山东省渤海海洋保护区典型海域表层海水微生物群落多样性分析

海洋微生物在生态系统循环中发挥重要作用。为系统了解山东省渤海海洋保护区表层海水微生物群落多样性,作者利用Illumina高通量测序及生物信息学分析技术研究了12个水体样本的菌群构成和多样性特征。实验结果表明,山东渤海海洋保护区典型海域表层海水微生物群落丰富,12个水体样品OTU分属于25门、56纲、103目、163科、227属;门、纲、目、科、属分类等级上的优势类群分别为变形菌门(Proteobacteria)(57.95%)、α-变形菌纲(Alphaproteobacteria)(21.88%)、黄杆菌目(Flavobacteriales)(4.31%)、红细菌科(Rhodobacteraceae)(10.68%)、Candidatus portiera(7.94%);保护区内表层海水微生物具有其独特的菌群特征和多样性。本研究结果为进一步认识海洋微生物多样性与海洋生态环境保护的关系奠定了基础。     

开垦对荒漠土壤微生物群落结构特征的影响

以古尔班通古特沙漠南缘典型流域（玛纳斯河、吉木萨尔河、三工河、四工河、水磨河）的绿洲农田与毗邻荒漠土壤为研究对象,采用磷脂脂肪酸（PLFA）方法分析不同开垦年限的土壤微生物生物量、群落结构、多样性变化特征。结果表明：荒漠开垦后,土壤微生物总PLFA含量、真菌PLFA、细菌PLFA、革兰氏阳性菌（G⁺）和革兰氏阴性菌（G^-）PLFA含量均显著增加。荒漠开垦5 a内,细菌PLFA与G^-PLFA增长更强烈,使得真菌PLFA/细菌PLFA比值降低了48%,G⁺PLFA/G^-PLFA比值（革兰氏阳性菌与革兰氏阴性菌的PLFA比值）降低了67%。但随着开垦年限的延长,这两个比值没有显著变化,表明与开垦年限相比,荒漠的开垦行为对土壤微生物群落结构有着更加强烈的影响。随着开垦年限的增加,土壤微生物群落多样性总体呈上升趋势。虽然荒漠在开垦50 a后多样性指数略有下降,但仍远高于荒漠土壤。土壤微生物总PLFA含量和大部分菌群PLFA含量与土壤电导率显著负相关,与全氮和有机碳显著正相关。荒漠在开垦过程中灌溉增加了土壤水分且降低了土壤盐分,全氮和有机碳含量增加,这些改变是土壤微生物群落变化的主要原因。荒漠开垦有助于提高土壤微生物PLFA含量、改善土壤微生物的群落结构、丰富土壤微生物群落多样性,有利于土壤质量的提高。     

马衔山多年冻土与季节冻土区土壤微生物量及酶活性的季节动态

为了研究马衔山多年冻土区和非多年冻土区土壤微生物碳氮、土壤酶活性的差异,选取多年冻土区、季节冻土区和交界区为对象,分析了0~30 cm土层微生物碳氮和转化酶、脲酶、中性磷酸酶、淀粉酶、过氧化氢酶、多酚氧化酶酶活性不同季节的变化特征。结果表明：全氮、总有机碳、微生物量碳氮与多数土壤酶之间呈显著相关关系。在不同区域,土壤微生物碳氮均在0~10 cm含量最高,10~20 cm次之,20~30 cm最低。土壤微生物碳氮在生长季表现为含量逐渐增加,但是多年冻土区与季节冻土区差异不大。土壤酶活性在深度方面表现与微生物碳氮含量变化一致。土壤酶并无的季节变化规律。在多年冻土区,转化酶、多酚氧化酶和磷酸酶活性明显高于非多年冻土区。本研究表明,尽管多年冻土区的植被和土壤总有机碳明显高于非多年冻土区,其土壤微生物碳氮含量相当,且一些土壤酶活性也相当。说明非多年冻土区土壤的生物地球化学相对强度较大。因此,多年冻土退化后可能会导致生态系统的退化。     

冻融交替对不同年代排水造林湿地土壤微生物活性及有机碳密度的影响

以小兴安岭湿地土壤为研究对象,基于室内分析和冻融实验,分析了冻融作用下不同年代排水造林湿地土壤微生物量、酶活性以及有机碳密度的变化趋势,探讨了不同年代排水造林湿地土壤微生物活性与有机碳密度之间的相关关系,以期为深入认识冻融期间高寒高纬度地区土壤碳循环过程提供参考依据。结果表明：（1）冻融次数对土壤微生物量碳、氮含量影响显著（P<0.05）,经历9次冻融循环后,土壤微生物量碳、氮含量比冻融前明显减少;在三种不同年代排水造林的湿地中,排水时间越短,土壤微生物量碳、氮含量下降幅度越大,表明长时间的反复冻融交替可能导致土壤微生物量的进一步减少。（2）冻融前后,土壤蔗糖酶和淀粉酶活性均表现为下降趋势,且多次冻融交替后,-25~5℃冻融处理比-5~5℃冻融处理酶活性更低,表明较大的冻融温差更能降低土壤酶的活性度。（3）随着冻融次数和冻融温度的变化,四种湿地的土壤有机碳密度基本保持稳定,但其与土壤微生物量、酶活性却存在着高度的正相关性,通过探究微生物活性所调控的土壤过程,可以直接或间接了解土壤有机碳密度的变化趋势,便于从本质上验证其响应机制。     

黄土高原弃耕地自然恢复过程中微生物碳的大小和活性的动态

耕地弃耕后植被次生演替过程中土壤微生物碳的大小和活性的研究结果表明,与耕地相比,各种演替阶段的弃耕地均有较高的有机碳和微生物碳含量,在26 a限弃耕地中,有机碳和微生物碳的含量达到天然植被的64.56%和48.69%,而且有机碳和微生物碳与演替的时间表现为显著正相关（P<0.01）,而微生物碳和有机碳的比值却随着演替没有显示明显的变化趋势。有机碳和微生物碳的大小顺序为：自然植被>各种演替阶段的弃耕地>小麦地。代谢熵（qCO2）随着演替的进程没有明显的变化趋势。与各种弃耕地和耕地相比,自然植被有较低的qCO2。这说明耕地弃耕后植被的自然演替有利于提高土壤微生物碳,改善土壤肥力。     

Morphometry of microstromatolites in calcrete laminar crusts and a fractal model of their growth

The laminar crust, constituting the upper part of calcretes (terrestrial CaCO₃ accumulations inside surficial sediments), is a succession of thin layers of various colors and shapes resembling micro-stromatolites. The crust structure and its diagenetic evolution are similar to stromatolites. A quantitative study of its structure was made using image analysis. Euclidian parameters were calculated to describe lamina shape. Eight hundred and eighty-six laminae were divided into six classes from the flatest forms to columnar shapes. The geometrical relationships between the shapes are interpreted as steps in the growth process of the microstromatolite. A fractal model of laminar crust growth was developed, using the diffusion-limited aggregation model (DLA) and dilation (an operation of mathematical morphology). This model simulates all growth steps observed in thin section and emphasizes the necessity of an interface with the atmosphere to explain the variety of shapes. This growth model supports the theory of a surficial and biogenic origin for certain calcrete laminar crusts.     

Community Metabolism in Microbial Mats: The Occurrence of Biologically-mediated Iron and Manganese Reduction

Community metabolism and nutrient, iron (Fe) and manganese (Mn) cycling were examined in two intertidal, marine, microbial mat communities during short (4–5 days) incubations in closed, flow-through microcosms. Sediment microcosms were incubated under either light (light–dark cycles) or dark (continuous darkness) conditions to assess the effect(s) of photosynthetic oxygen production and microalgal activity on nutrient, Fe and Mn cycling. The effects of chemical redox reactions between reduced sulphur (S), Fe and Mn cycling were examined by blocking sulphate reduction, and reduced S production, with 25 mM molybdate while incubating under dark conditions.In light-incubated microcosms, negligible fluxes of nutrients (nitrogen and phosphorus) and trace metals were observed. A substantial sediment–water flux of reduced Fe (Fe²⁺) and Mn (Mn²⁺) was observed in microcosms incubated under continuous darkness; highest fluxes were observed in molybdate-amended microcosms. At both sites, biologically-mediated redox reactions accounted for a substantial (>50%) portion of the Fe²⁺and Mn²⁺flux. Both microbial mat communities exhibited similar rates of gross photosynthetic oxygen (O₂) production, but dramatically different rates of net benthic O₂flux. Distinct patterns of net O₂production and trace metal cycling arose from differences in either trace metal oxide availability or reactivity (mineralogy), organic carbon mineralization rates, or sediment characteristics (porosity). Variations in the microbial community responsible for trace metal cycling could have also contributed to the pattern. The present data illustrate that chemically-mediated redox reactions between metal oxides and reduced S complicate interpretation of Fe and Mn fluxes, underscoring the need to separate chemical and biological reactions when attempting to determine the role of biological trace metal reduction in organic carbon oxidation.     

Submarine-spring controlled calcification and growth of large Rivularia bioherms, Late Pleistocene (MIS 5e), Gulf of Corinth, Greece

The cyanobacterium Rivularia haematites has calcified to form unusually large (up to 10 m high) bioherms in the Pleistocene Gulf of Corinth. Today R. haematites calcifies only in freshwater environments but these Gulf of Corinth bioherms have a brackish affinity, limited areal extent, and occur within marine deposits. Field relations and preliminary U-series dating suggest a marine isotope stage (MIS) 5e age for the bioherms. This age is compatible with published MIS 5e ages for corals in the marine sediments above the bioherms and is consistent with their current elevation based on average uplift rates. Bioherm growth during MIS 5e constrains their formation during a time of near sea-level highstand when the Gulf of Corinth was marine. Growth cavities in the bioherms are encrusted by brackish tolerant coralline algae. Field mapping of the MIS 5e highstand palaeoshoreline shows the bioherms grew in water <16 m deep. Mg contents of the bioherm calcites, and associated coralline algal skeletons, are both much lower than expected for marine MIS 5e carbonates. They are best explained if the calcites precipitated from brackish fluids with Mg/Ca ratios below 2, implying at least 60% input of freshwater with low Mg/Ca ratio. Sr isotopes confirm a strong input of groundwater that had partially equilibrated with Mesozoic limestones. The limited areal extent of the bioherms and their close association with karstified fault scarps suggest that they formed in shallow sea water where freshwater submarine springs delivered CaCO₃ saturated water that promoted rapid calcification of cyanobacteria. Rapid calcification and strong degassing of CO₂ from the spring water resulted in disequilibrium stable isotope compositions for the calcites.     

Microbial production and photobleaching of CDOM in an estuarine brackish lake on Chongming Island, Shanghai

Chromophoric dissolved organic matter （CDOM）, one of the important components in freshwater and seawater ecosystems, plays a role in underwater light absorption and primary productivity. The Lake Beihu was a part of the North Branch of the Yangtze （Changjiang） River estuary in the past, but now the Lake Beihu has become the biggest manmade brackish lake in East China. The lake is a unique brackish ecosystem, however, little study deals with the fate of CDOM in it and whether this type of lake ecosystem will face eutrophication problem. This paper focuses on the transformation of CDOM, and the impact of microbe and light in the Lake Beihu. Microbial production and natural photobleaching simulative experiment was done on water samples from the Lake Beihu, yielding the following results. Water samples were collected from the Lake Beihu in May 2006. The filtrates through Whatman GF/F filters and polycarbonate membranes （μm） were exposed to microbe and microbe plus light condition, respectively. Three-dimensional excitation emission matrix （3-DEEM） fluorescence spectra were analyzed. It was shown that the amount of CDOM increased with time in the microbe exposure experiment, which means that microbes may play an important role in the production of CDOM instead of degrading CDOM. The .productivity was enhanced with increasing temperature, e.g. the value of UV260 increased by 62.4% in 4.5 days at 30℃, 26.9% at 20℃, 5.0% at 10℃. In addition, photobleaching was observed in the study as other papers reported. With the impact of microbes, the fluorescence signal of fulvic acid became stronger as the time went by. At 30℃, the fulvic acid fluorescence, which was expressed by QSU, increased by 35%-39%.