to the CMP. Genes that differentially up- or down-regulated under consecutive monoculture practice may play important roles in the CMP or replanting disease in R. glutinosa.

Suppression of Fusarium wilt of cucumber by ammonia gas fumigation via reduction of Fusarium population in the field

Cucumber plants subjected to consecutive monoculture for 9 years were found to suffer from severe Fusarium wilt disease, caused by the soil-borne fungus Fusarium oxysporum f. sp. Cucumerinum J. H. Owen. In the present study, greenhouse experiments were performed to evaluate the influence of ammonia gas fumigation on Fusarium wilt suppression, fungal abundance and fungal community composition. Results showed that ammonia gas fumigation remarkably reduced disease incidence from 80% to 27%, resulting in a four-fold increase in yield, compared to the control. Total fungal abundance declined dramatically after fumigation and reached the lowest level at day 32, at 243 times lower than the control. Moreover, fumigation significantly increased soil fungal diversity, though it also decreased considerably coinciding with cucumber growth. Fumigation also significantly altered soil fungal community composition, relative to the control. Fusarium was strongly inhibited by fumigation in both relative abundance (3.8 times lower) and targeted quantification (a decrease of 167 fold). Collectively, the application of ammonia gas fumigation to control Fusarium wilt of cucumber resulted in a re-assembly of the fungal community to resemble that of a non-disease conducive consortium. Additional strategies, such as bioorganic fertilizer application, may still be required to develop sustainable disease suppression following fumigation.

Advances on molecular mechanisms of Rehmannia glutinosa consecutive monoculture problem formation in multi-omics era

Although consecutive monoculture problems have been studied for many years, no effective treatments are currently available. The complexity of systems triggered the formation of consecutive monoculture problems was one major cause. This paper elaborated the physiological and ecological mechanisms of consecutive monoculture problem formation based on the interaction relationship among multiple factors presented in the rhizosphere soil of consecutive monoculture plants. At same time, in this paper the multiple interactions among cultivated medicinal plants, autotoxic allelochemicals and rhizosphere microbial were proposed to be most important causes that derived the formation of consecutive monoculture problem. The paper also highlighted the advantage of 'omics' technologies integrating plant functional genomics and metabolomics as well as microbial macro-omics in understanding the multiple factor interaction under a particular ecological environment. Additionally, taking R. glutinosa as an example, the paper reviewed the molecular mechanism for the formation of R. glutinosa consecutive monoculture problem from the perspective of the accumulation of allelopathic autotoxins, the rhizosphere microecology catastrophe and theresponding of consecutive monoculture plants. Simultaneously, the roles of mutilple 'omics' technologies in comprehending these formation mechanism were described in detail. This paper provides finally a new insight to solve systematically the mechanism of consecutive monoculture problem formation on molecular level.

A consideration on screening of allelochemicals by using "knock-out/in" of targeting ingredients based on identification model of medicinal effect

This paper clarified in detail the definition, characteristics of allelopathy and its association with consecutive monoculture problem.Most of studies have indicated that it is critical to parse the formation mechanisms of consecutive monoculture problem that identification of allelochemicals and verification of its function. Here, we proposed a new approach to separate and identify the allelochemical group precisely and effectively, in which the "knock-out/in" methods of targeting ingredients in the model of medicinal effect identification and quality control were applied. This method will contribute to deep understanding plant allelopathy, and provide theoretical basis and technical support for alleviating consecutive monoculture problems simultaneously.

不同连作年限怀牛膝根际土壤理化性质及微生物多样性

PDF HTML阅读 XML下载 导出引用 引用提醒 不同连作年限怀牛膝根际土壤理化性质及微生物多样性 DOI: 10.5846/stxb201606071097 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（81303170，81573530，31401950，U1205021）；闽台作物特色种质创制与绿色栽培协同创新中心（2015-75） Analysis of physicochemical properties and microbial diversity in rhizosphere soil of Achyranthes bidentata under different cropping years Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以不同连作年限怀牛膝根际土壤为材料，采用土壤农化分析技术和磷脂脂肪酸生物标记法，对土壤理化性质以及根际微生物群落结构进行分析。结果表明：怀牛膝连作会使大部分大量元素（全磷、碱解氮、速效磷和速效钾）含量上升，而全氮、全钾的变化并无明显趋势。全量钙、全量镁、全量锰和有效锌的含量也会随着连作年限的增加而增加。研究发现，怀牛膝连作1a的土壤与对照相比，根际土壤微生物群落结构差别不大，但是与连作10a和30a的土壤相比微生物多样性却发生了明显变化。土壤中总PLFAs、细菌、革兰氏阴性菌Gram（-）及真菌含量都随连作年限增加而明显上升，微生物多样性增加，且革兰氏阳性菌Gram（+）/革兰氏阴性菌Gram（-）的比值随着连作年限的增加而下降。此外，土壤中一些嗜热解氢杆菌和真菌等参与土壤物质循环和木质素降解的微生物类群数量明显增加，假单胞菌等有益微生物类群也显著增多，这是牛膝连作促进作用的生物学基础。研究用药用植物怀牛膝证明了植物根际微生物结构和功能多样性对植物连作促进或连作抑制作用的产生与控制的生态学意义。 Abstract:In this study, the rhizosphere soils of Achyranthes bidentata, which was grown in a monoculture for multiple years, were investigated for analyzing the major elements, trace elements and rhizosphere microbial community structure by means of agricultural chemistry and phospholipid fatty acid (PLFA) analysis techniques. The results showed that consecutive monocultures of A. bidentata increased the contents of major elements (total phosphorus, alkaline hydrolysis nitrogen, available phosphorus, and available potassium). However, the ability of consecutive monocultures to change the total nitrogen content and total potassium was not obvious. In addition, total calcium, total magnesium, total manganese, and available zinc contents also increased with the increasing years of monoculture. Further analysis of PLFA profiles showed that there were no obvious differences in the rhizosphere microbial community structures between the control and newly planted A. bidentata. Besides, different results were depicted by 10 years and 30 years of consecutive monoculture, which showed that the total PLFA, bacteria (especially G-), and fungal content increased significantly, and the G+/G- ratio decreased with increasing years of monoculture. Moreover, some microbes involved in material cycling and lignin degradation, such as Hydrogenobacter, fungi (PLFA18:2ω6,9), and some beneficial bacteria including Pseudomonas increased significantly with increasing years of monoculture. These results suggest the important biological basis for the promotion mechanism of A. bidentata under a monoculture system. The case study exemplifies the ecological significance of rhizosphere microbial structure and its functional diversity in monoculture promotion or monoculture inhibition. 参考文献 相似文献 引证文献

Dynamic change of the rhizosphere microbial community in response to growth stages of consecutively monocultured Rehmanniae glutinosa

Abstract, an important medical plant in China, has distinct regional characteristics. It has long suffered from consecutive monoculture obstacles, resulting in severe reduction of quality and yield. The microbial community is believed to play an important role in the monoculture process. However, there are no reports on how microbial compositions change in response to growth of

Effects of different amendments on contents of phenolic acids and specific microbes in rhizosphere of Pseudostellaria heterophylla.

Pseudostellaria heterophylla is a perennial herbaceous plant in the family Caryophyllaceae. The tuberous roots of P. heterophylla are highly valued in traditional Chinese medicine and have a high market demand. However, extended monoculture of P. heterophylla results in a significant decline in the biomass and quality, and escalates disease and pest problems. Therefore, it is important to understand the underlying mechanism and biocontrol methods for consecutive monoculture problems. With "Zheshen 2" as an experimental material, the changes in the contents of main nutrients in soil, phenolic acids and specific microbes under monoculture and different amendments were analyzed by using high performance liquid chromatography (HPLC) and qPCR. The results showed that consecutive monoculture of P. heterophylla led to a decrease in yield by 43.5% while the microbial fertilizer treatment and the paddy-upland rotation could relieve the consecutive monoculture problems. Available nitrogen, available phosphorus, available potassium and total potassium were significantly higher in the consecutively monocultured soils than in the newly planted soils. But consecutive monoculture resulted in soil acidification. HPLC analysis showed that conse-cutive monoculture of this plant did not lead to a consistent accumulation of soil phenolic acids. At middle stage of root expansion and at harvest stage, most of phenolic acids were even higher in the newly planted soils than in the consecutively monocultured soils. Furthermore, qPCR analysis showed that the amounts of three specific pathogens identified previously (i.e. Fusarium oxysporum, Talaromyces helicus, Kosakonia sacchari) were significantly higher in the consecutively monocultured soils than in the newly planted soils. However, the microbial fertilizer treatment and the paddy-upland rotation resulted in a significant decline in the population of these specific pathogens and improved the soil environment. In conclusion, the consecutive monoculture problems of P. heterophylla may be due to the rapid proliferation of host-specific pathogens, rather than the deficiency of soil nutrients and the autotoxicity of allelochemicals in root exudates. The results in this study could provide the theoretical basis to explore the underlying mechanism of replanting disease of P. heterophylla and its biocontrol strategies.

Different responses of rhizosphere and non-rhizosphere soil microbial communities to consecutive Piper nigrum L. monoculture.

Soil microorganisms have important influences on plant growth and health. In this study, four black pepper fields consecutively monocultured for 12, 18, 28 and 38 years were selected for investigating the effect of planting age on rhizosphere and non-rhizosphere soil microbial communities and soil physicochemical properties. The results revealed that the relative abundance of the dominant bacterial phyla in rhizosphere soil increased considerably with long-term consecutive monoculture but decreased in non-rhizosphere soil with a significant decline in Firmicutes. For fungi, an increasing trend over time was observed in both rhizosphere and non-rhizosphere soils, with the abundance of the pathogenic fungi Fusarium increasing significantly accompanied by a decrease in the bacteria Pseudomonas and Bacillus that is beneficial for black pepper. Consecutive monoculture, especially for 38 years, considerably decreased soil microbial diversity. Additionally, the rhizosphere soil pH and organic matter and available K contents decreased with increasing planting duration, though available N and P increased. All soil nutrient contents and microbial diversity indices were higher in rhizosphere soil compared to non-rhizosphere soil. The results suggest that long-term consecutive monoculture leads to variations in soil microbial community composition and physicochemical properties in both rhizosphere and non-rhizosphere soils, thus inhibiting the black pepper growth.

Interaction of Pseudostellaria heterophylla with Quorum Sensing and Quorum Quenching Bacteria Mediated by Root Exudates in a Consecutive Monoculture System.

Many plant-pathogenic bacteria are dependent on quorum sensing (QS) to evoke disease. In this study, the population of QS and quorum quenching (QQ) bacteria was analyzed in a consecutive monoculture system of Pseudostellaria heterophylla. The isolated QS strains were identified as Serratia marcescens with SwrIR-type QS system and exhibited a significant increase over the years of monoculture. Only one QQ strain was isolated from newly planted soil sample and was identified as Bacillus thuringiensis, which secreted lactonase to degrade QS signal molecules. Inoculation of S. marcescens to P. heterophylla root could rapidly cause wilt disease, which was alleviated by B. thuringiensis. Furthermore, the expression of lactonase encoded by the aiiA gene in S. marcescens resulted in reduction of its pathogenicity, implying that the toxic effect of S. marcescens on the seedlings was QS-regulated. Meanwhile, excess lactonase in S. marcescens led to reduction in antibacterial substances, exoenzymes, and swarming motility, which might contribute to pathogensis on the seedlings. Root exudates and root tuber extracts of P. heterophylla significantly promoted the growth of S. marcescens, whereas a slight increase of B. thuringiensis was observed in both samples. These results demonstrated that QS-regulated behaviors in S. marcescens mediated by root exudates played an important role in replanting diseases of P. heterophylla.