共查询到20条相似文献,搜索用时 31 毫秒
1.
Marcelo Perantoni Darci M. S. Esquivel Eliane Wajnberg Daniel Acosta-Avalos Geraldo Cernicchiaro Henrique Lins de Barros 《Die Naturwissenschaften》2009,96(6):685-690
Magnetotactic microorganisms use the interaction of internal biomineralized nanoparticles with the geomagnetic field to orientate.
The movement of the magnetotactic multicellular prokaryote Candidatus Magnetoglobus multicellularis under an applied magnetic field was observed. A method using digital image processing techniques
was used to track the organism trajectory to simultaneously obtain its body radius, velocity, U-turn diameter, and the reorientation
time. The magnetic moment was calculated using a self-consistent method. The distribution of magnetic moments and radii present
two well-characterized peaks at (9 ± 2) × 10−15 and (20 ± 3) × 10−15 A m2 and (3.6 ± 0.1) and (4.3 ± 0.1) μm, respectively. For the first time, simultaneous determination of the distribution of the
organism radii and magnetic moment was obtained from the U-turn method by a new digital imaging processing. The bimodal distributions
support an organism reproduction process model based on electron microscopy observations. These results corroborate the prokaryote
multicellular hypothesis for Candidatus M. multicellularis. 相似文献
2.
Fruits of Garden Lettuce, imbibed in 0.01 M KNO3, were depleted of maternal active phytochrome B by saturating deep-red exposure and photosensitized by chilling for 1 week
at 4 °C. Twenty saturated fluence-response curves for photoinduced germination were elaborated between 300 and 800 nm, using
exposure periods from 6 to 600 s at 22.5 °C; there is linear and closely parallel regression in the logarithmic probability
net. The reciprocals of the half-response fluences obtained gave the apparent conversion spectrum of the controlling pigments
and this was corrected for the transmittance of the seed-coat. It is a phytochrome spectrum of P
r with photoconversion cross-sections of 1.2·109 and 4.5·103 m2 mol–1 at 666 and 800 nm, respectively. This means that for half-saturated germination of sensitized seed, fewer than 1 out of 200,000
phytochrome A molecules have to be photoconverted to P
fr, and no photo-reversibility by deep-red was found. Therefore, all spectral colours of nightly moon- or skylight should stimulate
the germination of sensitized weed seeds if they are exposed at the soil surface between sequential tillage operations.
Received: 28 April 2000 / Accepted in revised form: 28 July 2000 相似文献
3.
Summer phytoplankton assemblages from surface waters off Kuwait were enriched with levels of eolian dust (105, 106, and 107 mg/m3), similar to seasonal dust fallout for this region. Algal growth was positive and dose dependent. Highest biomass was up
to 527 μg chlorophyll a/l on day 5. The maximum doublings of biomass per day were 0.64, 0.77, and 1.42, corresponding to 105, 106, and 107 mg/m3 enrichment and were significantly higher than the 0.56 for control. Changes in the phytoplankton species composition occurred
with changes in biomass, with small algae dominating peak populations. It is suggested that through enrichment of trace elements
via eolian dust, a high level of phytoplankton biomass and growth can be sustained in this arid environment.
Received: 15 October / Accepted in revised form: 16 June 1999 相似文献
4.
Vincent WF Gibson JA Pienitz R Villeneuve V Broady PA Hamilton PB Howard-Williams C 《Die Naturwissenschaften》2000,87(3):137-141
The Ward Hunt Ice Shelf (83°N, 74°W) is the largest remaining section of thick (>10 m) landfast sea ice along the northern
coastline of Ellesmere Island, Canada. Extensive meltwater lakes and streams occur on the surface of the ice and are colonized
by photosynthetic microbial mat communities. This High Arctic cryo-ecosystem is similar in several of its physical, biological
and geochemical features to the McMurdo Ice Shelf in Antarctica. The ice-mats in both polar regions are dominated by filamentous
cyanobacteria but also contain diatoms, chlorophytes, flagellates, ciliates, nematodes, tardigrades and rotifers. The luxuriant
Ward Hunt consortia also contain high concentrations (107–108 cm–2) of viruses and heterotrophic bacteria. During periods of extensive ice cover, such as glaciations during the Proterozoic,
cryotolerant mats of the type now found in these polar ice shelf ecosystems would have provided refugia for the survival,
growth and evolution of a variety of organisms, including multicellular eukaryotes.
Received: 30 August 1999 / Accepted in revised form: 15 December 1999 相似文献
5.
Jie Tang Xiaoming Xu Zhaoyang Li Weizheng Han 《Mitigation and Adaptation Strategies for Global Change》2012,17(1):103-109
The study area of this article, Western Jilin province of China, was a typical area responding to global changing in middle
latitude areas. In this paper, by interpreting the thematic mapper (TM) images of the study area in the years of 1989, 1996,
2000 and 2004, the land use/cover change (LUCC) data were achieved, which included the area of paddy fields and its spatial
distributions. 113 soil samples were collected to obtain soil organic carbon (SOC) data of different land use types. After
that, the organic matter contents of these samples were measured by using the potassium dichromate oxidation-outer heating
method. Based on the data above, the amount of SOC sequestrated by the surface soil (0~30 cm) of paddy fields was calculated.
The result showed that: the area of paddy fields was increasing continuously in western Jilin, from 11.28 × 104 hm2 in 1989 to 22.77 × 104 hm2 in 2004. Paddy fields transferred from wetlands, grasslands and water areas accounted for the main part of the paddy fields
in 2004, the areas were 3.09 × 104 hm2, 2.98 × 104 hm2 and 2.8 × 104 hm2, respectively. And paddy fields with a total area of 0.83 × 104 hm2 degraded into saline-alkali lands. The amount of organic carbon sequestration in the surface layer (0–30 cm) of paddy fields
was 658.86 × 104 t. The primary SOC sinks located around the joint of Baicheng City and Zhenlai County, while the major SOC source located
at Songyuan City and northern Qianguo County. 相似文献
6.
Stephan Baumgartner Martin Wolf Peter Skrabal Felix Bangerter Peter Heusser André Thurneysen Ursula Wolf 《Die Naturwissenschaften》2009,96(9):1079-1089
Quantitative meta-analyses of randomized clinical trials investigating the specific therapeutic efficacy of homeopathic remedies
yielded statistically significant differences compared to placebo. Since the remedies used contained mostly only very low
concentrations of pharmacologically active compounds, these effects cannot be accounted for within the framework of current
pharmacology. Theories to explain clinical effects of homeopathic remedies are partially based upon changes in diluent structure.
To investigate the latter, we measured for the first time high-field (600/500 MHz) 1H T1 and T2 nuclear magnetic resonance relaxation times of H2O in homeopathic preparations with concurrent contamination control by inductively coupled plasma mass spectrometry (ICP-MS).
Homeopathic preparations of quartz (10c–30c, n = 21, corresponding to iterative dilutions of 100−10–100−30), sulfur (13x–30x, n = 18, 10−13–10−30), and copper sulfate (11c–30c, n = 20, 100−11–100−30) were compared to n = 10 independent controls each (analogously agitated dilution medium) in randomized and blinded experiments. In none of the
samples, the concentration of any element analyzed by ICP-MS exceeded 10 ppb. In the first measurement series (600 MHz), there
was a significant increase in T1 for all samples as a function of time, and there were no significant differences between homeopathic potencies and controls.
In the second measurement series (500 MHz) 1 year after preparation, we observed statistically significant increased T1 relaxation times for homeopathic sulfur preparations compared to controls. Fifteen out of 18 correlations between sample
triplicates were higher for controls than for homeopathic preparations. No conclusive explanation for these phenomena can
be given at present. Possible hypotheses involve differential leaching from the measurement vessel walls or a change in water
molecule dynamics, i.e., in rotational correlation time and/or diffusion. Homeopathic preparations thus may exhibit specific
physicochemical properties that need to be determined in detail in future investigations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
7.
Light-dependent magnetoreception in birds: the effect of intensity of 565-nm green light 总被引:1,自引:0,他引:1
In a previous study, Australian silvereyes tested in autumn under monochromatic 565-nm green light at intensities of 2.1
and 7.5 mW m–2 preferred their normal northerly migratory direction, whereas they showed a significantly different tendency towards northwest
at 15.0 mW m–2. Repeating these experiments in spring with silvereyes migrating southward, we again observed well-oriented tendencies in
the migratory direction at 2.1 and 7.5 mW m–2. At 15.0 mW m–2, however, the birds once more preferred northwesterly directions, i.e. their response under this condition proved to be independent
of the migratory direction. This contradicts the interpretation that monochromatic green light of this high intensity leads
to a rotation of compass information; instead, it appears to produce sensory input that causes birds to give up their migratory
direction in favor of a fixed direction of as yet unknown origin.
Received: 3 April 2000 / Accepted in revised form: 19 June 2000 相似文献
8.
Inmaculada de Vicente Victoria Amores Francisco Guerrero Luis Cruz-Pizarro 《Die Naturwissenschaften》2010,97(7):627-635
Electron transport system (ETS) activity of sediments as an indication of microbial metabolic activity was examined in two
adjacent Mediterranean wetlands (southern Spain). We determined the spatio-temporal variation in ETS, and we explored the
potential biological [organic matter (OM), chlorophyll a (Chl a), aerobic and anaerobic bacteria] drivers of sediment ETS
activity. ETS activity was notably higher in the eutrophic Lake Nueva (34.91 μl O2 g−1 D.W. h−1) than in the hypertrophic Lake Honda (24.99 μl O2 g−1 D.W. h−1). Strong spatial differences were observed in ETS in both study sites. Highest ETS values were achieved at the surface sediment
at the deepest sampling station in each lake and a notable reduction in ETS with sediment depth was observed. By using linear
regression and multiple regression analysis, OM was identified as the best predictor of ETS in Lake Honda while Chl a was
the best predictor in Lake Nueva. The strong influence of OM supply on ETS activity in sediment from Lake Honda was the consequence
of the labile nature of sedimentary OM, while a more refractory OM (with a higher contribution of vascular plants) comprised
most of the sedimentary OM from Lake Nueva. By contrast, a large contribution of phytobenthos (supported by a higher lake
water transparency) to ETS has been recognized in sediments from Lake Nueva. In summary, the results of this study revealed
that the relative importance of planktonic primary producers (phytoplankton), benthic algae and vascular plants in the study
sites could explain the differences observed in the intensity of sediment ETS as well as in their drivers. 相似文献
9.
Numerical dating of the Eckfeld maar fossil site, Eifel, Germany: a calibration mark for the Eocene time scale 总被引:1,自引:0,他引:1
Sediments of the Eckfeld maar (Eifel, Germany) bear a well-preserved Eocene fauna and flora. Biostratigraphically, Eckfeld
corresponds to the Middle Eocene mammal reference level MP (Mammals Paleogene) 13 of the ELMA (European Land Mammal Age) Geiseltalian.
In the maar crater, basalt fragments were drilled, representing explosion crater eruption products. By 40Ar/39Ar dating of the basalt, for the first time a direct numerical calibration mark for an Eocene European mammal locality has
been established. The Eckfeld basalt inverse isochron date of 44.3±0.4 Ma suggests an age for the Geiseltalian/Robiacian boundary
at 44 Ma and, together with the 1995 time scale of Berggren et al., a time span ranging from 49 to 44 Ma for the Geiseltalian
and from 44 to 37 Ma for the Robiacian, respectively. Additional 40Ar/39Ar dating on a genetically related basalt occurrence close to the maar confirms a period of volcanism of ca. 0.6 m.y. in the
Eckfeld area, matching the oldest Eocene volcanic activity of the Hocheifel volcanic field.
Received: 27 December 1999 / Accepted in revised form: 6 April 2000 相似文献
10.
在厌氧条件下,以亚硝酸盐作为电子受体将甲烷氧化的反硝化厌氧甲烷氧化反应(nitrite-dependent anaerobic methane-oxidizing,n-damo)的发现,彻底颠覆了人们对甲烷循环的传统理解.通过分子生物学方法及13C和15N稳定同位素示踪技术,对河北省北澧河附近的旱地农田土壤(0~1 m)中n-damo菌的群落结构、丰度和活性进行了研究,深入探究了n-damo菌的亚硝酸盐底物来源.结果显示,n-damo菌更多存在于旱地浅层土壤中,并且随季节变化分布在不同深度的土壤中.针对其pmo A基因的系统发育分析显示,旱地土壤中n-damo菌的群落结构具有明显的空间异质性,来自土壤0~20 cm和40~60 cm土层的序列完全分开,处于系统发育树不同分枝.针对其16S rRNA基因的实时荧光定量PCR结果显示,n-damo菌丰度随土壤深度的增加而降低,夏季丰度(1.44×10~4~1.02×10~5copies·g~(-1))低于冬季(3.66×104~2.67×105copies·g-1).在浅层土壤(0~20 cm)中,硝化反应和反硝化反应共同为n-damo菌提供亚硝酸盐底物来源;而在深层土壤(60~80 cm)中,亚硝酸盐底物主要来源于硝化反应.n-damo菌的活性(0.18 nmol·g~(-1)·d~(-1),以CO_2计)只能在夏季表层土壤(0~20 cm)中检测到,其余深度均未检测到其活性.在旱地农田土壤中,反硝化厌氧甲烷氧化菌对农田碳循环的影响可能不大. 相似文献
11.
巢湖完全氨氧化细菌的丰度、群落结构及其影响因素研究 总被引:1,自引:0,他引:1
完全氨氧化过程(complete ammonia oxidation, comammox)的发现使研究者们对硝化作用和氮循环都有了新的认识.本研究选取巢湖冬夏季表层(0~10 cm)沉积物样品,运用高通量测序、实时定量PCR等分子生物学技术对comammox细菌的丰度和群落结构进行研究.结果表明:基于amoA基因的comammox细菌的丰度为(5.20±0.72)×106~(4.06±1.23)×107 copies·g-1;氨氧化古菌的丰度为(5.39±1.01)×105~(1.60±0.18)×107 copies·g-1;氨氧化细菌的丰度为(6.16±1.57)×105~(4.30±0.19)×106 copies·g-1.comammox细菌的绝对丰度显著高于氨氧化古菌和氨氧化细菌.多样性分析表明冬季巢湖表层沉积物中的comammox细菌的物种多样性大于夏季.其中Candidatus Nitrospira nitrificans、Candidatus Nitrospira nitrosa和Candidatus Nitrospira inopinata的相对丰度最高占比分别为78.72%、49.80%和6.28%,且夏季样点中Candidatus Nitrospira inopinata的相对丰度显著高于冬季样点.主坐标分析(Principle Coordinate Analysis, PcoA)结果表明,comammox细菌的群落结构具有明显的时间异质性.理化因子中,NH4+和NO3-与comammox细菌的丰度呈负相关关系.本研究在一定程度上揭示了comammox细菌的丰度、群落组成、多样性及其与理化因子的关系. 相似文献
12.
Jianguang LIU Xiaojian ZHANG Zhansheng WANG 《Frontiers of Environmental Science & Engineering in China》2008,2(1):94-98
Since the ammonia in the effluent of the traditional water purification process could not meet the supply demand, the advanced
treatment of a high concentration of NH4
+-N micro-polluted source water by biological activated carbon filter (BACF) was tested. The filter was operated in the downflow
manner and the results showed that the removing rate of NH4
+-N was related to the influent concentration of NH4
+-N. Its removing rate could be higher than 95% when influent concentration was under 1.0 mg/L. It could also decrease with
the increasing influent concentration when the NH4
+-N concentration was in the range from 1.5 to 4.9 mg/L and the dissolved oxygen (DO) in the influent was under 10 mg/L, and
the minimum removing rate could be 30%. The key factor of restricting nitrification in BACF was the influent DO. When the
influent NH4
+-N concentration was high, the DO in water was almost depleted entirely by the nitrifying and hetetrophic bacteria in the
depth of 0.4 m filter and the filter layer was divided into aerobic and anoxic zones. The nitrification and degradation of
organic matters existed in the aerobic zone, while the denitrification occurred in the anoxic zone. Due to the limited carbon
source, the denitrification could not be carried out properly, which led to the accumulation of the denitrification intermediates
such as NO2
−. In addition to the denitrification bacteria, the nitrification and the heterotrophic bacteria existed in the anoxic zone.
__________
Translated from Environmental Science, 2006, 27(1): 69–73 [译自: 环境科学] 相似文献
13.
During reproductive migration the electroreceptive African sharptooth catfish, Clarias gariepinus (Siluriformes), preys mainly on a weakly electric fish, the bulldog Marcusenius macrolepidotus (Mormyridae; Merron 1993). This is puzzling because the electric organ discharges of known Marcusenius species are pulses of a duration (<1 ms) too short for being detected by the catfishes' low-frequency electroreceptive system
(optimum sensitivity, 10–30 Hz; Peters and Bretschneider 1981). On the recent discovery that M. macrolepidotus males emit discharges lasting approximately ten times longer than those of females (Kramer 1997a) we determined behavioral
thresholds for discharges of both sexes, using synthetic playbacks of field-recorded discharges. C. gariepinus detected M. macrolepidotus male discharges down to a field gradient of 103 μVpeak-peak/cm and up to a distance of 1.5 m at natural field conditions. In contrast, thresholds for female discharges were not reached
with our setup, and we presume the bulldogs eaten by catfish are predominantly male.
Received: 7 October 1998 / Accepted in revised form: 29 December 1998 相似文献
14.
海洋厌氧氨氧化菌的富集培养及其脱氮特性 总被引:1,自引:0,他引:1
采用ASBR厌氧氨氧化反应器,通过接种胶州湾底泥,研究了海洋厌氧氨氧菌的富集培养及其脱氮特性.实验结果表明:海洋厌氧氨氧化菌的富集培养可分为4个阶段:菌体自溶期(1~15 d)、迟滞期(16~152 d)、活性提高期(153~183 d)与稳定运行期(184~192 d).与淡水厌氧氨氧化相比,其迟滞期(137 d)较长,活性提高期(30 d)较短,对基质浓度与HRT的变化更敏感,且由进出水导致的菌活性延迟时间为5 h,远长于淡水厌氧氨氧化菌,因此海洋厌氧氨氧化菌对新环境的适应能力更弱,更难富集培养.经过192 d运行,对NH_4~+-N与NO-2-N的去除率分别达到96.98%与95.66%,三氮转化比n(NH_4~+-N)∶n(NO-2-N)∶n(NO-3-N)为1∶(1.2±0.2)∶(0.22±0.06),接近理论比(1∶1.32∶0.26),NRRNH_4~+-N升至0.080 kg·(m~3·d)-1,海洋厌氧氨氧化菌活性显著提高,这标志着海洋厌氧氨氧化菌富集成功.反应器运行过程中,污泥逐渐由黑色泥状变为砖红色颗粒状,扫描电镜观察,该砖红色颗粒为表面光滑,排列紧密、有类似火山口形状的球状菌相互黏聚而成的菌团. 相似文献
15.
Xiaoming Xu Jie Tang Zhaoyang Li Chang Liu Weizheng Han 《Mitigation and Adaptation Strategies for Global Change》2011,16(6):721-731
In this study, paddy fields in Jilin province which are flooded parcel of arable lands used for growing rice (Oryza sativa Linn.) were selected as the object. Long-term exploitation of paddy fields led to variations of soil organic carbon (SOC) and green
house gases (GHGs) emissions which might contribute to global warming. In order to calculate the amount of global warming
potentials (GWPs) of emissions from ricepaddies and find the correlations among rice yield, SOC storage and GWP, DeNitrification-DeComposition
(DNDC) model was used to simulate SOC densities and fluxes of main GHGs emitted from paddy fields. After verification, simulation
results were used to calculate SOC storages and 100-year GWPs from 1949 to 2009. Results indicated that SOC densities in depths
of 0–10 cm, 10–20 cm and 20–30 cm all kept increasing. Average methane (CH4) and nitrous oxide (N2O) fluxes were 278.55 kg carbon (kgC) ha−1 a−1 and 2.22 kg nitrogen (kgN) ha−1 a−1. The SOC storage (0–30 cm) had increased from 3.96 × 109kgC in 1949 to 47.85 × 109kgC in 2009. In addition, GWP emission was increasing exponentially in the past 61 years, from 0.16 × 106 Mg carbon dioxide equivalents (CO2-equivalents) to 66.36 × 106 Mg CO2-equivalents. Both SOC storage and GWP presented obviously linear relation to rice yields. Overall, the research suggested
that long-term rice yields could be used to estimate the SOC storage and GWP variations. 相似文献
16.
Light-Dependent Magnetoreception in Birds: Does Directional Information Change with Light Intensity?
Magnetic compass orientation in birds is based on light-dependent processes, with magnetoreception being possible only under
light containing blue and green wavelengths. To look for possible intensity-dependent effects we tested Australian silvereyes
during autumn migration under monochromatic green light (565 nm) produced by light-emitting diodes at various light levels.
At intensities of 0.0021 and 0.0075 W/m2, the birds showed normal activity and were oriented in their seasonally appropriate migratory direction. Under low light
of 0.0002 W/m2 the birds were less active; scatter increased, but they still oriented in their migratory direction. Under a high light level
of 0.0150 W/m2, however, the test birds showed a counterclockwise shift in direction, preferring west-northwest instead of north. This change
in behavior may reflect a change in the output of the magnetoreception system, resulting from a disruption of the natural
balance between the wavelengths of light.
Received: 18 June 1999 / Accepted in revised form: 20 September 1999 相似文献
17.
Nitrifying and denitrifying bacteria in aerobic granules formed in sequencing batch airlift reactors
Wang Fang Yang Fenglin Qi Aijiu 《Frontiers of Environmental Science & Engineering in China》2007,1(2):184-189
The purpose of this study was to investigate nitrifying bacteria and denitrifying bacteria isolated from aerobic granules.
Aerobic granules were formed in an internal-circulate sequencing batch airlift reactor (SBAR) and biodegradation of NH3
−-N was analyzed in the reactor. Bacteria were isolated and determined from aerobic granules using selected media. The growth
properties and morphology of bacteria colonies were observed by controlling aerobic or anaerobic conditions in the culture
medium. It was found that bacteria in aerobic granules were diverse and some of them were facultative aerobes. The diversity
of bacteria in aerobic granules was a premise of simultaneous nitrification and denitrification.
Translated from China Environmental Science, 2005, 25(2): 218–221 [译自: 中国环境科学] 相似文献
18.
Rongchang Wang Xinmin Zhan Yalei Zhang Jianfu Zhao 《Frontiers of Environmental Science & Engineering in China》2011,5(1):48-56
Nitrogen removal performance and nitrifying population dynamics were investigated in a redox stratified membrane biofilm reactor
(RSMBR) under oxygen limited condition to treat ammonium-rich wastewater. When the NHt4+-N loading rate increased from 11.1±1.0 to 37:2 ± 3:2 gNHt4+-N·m−2·d−1, the nitrogen removal in the RSMBR system increased from 18.0±9.6 mgN·d−1 to 128.9±61.7 mgN·d−1. Shortcut nitrogen removal was achieved with nitrite accumulation of about 22:3 ± 5:3 mgNO2−-N·L−1. Confocal micrographs showed the stratified distributions of nitrifiers and denitrifiers in the membrane aerated biofilms
(MABs) at day 120, i.e., ammonia and nitrite oxidizing bacteria (AOB and NOB) were dominant in the region adjacent to the
membrane, while heterotrophic bacteria propagated at the top of the biofilm. Real-time qPCR results showed that the abundance
of amoA gene was two orders of magnitude higher than the abundance of nxrA gene in the MABs. However, the nxrA gene was always detected during the operation time, which indicates the difficulty of complete washout of NOB in MABs. The
growth of heterotrophic bacteria compromised the dominance of nitrifiers in biofilm communities, but it enhanced the denitrification
performance of the RSMBR system. Applying a high ammonia loading together with oxygen limitation was found to be an effective
way to start nitrite accumulation in MABs, but other approaches were needed to sustain or improve the extent of nitritation
in nitrogen conversion in MABs. 相似文献
19.
采用稳定运行在高盐高碱环境厌氧/好氧/缺氧(A_n/O/A)模式下的序批式生物膜反应器(SBBR),考察在不同碳氮比(C/N)条件下,硝化反硝化过程及N_2O产生特征.结果表明,在C/N为5、2和对照组(C/N=0)时,总氮去除率分别为(98. 17±0. 42)%、(65. 78±2. 47)%和(44. 08±0. 27)%; N_2O的产生量分别为(32. 07±2. 03)、(21. 81±0. 85)和(17. 32±0. 95) mg·L~(-1); N_2O转化率(N_2O产生量在去除总氮中的比例)分别为(29. 75±0. 93)%、(30. 04±2. 17)%和(41. 69±0. 80)%.高盐高碱条件下,亚硝酸盐氧化菌(NOB)受到很强的抑制作用,硝化过程基本停留在亚硝酸盐阶段.由于高盐高碱环境对N_2O还原酶活性的抑制,使得异养反硝化过程产生了大量N_2O,随着碳氮比的增大,有更多的碳源用于反硝化过程,因而总氮去除率和N_2O产生量均随之增加.随着碳氮比的增大,N_2O转化率随之降低,这可能是由于异养反硝化过程氮素还原酶对电子的竞争所形成的,碳氮比越高,电子竞争越弱.高通量测序表明:在SBBR中,氨氧化细菌(AOB)被富集,而几乎不存在NOB;优势异养反硝化菌属主要是Thauera、Azoarcus和Gemmobacter. 相似文献
20.
Humin, the most recalcitrant and abundant organic fraction of soils and of sediments, is a significant contributor to the
stable carbon pool in soils and is important for the global carbon budget. It has significant resistance to transformations
by microorganisms. Based on the classical operational definition, humin can include any humic-type substance that is not soluble
in water at any pH. We demonstrate in this study how sequential exhaustive extractions with 0.1 M sodium hydroxide (NaOH) + 6 M
urea, followed by dimethylsulphoxide (DMSO) + 6% (v/v) sulphuric acid (H2SO4) solvent systems, can extract 70–80% of the residual materials remaining after prior exhaustive extractions in neutral and
aqueous basic media. Solid-state 13C NMR spectra have shown that the components isolated in the base + urea system were compositionally similar to the humic
and fulvic acid fractions isolated at pH 12.6 in the aqueous media. The NMR spectra indicated that the major components isolated
in the DMSO + H2SO4 medium had aliphatic hydrocarbon associated with carboxyl functionalities and with lesser amounts of carbohydrate and peptide
and minor amounts of lignin-derived components. The major components will have significant contributions from long-chain fatty
acids, waxes, to cuticular materials. The isolates in the DMSO + H2SO4 medium were compositionally similar to the organic components that resisted solvation and remained associated with the soil
clays. It is concluded that the base + urea system released humic and fulvic acids held by hydrogen bonding or by entrapment
within the humin matrix. The recalcitrant humin materials extracted in DMSO + H2SO4 are largely biological molecules (from plants and the soil microbial population) that are likely to be protected from degradation
by their hydrophobic moieties and by sorption on the soil clays. Thus, the major components of humin do not satisfy the classical
definitions for humic substances which emphasise that these arise from microbial or chemical transformations in soils of the
components of organic debris. 相似文献