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排序方式: 共有211条查询结果,搜索用时 15 毫秒
101.
LISA WINGATE ULLI SEIBT† KADMIEL MASEYK‡ JÉRÔME OGÉE§ PEDRO ALMEIDA¶ DAN YAKIR‡ JOAO S. PEREIRA¶ MAURIZIO MENCUCCINI 《Global Change Biology》2008,14(9):2178-2193
The oxygen stable isotope composition (δ18O) of CO2 is a valuable tool for studying the gas exchange between terrestrial ecosystems and the atmosphere. In the soil, it records the isotopic signal of water pools subjected to precipitation and evaporation events. The δ18O of the surface soil net CO2 flux is dominated by the physical processes of diffusion of CO2 into and out of the soil and the chemical reactions during CO2–H2O equilibration. Catalytic reactions by the enzyme carbonic anhydrase, reducing CO2 hydration times, have been proposed recently to explain field observations of the δ18O signatures of net soil CO2 fluxes. How important these catalytic reactions are for accurately predicting large‐scale biosphere fluxes and partitioning net ecosystem fluxes is currently uncertain because of the lack of field data. In this study, we determined the δ18O signatures of net soil CO2 fluxes from soil chamber measurements in a Mediterranean forest. Over the 3 days of measurements, the observed δ18O signatures of net soil CO2 fluxes became progressively enriched with a well‐characterized diurnal cycle. Model simulations indicated that the δ18O signatures recorded the interplay of two effects: (1) progressive enrichment of water in the upper soil by evaporation, and (2) catalytic acceleration of the isotopic exchange between CO2 and soil water, amplifying the contributions of ‘atmospheric invasion’ to net signatures. We conclude that there is a need for better understanding of the role of enzymatic reactions, and hence soil biology, in determining the contributions of soil fluxes to oxygen isotope signals in atmospheric CO2. 相似文献
102.
Margot ME Gosman Dirkje S Postma Judith M Vonk Bea Rutgers Monique Lodewijk Mieke Smith Marjan A Luinge Nick HT ten Hacken Wim Timens 《Respiratory research》2008,9(1):1-9
Background
Surfactant protein D (SP-D), an innate immune molecule, plays an important protective role during airway inflammation. Deficiency of this molecule induces emphysematous changes in murine lungs, but its significance in human COPD remains unclear.Methods
We collected bronchoalveolar lavage fluid from 20 subjects with varying degrees of COPD (8 former smokers and 12 current smokers) and 15 asymptomatic healthy control subjects (5 never smokers, 3 remote former smokers, and 7 current smokers). All subjects underwent a complete medical history and pulmonary function testing. SP-D was measured by Enzyme-Linked ImmunoSorbent Assay. Statistical analysis was performed using nonparametric methods and multivariable linear regression for control of confounding. The effect of corticosteroid treatment on SP-D synthesis was studied in vitro using an established model of isolated type II alveolar epithelial cell culture.Results
Among former smokers, those with COPD had significantly lower SP-D levels than healthy subjects (median 502 and 1067 ng/mL, respectively, p = 0.01). In a multivariable linear regression model controlling for age, sex, race, and pack-years of tobacco, COPD was independently associated with lower SP-D levels (model coefficient -539, p = 0.04) and inhaled corticosteroid use was independently associated with higher SP-D levels (398, p = 0.046). To support the hypothesis that corticosteroids increase SP-D production we used type II alveolar epithelial cells isolated from adult rat lungs. These cells responded to dexamethasone treatment by a significant increase of SP-D mRNA (p = 0.041) and protein (p = 0.037) production after 4 days of culture.Conclusion
Among former smokers, COPD is associated with lower levels of SP-D and inhaled corticosteroid use is associated with higher levels of SP-D in the lung. Dexamethasone induced SP-D mRNA and protein expression in isolated epithelial cells in vitro. Given the importance of this molecule as a modulator of innate immunity and inflammation in the lung, low levels may play a role in the pathogenesis and/or progression of COPD. Further, we speculate that inhaled steroids may induce SP-D expression and that this mechanism may contribute to their beneficial effects in COPD. Larger, prospective studies are warranted to further elucidate the role of surfactant protein D in modulating pulmonary inflammation and COPD pathogenesis. 相似文献103.
1998年5月-2000年10月间调查了梅州柚果贮藏期的真菌病害,它们是:①柚果绿霉病(Penicilliumdigitatum),②柚果炭疽病(Collettrichumgloeosporioides),③柚果黑腐病(Alternariacitri),④柚果焦腐病(Diplodianatalensis)和⑤柚果酸腐病(Oosporacitri-aurantii)等5种.从几种安全性高的保鲜剂中筛选出1个混用配方,该配方对柚果贮藏防腐保鲜效果明显,贮藏5个月无病斑果达100%,6个月也只有20%的柚果出现少量病斑,且柚果几项质量指标较好. 相似文献
104.
105.
106.
RAFAEL G. SEVILLA AMALIA DIEZ MICHAEL NORN OLIVIER MOUCHEL MARC JR
ME VRONIQUE VERREZ‐BAGNIS HILDE VAN PELT LAURENCE FAVRE‐KREY GRIGORIOS KREY THE FISHTRACE CONSORTIUM JOS M. BAUTISTA 《Molecular ecology resources》2007,7(5):730-734
This report describes a set of 21 polymerase chain reaction primers and amplification conditions developed to barcode practically any teleost fish species according to their mitochondrial cytochrome b and nuclear rhodopsin gene sequences. The method was successfully tested in more than 200 marine fish species comprising the main Actinopterygii family groups. When used in phylogenetic analyses, its combination of two genes with different evolutionary rates serves to identify fish at the species level. We provide a flow diagram indicating our validated polymerase chain reaction amplification conditions for barcoding and species identification applications as well as population structure or haplotyping analyses, adaptable to high‐throughput analyses. 相似文献
107.
Background
Speciation often occurs in complex or uncertain temporal and spatial contexts. Processes such as reinforcement, allopatric divergence, and assortative mating can proceed at different rates and with different strengths as populations diverge. The Central American Midas cichlid fish species complex is an important case study for understanding the processes of speciation. Previous analyses have demonstrated that allopatric processes led to species formation among the lakes of Nicaragua as well as sympatric speciation that is occurring within at least one crater lake. However, since speciation is an ongoing process and sampling genetic diversity of such lineages can be biased by collection scheme or random factors, it is important to evaluate the robustness of conclusions drawn on individual time samples. 相似文献108.
109.
110.
GUY M. L. PERRY TIM L. KING JR
ME ST.‐CYR MANON VALCOURT LOUIS BERNATCHEZ 《Molecular ecology resources》2005,5(2):346-351
The brook charr (Salvelinus fontinalis; Osteichthyes: Salmonidae) is a phenotypically diverse fish species inhabiting much of North America. But relatively few genetic diagnostic resources are available for this fish species. We isolated 41 microsatellites from S. fontinalis polymorphic in one or more species of salmonid fish. Thirty‐seven were polymorphic in brook charr, 15 in the congener Arctic charr (Salvelinus alpinus) and 14 in the lake charr (Salvelinus namaycush). Polymorphism was also relatively high in Oncorhynchus, where 21 loci were polymorphic in rainbow trout (Oncorhynchus mykiss) and 16 in cutthroat trout (Oncorhynchus clarkii) but only seven and four microsatellite loci were polymorphic in the more distantly related lake whitefish (Coregonus clupeaformis) and Atlantic salmon (Salmo salar), respectively. One duplicated locus (Sfo228Lav) was polymorphic at both duplicates in S. fontinalis. 相似文献