Coupling of heterotrophic bacteria to phytoplankton bloom development at different pCO₂ levels: a mesocosm study

The predicted rise in anthropogenic CO2 emissions will increase CO2 concentrations and decrease seawater pH in the upper ocean. Recent studies have revealed effects of pCO2 induced changes in seawater chemistry on a variety of marine life forms, in particular calcifying organisms. To test whether the predicted increase in pCO2 will directly or indirectly (via changes in phytoplankton dynamics) affect abundance, activities, and community composition of heterotrophic bacteria during phytoplankton bloom development, we have aerated mesocosms with CO2 to obtain triplicates with three different partial pressures of CO2 (pCO2): 350 μatm (1×CO2), 700 μatm (2×CO2) and 1050 μatm (3×CO2). The development of a phytoplankton bloom was initiated by the addition of nitrate and phosphate. In accordance to an elevated carbon to nitrogen drawdown at increasing pCO2, bacterial production (BPP) of free-living and attached bacteria as well as cell-specific BPP (csBPP) of attached bacteria were related to the C:N ratio of suspended matter. These relationships significantly differed among treatments. However, bacterial abundance and activities were not statistically different among treatments. Solely community structure of free-living bacteria changed with pCO2 whereas that of attached bacteria seemed to be independent of pCO2 but tightly coupled to phytoplankton bloom development. Our findings imply that changes in pCO2, although reflected by changes in community structure of free-living bacteria, do not directly affect bacterial activity. Furthermore, bacterial activity and dynamics of heterotrophic bacteria, especially of attached bacteria, were tightly correlated to phytoplankton development and, hence, may also potentially depend on changes in pCO2

Unexpected consequences of increasing CO2 and ocean acidity on marine production of DMS and CH2ClI: Potential climate impacts

Increasing atmospheric mixing ratios of CO2 have already lowered surface ocean pH by 0.1 units compared to preindustrial values and pH is expected to decrease an additional 0.3 units by the end of this century. Pronounced physiological changes in some phytoplankton have been observed during previous CO2 perturbation experiments. Marine microorganisms are known to consume and produce climate-relevant organic gases. Concentrations of (CH3)2S (DMS) and CH2ClI were quantified during the Third Pelagic Ecosystem CO2 Enrichment Study. Positive feedbacks were observed between control mesocosms and those simulating future CO2. Dimethyl sulfide was 26% (±10%) greater than the controls in the 2x ambient CO2 treatments, and 18% (±10%) higher in the 3xCO2 mesocosms. For CH2ClI the 2xCO2 treatments were 46% (±4%) greater than the controls and the 3xCO2 mesocosms were 131% (±11%) higher. These processes may help contribute to the homeostasis of the planet

Genotyping a second growth coast redwood forest : a high throughput methodology

The idea that excitonic (electronic) coherences are of fundamental importance to natural photosynthesis gained popularity when slowly dephasing quantum beats (QBs) were observed in the two-dimensional electronic spectra of the Fenna–Matthews–Olson (FMO) complex at 77 K. These were assigned to superpositions of excitonic states, a controversial interpretation, as the strong chromophore–environment interactions in the complex suggest fast dephasing. Although it has been pointed out that vibrational motion produces similar spectral signatures, a concrete assignment of these oscillatory signals to distinct physical processes is still lacking. Here we revisit the coherence dynamics of the FMO complex using polarization-controlled two-dimensional electronic spectroscopy, supported by theoretical modelling. We show that the long-lived QBs are exclusively vibrational in origin, whereas the dephasing of the electronic coherences is completed within 240 fs even at 77 K. We further find that specific vibrational coherences are produced via vibronically coupled excited states. The presence of such states suggests that vibronic coupling is relevant for photosynthetic energy transfer

Coupling of heterotrophic bacteria to phytoplankton bloom development at different <i>p</i>CO₂ levels: a mesocosm study

The predicted rise in anthropogenic CO₂ emissions will increase CO₂ concentrations and decrease seawater pH in the upper ocean. Recent studies have revealed effects of <i>p</i>CO₂ induced changes in seawater chemistry on a variety of marine life forms, in particular calcifying organisms. To test whether the predicted increase in <i>p</i>CO₂ will directly or indirectly (via changes in phytoplankton dynamics) affect abundance, activities, and community composition of heterotrophic bacteria during phytoplankton bloom development, we have aerated mesocosms with CO₂ to obtain triplicates with three different partial pressures of CO₂ (<i>p</i>CO₂): 350 μatm (1&times;CO₂), 700 μatm (2&times;CO₂) and 1050 μatm (3&times;CO₂). The development of a phytoplankton bloom was initiated by the addition of nitrate and phosphate. In accordance to an elevated carbon to nitrogen drawdown at increasing <i>p</i>CO₂, bacterial production (BPP) of free-living and attached bacteria as well as cell-specific BPP (csBPP) of attached bacteria were related to the C:N ratio of suspended matter. These relationships significantly differed among treatments. However, bacterial abundance and activities were not statistically different among treatments. Solely community structure of free-living bacteria changed with <i>p</i>CO₂ whereas that of attached bacteria seemed to be independent of <i>p</i>CO₂ but tightly coupled to phytoplankton bloom development. Our findings imply that changes in <i>p</i>CO₂, although reflected by changes in community structure of free-living bacteria, do not directly affect bacterial activity. Furthermore, bacterial activity and dynamics of heterotrophic bacteria, especially of attached bacteria, were tightly correlated to phytoplankton development and, hence, may also potentially depend on changes in <i>p</i>CO₂

Marine viral populations detected during a nutrient induced phytoplankton bloom at elevated pCO₂ levels

International audienceDuring the PEeCE III mesocosm experiment in 2005 we investigated how the virioplankton community responded to increased levels of nutrients (N and P) and CO2. We applied a combination of flow cytometry, Pulsed Field Gel Electrophoresis and degenerated PCR primers to categorize and quantify individual viral populations, and to investigate their temporal dynamics. Species specific and degenerated primers enabled us to identify two specific large dsDNA viruses, EhV and CeV, infecting the haptophytes Emiliania huxleyi and Crysochromulina ericina, respectively. Some of the viral populations detected and enumerated by flow cytometry did not respond to altered CO2-levels, but the abundance of EhV and an unidentified dsDNA virus decreased with increasing CO2 levels. Our results thus indicate that CO2 conditions may affect the marine pelagic food web at the viral level. Our results also demonstrate that in order to unravel ecological problems as how CO2 and nutrient levels affect the relationship between marine algal viruses and their hosts, we need to continue the effort to develop molecular markers used to identify both hosts and viruses

Response of marine viral populations to a nutrient induced phytoplankton bloom at different pCO₂ levels

International audienceDuring the PeECE III mesocosm experiment in 2005 we investigated how the virioplankton community responded to increased levels of nutrients (N and P) and CO2. We applied a combination of flow cytometry, Pulsed Field Gel Electrophoresis and degenerate PCR primers to categorize and quantify individual viral populations, and to investigate their temporal dynamics. Species specific and degenerate primers enabled us to identify two specific large dsDNA viruses, EhV and CeV, infecting the haptophytes Emiliania huxleyi and Crysochromulina ericina, respectively. Some of the viral populations detected and enumerated by flow cytometry did not respond to altered CO2-levels, but the abundance of EhV and an unidentified dsDNA virus decreased with increasing CO2 levels. Our results thus indicate that CO2 conditions, or the related change in pH, may affect the marine pelagic food web at the viral level. Our results also demonstrate that in order to unravel ecological problems as how CO2 and nutrient levels affect the relationship between marine algal viruses and their hosts, we need to continue the effort to develop molecular markers used to identify both hosts and viruses

Microbial communities and processes in ice-covered Arctic waters of the northwestern Fram Strait (75 to 80° N) during the vernal pre-bloom phase

Marine microbial communities have been little studied in Arctic waters, especially during the winter-spring transition before the development of extensive phytoplankton blooms. This study investigated microbial plankton in the ice-covered polar surface waters of the northwestern Fram Strait (75 to 80°N) at the onset of the 24 h light period in spring (April to May). The system we encountered was characterised by low concentrations of chlorophyll a (<0.2 μg l-1) and a low abundance of both bacteria (1.4 to 2.5 × 108 cells l-1) and protists (1 to 1.7 × 105 cells l-1). Bacterial production was very low (≤0.63 μg C l-1 d-1), despite the dominance of nucleic-acid-rich bacteria (58 ± 6% of total bacterial abundance). Small (2 to 5 μm) phototrophs dominated the eukaryotic assemblage in the surface and most probably had profound effects on the composition and metabolic balance of the microbial community as a whole. Most stations appeared to have been net-autotrophic, and calculations of phagotrophy indicated a balanced carbon budget for the microbial community. Mixotrophy was seen in a large part of the ciliate assemblage and may have contributed to the productivity and stability of the pre-bloom system that we encountered. © Inter-Research 2011.Peer Reviewe

www.biogeosciences.net/5/523/2008/ © Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License.

Response of marine viral populations to a nutrient induced phytoplankton bloom at different pCO2 level