排序方式: 共有17条查询结果,搜索用时 15 毫秒
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Climate-driven trends in contemporary ocean productivity 总被引:6,自引:0,他引:6
Behrenfeld MJ O'Malley RT Siegel DA McClain CR Sarmiento JL Feldman GC Milligan AJ Falkowski PG Letelier RM Boss ES 《Nature》2006,444(7120):752-755
Contributing roughly half of the biosphere's net primary production (NPP), photosynthesis by oceanic phytoplankton is a vital link in the cycling of carbon between living and inorganic stocks. Each day, more than a hundred million tons of carbon in the form of CO2 are fixed into organic material by these ubiquitous, microscopic plants of the upper ocean, and each day a similar amount of organic carbon is transferred into marine ecosystems by sinking and grazing. The distribution of phytoplankton biomass and NPP is defined by the availability of light and nutrients (nitrogen, phosphate, iron). These growth-limiting factors are in turn regulated by physical processes of ocean circulation, mixed-layer dynamics, upwelling, atmospheric dust deposition, and the solar cycle. Satellite measurements of ocean colour provide a means of quantifying ocean productivity on a global scale and linking its variability to environmental factors. Here we describe global ocean NPP changes detected from space over the past decade. The period is dominated by an initial increase in NPP of 1,930 teragrams of carbon a year (Tg C yr(-1)), followed by a prolonged decrease averaging 190 Tg C yr(-1). These trends are driven by changes occurring in the expansive stratified low-latitude oceans and are tightly coupled to coincident climate variability. This link between the physical environment and ocean biology functions through changes in upper-ocean temperature and stratification, which influence the availability of nutrients for phytoplankton growth. The observed reductions in ocean productivity during the recent post-1999 warming period provide insight on how future climate change can alter marine food webs. 相似文献
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Molecular data and methods have become centrally important to evolutionary analysis, largely because they have enabled global phylogenetic reconstructions of the relationships between organisms in the tree of life. Often, however, molecular stories conflict dramatically with morphology-based histories of lineages. The evolutionary origin of animal groups provides one such case. In other instances, different molecular analyses have so far proved irreconcilable. The ancient and major divergence of eukaryotes from prokaryotic ancestors is an example of this sort of problem. Efforts to overcome these conflicts highlight the role models play in phylogenetic reconstruction. One crucial model is the molecular clock; another is that of ‘simple-to-complex’ modification. I will examine animal and eukaryote evolution against a backdrop of increasing methodological sophistication in molecular phylogeny, and conclude with some reflections on the nature of historical science in the molecular era of phylogeny. 相似文献
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Microbial model systems have a long history of fruitful use in fields that include evolution and ecology. In order to develop further insight into modelling practice, we examine how the competitive exclusion and coexistence of competing species have been modelled mathematically and materially over the course of a long research history. In particular, we investigate how microbial models of these dynamics interact with mathematical or computational models of the same phenomena. Our cases illuminate the ways in which microbial systems and equations work as models, and what happens when they generate inconsistent findings about shared targets. We reveal an iterative strategy of comparative modelling in different media, and suggest reasons why microbial models have a special degree of epistemic tractability in multimodel inquiry. 相似文献
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J F Catterall J P Stein E C Lai S L Woo A Dugaiczyk M L Mace A R Means B W O'Malley 《Nature》1979,278(5702):323-327
A 15-kilobase pair EcoRI chick DNA fragment, containing both the termination codon UGA and the 5'-portion of the structural ovomucoid gene, has been cloned in lambda phage Charon 4A by in vitro packaging. Restriction mapping and electron microscopic analyses of this cloned DNA have revealed that the structural ovomucoid gene sequences are separated by at least six intervening sequences. 相似文献
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Sequence of chicken ovalbumin mRNA 总被引:63,自引:0,他引:63
L McReynolds B W O'Malley A D Nisbet J E Fothergill D Givol S Fields M Robertson G G Brownlee 《Nature》1978,273(5665):723-728
The complete sequence of chicken ovalbumin mRNA is presented; it is 1,859 residues long, excluding its terminal 'cap' and poly(A). The region coding for ovalbumin lies close to the 'cap' but is separated from the poly(A) by an extensive 3' noncoding region of 637 nucleotides which may have no function that is precisely dependent on its sequence. 相似文献
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Actively transcribed genes are associated with the nuclear matrix 总被引:13,自引:0,他引:13
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