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Oligotrophic Ocean (oligotrophic + ocean)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

A PERSPECTIVE ON PHOTOSYNTHESIS IN THE OLIGOTROPHIC OCEANS: HYPOTHESES CONCERNING ALTERNATE ROUTES OF ELECTRON FLOW,

JOURNAL OF PHYCOLOGY, Issue 4 2010
Arthur R. Grossman
Many regions of the open, oligotrophic oceans are depleted of nutrients, especially nitrogen and iron. The biogenesis and the functioning of the photosynthetic apparatus may be specialized and tailored to the various marine habitats. In this minireview, we discuss some new findings with respect to photosynthetic processes in the oceans. We focus on findings that suggest that some cyanobacteria may route electrons derived from the splitting of H2O to the reduction of O2 and H+ in a water-to-water cycle, and that other cyanobacteria that fix nitrogen during the day are likely missing PSII and enzymes involved in the fixation of inorganic carbon. Both of these proposed "variant" forms of photosynthetic electron flow provide new insights into ways in which marine phytoplankton satisfy their energetic and nutritive requirements. [source]

Solar Radiation-induced Mortality of Marine Pico-phytoplankton in the Oligotrophic Ocean,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007
Susana Agustí
ABSTRACT We examined the response of pico-phytoplankton communities sampled at the equatorial, tropical and temperate Central Atlantic Ocean to subsurface underwater solar radiation in order to test the generality of the reported cell mortality for these populations when exposed to high ultra violet radiation (UVR) and photosynthetically active radiation. The natural communities of pico-phytoplankton populations tested experienced high cell mortality when exposed to high solar radiation, despite inhabiting tropical waters. Synechococcus and eukaryotes were more resistant to solar radiation than Prochlorococcus. The decay rates of all pico-phytoplankton groups examined tended to be much higher when exposed to total solar radiation than when UVB-R was filtered out. We also show that even short exposures of 30 min to high solar radiation were able to induce cell mortality in Prochlorococcus. The variability in the decay rates of living Prochlorococcus cells were strongly related to the condition of the original population. However, Synechococcus decay rates were higher in populations from the tropical area, with eukaryotes sensitivity increasing with increasing the trophic degree. The data reported in this study and in the literature revealed contrasting capacities of Prochlorococcus, Synechococcus and eukaryotes to survive under high solar radiation. Although the mechanisms involved are as yet unclear, their elucidation may help explain niche partitioning among these organisms in the ocean. [source]

A molecular assessment of the iron stress response in the two phylogenetic clades of Trichodesmium

ENVIRONMENTAL MICROBIOLOGY, Issue 1 2010
P. Dreux Chappell
Summary Trichodesmium spp. play key roles in global carbon and nitrogen budgets and thus defining what controls their productivity is important for understanding climate change. While iron availability has been shown to be an important chemical factor for controlling both growth and nitrogen fixation rates in Trichodesmium, all culture experiments to date have focused solely on representatives from one clade of Trichodesmium. Genomic sequence analysis determined that the Trichodesmium erythraeum (IMS101) genome contains many of the archetypical genes involved in the prokaryotic iron stress response. Focusing on three of these genes, isiB, idiA and feoB, we found that all three showed an iron stress response in axenic T. erythraeum (IMS101), and their sequences were well conserved across four species in our Trichodesmium culture collection [consisting of two T. erythraeum strains (IMS101 and GBRTRLI101), two Trichodesmium tenue strains (Z-1 and H9-4), Trichodesmium thiebautii and Trichodesmium spiralis]. With clade-specific quantitative PCR (qPCR) primers for one of these genes, isiB, we found that high isiB expression at low Fe levels corresponded to specific reductions in N2 fixation rates in both major phylogenetic clades of Trichodesmium (the T. erythraeum clade and T. tenue clade). With regard to the two clades, the most significant difference determined was temperature optima, while more subtle differences in growth, N2 fixation rate and gene expression responses to Fe stress were also observed. However the apparent conservation of the Fe stress response in the Trichodesmium genus suggests that it is an important adaptation for their niche in the oligotrophic ocean. [source]

Size-fractionated phytoplankton biomass and its implications for the dynamics of an oligotrophic tropical lake

FRESHWATER BIOLOGY, Issue 1 2008
MARÍA FERNANDA ADAME
Summary 1. Size-fractionated phytoplankton biomass was examined in relation to the hydrodynamics of tropical Lake Alchichica from 1999 to 2002. 2. Alchichica is a warm monomictic lake, in which mixing takes place from late December to early March. The lake is oligotrophic (mean total chlorophyll- a concentration 4.2 ± 4.2 ,g L,1) and its phytoplankton biomass is dominated (72.3 ± 16.4%) by large individuals (>2 ,m). The degree of dominance of the large size class (nano- and microplankton) over the small size class (picoplankton) throughout the year is mainly determined by the availability of silicate and the Si/N ratio in the hypolimnion prior to the mixing period. 3. This is the first record of an oligotrophic tropical lake dominated by large size fractions of phytoplankton. Because of this dominance, the fate of most primary productivity is rapid sedimentation to the bottom followed by decomposition that promotes an anoxic hypolimnion. 4. Our findings in tropical Lake Alchichica challenge the idea that oligotrophic waters are dominated by small phytoplankton, as has been well established for the oligotrophic ocean and temperate lakes. [source]

Nitrogenase gene diversity and microbial community structure: a cross-system comparison

ENVIRONMENTAL MICROBIOLOGY, Issue 7 2003
Jonathan P. Zehr
Summary Biological nitrogen fixation is an important source of fixed nitrogen for the biosphere. Microorganisms catalyse biological nitrogen fixation with the enzyme nitrogenase, which has been highly conserved through evolution. Cloning and sequencing of one of the nitrogenase structural genes, nifH, has provided a large, rapidly expanding database of sequences from diverse terrestrial and aquatic environments. Comparison of nifH phylogenies to ribosomal RNA phylogenies from cultivated microorganisms shows little conclusive evidence of lateral gene transfer. Sequence diversity far outstrips representation by cultivated representatives. The phylogeny of nitrogenase includes branches that represent phylotypic groupings based on ribosomal RNA phylogeny, but also includes paralogous clades including the alternative, non-molybdenum, non-vanadium containing nitrogenases. Only a few alternative or archaeal nitrogenase sequences have as yet been obtained from the environment. Extensive analysis of the distribution of nifH phylotypes among habitats indicates that there are characteristic patterns of nitrogen fixing microorganisms in termite guts, sediment and soil environments, estuaries and salt marshes, and oligotrophic oceans. The distribution of nitrogen-fixing microorganisms, although not entirely dictated by the nitrogen availability in the environment, is non-random and can be predicted on the basis of habitat characteristics. The ability to assay for gene expression and investigate genome arrangements provides the promise of new tools for interrogating natural populations of diazotrophs. The broad analysis of nitrogenase genes provides a basis for developing molecular assays and bioinformatics approaches for the study of nitrogen fixation in the environment. [source]