Bacterial diversity of the rhizosphere of maize (Zea mays) grown in tropical soil studied by temperature gradient gel electrophoresis

The bacterial diversity and population dynamics in the rhizosphere of two maize cultivars (Nitroflint and Nitrodent) grown in tropical soils was studied, by traditional cultivation techniques and 16S rRNA gene-based molecular analysis of DNA directly extracted from soil and rhizosphere samples. Rhizosphere and soil samples were taken at three different plant growth stages. Total aerobic bacterial counts were determined. Fingerprints of the most dominant bacterial population were generated by TGGE separation of 16S rRNA gene fragments amplified from total community DNA using eubacterial specific primers. To reduce the complexity of TGGE fingerprints or to analyse less abundant populations, primers specific for different phylogenetic groups have been used. A comparison of the cfu obtained for rhizosphere of both cultivars indicated significant differences only for rhizosphere and soil samples taken 40 days after sowing. However, a comparison of TGGE patterns indicated that the composition of the bacterial community analysed at different plant growth stages for both cultivars was similar. A comparison of -, -proteobacterial and actinomycete TGGE patterns of both cultivars confirmed this observation. The eubacterial TGGE profiles reflected strong seasonal population shifts in the bacterial rhizosphere community of both maize cultivars which could be also observed in the TGGE patterns of - and -proteobacteria and to a lesser extent for actinomycetes. The rhizosphere effect was much more pronounced for young roots compared to samples taken from mature maize plants. The rhizosphere fingerprints showed a reduced complexity for young plants with up to five dominating bands while for mature plants patterns similar to those of soil were observed. Sequencing of dominant clones indicated that the dominant population found at all plant growth stages can be assigned to Arthrobacter populations.     

Bacterial Community Composition in Central European Running Waters Examined by Temperature Gradient Gel Electrophoresis and Sequence Analysis of 16S rRNA Genes

The bacterial community composition in small streams and a river in central Germany was examined by temperature gradient gel electrophoresis (TGGE) with PCR products of 16S rRNA gene fragments and sequence analysis. Complex TGGE band patterns suggested high levels of diversity of bacterial species in all habitats of these environments. Cluster analyses demonstrated distinct differences among the communities in stream and spring water, sandy sediments, biofilms on stones, degrading leaves, and soil. The differences between stream water and sediment were more significant than those between sites within the same habitat along the stretch from the stream source to the mouth. TGGE data from an entire stream course suggest that, in the upper reach of the stream, a special suspended bacterial community is already established and changes only slightly downstream. The bacterial communities in water and sediment in an acidic headwater with a pH below 5 were highly similar to each other but deviated distinctly from the communities at the other sites. As ascertained by nucleotide sequence analysis, stream water communities were dominated by Betaproteobacteria (one-third of the total bacteria), whereas sediment communities were composed mainly of Betaproteobacteria and members of the Fibrobacteres/Acidobacteria group (each accounting for about 25% of bacteria). Sequences obtained from bacteria from water samples indicated the presence of typical cosmopolitan freshwater organisms. TGGE bands shared between stream and soil samples, as well as sequences found in bacteria from stream samples that were related to those of soil bacteria, demonstrated the occurrence of some species in both stream and soil habitats. Changes in bacterial community composition were correlated with geographic distance along a stream, but in comparisons of different streams and rivers, community composition was correlated only with environmental conditions.     

The Effects of Soil Bacterial Community Structure on Decomposition in a Tropical Rain Forest

Soil microorganisms are key drivers of terrestrial biogeochemical cycles, yet it is still unclear how variations in soil microbial community composition influence many ecosystem processes. We investigated how shifts in bacterial community composition and diversity resulting from differences in carbon (C) availability affect organic matter decomposition by conducting an in situ litter manipulation experiment in a tropical rain forest in Costa Rica. We used bar-coded pyrosequencing to characterize soil bacterial community composition in litter manipulation plots and performed a series of laboratory incubations to test the potential functional significance of community shifts on organic matter decomposition. Despite clear effects of the litter manipulation on soil bacterial community composition, the treatments had mixed effects on microbial community function. Distinct communities varied in their ability to decompose a wide range of C compounds, and functional differences were related to both the relative abundance of the two most abundant bacterial sub-phyla (Acidobacteria and Alphaproteobacteria) and to variations in bacterial alpha-diversity. However, distinct communities did not differ in their ability to decompose native dissolved organic matter (DOM) substrates that varied in quality and quantity. Our results show that although resource-driven shifts in soil bacterial community composition have the potential to influence decomposition of specific C substrates, those differences may not translate to differences in DOM decomposition rates in situ. Taken together, our results suggest that soil bacterial communities may be either functionally dissimilar or equivalent during decomposition depending on the nature of the organic matter being decomposed.     

不同填闲模式对黄瓜根际土壤酶活性及细菌群落的影响

以温室连作3年黄瓜土壤为研究对象,以黄瓜为主栽作物,以青葱、小麦、油菜为不同季节填闲作物设置盆栽试验,采用常规化学方法、PCR-DGGE及qPCR技术,研究不同填闲模式对黄瓜土壤酶活性及细菌群落的影响.结果表明: 随着种植茬次的增加,填闲小麦处理的土壤脲酶、中性磷酸酶及转化酶活性均显著高于填闲青葱和油菜处理,同时油菜处理显著高于青葱处理;不同填闲模式间黄瓜根际土壤细菌群落结构不同,冬季填闲青葱和夏季填闲小麦处理维持了相对较高的多样性指数.qPCR检测结果表明: 随着种植茬次的增加,小麦处理的土壤细菌数量显著高于青葱和油菜处理.综上,不同填闲模式对土壤酶活性和细菌群落均产生一定影响,改变了土壤环境,其中夏季填闲小麦能保持相对较高的土壤酶活性、土壤细菌群落结构多样性及细菌数量.
     

Analyses of soil fungal communities in adjacent natural forest and hoop pine plantation ecosystems of subtropical Australia using molecular approaches based on 18S rRNA genes

Soil fungal communities were studied using 18S rDNA-based molecular techniques. Soil DNA was analyzed using temperature gradient gel electrophoresis (TGGE), single-stranded conformational polymorphism (SSCP), cloning and sequencing methods, following community DNA extraction and polymerase chain reaction (PCR). The extracted community DNA was successfully amplified using the primer pair of EF4f-Fung5r which produced ca. 550bp 18S rDNA fragments. TGGE screening of the PCR products showed some differences in band position and intensity between two soil samples in adjacent natural forest (YNF) and hoop pine plantation (YHP) ecosystems at Yarraman in subtropical Australia. TGGE and SSCP could be used for screening PCR products. However, care must be exercised when interpreting the TGGE and SSCP results with respect to microbial diversity, because one band may not necessarily represent one species. It is recommended that the PCR products should be purified before TGGE or SSCP screening. SSCP screening of the clone sequences revealed differences among the clones. Sequence and phylogenetic analyses revealed that all obtained clones were affiliated to the kingdom Fungi, including three phyla, i.e., Zygomycota, Ascomycota and Basidiomycota. Our results suggested that community DNA extraction, PCR, cloning, SSCP screening of clones, sequencing of selected clones and phylogentic analyses could be a good strategy in investigation of soil fungal community and diversity.     

Thermal Gradient Gel Electrophoresis Analysis of Bioprotection from Pollutant Shocks in the Activated Sludge Microbial Community

We used a culture-independent approach, namely, thermal gradient gel electrophoresis (TGGE) analysis of ribosomal sequences amplified directly from community DNA, to determine changes in the structure of the microbial community following phenol shocks in the highly complex activated sludge ecosystem. Parallel experimental model sewage plants were given shock loads of chlorinated and methylated phenols and simultaneously were inoculated (i) with a genetically engineered microorganism (GEM) able to degrade the added substituted phenols or (ii) with the nonengineered parental strain. The sludge community DNA was extracted, and 16S rDNA was amplified and analyzed by TGGE. To allow quantitative analysis of TGGE banding patterns, they were normalized to an external standard. The samples were then compared with each other for similarity by using the coefficient of Dice. The Shannon index of diversity, H, was calculated for each sludge sample, which made it possible to determine changes in community diversity. We observed a breakdown in community structure following shock loads of phenols by a decrease in the Shannon index of diversity from 1.13 to 0.22 in the noninoculated system. Inoculation with the GEM (Pseudomonas sp. strain B13 SN45RE) effectively protected the microbial community, as indicated by the maintenance of a high diversity throughout the shock load experiment (H decreased from 1.03 to only 0.82). Inoculation with the nonengineered parental strain, Pseudomonas sp. strain B13, did not protect the microbial community from being severely disturbed; H decreased from 1.22 to 0.46 for a 3-chlorophenol–4-methylphenol shock and from 1.03 to 0.70 for a 4-chlorophenol–4-methylphenol shock. The catabolic trait present in the GEM allowed for bioprotection of the activated sludge community from breakdown caused by toxic shock loading. In-depth TGGE analysis with similarity and diversity algorithms proved to be a very sensitive tool to monitor changes in the structure of the activated sludge microbial community, ranging from subtle shifts during adaptation to laboratory conditions to complete collapse following pollutant shocks.     

Increased microbial functional diversity under long-term organic and integrated fertilization in a paddy soil

Microbes play key roles in diverse biogeochemical processes including nutrient cycling. However, responses of soil microbial community and functional genes to long-term integrated fertilization (chemical combined with organic fertilization) remain unclear. Here, we used pyrosequencing and a microarray-based GeoChip to explore the shifts of microbial community and functional genes in a paddy soil which received over 21-year fertilization with various regimes, including control (no fertilizer), rice straw (R), rice straw plus chemical fertilizer nitrogen (NR), N and phosphorus (NPR), NP and potassium (NPKR), and reduced rice straw plus reduced NPK (L-NPKR). Significant shifts of the overall soil bacterial composition only occurred in the NPKR and L-NPKR treatments, with enrichment of certain groups including Bradyrhizobiaceae and Rhodospirillaceae families that benefit higher productivity. All fertilization treatments significantly altered the soil microbial functional structure with increased diversity and abundances of genes for carbon and nitrogen cycling, in which NPKR and L-NPKR exhibited the strongest effect, while R exhibited the least. Functional gene structure and abundance were significantly correlated with corresponding soil enzymatic activities and rice yield, respectively, suggesting that the structural shift of the microbial functional community under fertilization might promote soil nutrient turnover and thereby affect yield. Overall, this study indicates that the combined application of rice straw and balanced chemical fertilizers was more pronounced in shifting the bacterial composition and improving the functional diversity toward higher productivity, providing a microbial point of view on applying a cost-effective integrated fertilization regime with rice straw plus reduced chemical fertilizers for sustainable nutrient management.

     

Bacterial community in the rhizosphere of the cactus species Mammillaria carnea during dry and rainy seasons assessed by deep sequencing

Background and aims

The Tehuacán-Cuitcatlán reserve is an area of unique plant biodiversity mostly in the form of xerophytes, with exceptionally high numbers of rare and endemic species. This endemism results partly from the characteristics of the climate of this area, with two distinct seasons: rainy and dry seasons. Although rhizosphere communities must be critical in the function of this ecosystem, understanding the structure of these communities is currently limited. This is the first molecular study of the microbial diversity present in the rhizosphere of Mamillaria carnea.

Methods

Total DNA was obtained from soil and rhizosphere samples at three locations in the Tehuacán Cuicatlán Reserve, during dry and rainy seasons. Temperature gradient gel electrophoresisis (TGGE) fingerprinting, 16S rRNA gene libraries and pyrosequencing were used to investigate bacterial diversity in the rhizosphere of Mammillaria carnea and changes in the microbial community between seasons.

Results

Deep sequencing data reveal a higher level of biodiversity in the dry season. Statistical analyses based on these data indicates that the composition of the bacterial community differed between both seasons affecting to members of the phyla Acidobacteria, Cyanobacteria, Gemmatimonadetes, Plantomycetes, Actinobacteria and Firmicutes. In addition, the depth of sequencing performed (>24,000 reads) enables detection of changes in the relative abundance of lower bacterial taxa (novel bacterial phylotypes) indicative of the increase of specific bacterial populations due to the season.

Conclusions

This study states the basis of the bacterial diversity in the rhizosphere of cacti in semi-arid environments and it is a sequence-based demonstration of community shifts in different seasons.     

不同大豆连作年限对黑土细菌群落结构的影响

大豆连作导致作物产量下降、病原微生物富集和土壤退化等问题日趋严重。然而,目前关于大豆连作对土壤细菌群落结构组成及多样性分布的影响及发生机制尚不清楚。采用高通量测序技术,对大豆连作(不同年限)和大豆-玉米轮作下的黑土细菌16S rRNA基因进行测序分析。结果表明:轮作5年(CR5)和13年长期连作(CC13)处理显著增加了土壤pH、全氮(TN)、全磷(TP)和速效养分(AN、AP和AK)含量。与短期连作相比,CR5和CC13处理均提高了细菌群落的OTUs数量、PD值、Chao1指数和Shannon指数。聚类分析图谱结果显示细菌群落结构组成受到轮作和连作年限的双重影响,而土壤pH、TN、TP、AN、AP和AK是细菌群落结构发生变化的主要驱动因子(P0.05)。此外,VPA分析发现上述土壤因子中,土壤pH对细菌群落结构变化的贡献度最大。本研究证明大豆长期连作提高了土壤养分含量和细菌群落的丰富度和多样性指数,从分子生物学的角度证实大豆长期连作在一定程度上改善了土壤环境,为大豆连作障碍的研究提供了理论依据。     

Dynamics of bacterial community in up-flow anaerobic packed bed system for acid mine drainage treatment using wine wastes as carbon source

The dynamics of the bacterial populations in an up-flow anaerobic packed bed system (UAPB), applied in acid mine drainage treatment using wine wastes as carbon and nutrients source was elucidated by temperature gradient gel electrophoresis (TGGE) analysis. Moreover, TGGE fingerprints of the bacterial communities developed in a UAPB fed with wine wastes and a UAPB fed with pure ethanol were compared. TGGE fingerprinting and phylogenetic analysis showed that the composition of the community in the UAPB fed with wine wastes remained stable during whole time of operation and its bacterial diversity was higher. The bacterial community of the UAPB fed with wine wastes was composed by bacteria affiliated with Desulfovibrio, Clostridium, Citrobacter and Cronobacter genera and with Bacteroidales order, sp. The dominant community developed in the UAPB fed with ethanol was composed by bacteria affiliated with Desulfovibrio sp. The presence of several bacterial groups in the bioreactor fed with wine wastes suggests a synergistic interaction between the different populations. Syntrophic interaction may be the key factor for the utilization of wine wastes, a complex organic substrate, as carbon and electron source for sulphate reduction.     

土壤微生物群落对麻栎-刺槐混交林凋落物分解的影响

以麻栎-刺槐混交林和麻栎纯林为研究对象,采用野外定点采样、室内分析与高通量测序的方法,对凋落物分解过程中土壤微生物菌群多样性特征及其对凋落物分解速率的影响进行了研究。结果表明:(1)麻栎-刺槐混交林凋落物的分解速率高于麻栎纯林。两种林分凋落物有机碳(TOC)、全氮(TN)发生释放,全磷(TP)发生积累-释放的过程。(2)两种林分土壤细菌优势类群为放线菌门(Acidobacteria)、变形菌门(Proteobacteria)、酸杆菌门(Actinobacteria)和疣微菌门(Verrucomicrobia),土壤真菌优势类群为担子菌门(Basidiomycota)、子囊菌门(Ascomycota)和被孢霉门(Moritierellomycota)。(3)凋落物分解过程中,麻栎-刺槐混交林土壤微生物菌群丰富度指数和菌群多样性指数变化范围小于麻栎纯林。(4)凋落物分解速率与土壤细菌菌群丰富度指数和菌群多样性指数呈显著正相关,与土壤真菌菌群丰富度指数呈显著正相关。土壤微生物群落对麻栎-刺槐混交林和麻栎纯林凋落物分解速率具有重要影响,研究结果为深入开展混交林土壤微生物多样性对凋落物分解的影响研究提供理论依据。     

Analysis of actinomycete communities by specific amplification of genes encoding 16S rRNA and gel-electrophoretic separation in denaturing gradients.

A group-specific primer, F243 (positions 226 to 243, Escherichia coli numbering), was developed by comparison of sequences of genes encoding 16S rRNA (16S rDNA) for the detection of actinomycetes in the environment with PCR and temperature or denaturing gradient gel electrophoresis (TGGE or DGGE, respectively). The specificity of the forward primer in combination with different reverse ones was tested with genomic DNA from a variety of bacterial strains. Most actinomycetes investigated could be separated by TGGE and DGGE, with both techniques giving similar results. Two strategies were employed to study natural microbial communities. First, we used the selective amplification of actinomycete sequences (E. coli positions 226 to 528) for direct analysis of the products in denaturing gradients. Second, a nested PCR providing actinomycete-specific fragments (E. coli positions 226 to 1401) was used which served as template for a PCR when conserved primers were used. The products (E. coli positions 968 to 1401) of this indirect approach were then separated by use of gradient gels. Both approaches allowed detection of actinomycete communities in soil. The second strategy allowed the estimation of the relative abundance of actinomycetes within the bacterial community. Mixtures of PCR-derived 16S rDNA fragments were used as model communities consisting of five actinomycetes and five other bacterial species. Actinomycete products were obtained over a 100-fold dilution range of the actinomycete DNA in the model community by specific PCR; detection of the diluted actinomycete DNA was not possible when conserved primers were used. The methods tested for detection were applied to monitor actinomycete community changes in potato rhizosphere and to investigate actinomycete diversity in different soils.     

Computer-assisted PCR-single-strand-conformation polymorphism analysis for assessing shift in soil bacterial community structure during bioremediational treatments

The extent of shift in soil bacterial community structure during bioremediational treatments was investigated by PCR-single-strand-conformation polymorphism (SSCP) analysis, which was followed by computer-assisted cluster analysis of the community fingerprints. While biostimulation as well as bioaugmentation enhanced the degradation of phenanthrene in soil, both bioremediational treatments caused shifts in the bacterial community structure. Drastic changes were observed in the initial phase of bioaugmentation. Our results demonstrate that computer-assisted fingerprint analysis is readily applicable to the study for the comparative analysis of microbial community structure using molecular profiling techniques.     

The legacy of bacterial invasions on soil native communities

Soil microbial communities are often not resistant to the impact caused by microbial invasions, both in terms of structure and functionality, but it remains unclear whether these changes persist over time. Here, we used three strains of Escherichia coli O157:H7 (E. coli O157:H7), a species used for modelling bacterial invasions, to evaluate the resilience of the bacterial communities from four Chinese soils to invasion. The impact of E. coli O157:H7 strains on soil native communities was tracked for 120 days by analysing bacterial community composition as well as their metabolic potential. We showed that soil native communities were not resistant to invasion, as demonstrated by a decline in bacterial diversity and shifts in bacterial composition in all treatments. The resilience of native bacterial communities (diversity and composition) was inversely correlated with invader's persistence in soils (R² = 0.487, p < 0.001). Microbial invasions also impacted the functionality of the soil communities (niche breadth and community niche), the degree of resilience being dependent on soil or native community diversity. Collectively, our results indicate that bacteria invasions can potentially leave a footprint in the structure and functionality of soil communities, indicating the need of assessing the legacy of introducing exotic species in soil environments.     

Effect of the concentration of suspended solids on the enzymatic activities and biodiversity of a submerged membrane bioreactor for aerobic treatment of domestic wastewater

A pilot-scale submerged membrane bioreactor was used for the treatment of domestic wastewater in order to study the influence of the variations in the concentration of volatile suspended solids (VSS) on the enzymatic activities (acid and alkaline phosphatases, glucosidase, protease, esterase, and dehydrogenase) and biodiversity of the bacterial community in the sludge. The influence of VSS concentration was evaluated in two separated experiments, which were carried out in two different seasons of the year (experiment 1 through spring–summer and experiment 2 through autumn–winter). Cluster analysis of the temperature gradient gel electrophoresis (TGGE) profiles demonstrated that the community composition was significantly different in both experiments. Within the same experiment, the bacterial community experienced sequential shifts as the biomass accumulated, as shown by the evolution of the population profiles through time as VSS concentration increased. All enzymatic activities studied were significantly lower during experiment 2, except for glucosidase. Concentrations of VSS over 8 g/l induced a strong descent of all enzymatic activities, which overlapped with a significant modification of the community composition. Sequences of the major TGGE bands were identified as representatives of the Alpha-proteobacteria, filamentous bacteria (Thiotrix), and nitrite oxidizers (Nitrospira). Some sequences which were poorly related to any validated bacterial taxon were obtained.     

不同轮作茬口土壤细菌群落及后茬小麦产量

评估不同轮作模式的生态可持续性和作物生产力,可为调整优化种植结构提供理论依据。设置7个不同轮作作物和周期茬口处理,采用实时荧光定量PCR技术测定不同轮作茬口的土壤细菌群落丰度,采用16S rRNA基因扩增子高通量测序技术分析土壤细菌群落多样性与物种组成,并测定土壤速效养分状况和后茬小麦产量。结果表明: 与夏玉米茬口相比,不同轮作周期夏花生或夏大豆茬口处理降低了土壤有机碳、无机氮和速效钾含量,显著增加了土壤有效磷含量。不同轮作周期夏花生或夏大豆茬口处理的土壤细菌16S rRNA基因拷贝数显著降低,而群落丰富度和多样性有所增加。不同轮作作物显著改变了土壤细菌群落结构和物种组成。与夏玉米茬口相比,不同轮作周期夏大豆茬口显著增加了后茬冬小麦籽粒千粒重和产量。综上,不同轮作周期夏花生或夏大豆茬口有利于增加土壤有效磷含量和细菌群落多样性,显著改变土壤细菌群落结构,其中,夏大豆茬口对后茬冬小麦产量形成具有积极作用。     

Mycobacterium diversity and pyrene mineralization in petroleum-contaminated soils

Degradative strains of fast-growing Mycobacterium spp. are commonly isolated from polycyclic aromatic hydrocarbon (PAH)-contaminated soils. Little is known, however, about the ecology and diversity of indigenous populations of these fast-growing mycobacteria in contaminated environments. In the present study 16S rRNA genes were PCR amplified using Mycobacterium-specific primers and separated by temperature gradient gel electrophoresis (TGGE), and prominent bands were sequenced to compare the indigenous Mycobacterium community structures in four pairs of soil samples taken from heavily contaminated and less contaminated areas at four different sites. Overall, TGGE profiles obtained from heavily contaminated soils were less diverse than those from less contaminated soils. This decrease in diversity may be due to toxicity, since significantly fewer Mycobacterium phylotypes were detected in soils determined to be toxic by the Microtox assay than in nontoxic soils. Sequencing and phylogenetic analysis of prominent TGGE bands indicated that novel strains dominated the soil Mycobacterium community. Mineralization studies using [(14)C]pyrene added to four petroleum-contaminated soils, with and without the addition of the known pyrene degrader Mycobacterium sp. strain RJGII-135, indicated that inoculation increased the level of degradation in three of the four soils. Mineralization results obtained from a sterilized soil inoculated with strain RJGII-135 suggested that competition with indigenous microorganisms may be a significant factor affecting biodegradation of PAHs. Pyrene-amended soils, with and without inoculation with strain RJGII-135, experienced both increases and decreases in the population sizes of the inoculated strain and indigenous Mycobacterium populations during incubation.     

古大湖湿地盐碱土壤微生物群落结构及多样性分析

以黑龙江省古大湖湿地原生、林地、耕地及湖岸盐碱土壤微生物为研究对象,基于高通量测序方法,分析4种生境类型条件下土壤细菌和真菌群落结构及多样性。结合土壤理化指标,进一步分析影响微生物群落多样性的环境因子。结果表明:细菌群落中变形菌门的相对丰度值最高,真菌群落中为子囊菌门。同一生境细菌群落多样性具有相似性,而真菌具有一定的差异;不同生境间两者均具有差异。耕地土壤和林地土壤的细菌群落多样性接近,但与湖岸土壤真菌的更相近。前两者中细菌群落多样性较高,其次为原生土壤,而湖岸土壤中的最低。耕地土壤与湖岸土壤真菌群落多样性较高,原生土壤较低,而林地土壤中最低。与真菌相比,细菌的群落多样性受土壤环境因子影响更大,其中pH值、含水量对土壤细菌和真菌群落多样性均具有显著影响。     

Effects of Manure Compost Application on Soil Microbial Community Diversity and Soil Microenvironments in a Temperate Cropland in China

The long-term application of excessive chemical fertilizers has resulted in the degeneration of soil quality parameters such as soil microbial biomass, communities, and nutrient content, which in turn affects crop health, productivity, and soil sustainable productivity. The objective of this study was to develop a rapid and efficient solution for rehabilitating degraded cropland soils by precisely quantifying soil quality parameters through the application of manure compost and bacteria fertilizers or its combination during maize growth. We investigated dynamic impacts on soil microbial count, biomass, basal respiration, community structure diversity, and enzyme activity using six different treatments [no fertilizer (CK), N fertilizer (N), N fertilizer + bacterial fertilizer (NB), manure compost (M), manure compost + bacterial fertilizer (MB), and bacterial fertilizer (B)] in the plowed layer (0–20 cm) of potted soil during various maize growth stages in a temperate cropland of eastern China. Denaturing gradient electrophoresis (DGGE) fingerprinting analysis showed that the structure and composition of bacterial and fungi communities in the six fertilizer treatments varied at different levels. The Shannon index of bacterial and fungi communities displayed the highest value in the MB treatments and the lowest in the N treatment at the maize mature stage. Changes in soil microorganism community structure and diversity after different fertilizer treatments resulted in different microbial properties. Adding manure compost significantly increased the amount of cultivable microorganisms and microbial biomass, thus enhancing soil respiration and enzyme activities (p<0.01), whereas N treatment showed the opposite results (p<0.01). However, B and NB treatments minimally increased the amount of cultivable microorganisms and microbial biomass, with no obvious influence on community structure and soil enzymes. Our findings indicate that the application of manure compost plus bacterial fertilizers can immediately improve the microbial community structure and diversity of degraded cropland soils.     

施肥和土壤管理对土壤微生物生物量碳、氮和群落结构的影响

以中国科学院沈阳生态试验站的长期定位试验为平台,研究了不同施肥和土壤管理对潮棕壤微生物生物量碳、氮和群落结构的影响。结果表明,裸地和农田处理的微生物生物量碳、氮较低,但是农田处理下施肥增加了微生物生物量,其中NPK+M效果最明显。DGGE图谱显示,处理间细菌条带分布较相似,其中裸地的细菌多样性最高;长期施肥和土壤管理改变了土壤真菌群落结构,施肥增加了真菌多样性,且有机肥的影响大于化肥;不同处理间氨氧化细菌群落结构差异显著,NPK+M显著增加了氨氧化细菌多样性,且无机肥和有机肥对氨氧化细菌群落影响不同。施肥和土壤管理对细菌影响较小,但显著改变了真菌和氨氧化细菌的群落结构。聚类分析结果显示,土壤管理措施较施肥对细菌、真菌和氨氧化细菌群落的影响更为显著。