Posts Tagged 'photosynthesis'

Dual role of DOM in a scenario of global change on photosynthesis and structure of coastal phytoplankton from the South Atlantic Ocean

Highlights

• In a future scenario, attenuation by DOM outcompetes its physico-chemical role.
• Global change conditions will favor growth and photosynthesis of nanoplankton.
• Global change favors growth and photosynthesis of nano- as compared to microplankton.

Abstract

We evaluated the dual role of DOM (i.e., as a source of inorganic nutrients and as an absorber of solar radiation) on a phytoplankton community of the western South Atlantic Ocean. Using a combination of microcosms and a cluster approach, we simulated the future conditions of some variables that are highly influenced by global change in the region. We increased nutrients (i.e., anthropogenic input) and dissolved organic matter (DOM), and we decreased the pH, to assess their combined impact on growth rates (μ), species composition/abundance and size structure, and photosynthesis (considering in this later also the effects of light quality i.e., with and without ultraviolet radiation). We simulated two Future conditions (Fut) where nutrients and pH were similarly manipulated, but in one the physical role of DOM (Futout) was assessed whereas in the other (Futin) the physico-chemical role was evaluated; these conditions were compared with a control (Present condition, Pres). The μ significantly increased in both Fut conditions as compared to the Pres, probably due to the nutrient addition and acidification in the former. The highest μ were observed in the Futout, due to the growth of nanoplanktonic flagellates and diatoms. Cells in the Futin were photosynthetically less efficient as compared to those of the Futout and Pres, but these physiological differences, also between samples with or without solar UVR observed at the beginning of the experiment, decreased with time hinting for an acclimation process. The knowledge of the relative importance of both roles of DOM is especially important for coastal areas that are expected to receive higher inputs and will be more acidified in the future.

Continue reading ‘Dual role of DOM in a scenario of global change on photosynthesis and structure of coastal phytoplankton from the South Atlantic Ocean’

Inorganic carbon and pH dependency of Trichodesmium’s photosynthetic rates

We established the relationship between photosynthetic carbon fixation rates and pH, CO2 and HCO3 concentrations in the diazotroph Trichodesmium erythraeum IMS101. Inorganic 14C-assimilation was measured in TRIS-buffered ASW medium where the absolute and relative concentrations of CO2, pH and HCO3 were manipulated. First, we varied the total dissolved inorganic carbon concentration (TIC) (< 0 to ~ 5 mM) at constant pH, so ratios of CO2 and HCO3 remained relatively constant. Second, we varied pH (~ 8.54 to 7.52) at constant TIC, so CO2 increased whilst HCO3 declined. We found that 14C-assimilation could be described by the same function of CO2 for both approaches but showed different dependencies on HCO3 when pH was varied at constant TIC than when TIC was varied at constant pH. A numerical model of Trichodesmium’s CCM showed carboxylation rates are modulated by HCO3 and pH. The decrease in Ci assimilation at low CO2, when TIC was varied, is due to HCO3 uptake limitation of the carboxylation rate. Conversely, when pH was varied, Ci assimilation declined due to a high-pH mediated increase in HCO3 and CO2 leakage rates, potentially coupled to other processes (uncharacterised within the CCM model) that restrict Ci assimilation rates under high-pH conditions.

Continue reading ‘Inorganic carbon and pH dependency of Trichodesmium’s photosynthetic rates’

The interactive effects of elevated CO2 and ammonium enrichment on the physiological performances of Saccharina japonica (Laminariales, Phaeophyta)

Environmental challenges such as ocean acidification and eutrophication influence the physiology of kelp species. We investigated their interactive effects on Saccharina japonica (Laminariales, Phaeophyta) under two pH conditions [Low, 7.50; High (control), 8.10] and three NH 4 + concentrations (Low, 4; Medium, 60; High, 120 μM). The degree of variation of pH values in the culture medium and inhibition rate of photosynthetic oxygen evolution by acetazolamide were affected by pH treatments. Relative growth rates, carbon, nitrogen, and the C:N ratio in tissue samples were influenced by higher concentrations of NH 4 + . Rates of photosynthetic oxygen evolution were enhanced under elevated CO2 or NH 4 + conditions, independently, but these two factors did not show an interactive effect. However, rates of NH 4 + uptake were influenced by the interactive effect of increased CO2 under elevated NH 4 + treatment. Although ocean acidification and eutrophication states had an impact on physiological performance, chlorophyll fluorescence was not affected by those conditions. Our results indicated that the physiological reactions by this alga were influenced to some extent by a rise in the levels of CO2 and NH 4 + . Therefore, we expect that the biomass accumulation of S. japonica may well increase under future scenarios of ocean acidification and eutrophication.

Continue reading ‘The interactive effects of elevated CO2 and ammonium enrichment on the physiological performances of Saccharina japonica (Laminariales, Phaeophyta)’

An integrated response of Trichodesmium erythraeum IMS101 growth and photo-physiology to iron, CO2, and light intensity

We have assessed how varying CO2 (180, 380, and 720 μatm) and growth light intensity (40 and 400 μmol photons m−2 s−1) affected Trichodesmium erythraeum IMS101 growth and photophysiology over free iron (Fe′) concentrations between 20 and 9,600 pM. We found significant iron dependencies of growth rate and the initial slope and maximal relative PSII electron transport rates (rPm). Under iron-limiting concentrations, high-light increased growth rates and rPm; possibly indicating a lower allocation of resources to iron-containing photosynthetic proteins. Higher CO2 increased growth rates across all iron concentrations, enabled growth to occur at lower Fe′ concentrations, increased rPm and lowered the iron half saturation constants for growth (Km). We attribute these CO2 responses to the operation of the CCM and the ATP spent/saved for CO2 uptake and transport at low and high CO2, respectively. It seems reasonable to conclude that T. erythraeum IMS101 can exhibit a high degree of phenotypic plasticity in response to CO2, light intensity and iron-limitation. These results are important given predictions of increased dissolved CO2 and water column stratification (i.e., higher light exposures) over the coming decades.

Continue reading ‘An integrated response of Trichodesmium erythraeum IMS101 growth and photo-physiology to iron, CO2, and light intensity’

Response of Antarctic sea-ice algae to an experimental decrease in pH: a preliminary analysis from chlorophyll fluorescence imaging of melting ice

Microorganisms confined to annual sea ice in the Southern Ocean are exposed to highly variable oxygen and carbonate chemistry dynamics because of the seasonal increase in biomass and limited exchange with the underlying water column. For sea-ice algae, physiological stress is likely to be exacerbated when the ice melts; however, variation in carbonate speciation has rarely been monitored during this important state-transition. Using pulse amplitude modulated fluorometry (Imaging-PAM, Walz), we documented in situ changes in the maximum quantum yield of photosystem II (Fv/Fm) of sea-ice algae melting out into seawater with initial pH values ranging from 7.66 to 6.39. Although the process of ice-melt elevated seawater pH by 0.2–0.55 units, we observed a decrease in Fv/Fm between 0.02 and 0.06 for each unit drop in pH during real-time fluorescence imaging. These results are considered preliminary but provide context for including carbonate chemistry monitoring in the design of future sea ice state-transition experiments. Imaging-PAM is a reliable technology for determining Fv/Fm, but is of limited use for obtaining additional photosynthetic parameters when imaging melting ice.

Continue reading ‘Response of Antarctic sea-ice algae to an experimental decrease in pH: a preliminary analysis from chlorophyll fluorescence imaging of melting ice’

Future warming and acidification result in multiple ecological impacts to a temperate coralline alga

Coralline algae are a crucial component of reef systems, stabilising reef substrate, providing habitat and contributing to accretion. Coralline algae and their surface microbial biofilms are also important as settlement cues for marine invertebrates, yet few studies address the impact of future environmental conditions on interactions between coralline algae, reef microbes and settlement by larvae of marine invertebrates. We exposed the temperate coralline algal species Amphiroa gracilis to warming and/or acidification scenarios for 21 days. Algae became bleached but photosystem II (PSII) function was not measurably impacted. Settlement by larvae of the sea urchin Heliocidaris erythrogramma was reduced and the structure of the prokaryotic community associated with A. gracilis was altered. Coralline algae in ambient conditions were dominated by Alphaproteobacteria from the Rhodobacteraceae including Loktonella; those under warming were dominated by Bacteroidetes and Verrucomicrobia; acidification resulted in less Loktonella and more Planctomycetes; and a combination of warming and acidification caused increases in Bacteroidetes, Verrucomicrobia and the Alphaproteobacteria family Hyphomonadaceae. These experiments indicate that predicted future environmental change may reduce the ability of some temperate reef coralline algae and associated reef microbes to facilitate settlement of invertebrate larvae as well as having a direct impact to algae via bleaching.

Continue reading ‘Future warming and acidification result in multiple ecological impacts to a temperate coralline alga’

Effects of increasing atmospheric CO2 on the marine phytoplankton and bacterial metabolism during a bloom: a coastal mesocosm study

Highlights

• The effects of increasing atmospheric CO2 were assessed in a coastal mesocosm.
• CO2 enrichment enhanced primary production and photosynthesis efficiency.
• Elevation of atmospheric CO2 decreased bacterial respiration.
• CO2 enrichment enhanced carbon transfer efficiency through the microbial loop.
• The contemporaneous responses have profound implications on carbon cycle.

Abstract

Increases of atmospheric CO2 concentrations due to human activity and associated effects on aquatic ecosystems are recognized as an environmental issue at a global scale. Growing attention is being paid to CO2 enrichment effects under multiple stresses or fluctuating environmental conditions in order to extrapolate from laboratory-scale experiments to natural systems. We carried out a mesocosm experiment in coastal water with an assemblage of three model phytoplankton species and their associated bacteria under the influence of elevated CO2 concentrations. Net community production and the metabolic characteristics of the phytoplankton and bacteria were monitored to elucidate how these organisms responded to CO2 enrichment during the course of the algal bloom. We found that CO2 enrichment (1000 μatm) significantly enhanced gross primary production and the ratio of photosynthesis to chlorophyll a by approximately 38% and 39%, respectively, during the early stationary phase of the algal bloom. Although there were few effects on bulk bacterial production, a significant decrease of bulk bacterial respiration (up to 31%) at elevated CO2 resulted in an increase of bacterial growth efficiency. The implication is that an elevation of CO2 concentrations leads to a reduction of bacterial carbon demand and enhances carbon transfer efficiency through the microbial loop, with a greater proportion of fixed carbon being allocated to bacterial biomass and less being lost as CO2. The contemporaneous responses of phytoplankton and bacterial metabolism to CO2 enrichment increased net community production by about 45%, an increase that would have profound implications for the carbon cycle in coastal marine ecosystems.

Continue reading ‘Effects of increasing atmospheric CO2 on the marine phytoplankton and bacterial metabolism during a bloom: a coastal mesocosm study’


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