Response of a natural phytoplankton community from the Qingdao coast (Yellow Sea, China) to variable CO2 levels over a short-term incubation experiment

Since marine phytoplankton play a vital role in stabilizing earth's climate by removing significant amount of atmospheric CO2, their responses to increasing CO2 levels are indeed vital to address. The responses of a natural phytoplankton community from the Qingdao coast (NW Yellow Sea, China) was studied under different CO2 levels in microcosms. HPLC pigment analysis revealed the presence of diatoms as a dominant microalgal group; however, members of chlorophytes, prasinophytes, cryptophytes and cyanophytes were also present. delta 13CPOM values indicated that the phytoplankton community probably utilized bicarbonate ions as dissolved inorganic carbon source through a carbon concentration mechanism (CCM) under low CO2 levels, and diffusive CO2 uptake increased upon the increase of external CO2 levels. Although, considerable increase in phytoplankton biomass was noticed in all CO2 treatments, CO2-induced effects were absent. Higher net nitrogen uptake under low CO2 levels could be related to the synthesis of CCM components. Flow cytometry analysis showed slight reduction in the abundance of Synechococcus and pico-eukaryotes under the high CO2 treatments. Diatoms did not show any negative impact in response to increasing CO2 levels; however, chlorophytes revealed a reverse tend. Heterotrophic bacterial count enhanced with increasing CO2 levels and indicated higher abundance of labile organic carbon. Thus, the present study indicates that any change in dissolved CO2 concentrations in this area may affect phytoplankton physiology and community structure and needs further long-term study.

Effects of increasing seawater carbon dioxide concentrations on chain formation of the diatom Asterionellopsis glacialis

Diatoms can occur as single cells or as chain-forming aggregates. These two strategies affect buoyancy, predator evasion, light absorption and nutrient uptake. Adjacent cells in chains establish connections through various processes that determine strength and flexibility of the bonds, and at distinct cellular locations defining colony structure. Chain length has been found to vary with temperature and nutrient availability as well as being positively correlated with growth rate. However, the potential effect of enhanced carbon dioxide (CO2) concentrations and consequent changes in seawater carbonate chemistry on chain formation is virtually unknown. Here we report on experiments with semi-continuous cultures of the freshly isolated diatom Asterionellopsis glacialis grown under increasing CO2 levels ranging from 320 to 3400 µatm. We show that the number of cells comprising a chain, and therefore chain length, increases with rising CO2 concentrations. We also demonstrate that while cell division rate changes with CO2 concentrations, carbon, nitrogen and phosphorus cellular quotas vary proportionally, evident by unchanged organic matter ratios. Finally, beyond the optimum CO2 concentration for growth, carbon allocation changes from cellular storage to increased exudation of dissolved organic carbon. The observed structural adjustment in colony size could enable growth at high CO2 levels, since longer, spiral-shaped chains are likely to create microclimates with higher pH during the light period. Moreover increased chain length of Asterionellopsis glacialis may influence buoyancy and, consequently, affect competitive fitness as well as sinking rates. This would potentially impact the delicate balance between the microbial loop and export of organic matter, with consequences for atmospheric carbon dioxide.

Seawater carbonate chemistry, nutrients, chlorophyll and diatom Proboscia alata during experiments, 2012

The combined effects of different light and aqueous CO2 conditions were assessed for the Southern Ocean diatom Proboscia alata(Brightwell) Sundström in laboratory experiments. Selected culture conditions (light and CO2(aq)) were representative for the natural ranges in the modern Southern Ocean. Light conditions were 40 (low) and 240 (high) µmol photons/m**2/s. The three CO2(aq) conditions ranged from 8 to 34 µmol/kg CO2(aq) (equivalent to a pCO2 from 137 to 598 µatm, respectively). Clear morphological changes were induced by these different CO2(aq) conditions. Cells in low [CO2(aq)] formed spirals, while many cells in high [CO2(aq)] disintegrated. Cell size and volume were significantly affected by the different CO2(aq) concentrations. Increasing CO2(aq) concentrations led to an increase in particulate organic carbon concentrations per cell in the high light cultures, with exactly the opposite happening in the low light cultures. However, other parameters measured were not influenced by the range of CO2(aq) treatments. This included growth rates, chlorophyll aconcentration and photosynthetic yield (FV/FM). Different light treatments had a large effect on nutrient uptake. High light conditions caused an increased nutrient uptake rate compared to cells grown in low light conditions. Light and CO2 conditions co-determined in various ways the response of P. alata to changing environmental conditions. Overall P. alata appeared to be well adapted to the natural variability in light availability and CO2(aq) concentration of the modern Southern Ocean. Nevertheless, our results showed that P. alata is susceptible to future changes in inorganic carbon concentrations in the Southern Ocean.

Comparative responses of two dominant Antarctic phytoplankton taxa to interactions between ocean acidification, warming, irradiance, and iron availability

We investigated the responses of the ecologically dominant Antarctic phytoplankton species Phaeocystis antarctica (a prymnesiophyte) and Fragilariopsis cylindrus (a diatom) to a clustered matrix of three global change variables (CO2, mixed-layer depth, and temperature) under both iron (Fe)-replete and Fe-limited conditions based roughly on the Intergovernmental Panel on Climate Change (IPCC) A2 scenario: (1) Current conditions, 39 Pa (380 ppmv) CO2, 50 µmol photons/m**2/s light, and 2°C; (2) Year 2060, 61 Pa (600 ppmv) CO2, 100 µmol photons/m**2/s light, and 4°C; (3) Year 2100, 81 Pa (800 ppmv) CO2, 150 µmol photons/m**2/s light, and 6°C. The combined interactive effects of these global change variables and changing Fe availability on growth, primary production, and cell morphology are species specific. A competition experiment suggested that future conditions could lead to a shift away from P. antarctica and toward diatoms such as F. cylindrus. Along with decreases in diatom cell size and shifts from prymnesiophyte colonies to single cells under the future scenario, this could potentially lead to decreased carbon export to the deep ocean. Fe : C uptake ratios of both species increased under future conditions, suggesting phytoplankton of the Southern Ocean will increase their Fe requirements relative to carbon fixation. The interactive effects of Fe, light, CO2, and temperature on Antarctic phytoplankton need to be considered when predicting the future responses of biology and biogeochemistry in this region.

CO2 and vitamin B12 interactions determine bioactive trace metal requirements of a subarctic Pacific diatom

Phytoplankton growth can be limited by numerous inorganic nutrients and organic growth factors. Using the subarctic diatom Attheya sp. in culture studies, we examined how the availability of vitamin B(12) and carbon dioxide partial pressure (pCO(2)) influences growth rate, primary productivity, cellular iron (Fe), cobalt (Co), zinc (Zn) and cadmium (Cd) quotas, and the net use efficiencies (NUEs) of these bioactive trace metals (mol C fixed per mol cellular trace metal per day). Under B(12)-replete conditions, cells grown at high pCO(2) had lower Fe, Zn and Cd quotas, and used those trace metals more efficiently in comparison with cells grown at low pCO(2). At high pCO(2), B(12)-limited cells had ~50% lower specific growth and carbon fixation rates, and used Fe ~15-fold less efficiently, and Zn and Cd ~3-fold less efficiently, in comparison with B(12)-replete cells. The observed higher Fe, Zn and Cd NUE under high pCO(2)/B(12)-replete conditions are consistent with predicted downregulation of carbon-concentrating mechanisms. Co quotas of B(12)-replete cells were 5- to 14-fold higher in comparison with B(12)-limited cells, suggesting that >80% of cellular Co of B(12)-limited cells was likely from B(12). Our results demonstrate that CO(2) and vitamin B(12) interactively influence growth, carbon fixation, trace metal requirements and trace metal NUE of this diatom. This suggests the need to consider complex feedback interactions between multiple environmental factors for this biogeochemically critical group of phytoplankton in the last glacial maximum as well as the current and future changing ocean.

(Table 2, page 50) Toolik lake sediment chemistry (0-1 cm interval)

The sediments within Toolik Lake in arctic Alaska are characterized by extremely low rates of organic matter sedimentation and unusually high concentrations of iron and manganese. Pore water and solid phase measurements of iron, manganese, trace metals, carbon, nitrogen, phosphorus, and sulfur are consistent with the hypothesis that the reduction of organic matter by iron and manganese is the most important biogeochemical reaction within the sediment. Very low rates of dissolved oxygen consumption by the sediments result in an oxidizing environment at the sediment-water interface. This results in high retention of upwardly-diffusing iron and manganese and the formation of metal-enriched sediment. Phosphate in sediment pore waters is strongly adsorbed by the metal-enriched phases. Consequently, fluxes of phosphorus from the sediments to overlying waters are very small and contribute to the oligotrophic nature of the Toolik Lake aquatic system. Toolik Lake contains an unusual type of lacustrine sediment, and in many ways the sediments are similar to those found in oligotrophic oceanic environments.

Nutrient availability affects the response of the calcifying chlorophyte Halimeda opuntia (L.) J.V. Lamouroux to low pH

Atmospheric carbon dioxide emissions cause a decrease in the pH and aragonite saturation state of surface ocean water. As a result, calcifying organisms are expected to suffer under future ocean conditions, but their physiological responses may depend on their nutrient status. Because many coral reefs experience high inorganic nutrient loads or seasonal changes in nutrient availability, reef organisms in localized areas will have to cope with elevated carbon dioxide and changes in inorganic nutrients. Halimeda opuntia is a dominant calcifying primary producer on coral reefs that contributes to coral reef accretion. Therefore, we investigated the carbon and nutrient balance of H. opuntia exposed to elevated carbon dioxide and inorganic nutrients. We measured tissue nitrogen, phosphorus and carbon content as well as the activity of enzymes involved in inorganic carbon uptake and nitrogen assimilation (external carbonic anhydrase and nitrate reductase, respectively). Inorganic carbon content was lower in algae exposed to high CO2, but calcification rates were not significantly affected by CO2 or inorganic nutrients. Organic carbon was positively correlated to external carbonic anhydrase activity, while inorganic carbon showed the opposite correlation. Carbon dioxide had a significant effect on tissue nitrogen and organic carbon content, while inorganic nutrients affected tissue phosphorus and N:P ratios. Nitrate reductase activity was highest in algae grown under elevated CO2 and inorganic nutrient conditions and lowest when phosphate was limiting. In general, we found that enzymatic responses were strongly influenced by nutrient availability, indicating its important role in dictating the local responses of the calcifying primary producer H. opuntia to ocean acidification.

Seawater carbonate chemistry, structural and chemical characteristics of the seagrass Thalassia testudinum in an situ CO2 enrichment experiment

Seagrasses commonly display carbon-limited photosynthetic rates. Thus, increases in atmospheric pCO2, and consequentially oceanic CO2(aq) concentrations, may prove beneficial. While addressed in mesocosms, these hypotheses have not been tested in the field with manipulative experimentation. This study examines the effects of in situ CO2(aq) enrichment on the structural and chemical characteristics of the tropical seagrass, Thalassia testudinum. CO2(aq) availability was manipulated for 6 months in clear, open-top chambers within a shallow seagrass meadow in the Florida Keys (USA), reproducing forecasts for the year 2100. Structural characteristics (leaf area, leaf growth, shoot mass, and shoot density) were unresponsive to CO2(aq) enrichment. However, leaf nitrogen and phosphorus content declined on average by 11 and 21 %, respectively. Belowground, non-structural carbohydrates increased by 29 %. These results indicate that increased CO2(aq) availability may primarily alter the chemical composition of seagrasses, influencing both the nutrient status and resilience of these systems.

Organic nitrogen and organic phosphorus concentrations bays of the White Sea

Concentrations of organic and mineral nitrogen and phosphorus in waters from different types of bays were determined during summer of 1987. Content of organic nitrogen in surface waters reached 80-97% of total; content of mineral phosphorus was 60-100%. Concentrations of N_org and P_org in deep waters decreased to 70 and 40%, respectively. Distribution of organic matter in the bays was controlled by river run-off.