Soil Health,Crop Productivity,Microbial Transport,and Mine Spoil Response to Biochars

Biochars vary widely in pH, surface area, nutrient concentration, porosity, and metal binding capacity due to the assortment of feedstock materials and thermal conversion conditions under which it is formed. The wide variety of chemical and physical characteristics have resulted in biochar being used as an amendment to rebuild soil health, improve crop yields, increase soil water storage, and restore soils/spoils impacted by mining. Meta-analysis of the biochar literature has shown mixed results when using biochar as a soil amendment to improve crop productivity. For example, in one meta-analysis, biochar increased crop yield by approximately 10 %, while in another, approximately 50 % of the studies reported minimal to no crop yield increases. In spite of the mixed crop yield reports, biochars have properties that can improve soil health characteristics, by increasing carbon (C) sequestration and nutrient and water retention. Biochars also have the ability to bind enteric microbes and enhance metal binding in soils impacted by mining. In this review, we present examples of both effective and ineffective uses of biochar to improve soil health for agricultural functions and reclamation of degraded mine spoils. Biochars are expensive to manufacture and cannot be purged from soil after application, so for efficient use, they should be targeted for specific uses in agricultural and environmental sectors. Thus, we introduce the designer biochar concept as an alternate paradigm stating that biochars should be designed with properties that are tailored to specific soil deficiencies or problems. We then demonstrate how careful selection of biochars can increase their effectiveness as a soil amendment.     

Changes in Bacterial Community Structure of Agricultural Land Due to Long-Term Organic and Chemical Amendments

Community level physiological profiling and pyrosequencing-based analysis of the V1-V2 16S rRNA gene region were used to characterize and compare microbial community structure, diversity, and bacterial phylogeny from soils of chemically cultivated land (CCL), organically cultivated land (OCL), and fallow grass land (FGL) for 16 years and were under three different land use types. The entire dataset comprised of 16,608 good-quality sequences (CCL, 6,379; OCL, 4,835; FGL, 5,394); among them 12,606 sequences could be classified in 15 known phylum. The most abundant phylum were Proteobacteria (29.8%), Acidobacteria (22.6%), Actinobacteria (11.1%), and Bacteroidetes (4.7%), while 24.3% of the sequences were from bacterial domain but could not be further classified to any known phylum. Proteobacteria, Bacteroidetes, and Gemmatimonadetes were found to be significantly abundant in OCL soil. On the contrary, Actinobacteria and Acidobacteria were significantly abundant in CCL and FGL, respectively. Our findings supported the view that organic compost amendment (OCL) activates diverse group of microorganisms as compared with conventionally used synthetic chemical fertilizers. Functional diversity and evenness based on carbon source utilization pattern was significantly higher in OCL as compared to CCL and FGL, suggesting an improvement in soil quality. This abundance of microbes possibly leads to the enhanced level of soil organic carbon, soil organic nitrogen, and microbial biomass in OCL and FGL soils as collated with CCL. This work increases our current understanding on the effect of long-term organic and chemical amendment applications on abundance, diversity, and composition of bacterial community inhabiting the soil for the prospects of agricultural yield and quantity of soil.     

Mid‐term effects on ecosystem services of quarry restoration with Technosols under Mediterranean conditions: 10‐year impacts on soil organic carbon and vegetation development

The use of Technosols for the restoration of limestone quarries overcomes the usual “in situ” scarcity of soil and/or its poor quality. The use of mine spoils, improved with mineral and/or organic amendments, could be an efficient and environmentally friendly option. Properly treated sewage sludge from urban wastewater treatment plants could be a suitable organic amendment and fertilizer (rich in N and P) whenever its pollutant burden is low (heavy metals and/or organic pollutants). Its appropriate use could improve essential soil physical and chemical properties and, therefore, promote key ecosystem services of restored areas, such as biomass production and carbon sequestration, as well as biodiversity and landscape recovery. However, the mid‐term impacts of these restoration practices on soil functioning and their services have rarely been reported in the available literature. In this study we assess the mid‐term effects (10 years) of the use of sewage sludge as a Technosol amendment on soil organic carbon (SOC), nutrient status, and plant development in several restored quarries. Soils restored using sewage sludge showed a threefold increase in SOC compared to the corresponding unamended ones, despite the moderate sludge dosage applied (below 50 tonnes/ha). Plant cover was also higher in amended soils, and recruitment was not affected by sludge amendment at these doses. This study demonstrates that, used at an appropriate rate, sewage sludge is a good alternative for the valorization of mine spoils in quarry restoration, improving some important regulatory ecosystem services such as carbon sequestration, without compromising woody plant encroachment.     

Long-Term Nitrogen Amendment Alters the Diversity and Assemblage of Soil Bacterial Communities in Tallgrass Prairie

Anthropogenic changes are altering the environmental conditions and the biota of ecosystems worldwide. In many temperate grasslands, such as North American tallgrass prairie, these changes include alteration in historically important disturbance regimes (e.g., frequency of fires) and enhanced availability of potentially limiting nutrients, particularly nitrogen. Such anthropogenically-driven changes in the environment are known to elicit substantial changes in plant and consumer communities aboveground, but much less is known about their effects on soil microbial communities. Due to the high diversity of soil microbes and methodological challenges associated with assessing microbial community composition, relatively few studies have addressed specific taxonomic changes underlying microbial community-level responses to different fire regimes or nutrient amendments in tallgrass prairie. We used deep sequencing of the V3 region of the 16S rRNA gene to explore the effects of contrasting fire regimes and nutrient enrichment on soil bacterial communities in a long-term (20 yrs) experiment in native tallgrass prairie in the eastern Central Plains. We focused on responses to nutrient amendments coupled with two extreme fire regimes (annual prescribed spring burning and complete fire exclusion). The dominant bacterial phyla identified were Proteobacteria, Verrucomicrobia, Bacteriodetes, Acidobacteria, Firmicutes, and Actinobacteria and made up 80% of all taxa quantified. Chronic nitrogen enrichment significantly impacted bacterial community diversity and community structure varied according to nitrogen treatment, but not phosphorus enrichment or fire regime. We also found significant responses of individual bacterial groups including Nitrospira and Gammaproteobacteria to long-term nitrogen enrichment. Our results show that soil nitrogen enrichment can significantly alter bacterial community diversity, structure, and individual taxa abundance, which have important implications for both managed and natural grassland ecosystems.     

Microbial responses to inorganic nutrient amendment overridden by warming: Consequences on soil carbon stability

Eutrophication and climate warming, induced by anthropogenic activities, are simultaneously occurring worldwide and jointly affecting soil carbon stability. Therefore, it is of great interest to examine whether and how they interactively affect soil microbial community, a major soil carbon driver. Here, we showed that climate warming, simulated by southward transferring Mollisol soil in agricultural ecosystems from the cold temperate climate zone (N) to warm temperate climate (C) and subtropical climate zone (S), decreased soil organic matter (SOM) by 6%–12%. In contrast, amendment with nitrogen, phosphorus and potassium enhanced plant biomass by 97% and SOM by 6% at the N site, thus stimulating copiotrophic taxa but reducing oligotrophic taxa in relative abundance. However, microbial responses to nutrient amendment were overridden by soil transfer in that nutrient amendment had little effect at the C site but increased recalcitrant carbon‐degrading fungal Agaricomycetes and Microbotryomycetes taxa derived from Basidiomycota by 4‐17 folds and recalcitrant carbon‐degrading genes by 23%–40% at the S site, implying a possible priming effect. Consequently, SOM at the S site was not increased by nutrient amendment despite increased plant biomass by 108%. Collectively, we demonstrate that soil transfer to warmer regions overrides microbial responses to nutrient amendment and weakens soil carbon sequestration.     

Impact of biochar application to soil on the root-associated bacterial community structure of fully developed greenhouse pepper plants

Adding biochar to soil has environmental and agricultural potential due to its long-term carbon sequestration capacity and its ability to improve crop productivity. Recent studies have demonstrated that soil-applied biochar promotes the systemic resistance of plants to several prominent foliar pathogens. One potential mechanism for this phenomenon is root-associated microbial elicitors whose presence is somehow augmented in the biochar-amended soils. The objective of this study was to assess the effect of biochar amendment on the root-associated bacterial community composition of mature sweet pepper (Capsicum annuum L.) plants. Molecular fingerprinting (denaturing gradient gel electrophoresis and terminal restriction fragment length polymorphism) of 16S rRNA gene fragments showed a clear differentiation between the root-associated bacterial community structures of biochar-amended and control plants. The pyrosequencing of 16S rRNA amplicons from the rhizoplane of both treatments generated a total of 20,142 sequences, 92 to 95% of which were affiliated with the Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes phyla. The relative abundance of members of the Bacteroidetes phylum increased from 12 to 30% as a result of biochar amendment, while that of the Proteobacteria decreased from 71 to 47%. The Bacteroidetes-affiliated Flavobacterium was the strongest biochar-induced genus. The relative abundance of this group increased from 4.2% of total root-associated operational taxonomic units (OTUs) in control samples to 19.6% in biochar-amended samples. Additional biochar-induced genera included chitin and cellulose degraders (Chitinophaga and Cellvibrio, respectively) and aromatic compound degraders (Hydrogenophaga and Dechloromonas). We hypothesize that these biochar-augmented genera may be at least partially responsible for the beneficial effect of biochar amendment on plant growth and viability.     

Use of Arbuscular Mycorrhiza and Organic Amendments to Enhance Growth of Macaranga peltata (Roxb.) Müll. Arg. in Iron Ore Mine Wastelands

Macaranga peltata (Roxb.) Mull. Arg. is a disturbance tolerant plant species with potential in mine wasteland reclamation. Our study aims at studying the phyto-extraction potential of M. peltata and determining plant-soil interaction factors effecting plant growth in iron ore mine spoils. Plants were grown in pure mine spoil and spoil amended with Farm Yard Manure (FYM) and Vermicompost (VC) along with arbuscular mycorrhizal (AM) species Rhizophagus irregularis. Pure and amended mine spoils were evaluated for nutrient status. Plant growth parameters and foliar nutrient contents were determined at the end of one year. FYM amendment in spoil significantly increased plant biomass compared to pure mine spoil and VC amended spoil. Foliar Fe accumulation was recorded highest (594.67μg/g) in pure spoil with no mortality but considerably affecting plant growth, thus proving to exhibit phyto-extraction potential. FYM and VC amendments reduced AM colonization (30.4% and 37% resp.) and plants showed a negative mycorrhizal dependency (–30.35 and –39.83 resp.). Soil pH and P levels and, foliar Fe accumulation are major factors determining plant growth in spoil. FYM amendment was found to be superior to VC as a spoil amendment for hastening plant growth and establishment in iron ore mine spoil     

Development of bacterial community during spontaneous succession on spoil heaps after brown coal mining

Changes in the abundance of bacteria and fungi and in the composition of bacterial communities during primary succession were investigated in a brown coal mine deposit area near Sokolov, the Czech Republic, using phospholipid fatty acids analysis, microarray and 16S rRNA gene sequencing. The study considered a chronosequence of sites undergoing spontaneous succession: 6-, 12-, 21- and 45-year-old and a 21-year-old site revegetated with Alnus glutinosa. During succession, organic carbon and the total nitrogen content increased while the pH and the C/N ratio decreased. Microbial biomass and bacterial diversity increased until 21 years and decreased later; bacteria dominated over fungi in the initial and late phases of succession. Bacterial community composition of the 6-year-old site with no vegetation cover largely differed from the older sites, especially by a higher content of Gammaproteobacteria, Cyanobacteria and some Alphaproteobacteria. Bacteria belonging to the genera Acidithiobacillus, Thiobacillus and related taxa, the CO(2) and N(2) fixers, dominated the community at this site. In the later phases, bacterial community development seemed to reflect more the changes in soil nutrient content and pH than vegetation with a decrease of Actinobacteria and an increase of Acidobacteria. The site revegetated with A. glutinosa resembled the 45-year-old primary succession site and exhibited an even lower pH and C/N ratio, indicating that recultivation is able to accelerate soil development.     

长期施用化肥及秸秆还田对砂姜黑土细菌群落的影响

【目的】在施用化肥的基础上进行秸秆还田是提高砂姜黑土肥力的有效措施,以往的研究只注重秸秆还田对土壤结构、肥力等物理化学性状方面的研究,缺少施肥对砂姜黑土微生物群落影响的研究。本研究以安徽蒙城典型的砂姜黑土为研究对象,以期揭示长期施用化肥和秸秆还田对砂姜黑土细菌群落的影响。【方法】采用454高通量测序对砂姜黑土不同农业施肥措施下的细菌群落进行分析研究,并通过生物信息学的分析方法揭示影响砂姜黑土细菌群落的主要因素。【结果】通过对454高通量测序数据的分析,发现砂姜黑土主要的细菌门类为放线菌、变形菌、酸杆菌、绿弯菌和拟杆菌。长期施用化肥显著提高了砂姜黑土肥力和作物产量,但导致了细菌群落结构的显著变化和多样性的显著降低。秸秆还田有利于土壤肥力的进一步提高,但是并没有缓解长期施用化肥对土壤细菌群落产生的不利影响。分析发现土壤pH的变化是导致土壤细菌群落变异的主要因素。【结论】在施用化肥的基础上进行秸秆还田有利于砂姜黑土肥力的提升,然而并没有缓解由施肥导致的土壤酸化对土壤细菌群落组成和多样性产生的不利影响。这暗示秸秆还田可能并未对砂姜黑土微生物生态产生根本性的有益影响,对于秸秆农田的利用方式还需要进一步研究,以达到农业生产效益和生态效益的并重。     

Bacterial diversity in Greenlandic soils as affected by potato cropping and inorganic versus organic fertilization

Arctic and Subarctic ecosystems will in the near future be exposed to severe environmental stresses due to global warming. For example, the microbial community structure and function may change as a result of increased temperatures. In Greenland, agriculture is carried out in the Subarctic regions with only limited pest management, despite the presence of plant pathogenic fungi. The microbial community composition in agricultural soils, which plays an important role for soil and plant health and for crop yield, may be affected by the use of different fertilizer treatments. Currently, only limited research has been performed on the effects of these treatments on bacterial communities in Arctic and Subarctic agricultural soils. The major objective of this study was to investigate the short-term impact of conventional (NPK) and organic (sheep manure supplemented with nitrogen) fertilizer treatments on bacterial diversity, nutrient composition and crop yield in two Greenlandic agricultural soils. An effect of fertilizer was found on soil and plant nutrient levels and on crop yields. Pyrosequencing of 16S rRNA gene sequences did not reveal any major changes in the overall bacterial community composition as a result of different fertilizer treatments, indicating a robust microbial community in these soils. In addition, differences in nutrient levels, crop yields and bacterial abundances were found between the two field sites and the two experimental growth seasons, which likely reflect differences in physical–chemical soil parameters.     

Soil pH is the primary factor driving the distribution and function of microorganisms in farmland soils in northeastern China

Purpose

To understand which environmental factors influence the distribution and ecological functions of bacteria in agricultural soil.

Method

A broad range of farmland soils was sampled from 206 locations in Jilin province, China. We used 16S rRNA gene-based Illumina HiSeq sequencing to estimated soil bacterial community structure and functions.

Result

The dominant taxa in terms of abundance were found to be, Actinobacteria, Acidobacteria, Gemmatimonadetes, Chloroflexi, and Proteobacteria. Bacterial communities were dominantly affected by soil pH, whereas soil organic carbon did not have a significant influence on bacterial communities. Soil pH was significantly positively correlated with bacterial operational taxonomic unit abundance and soil bacterial α-diversity (P<0.05) spatially rather than with soil nutrients. Bacterial functions were estimated using FAPROTAX, and the relative abundance of anaerobic and aerobic chemoheterotrophs, and nitrifying bacteria was 27.66%, 26.14%, and 6.87%, respectively, of the total bacterial community. Generally, the results indicate that soil pH is more important than nutrients in shaping bacterial communities in agricultural soils, including their ecological functions and biogeographic distribution.

     

十八河铜尾矿库坝面细菌群落时空动态及其驱动力

群落多样性的维持机制是群落生态学研究的热点问题.尾矿库作为人工原生裸地,土壤重金属含量较高,随着恢复年限的延长,土壤理化性质发生变化,是研究土壤微生物群落多样性驱动机制的理想场地.本研究在调查十八河尾矿库土壤因子、植物群落多样性和土壤细菌群落多样性的基础上,探究了局域小尺度下细菌群落结构和多样性的驱动机制.结果表明: 尾矿库土壤养分含量随恢复年限的延长显著提高,并具有一定的季节变化,不同恢复年限土壤养分含量的季节动态存在差异.细菌群落的Shannon多样性和丰富度指数随恢复年限呈显著增加趋势,群落稳定性逐步提高;而其季节变化受到植物群落的影响,在不同恢复年限下具有一定的差异.RDA分析显示,环境因子对土壤细菌群落多样性有决定作用.结构方程模型分析表明,土壤养分(TC、TN、NO₃^--N、NO₂^--N)含量、植物群落多样性和土壤酶活性共同驱动该铜尾矿库土壤细菌群落的构建过程.     

Spoil characteristics and vegetation development of an age series of mine spoils in a dry tropical environment

A series of coal mine spoils (5, 10, 12, 16 and 20-yr old) in a dry tropical environment was sampled to assess the changes with time in spoil characteristics, species composition and plant biomass. Coarse fragments (>2 mm) decreased with age of mine spoil while the proportion of 0.2–0.1 mm particles increased. Total soil N, mineral N, NaHCO₃-extractable Pi, and exchangeable K increased with age of mine spoil and these parameters were lower in mine spoils than native forest soil even after 20 years of succession. Exchangeable Na decreased with age of mine spoil and in 20-yr old spoil it was higher than native forest soil. Plant community composition changed with age. Only a few species participated in community formation. Species richness increased with age, while evenness and species diversity declined from 5-yr old to 16-yr old community with an increase in the 20-yr old community. A reverse trend occurred for concentration of dominance. Area-weighted shoot and root biomass of other species increased with the age of the mine spoil while that of Xanthium strumarium patches declined with age. Data collected on spoil features, microbial C, N and P, and shoot and root biomass when subjected to Discriminant Analysis indicated a continued profound effect of age. 10 and 12-yr old mine spoils were closer to each other, and 5 and 20-yr old spoils were farthest apart.     

The application of the herbicide bromoxynil to a model soil-derived bacterial community: impact on degradation and community structure

AIMS: Bromoxynil degradation by soil micro-organisms has been shown to be co-oxidative in character. In this study, we investigate both the impact of the application of increasing bromoxynil concentrations on soil-derived bacterial communities and how these changes are reflected in the degradation of the compound. Our aim was to test the hypothesis that the addition of bromoxynil to a soil-derived bacterial community, and the availability of a readily utilizable carbon source would have an impact on bromoxynil degradation, and that would be reflected in the bacteria present in the soil community. METHODS AND RESULTS: Degradation of bromoxynil was observed in soil-derived communities containing 15 mg l(-1), but not 50 mg l(-1) of the compound, unless glucose was added. This suggests that the addition of carbon stimulates co-oxidative bromoxynil degradation by the members of the bacterial community. Measurable changes in the bacterial community indicated that the addition of bromoxynil led to deterministic selection on the bacterial population, i.e. the communities observed arise through the selection of specific micro-organisms that are best adapted to the conditions in the soil. The addition of bromoxynil was also shown to have a negative impact on the presence of alpha and gamma-proteobacteria in the soil community. CONCLUSION: Bromoxynil degradation is significantly inhibited in bacterial soil communities in the absence of readily accessible carbon. The application of bromoxynil appears to exert deterministic selection on the bacterial community. SIGNIFICANCE AND IMPACT OF THE STUDY: This study highlights the effects of increasing bromoxynil concentrations on a model bacterial population derived from soil. Soil communities show qualitative and quantitative differences to bromoxynil application depending on the availability of organic carbon. These findings might have implications for the persistence of bromoxynil in agricultural soils.     

退耕还湿后土壤细菌群落结构和生物量变化过程

土壤细菌对湿地生态系统功能和健康维持起着重要作用。以菜子湖原始湿地、不同退耕年限湿地(3a、7a、11a和21a)和仍耕作油菜地土壤为研究对象,应用聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)、高通量测序和磷脂脂肪酸(PLFAs)方法分析土壤细菌群落组成和生物量,探讨它们在退耕还湿后的变化过程及其影响因素。结果表明,退耕还湿后土壤变形菌门(α-变形菌纲、β-变形菌纲和δ-变形菌纲)、酸杆菌门(酸杆菌纲和全噬菌纲)、Nitrospinae(Nitrospinia纲)和硝化螺旋菌门(硝化螺旋菌纲)相对丰度先增高后降低;这些参与氮循环的土壤细菌对退耕后湿地生态恢复过程中土壤氮素提升起着重要作用。与农业生产活动密切关联的厚壁菌门(芽孢杆菌纲和梭菌纲)和放线菌门(放线菌纲)相对丰度逐渐降低。湿地土壤细菌多样性在退耕初期(3—7a)上升达到最大,退耕中后期逐渐降低。表层土壤各类群细菌生物量逐渐升高,亚表层土壤各类群细菌生物量则先降后升再降。水分条件和容重是与研究区土壤细菌群落结构和多样性密切相关的土壤因子,而全氮是与土壤细菌生物量密切相关的土壤因子。研究从生态过程视角解析了土壤细菌群落较详...     

Tropical Soil Bacterial Communities in Malaysia: pH Dominates in the Equatorial Tropics Too

The dominant factors controlling soil bacterial community variation within the tropics are poorly known. We sampled soils across a range of land use types--primary (unlogged) and logged forests and crop and pasture lands in Malaysia. PCR-amplified soil DNA for the bacterial 16S rRNA gene targeting the V1-V3 region was pyrosequenced using the 454 Roche machine. We found that land use in itself has a weak but significant effect on the bacterial community composition. However, bacterial community composition and diversity was strongly correlated with soil properties, especially soil pH, total carbon, and C/N ratio. Soil pH was the best predictor of bacterial community composition and diversity across the various land use types, with the highest diversity close to neutral pH values. In addition, variation in phylogenetic structure of dominant lineages (Alphaproteobacteria, Beta/Gammaproteobacteria, Acidobacteria, and Actinobacteria) is also significantly correlated with soil pH. Together, these results confirm the importance of soil pH in structuring soil bacterial communities in Southeast Asia. Our results also suggest that unlike the general diversity pattern found for larger organisms, primary tropical forest is no richer in operational taxonomic units of soil bacteria than logged forest, and agricultural land (crop and pasture) is actually richer than primary forest, partly due to selection of more fertile soils that have higher pH for agriculture and the effects of soil liming raising pH.     

Organic carbon and mineral nutrient limitation of oxygen consumption, bacterial growth and efficiency in the Norwegian Sea

To evaluate the role of bacteria in the transformation of organic matter in subarctic waters, we investigated the effect of mineral nutrients (ammonia and phosphate) and organic carbon (glucose) enrichment on heterotrophic bacterial processes and community structure. Eight experiments were done in the Norwegian Sea during May and June 2008. The growth-limiting factor (carbon or mineral nutrient) for heterotrophic bacteria was inferred from the combination of nutrient additions that stimulated highest bacterial oxygen consumption, biomass, production, growth rate and bacterial efficiency. We conclude that heterotrophic bacteria were limited by organic carbon and co-limited by mineral nutrients during the prevailing early nano-phytoplankton (1–10 μm) bloom conditions. High nucleic acid (HNA) bacteria became dominant (>80%) only when labile carbon and mineral nutrient sources were available. Changes in bacterial community structure were investigated using denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S ribosomal RNA genes. The bacterial community structure changed during incubation time, but neither carbon nor mineral nutrient amendment induced changes at the end of the experiments. The lack of labile organic carbon and the availability of mineral nutrients are key factors controlling bacterial activity and the role of the microbial food web in carbon sequestration.     

Physiology and microbial community structure in soil at extreme water content

A sandy loam soil was brought to 6 water contents (13-100% WHC) to study the effects of extreme soil moistures on the physiological status of microbiota (represented by biomass characteristics, specific respiration, bacterial growth, and phospholipid fatty acid, PLFA, stress indicators) and microbial community structure (assessed using PLFA fingerprints). In dry soils, microbial biomass and activity declined as a consequence of water and/or nutrient deficiency (indicated by PLFA stress indicators). These microbial communities were dominated by G+ bacteria and actinomycetes. Oxygen deficits in water-saturated soils did not eliminate microbial activity but the enormous accumulation of poly-3-hydroxybutyrate by bacteria showed the unbalanced growth in excess carbon conditions. High soil water content favored G bacteria.     

DNA-based monitoring of total bacterial community structure in environmental samples

Determining the structure of bacterial communities and their response to stimuli is key to understanding community function and the interactions that occur between microorganisms and the environment. However, bacterial communities often comprise complex assemblages of large numbers of different bacterial populations. An approach is presented which allows bacterial community structure to be determined by fractionation of the complex mixture of total bacterial community DNA using the DNA-binding dye bisbenzimidazole which imposes G + C-dependent changes in the buoyant density of DNA. Bacterial community structure presented as percentage of total DNA vs. percentage G + C content of DNA is an indication of the relative abundance of phylogenetic groups of bacteria. Changes in the composition of a soil bacterial community in response to perturbations in the form of carbon amendment and altered water status were monitored.     

模拟氮沉降和降雨变化对贝加尔针茅草原土壤细菌群落结构的影响

研究氮沉降和降雨变化对土壤细菌群落结构的影响,对未来预测多个气候变化因子对草地生态系统影响的交互作用具有重要意义。以施氮和灌溉分别模拟氮沉降和降雨增加,采用高通量测序技术,研究8个氮添加水平(0、15、30、50、100、150、200、300kg N hm-2a-1)和2个水分添加水平(不灌溉、模拟夏季增雨100 mm灌溉)对土壤细菌群落结构的影响。结果表明,氮素和水分输入增加后,土壤细菌群落组成、丰度均显著变化(P0.05)。在群落中占主导的细菌门类有疣微菌门Verrucomicrobia(30.61%—48.51%)、变形菌门Proteobacteria(21.37%—29.97%)、酸杆菌门Acidobacteria(9.54%—20.67%)和拟杆菌门Bacteroidetes(4.96%—9.74%)。在常规降雨和水分添加两种条件下,随着氮添加水平的增加,占主导的细菌门类(相对丰度1%)表现出不同的变化趋势。疣微菌门相对丰度在常规降雨N100—N300条件下显著降低,但在氮素和水分同时添加条件下随氮添加水平升高而逐渐升高,在N200—N300时显著升高。变形菌门和拟杆菌门相对丰度在常规降雨高氮添加条件下呈升高趋势,但在水分添加时却无明显变化。酸杆菌门相对丰度在常规降雨高氮添加条件下升高,但在水分添加后呈明显下降趋势。放线菌门Actinobacteria相对丰度在常规降雨N100—N300条件下显著升高,但在水分添加后高氮添加时显著降低。厚壁菌门Firmicutes相对丰度在常规降雨条件下无显著变化,但在水分和高氮添加条件下降低。浮霉菌门Planctomycetes相对丰度在两种不同的水分添加条件下均呈先升高后降低的趋势。氮素和水分添加对土壤细菌群落结构的变化存在明显的互作效应(P0.0001)。在不同氮素和水分输入条件下共有19个土壤细菌门类相对丰度有显著差异。土壤细菌群落结构的变化主要来自于疣微菌门和酸杆菌门的相对丰度变化,两者可作为土壤细菌群落结构变化的指示种。综上,氮素和水分添加显著改变了土壤细菌群落结构,氮素和水分对土壤细菌不同门类相对丰度变化存在明显的互作效应。