Posts Tagged 'photosynthesis'

Effects of elevated CO2 and temperature on phytoplankton community biomass, species composition and photosynthesis during an autumn bloom in the Western English Channel

The combined effects of elevated pCO2 and temperature were investigated during an autumn phytoplankton bloom in the Western English Channel (WEC). A full factorial 36-day microcosm experiment was conducted under year 2100 predicted temperature (+4.5 °C) and pCO2 levels (800 μatm). The starting phytoplankton community biomass was 110.2 (±5.7 sd) mg carbon (C) m−3 and was dominated by dinoflagellates (~ 50 %) with smaller contributions from nanophytoplankton (~ 13 %), cryptophytes (~ 11 %)and diatoms (~ 9 %). Over the experimental period total biomass was significantly increased by elevated pCO2 (20-fold increase) and elevated temperature (15-fold increase). In contrast, the combined influence of these two factors had little effect on biomass relative to the ambient control. The phytoplankton community structure shifted from dinoflagellates to nanophytoplankton at the end of the experiment in all treatments. Under elevated pCO2 nanophytoplankton contributed 90% of community biomass and was dominated by Phaeocystis spp., while under elevated temperature nanophytoplankton contributed 85 % of the community biomass and was dominated by smaller nano-flagellates. Under ambient conditions larger nano-flagellates dominated while the smallest nanophytoplankton contribution was observed under combined elevated pCO2 and temperature (~ 40 %). Dinoflagellate biomass declined significantly under the individual influences of elevated pCO2, temperature and ambient conditions. Under the combined effects of elevated pCO2 and temperature, dinoflagellate biomass almost doubled from the starting biomass and there was a 30-fold increase in the harmful algal bloom (HAB) species, Prorocentrum cordatum. Chlorophyll a normalised maximum photosynthetic rates (PBm) increased > 6-fold under elevated pCO2 and > 3-fold under elevated temperature while no effect on PBm was observed when pCO2 and temperature were elevated simultaneously. The results suggest that future increases in temperature and pCO2 do not appear to influence coastal phytoplankton productivity during autumn in the WEC which would have a negative feedback on atmospheric CO2.

Continue reading ‘Effects of elevated CO2 and temperature on phytoplankton community biomass, species composition and photosynthesis during an autumn bloom in the Western English Channel’

Global warming interacts with ocean acidification to alter PSII function and protection in the diatom Thalassiosira weissflogii


  • Global warming increases the photoinactivation rate.
  • Ocean acidification alleviates the effect of global warming on photoinactivation.
  • Global warming does not affect PsbA removal but ocean acidification enhances it.
  • Ocean acidification induces high nonphotochemical quenching.
  • Global warming increases antioxidant systems, but ocean acidification does not


Diatoms, as important contributors to aquatic primary production, are critical to the global carbon cycle. They tend to dominate phytoplankton communities experiencing rapid changes of underwater light. However, little is known regarding how climate change impacts diatoms’ capacity in coping with variable light environments. Here we grew a globally abundant diatom T. weissflogii, under two levels of temperature (18, 24 °C) and pCO2 (400, 1000 μatm), and then treated it with a light challenge to understand the combined effects of ocean warming and acidification on its exploitation of variable light environments. The higher temperature increased the photoinactivation rate at 400 μatm pCO2 and the higher pCO2 alleviated the negative effect of the higher temperature on PSII photoinactivation. Temperature did not affect the PsbA removal rate, but higher pCO2 stimulated PsbA removal. Photoinactivation outran repair, leading to decreased maximum photochemical yield in PSII. The higher pCO2 induced high sustained phase of nonphotochemical quenching when cells were less photoinhibited. The high light exposure induced the activity of both superoxide dismutase (SOD) and catalase (CAT) and the higher temperature stimulated them further, with insignificant effect of pCO2. Our findings suggest that ocean warming, ocean acidification and high light exposure would interact on PSII function and protection, and combination of these three environmental factors would lead to a reduced PSII activity in T. weissflogii. This study provides helpful insight into how climate change variables combined with local stressor impact diatoms’ photosynthetic physiology.

Continue reading ‘Global warming interacts with ocean acidification to alter PSII function and protection in the diatom Thalassiosira weissflogii’

Growth, ammonium metabolism, and photosynthetic properties of Ulva australis (Chlorophyta) under decreasing pH and ammonium enrichment

The responses of macroalgae to ocean acidification could be altered by availability of macronutrients, such as ammonium (NH4+). This study determined how the opportunistic macroalga, Ulva australis responded to simultaneous changes in decreasing pH and NH4+ enrichment. This was investigated in a week-long growth experiment across a range of predicted future pHs with ambient and enriched NH4+ treatments followed by measurements of relative growth rates (RGR), NH4+ uptake rates and pools, total chlorophyll, and tissue carbon and nitrogen content. Rapid light curves (RLCs) were used to measure the maximum relative electron transport rate (rETRmax) and maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm). Photosynthetic capacity was derived from the RLCs and included the efficiency of light harvesting (α), slope of photoinhibition (β), and the light saturation point (Ek). The results showed that NH4+ enrichment did not modify the effects of pH on RGRs, NH4+ uptake rates and pools, total chlorophyll, rETRmax, α, β, Fv/Fm, tissue C and N, and the C:N ratio. However, Ek was differentially affected by pH under different NH4+ treatments. Ek increased with decreasing pH in the ambient NH4+ treatment, but not in the enriched NH4+ treatment. NH4+ enrichment increased RGRs, NH4+ pools, total chlorophyll, rETRmax, α, β, Fv/Fm, and tissue N, and decreased NH4+ uptake rates and the C:N ratio. Decreased pH increased total chlorophyll content, rETRmax, Fv/Fm, and tissue N content, and decreased the C:N ratio. Therefore, the results indicate that U. australis growth is increased with NH4+ enrichment and not with decreasing pH. While decreasing pH influenced the carbon and nitrogen metabolisms of U. australis, it did not result in changes in growth.

Continue reading ‘Growth, ammonium metabolism, and photosynthetic properties of Ulva australis (Chlorophyta) under decreasing pH and ammonium enrichment’

The effects of eutrophication and acidification on the ecophysiology of Ulva pertusa Kjellman

In coastal environments, acidification and eutrophication affect the physiology of marine macroalgae. We investigated the responses of Ulva pertusa Kjellman (Ulvales, Chlorophyta) under such conditions. Samples were cultured at two different pH settings (low, 7.5; high, 8.0) and at three different ammonium levels (low, 4; medium, 60; high, 120 μM NH4+). Our objective was to analyze the influence that elevated CO2 and NH4+ might have on pH, oxygen evolution, rates of nutrient uptake, chlorophyll fluorescence, growth, and C/N ratio of that organism. Variability in pH value was enhanced under low pH/high NH4+ and was significantly different (p < 0.05) from changes measured when the high pH/low NH4+ combination was applied. Rates of NH4+ uptake and relative growth rates by U. pertusa were increased under low pH/high NH4+ conditions and that response was significantly different (p < 0.05) from the other treatments. The rate of photosynthetic oxygen evolution and chlorophyll fluorescence were increased under elevated NH4+ concentrations (p < 0.05). However, the C/N ratio of U. pertusa was not affected by higher concentrations of CO2 and NH4+ (p > 0.05). Our results indicated that the physiological reactions of this alga were heightened when exposed to either the elevated combination of CO2/NH4+ or even when only the level of NH4+ was raised. Although such excessive growth can lead to bloom formations in coastal areas, this species also has greater capacity for taking up nutrients and dissolved inorganic carbon.

Continue reading ‘The effects of eutrophication and acidification on the ecophysiology of Ulva pertusa Kjellman’

Ocean acidification impacts primary and bacterial production in Antarctic coastal waters during austral summer


• Elevated CO2 decreased primary productivity and gross primary production.
• Elevated CO2 decreased bacterial productivity but increased bacterial production.
• Increased bacterial production was associated with reduced grazing pressure.
• Elevated CO2 decreased net community production when nitrate was available.
• Under nitrate limitation net community production responses to CO2 were suppressed.


Polar waters may be highly impacted by ocean acidification (OA) due to increased solubility of CO2 at colder water temperatures. Three experiments examining the influence of OA on primary and bacterial production were conducted during austral summer at Davis Station, East Antarctica (68°35′ S, 77°58′ E). For each experiment, six minicosm tanks (650 L) were filled with 200 μm filtered coastal seawater containing natural communities of Antarctic marine microbes. Assemblages were incubated for 10 to 12 days at CO2 concentrations ranging from pre-industrial to post-2300. Primary and bacterial production rates were determined using NaH14CO3 and 14C-leucine, respectively. Net community production (NCP) was also determined using dissolved oxygen. In all experiments, maximum photosynthetic rates (Pmax, mg C mg chl a− 1 h− 1) decreased with elevated CO2, clearly reducing rates of total gross primary production (mg C L− 1 h− 1). Rates of cell-specific bacterial productivity (μg C cell− 1 h− 1) also decreased under elevated CO2, yet total bacterial production (μg C L− 1 h− 1) and cell abundances increased with CO2 over Days 0–4. Initial increases in bacterial production and abundance were associated with fewer heterotrophic nanoflagellates and therefore less grazing pressure. The main changes in primary and bacterial productivity generally occurred at CO2 concentrations > 2 × present day (> 780 ppm), with the same responses occurring regardless of seasonally changing environmental conditions and microbial assemblages. However, NCP varied both within and among experiments, largely due to changing nitrate + nitrite (NOx) availability. At NOx concentrations < 1.5 μM photosynthesis to respiration ratios showed that populations switched from net autotrophy to heterotrophy and CO2 responses were suppressed. Overall, OA may reduce production in Antarctic coastal waters, thereby reducing food availability to higher trophic levels and reducing draw-down of atmospheric CO2, thus forming a positive feedback to climate change. NOX limitation may suppress this OA response but cause a similar decline.

Continue reading ‘Ocean acidification impacts primary and bacterial production in Antarctic coastal waters during austral summer’

Responses of photosynthesis and CO2 concentrating mechanisms of marine crop Pyropia haitanensis thalli to large pH variations at different time scales


• A pH of 4, 5, and 9 resulted in the death of Pyropia haitanensis thalli.
• A pH of 6 and 7 increased the growth of Pyropia haitanensis thalli.
• The CO2 concentrating mechanisms may play a role in intracellular pH homeostasis.
• Actual pH variation needs to be considered in relative studies.

Wild and cultivated populations of Pyropia haitanensis have frequently experienced extremely low pH conditions in the last few decades. This could potentially threaten the development of the aquaculture of this economically important marine crop. To gain a broader perspective, we investigated the short- (4 h) and long- (7 days) term responses of CO2 concentrating mechanisms (CCMs) of P. haitanensis thalli to large variations in pH. Our study found that a pH of 4 and 5, which mimicked the decreased pH caused by acid rain, resulted in decreased photosynthesis and respiration while leading to the death of P. haitanensis thalli. Thus, acid rain would result in a decline in P. haitanensis production and threaten wild seaweed sources. However, a pH of 6 and 7 enhanced the growth of P. haitanensis thalli by > 30%, mainly because increased CO2 levels favored photosynthesis, while the algae need to effectively maintain intracellular pH homeostasis to support rapid growth rates. The contributions of extracellular carbonic anhydrases (eCAs) to photosynthetic rates remained at > 77% when pH ≥ 7, regardless of the treatment time. However, at pH 6, the contribution of eCAs to photosynthesis increased from 25% for a short-term treatment to 66% for a long-term treatment. Thus, except for work on carbon assimilation, this study proposes that the CCMs component involved in the movement and metabolism of inorganic carbon may play an important role in pH homeostasis. In addition, pH 9 also led to the death of P. haitanensis thalli, which is consistent with observations of the natural distribution of this algae and hints that P. haitanensis thalli prefer to use inorganic carbon via eCAs when pH ≥ 7. The present study suggested that the actual variation in pH experienced by marine organisms needs to be considered in the experimental design of related studies.

Continue reading ‘Responses of photosynthesis and CO2 concentrating mechanisms of marine crop Pyropia haitanensis thalli to large pH variations at different time scales’

Nutrient loading fosters seagrass productivity under ocean acidification

The effects of climate change are likely to be dependent on local settings. Nonetheless, the compounded effects of global and regional stressors remain poorly understood. Here, we used CO2 vents to assess how the effects of ocean acidification on the seagrass, Posidonia oceanica, and the associated epiphytic community can be modified by enhanced nutrient loading. P. oceanica at ambient and low pH sites was exposed to three nutrient levels for 16 months. The response of P. oceanica to experimental conditions was assessed by combining analyses of gene expression, plant growth, photosynthetic pigments and epiphyte loading. At low pH, nutrient addition fostered plant growth and the synthesis of photosynthetic pigments. Overexpression of nitrogen transporter genes following nutrient additions at low pH suggests enhanced nutrient uptake by the plant. In addition, enhanced nutrient levels reduced the expression of selected antioxidant genes in plants exposed to low pH and increased epiphyte cover at both ambient and low pH. Our results show that the effects of ocean acidification on P. oceanica depend upon local nutrient concentration. More generally, our findings suggest that taking into account local environmental settings will be crucial to advance our understanding of the effects of global stressors on marine systems.

Continue reading ‘Nutrient loading fosters seagrass productivity under ocean acidification’

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Ocean acidification in the IPCC AR5 WG II

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