Posts Tagged 'light'

Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore Emiliania huxleyi under future ocean climate change conditions

Effects of ocean acidification and warming on marine primary producers can be modulated by other environmental factors, such as levels of nutrients and light. Here, we investigated the interactive effects of five oceanic environmental drivers (CO2, temperature, light, dissolved inorganic nitrogen and phosphate) on growth rate, particulate organic (POC) and inorganic (PIC) carbon quotas of the cosmopolitan coccolithophore Emiliania huxleyi. Population growth rate increased with increasing temperature (16 to 20 °C) and light intensities (60 to 240 μmol photons m−2  s−1), but decreased with elevated pCO2 concentrations (370 to 960 μatm) and reduced availability of nitrate (24.3 to 7.8 μmol L−1) and phosphate (1.5 to 0.5 μmol L−1). POC quotas were predominantly enhanced by combined effects of increased pCO2 and decreased availability of phosphate. PIC quotas increased with decreased availability of nitrate and phosphate. Our results show that concurrent changes in nutrient concentrations and pCO2 levels predominantly affected growth, photosynthetic carbon fixation and calcification of E. huxleyi, and imply that plastic responses to progressive ocean acidification, warming and decreasing availability of nitrate and phosphate reduce population growth rate while increasing cellular quotas of particulate organic and inorganic carbon of E. huxleyi, ultimately affecting coccolithophore-related ecological and biogeochemical processes.

Continue reading ‘Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore Emiliania huxleyi under future ocean climate change conditions’

Effects of irradiance, temperature, nutrients, and pCO2 on the growth and biochemical composition of cultivated Ulva fenestrata

Ulva fenestrata is an economically and ecologically important green algal species with a large potential in seaweed aquaculture due to its high productivity, wide environmental tolerance, as well as interesting functional and nutritional properties. Here, we performed a series of manipulative cultivation experiments in order to investigate the effects of irradiance (50, 100, and 160 μmol photons m−2 s−1), temperature (13 and 18 °C), nitrate (< 5, 150, and 500 μM), phosphate (< 1 and 50 μM), and pCO2 (200, 400, and 2500 ppm) on the relative growth rate and biochemical composition (fatty acid, protein, phenolic, ash, and biochar content) in indoor tank cultivation of Swedish U. fenestrata. High irradiance and low temperature were optimal for the growth of this northern hemisphere U. fenestrata strain, but addition of nutrients or changes in pCO2 levels were not necessary to increase growth. Low irradiance resulted in the highest fatty acid, protein, and phenolic content, while low temperature had a negative effect on the fatty acid content but a positive effect on the protein content. Addition of nutrients (especially nitrate) increased the fatty acid, protein, and phenolic content. High nitrate levels decreased the total ash content of the seaweeds. The char content of the seaweeds did not change in response to any of the manipulated factors, and the only significant effect of changes in pCO2 was a negative relationship with phenolic content. We conclude that the optimal cultivation conditions for Swedish U. fenestrata are dependent on the desired biomass traits (biomass yield or biochemical composition).

Continue reading ‘Effects of irradiance, temperature, nutrients, and pCO2 on the growth and biochemical composition of cultivated Ulva fenestrata’

A multistressor model of carbon acquisition regulation for macroalgae in a changing climate

It is widely hypothesized that noncalcifying macroalgae will be more productive and abundant in increasingly warm and acidified oceans. Macroalgae vary greatly in the magnitudes and interactions of responses of photosynthesis and growth to multiple stressors associated with climate change. A knowledge gap that exists between the qualitative “macroalgae will benefit” hypothesis and the variable outcomes observed is regulation of physiological mechanisms that cause variation in the magnitudes of change in primary productivity, growth, and their covariation. In this context, we developed a model to quantitatively describe physiological responses to coincident variation in temperature, carbonate chemistry and light supply in a representative bicarbonate‐using marine macroalga. The model is based on Ulva spp., the best understood dissolved inorganic carbon uptake mechanism among macroalgae, with data enabling synthesis across all parameters. At boundary layer pH < 8.7 most inorganic carbon is taken up through the external carbonic anhydrase (CAext) mechanism under all conditions of photosynthetic photon flux density, temperature, and boundary layer thickness. Each 0.1 unit decline in pH causes a 20% increase in the fraction of diffusive uptake of CO2 thereby lessening reliance on active transport of bicarbonate. Modeled downregulation of anion exchange‐mediated active bicarbonate transport associated with a 0.4 unit decline in pH under ocean acidification is consistent with enhanced growth up to 4% per day without increasing photosynthetic rate. The model provides a means to quantify magnitudes of change in productivity under factorial combinations of changing temperature, CO2, and light supply anticipated as climate changes.

Continue reading ‘A multistressor model of carbon acquisition regulation for macroalgae in a changing climate’

Photosynthetic performances of marine microalgae under influences of rising CO2 and solar UV radiation

Marine photosynthesis contributes approximately half of the global primary productivity. Ocean climate changes, such as increasing dissolved CO2 in seawater and consequently declining pH (known as ocean acidification, OA), may alter marine photosynthetic performance. There are numerous studies on the effects of OA on photosynthetic organisms, but controversial findings indicate positive, neutral, and negative influences. Most of the studies so far have been conducted under controlled conditions that ignored the presence of solar UV radiation. Increased CO2 availability may play a fertilizing role, while the concurrent pH drop may exert pressure on microalgal cells, especially during the night period. It is known that elevated CO2 concentrations downregulate CO2-concentrating mechanisms (CCMs), and intracellular concentrations of dissolved inorganic carbon in diatoms grown under elevated CO2 levels can be much lower than that in low CO2-grown ones. Such a reduced CO2 availability within cells in response to increased CO2 in the water can lead to enhanced photorespiration due to an increased O2 to CO2 ratio around the carboxylating and oxygenating enzyme, RuBisCO. Therefore, negative and positive effects of OA may depend on light levels, since the saved energy due to downregulation of CCMs can benefit growth under light-limited conditions but enhance photoinhibition under light-excessive conditions. OA affects metabolic pathways in phytoplankton. It augments ß-oxidation and the citric acid cycle, which accumulates toxic phenolic compounds. In the upper mixed layer, phytoplankton are exposed to excessive PAR and UV radiation (UVR). The calcareous incrustations of calcified microalgae, known to shield the organisms from UVR, are thinned due to OA, exposing the cells to increased solar UV and further inhibiting their calcification and photosynthesis, reflecting a compounded impact. Such UV and OA interactive effects are expected to reduce primary productivity in oligotrophic pelagic surface waters. In this chapter, we review and analyze recent results on effects of OA and UV and their combined effects on marine photosynthesis of microalgae, which falls in the context of marine photosynthesis under changing ocean environments and multiple stressors.

Continue reading ‘Photosynthetic performances of marine microalgae under influences of rising CO2 and solar UV radiation’

Increased irradiance availability mitigates the physiological performance of species of the calcifying green macroalga Halimeda in response to ocean acidification

Highlights

•The effects of elevated pCO2 and irradiance on Halimeda were investigated.

•Elevated pCO2 negatively influences physiological processes of Halimeda.

•These negative effects could be mitigated by increased irradiance availability.

Abstract

Although negative responses of tropical calcifying organisms to ocean acidification have been widely reported, the modulating potential of irradiance combined with elevated pCO2 has not been well studied. In this study, the interactive effects of elevated pCO2 and irradiance availability on the physiology of calcifying macroalgae Halimeda cylindracea and Halimeda lacunalis were investigated using a fully factorial, 28-day aquaria coupling experiment. The results of the present study demonstrate that elevated pCO2 negatively influences growth, photosynthesis, calcification and other physiological processes of both Halimeda species. However, these negative effects could be mitigated to some extent by increased irradiance availability. Specific growth rate (SGR), net calcification rates (Gnet) and maximum quantum yield (Fv/Fm) decreased significantly by 6.84%–86.70%, 51.78%–62.29% and 2.37%–28.91% in elevated pCO2 treatments. However, SGRGnet and Fv/Fm increased by 3.39%–84.78%, 29.61%–40.68% and 1.68%–6.92% in high irradiance conditions, respectively. Chl-a in elevated pCO2 treatments was 7.75%–61.25% lower than ambient pCO2 conditions, while the carotenoid content increased by 12.12%–57.45% in low irradiance conditions from day 20–28. Malondialdehyde (MDA) content was higher in elevated pCO2 treatments. However, there was also a two- to four-fold increase in proline content in elevated pCO2 treatments. Tissue total organic carbon (TCorg) and nitrogen (TN) were positively correlated to CO2 enrichment. The results of the current study suggested that elevated pCO2 negatively influenced the physiological responses of Halimeda, while increased irradiance availability may enhance the metabolic performance in response to ocean acidification.

Continue reading ‘Increased irradiance availability mitigates the physiological performance of species of the calcifying green macroalga Halimeda in response to ocean acidification’

Ocean acidification interacts with variable light to decrease growth but increase particulate organic nitrogen production in a diatom

Highlights

• Variable light decreased growth rate and pigmentation contents in both LC and HC.

• Cells grown under variable light appeared more tolerant of high light.

• HC and varying light decreased carbon fixation rate but increased POC and PON.

• HC and varying light lead to less primary productivity but more PON per biomass.

Abstract

Phytoplankton in the upper oceans are exposed to changing light levels due to mixing, diurnal solar cycles and weather conditions. Consequently, effects of ocean acidification are superimposed upon responses to variable light levels. We therefore grew a model diatom Thalassiosira pseudonana under either constant or variable light but at the same daily photon dose, with current low (400 μatm, LC) and future high CO2 (1000 μatm, HC) treatments. Variable light, compared with the constant light regime, decreased the growth rate, Chl a, Chl c, and carotenoid contents under both LC and HC conditions. Cells grown under variable light appeared more tolerant of high light as indicated by higher maximum relative electron transport rate and saturation light. Light variation interacted with high CO2/lowered pH to decrease the carbon fixation rate, but increased particulate organic carbon (POC) and particularly nitrogen (PON) per cell, which drove a decrease in C/N ratio, reflecting changes in the efficiency of energy transfer from photo-chemistry to net biomass production. Our results imply that elevated pCO2 under varying light conditions can lead to less primary productivity but more PON per biomass of the diatom, which might improve the food quality of diatoms and thereby influence biogeochemical nitrogen cycles.

Continue reading ‘Ocean acidification interacts with variable light to decrease growth but increase particulate organic nitrogen production in a diatom’

Higher sensitivity towards light stress and ocean acidification in an Arctic sea‐ice associated diatom compared to a pelagic diatom

Thalassiosira hyalina and Nitzschia frigida are important members of Arctic pelagic and sympagic (sea‐ice associated) diatom communities. We investigated the effects of light stress (shift from 20 to 380 µmol photons m‐2 s‐1, resembling upwelling or ice break‐up) under contemporary and future pCO2 (400 vs. 1000 µatm).

The responses in growth, elemental composition, pigmentation and photophysiology were followed over 120 h and are discussed together with underlying gene expression patterns.

Stress response and subsequent re‐acclimation were efficiently facilitated by T. hyalina, which showed only moderate changes in photophysiology and elemental composition, and thrived under high‐light after 120 h. In N. frigida, photochemical damage and oxidative stress appeared to outweigh cellular defenses, causing dysfunctional photophysiology and reduced growth. pCO2 alone did not specifically influence gene expression, but amplified the transcriptomic reactions to light stress, indicating that pCO2 affects metabolic equilibria rather than sensitive genes.

Large differences in acclimation capacities towards high‐light and high pCO2 between T. hyalina and N. frigida indicate species‐specific mechanisms in coping with the two stressors, which may reflect their respective ecological niches. This could potentially alter the balance between sympagic vs. pelagic primary production in a future Arctic.

Continue reading ‘Higher sensitivity towards light stress and ocean acidification in an Arctic sea‐ice associated diatom compared to a pelagic diatom’

Combined effects of temperature, irradiance and pH on Teleaulax amphioxeia (Cryptophyceae) physiology and feeding ratio for its predator Mesodinium rubrum (Ciliophora)

The cryptophyte Teleaulax amphioxeia is a source of plastids for the ciliate Mesodinium rubrum and both organisms are members of the trophic chain of several species of Dinophysis. It is important to better understand the ecology of organisms at the first trophic levels before assessing the impact of principal factors of global change on Dinophysis spp. Therefore, combined effects of temperature, irradiance and pH on growth rate, photosynthetic activity and pigment content of a temperate strain of T. amphioxeia were studied using a full factorial design (central composite design 23*) in 17 individually controlled bioreactors. The derived model predicted an optimal growth rate of T. amphioxeia at a light intensity of 400 µmol photons · m‐2 · s‐1, more acidic pH (7.6) than the current average and a temperature of 17.6°C. An interaction between temperature and irradiance on growth was also found, while pH did not have any significant effect. Subsequently, to investigate potential impacts of prey quality and quantity on the physiology of the predator, M. rubrum was fed two separate prey: predator ratios with cultures of T. amphioxeia previously acclimated at two different light intensities (100 and 400 µmol photons · m‐2 · s‐1). M. rubrum growth appeared to be significantly dependant on prey quantity while effect of prey quality was not observed. This multi‐parametric study indicated a high potential for a significant increase of T. amphioxeia in future climate conditions but to what extent this would lead to increased occurrences of Mesodinium spp. and Dinophysis spp. should be further investigated.

Continue reading ‘Combined effects of temperature, irradiance and pH on Teleaulax amphioxeia (Cryptophyceae) physiology and feeding ratio for its predator Mesodinium rubrum (Ciliophora)’

Intercomparison of four methods to estimate coral calcification under various environmental conditions (update)

Coral reefs are constructed by calcifiers that precipitate calcium carbonate to build their shells or skeletons through the process of calcification. Accurately assessing coral calcification rates is crucial to determine the health of these ecosystems and their response to major environmental changes such as ocean warming and acidification. Several approaches have been used to assess rates of coral calcification, but there is a real need to compare these approaches in order to ascertain that high-quality and intercomparable results can be produced. Here, we assessed four methods (total alkalinity anomaly, calcium anomaly, 45Ca incorporation, and 13C incorporation) to determine coral calcification of the reef-building coral Stylophora pistillata. Given the importance of environmental conditions for this process, the study was performed under two starting pH levels (ambient: 8.05 and low: 7.2) and two light (light and dark) conditions. Under all conditions, calcification rates estimated using the alkalinity and calcium anomaly techniques as well as 45Ca incorporation were highly correlated. Such a strong correlation between the alkalinity anomaly and 45Ca incorporation techniques has not been observed in previous studies and most probably results from improvements described in the present paper. The only method which provided calcification rates significantly different from the other three techniques was 13C incorporation. Calcification rates based on this method were consistently higher than those measured using the other techniques. Although reasons for these discrepancies remain unclear, the use of this technique for assessing calcification rates in corals is not recommended without further investigations.

Continue reading ‘Intercomparison of four methods to estimate coral calcification under various environmental conditions (update)’

The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)

Compared to the rest of the globe, the Arctic Ocean is affected disproportionately by climate change. Despite these fast environmental changes, we currently know little about the effects of ocean acidification (OA) on marine key species in this area. Moreover, the existing studies typically test the effects of OA under constant, hence artificial, light fields. In this study, the abundant Arctic picoeukaryote Micromonas pusilla was acclimated to current (400 µatm) and future (1000 µatm) pCO2 levels under a constant as well as a dynamic light, simulating more realistic light fields as experienced in the upper mixed layer. To describe and understand the responses to these drivers, growth, particulate organic carbon (POC) production, elemental composition, photophysiology and reactive oxygen species (ROS) production were analysed. M. pusilla was able to benefit from OA on various scales, ranging from an increase in growth rates to enhanced photosynthetic capacity, irrespective of the light regime. These beneficial effects were, however, not reflected in the POC production rates, which can be explained by energy partitioning towards cell division rather than biomass build-up. In the dynamic light regime, M. pusilla was able to optimize its photophysiology for effective light usage during both low- and high-light periods. This photoacclimative response, which was achieved by modifications to photosystem II (PSII), imposed high metabolic costs leading to a reduction in growth and POC production rates when compared to constant light. There were no significant interactions observed between dynamic light and OA, indicating that M. pusilla is able to maintain effective photoacclimation without increased photoinactivation under high pCO2. Based on these findings, M. pusilla is likely to cope well with future conditions in the Arctic Ocean.

Continue reading ‘The Arctic picoeukaryote Micromonas pusilla benefits from ocean acidification under constant and dynamic light (update)’


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