北极苔原土壤中可培养细菌的分离及其抗菌活性测定

【目的】北极地区具有高纬度、低温、高辐射等独特的环境条件。北冰洋及周围大面积的陆地区域鲜有人类踪迹,其中微生物数量不可低估。本研究旨在了解北极土壤中的可培养微生物的多样性及其抗菌活性。【方法】对来源于北极黄河站附近的7份不同植物根下苔原土壤进行直接涂布和富集培养后涂布。【结果】共获得细菌菌株721株,对其中608株进行细菌16S rRNA基因序列测定,归属于86个属,229个种,主要分布于变形菌门(Proteobacteria,54.3%)、放线菌门(Actinobacteria,21.2%)、拟杆菌门(Bacteroidetes,12.8%)、厚壁菌门(Firmicutes,10.0%)和奇异球菌门(Deinococcus-Thermus,1.6%)。其中从16S rRNA基因序列同源性推测有22株细菌菌株为潜在新种/属。从分离菌株中筛选出16株可抑制金黄色葡萄球菌(Staphylococcusaureus)或鲍氏不动杆菌(Acinetobacterbaumannii)生长的拮抗菌。【结论】获得了北极土壤地区特有的微生物菌株资源,为进一步筛选拮抗菌的活性物质提供了菌株基础。     

Water, temperature, and vegetation regulation of methyl chloride and methyl bromide fluxes from a shortgrass steppe ecosystem

Temperate grasslands are considered to be a significant sink for CH₃Br, although large uncertainties exist about the magnitude of this sink because of a paucity of field measurements. Here, we report the results of a combined field and laboratory study that investigated the effects of water, temperature, and plant community composition on CH₃Cl and CH₃Br fluxes in a semiarid temperate grassland. A novel stable isotope tracer technique was also employed to deconvolute simultaneous production and oxidation of CH₃Cl and CH₃Br. Net and gross fluxes were measured from different landforms (ridges, floodplains) and cover types (grass‐dominated, shrub‐dominated) to capture a representative range of hydrologic regimes, temperatures, and plant communities. In field experiments, net CH₃Cl and CH₃Br uptake was observed at all grass‐dominated sites (?400±77 nmol CH₃Cl m^?2 day^?1 and ?3.4±0.9 nmol CH₃Br m^?2 day^?1), while net CH₃Cl emission (439±58 nmol CH₃Cl m^?2 day^?1) was observed at sites dominated by the shrub Atriplex canescens, indicating that this plant is a strong CH₃Cl producer. Gross CH₃Cl and CH₃Br oxidation were comparable with estimates from other dryland ecosystems (507±115 nmol CH₃Cl m^?2 day^?1 and 9.1±2.2 nmol CH₃Br m^?2 day^?1), although CH₃Br oxidation rates were at least five times lower than those observed in more mesic temperate grasslands. We suggest that estimates of the temperate grassland CH₃Br sink should be reduced by ≥19% (≥1.8 Gg yr^?1) to account for the weaker sink strength of semiarid environments. Identification of A. canescens as a ‘new’ CH₃Cl source may have important ramifications for the global atmospheric budget of CH₃Cl, given the global distribution of this plant and its congeners and their widespread presence in many dryland ecosystems. Laboratory experiments revealed that soil water was the chief regulator of CH₃Cl and CH₃Br oxidation, while temperature had no observed effect between 14 and 26 °C. Oxidation rates rose most rapidly between 0.4% and 5% volumetric water content, suggesting that methyl halide‐oxidizing bacteria respond strongly to small inputs of water under the very driest conditions. Soil drying and rewetting experiments did not appear to affect the oxidation of CH₃Cl and CH₃Br by soil microorganisms, which are presumably adapted to frequent wet/dry cycles.     

Methanogenesis at low temperatures by microflora of tundra wetland soil

Active methanogenesis from organic matter contained in soil samples from tundra wetland occurred even at 6 °C. Methane was the only end product in balanced microbial community with H₂/CO₂ as a substrate, besides acetate was produced as an intermediate at temperatures below 10°C. The activity of different microbial groups of methanogenic community in the temperature range of 6–28 °C was investigated using 5% of tundra soil as inoculum. Anaerobic microflora of tundra wetland fermented different organic compounds with formation of hydrogen, volatile fatty acids (VFA) and alcohols. Methane was produced at the second step. Homoacetogenic and methanogenic bacteria competed for such substrates as hydrogen, formate, carbon monoxide and methanol. Acetogens out competed methanogens in an excess of substrate and low density of microbial population. Kinetic analysis of the results confirmed the prevalence of hydrogen acetogenesis on methanogenesis. Pure culture of acetogenic bacteria was isolated at 6 °C. Dilution of tundra soil and supply with the excess of substrate disbalanced the methanoigenic microbial community. It resulted in accumulation of acetate and other VFA. In balanced microbial community obviously autotrophic methanogens keep hydrogen concentration below a threshold for syntrophic degradation of VFA. Accumulation of acetate- and H₂/CO₂-utilising methanogens should be very important in methanogenic microbial community operating at low temperatures.     

Inter-annual variability of NDVI in response to long-term warming and fertilization in wet sedge and tussock tundra

This study explores the relationship between the normalized difference vegetation index (NDVI) and aboveground plant biomass for tussock tundra vegetation and compares it to a previously established NDVI–biomass relationship for wet sedge tundra vegetation. In addition, we explore inter-annual variation in NDVI in both these contrasting vegetation communities. All measurements were taken across long-term experimental treatments in wet sedge and tussock tundra communities at the Toolik Lake Long Term Ecological Research (LTER) site, in northern Alaska. Over 15 years (for wet sedge tundra) and 14 years (for tussock tundra), N and P were applied in factorial experiments (N, P and N+P), air temperature was increased using greenhouses with and without N+P fertilizer, and light intensity was reduced by 50% using shade cloth. during the peak growing seasons of 2001, 2002, and 2003, NDVI measurements were made in both the wet sedge and tussock tundra experimental treatment plots, creating a 3-year time series of inter-annual variation in NDVI. We found that: (1) across all tussock experimental tundra treatments, NDVI is correlated with aboveground plant biomass (r ²=0.59); (2) NDVI–biomass relationships for tussock and wet sedge tundra communities are community specific, and; (3) NDVI values for tussock tundra communities are typically, but not always, greater than for wet sedge tundra communities across all experimental treatments. We suggest that differences between the response of wet sedge and tussock tundra communities in the same experimental treatments result from the contrasting degree of heterogeneity in species and functional types that characterize each of these Arctic tundra vegetation communities.     

Predator–prey relationships: arctic foxes and lemmings

1. The number of breeding dens and litter sizes of arctic foxes Alopex lagopus were recorded and the diet of the foxes was analysed during a ship-based expedition to 17 sites along the Siberian north coast. At the same time the cyclic dynamics of co-existing lemming species were examined.
2. The diet of arctic foxes was dominated by the Siberian lemming Lemmus sibiricus (on one site the Norwegian lemming L. lemmus ), followed by the collared lemming Dicrostonyx torquatus .
3. The examined Lemmus sibiricus populations were in different phases of the lemming cycle as determined by age profiles and population densities.
4. The numerical response of arctic foxes to varying densities of Lemmus had a time lag of 1 year, producing a pattern of limit cycles in lemming–arctic fox interactions. Arctic fox litter sizes showed no time lag, but a linear relation to Lemmus densities. We found no evidence for a numerical response to population density changes in Dicrostonyx .
5. The functional or dietary response of arctic foxes followed a type II curve for Lemmus , but a type III response curve for Dicrostonyx .
6. Arctic foxes act as resident specialist for Lemmus and may increase the amplitude and period of their population cycles. For Dicrostonyx , on the other hand, arctic foxes act as generalists which suggests a capacity to dampen oscillations.     

Bioventing in Shallow Tundra Overlying Permafrost

The purpose of this research was to investigate the feasibility of suction bioventing for treatment of contaminated tundra soil. Two laboratory-scale venting reactors were prepared with tundra from Arctic Alaska and operated, one for 32?d and the other for 52?d. For each rectangular reactor, suction was applied to a central well screened at mid-depth, while opposite ends of the reactor were screened to serve as air intake zones. The volume of liquid and gas recovered from the suction well was quantified daily. Numbers for heterotrophic organisms, pH, and dissolved organic carbon were quantified in the recovered liquid. The suction pump held a full vacuum (i.e., 101?kPa vac) for the duration of both experiments, indicating continuous obstruction of pneumatic and hydraulic conductivity. In both reactors, the soil in the proximity of the suction well separated from the bulk of the soil, precluding hydraulic communication. Furthermore, the soil nearest the well screen compacted, forming a barrier to appreciable pneumatic conductivity. At the end of operation, the soil was removed and sampled for moisture content, pH, and numbers of heterotrophic organisms at various locations. The results of this study showed that for suction bioventing to be successful in tundra, consolidation of the soil around the well screen must be prevented, as it will cause well isolation and limit both pneumatic and hydraulic conductivities.     

Methane emission from Arctic tundra

Concerns about a possible feedback effect on global warming following possible increased emissions of methane from tundra environments have lead to series of methane flux studies of northern wetland/tundra environments. Most of these studies have been carried out in boreal sub-Arctic regions using different techniques and means of assessing representativeness of the tundra. Here are reported a time series of CH₄ flux measurements from a true Arctic tundra site. A total of 528 independent observations were made at 22 fixed sites during the summers of 1991 and 1992. The data are fully comparable to the most extensive dataset yet produced on methane emissions from sub-Arctic tundra-like environments. Based on the data presented, from a thaw-season with approximately 55% of normal precipitation, a global tundra CH₄ source of 18–30 Tg CH₄ yr⁻¹ is estimated. This is within the range of 42±26 Tg CH₄ yr⁻¹ found in a similar sub-Arctic tundra environment. No single-parameter relationship between one environmental factor and CH₄ flux covering all sites was found. This is also in line with conclusions drawn in the sub-Arctic. However, inter-season variations in CH₄ flux at dry sites were largely controlled by the position of the water table, while flux from wetter sites seemed mainly to be controlled by soil temperature.     

Soil aeration in relation to soil physical properties, nitrogen availability, and root characteristics within an arctic watershed

The seasonal change in soil oxygen availability was determined in several habitats along a topographic moisture gradient in an arctic watershed. The effect of changes in soil aeration on soil chemical and plant properties was examined by comparison of the driest (tussocks) and wettest (wet sedge tundra) sites along this gradient. Spatial variability and seasonal change in soil oxygen availability was closely linked to the hydrologic regime and the thickness of the organic soil horizon. The greatest extension of the aerobic soil layer was found beneath well-drained tussocks, while less than 10% of the unfrozen soil layer is aerated in flooded wet sedge tundra. Intertussock areas and watertracks (channels of water drainage) have intermediate levels of aeration. In tussock tundra, soil oxygen diffusion is restricted in the mineral soil layer below the organic horizon due to reduced pore space. Organic matter constituents and their change with depth were similar beneath tussocks and in wet sedge tundra, indicating that factors other than soil aeration (e.g. low soil temperatures, short growing season) are the primary controls on decomposition in these two arctic tundra systems. NH₄ ⁺, the dominant form of inorganic N, was more available in wet sedge tundra than in tussock tundra. At both sites, extractable and soil solution NO₃ ^- concentrations increased 4 to 8 fold in the second part of the growing season, indicating increased nitrifier activity with improved soil oxygen availability. Although soils thawed as deep as 60 cm, approx. 90% of the root biomass was concentrated within 20 cm of the surface. Despite the anaerobic soil environment in wet sedge tundra, the dominant species there, Eriophorum angustifolium, reached slightly greater rooting depths than E. vaginatum, whose roots grow in the elevated, aerobic portion of tussocks. E. angustifolium had a root porosity of 31%, within the range found for wetland species, while roots of E. vaginatum had a porosity close to 12%. Rhizome porosity were low in both species (11%).     

Advancing the long view of ecological change in tundra systems

Despite uncertainties related to sustained funding, ideological rivalries and the turnover of research personnel, long-term studies and studies espousing a long-term perspective in ecology have a history of contributing landmark insights into fundamental topics, such as population- and community dynamics, species interactions and ecosystem function. They also have the potential to reveal surprises related to unforeseen events and non-stationary dynamics that unfold over the course of ongoing observation and experimentation. The unprecedented rate and magnitude of current and expected abiotic changes in tundra environments calls for a synthetic overview of the scope of ecological responses these changes have elicited. In this special issue, we present a series of contributions that advance the long view of ecological change in tundra systems, either through sustained long-term research, or through retrospective or prospective modelling. Beyond highlighting the value of long-term research in tundra systems, the insights derived herein should also find application to the study of ecological responses to environmental change in other biomes as well.     

Inhibition of bacterial perchlorate reduction by zero-valent iron

Perchlorate was reduced by a mixed bacterial culture over a pH range of 7.0–8.9. Similar rates of perchlorate reduction were observed between pH 7.0 and 8.5, whereas significantly slower reduction occurred at pH 8.9. Addition of iron metal, Fe(0), to the mixed bacterial culture resulted in slower rates of perchlorate reduction. Negligible perchlorate reduction was observed under abiotic conditions with Fe(0) alone in a reduced anaerobic medium. The inhibition of perchlorate reduction observed in the presence of Fe(0) is in contrast to previous studies that have shown faster rates of contaminant reduction when bacteria and Fe(0) were combined compared to bacteria alone. The addition of Fe(0) resulted in a rise in pH, as well as precipitation of Fe minerals that appeared to encapsulate the bacterial cells. In experiments where pH was kept constant, the addition of Fe(0) still resulted in slower rates of perchlorate reduction suggesting that encapsulation of bacteria by Fe precipitates contributed to the inhibition of the bacterial activity independent of the effect of pH on bacteria. These results provide the first evidence linking accumulation of iron precipitates at the cell surface to inhibition of environmental contaminant degradation. Fe(0) was not a suitable amendment to stimulate perchlorate-degrading bacteria and the bacterial inhibition caused by precipitation of reduced Fe species may be important in other combined anaerobic bacterial–Fe(0) systems. Furthermore, the inhibition of bacterial activity by iron precipitation may have significant implications for the design of in situ bioremediation technologies for treatment of perchlorate plumes.