Posts Tagged 'photosynthesis'

Effects of CO2 supply on growth and photosynthetic ability of young sporophytes of the economic seaweed Sargassum fusiforme (Sargassaceae, Phaeophyta)

Young sporophytes of Sargassum fusiforme were cultured at decreased CO2 (20 μatm), ambient CO2 (400 μatm), and high CO2 (1000 μatm), and then the quantum efficiency of open photosystem II (Fv′/Fm′), initial slope of the rapid light curves (α), and relative maximum photosynthetic electron transport rate (rETRm) of the algae under different temperatures and light levels were measured. The study aimed to investigate how the decreased CO2 and high CO2 supply affected the growth and photosynthetic functions of S. fusiforme young sporophytes. While both lowered and increased CO2 supply significantly reduced the growth rates of the alga, greater declines were observed under decreased CO2. The Fv′/Fm′, α, and rETRm of alga remained stable after short-term (120 min) exposures to 18, 22, and 26 °C, as well as to highlight (300 μmol photons m−2 s−1), with no significant difference among the three CO2 supply treatments. Hence, neither decreased nor increased CO2 affected the photosynthetic responses of S. fusiforme young sporophytes to temperature and high light. However, the Fv′/Fm′ of the three CO2 treatments declined by 72% under 60 μmol photons m−2 s−1, suggesting its sensitivity to short-term low light. These observations are crucial for the improved management of S. fusiforme for commercial farming, while ensuring its sustainable production and supply amid seawater pH shifts brought about by global climate change.

Continue reading ‘Effects of CO2 supply on growth and photosynthetic ability of young sporophytes of the economic seaweed Sargassum fusiforme (Sargassaceae, Phaeophyta)’

Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga

Ocean acidification (OA) and nutrient enrichment threaten the persistence of near shore ecosystems, yet little is known about their combined effects on marine organisms. Here, we show that a threefold increase in nitrogen concentrations, simulating enrichment due to coastal eutrophication or consumer excretions, offset the direct negative effects of near-future OA on calcification and photophysiology of the reef-building crustose coralline alga, Porolithon onkodes. Projected near-future pCO2 levels (approx. 850 µatm) decreased calcification by 30% relative to ambient conditions. Conversely, nitrogen enrichment (nitrate + nitrite and ammonium) increased calcification by 90–130% in ambient and high pCO2 treatments, respectively. pCO2 and nitrogen enrichment interactively affected instantaneous photophysiology, with highest relative electron transport rates under high pCO2 and high nitrogen. Nitrogen enrichment alone increased concentrations of the photosynthetic pigments chlorophyll a, phycocyanin and phycoerythrin by approximately 80–450%, regardless of pCO2. These results demonstrate that nutrient enrichment can mediate direct organismal responses to OA. In natural systems, however, such direct benefits may be counteracted by simultaneous increases in negative indirect effects, such as heightened competition. Experiments exploring the effects of multiple stressors are increasingly becoming important for improving our ability to understand the ramifications of local and global change stressors in near shore ecosystems.

Continue reading ‘Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga’

The role of irradiance and C-use strategies in tropical macroalgae photosynthetic response to ocean acidification

Fleshy macroalgae may increase photosynthesis with greater CO2 availability under ocean acidification (OA) and outcompete calcifying macroalgae important for tropical reef accretion. Macroalgae use energy-dependent carbon concentrating mechanisms (CCMs) to take up HCO3, the dominant inorganic carbon for marine photosynthesis, but carbon-use strategies may depend on the pCO2, pH and irradiance. We examined photosynthesis in eight tropical macroalgae across a range of irradiances (0–1200 μmol photon m−2 s−1), pH levels (7.5–8.5) and CO2 concentrations (3–43 μmol kg−1). Species-specific CCM strategies were assessed using inhibitors and δ13C isotope signatures. Our results indicate that the log of irradiance is a predictor of the photosynthetic response to elevated pCO2 (R2 > 0.95). All species utilized HCO3, exhibited diverse C-use pathways and demonstrated facultative HCO3 use. All fleshy species had positive photosynthetic responses to OA, in contrast to a split amongst calcifiers. We suggest that shifts in photosynthetically-driven tropical macroalgal changes due to OA will most likely occur in moderate to high-irradiance environments when CCMs are ineffective at meeting the C-demands of photosynthesis. Further, facultative use of HCO3 allows greater access to CO2 for photosynthesis under OA conditions, particularly amongst fleshy macroalgae, which could contribute to enhance fleshy species dominance over calcifiers.

Continue reading ‘The role of irradiance and C-use strategies in tropical macroalgae photosynthetic response to ocean acidification’

Ocean acidification conditions increase resilience of marine diatoms

The fate of diatoms in future acidified oceans could have dramatic implications on marine ecosystems, because they account for ~40% of marine primary production. Here, we quantify resilience of Thalassiosira pseudonana in mid-20th century (300 ppm CO2) and future (1000 ppm CO2) conditions that cause ocean acidification, using a stress test that probes its ability to recover from incrementally higher amount of low-dose ultraviolet A (UVA) and B (UVB) radiation and re-initiate growth in day–night cycles, limited by nitrogen. While all cultures eventually collapse, those growing at 300 ppm CO2 succumb sooner. The underlying mechanism for collapse appears to be a system failure resulting from “loss of relational resilience,” that is, inability to adopt physiological states matched to N-availability and phase of the diurnal cycle. Importantly, under elevated CO2 conditions diatoms sustain relational resilience over a longer timeframe, demonstrating increased resilience to future acidified ocean conditions. This stress test framework can be extended to evaluate and predict how various climate change associated stressors may impact microbial community resilience.

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Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga Ulva linza (update)

Large-scale green tides have been invading the coastal zones of the western Yellow Sea annually since 2008. Meanwhile, oceans are becoming more acidic due to continuous absorption of anthropogenic carbon dioxide, and intensive seaweed cultivation in Chinese coastal areas is leading to severe regional nutrient limitation. However, little is known about the combined effects of global and local stressors on the eco-physiology of bloom-forming algae. We cultured Ulva linza for 9–16 days under two levels of pCO2 (400 and 1000 µatm) and four treatments of nutrients (nutrient repletion, N limitation, P limitation, and N–P limitation) to investigate the physiological responses of this green tide alga to the combination of ocean acidification and nutrient limitation. For both sporelings and adult plants, elevated pCO2 did not affect the growth rate when cultured under nutrient-replete conditions but reduced it under P limitation; N or P limitations by themselves reduced growth rate. P limitation resulted in a larger inhibition in growth for sporelings compared to adult plants. Sporelings under P limitation did not reach the mature stage after 16 days of culture while those under P repletion became mature by day 11. Elevated pCO2 reduced net photosynthetic rate for all nutrient treatments but increased nitrate reductase activity and soluble protein content under P-replete conditions. N or P limitation reduced nitrate reductase activity and soluble protein content. These findings indicate that ocean acidification and nutrient limitation would synergistically reduce the growth of Ulva species and may thus hinder the occurrence of green tides in a future ocean environment.

Continue reading ‘Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga Ulva linza (update)’

Effects of elevated pCO2 on physiological performance of marine microalgae Dunaliella salina (Chlorophyta, Chlorophyceae)

The present study was conducted to determine the effects of elevated pCO2 on growth, photosynthesis, dark respiration and inorganic carbon acquisition in the marine microalga Dunaliella salina. To accomplish this, D. salina was incubated in semi-continuous cultures under present-day CO2 levels (390 μatm, pHNBS: 8.10), predicted year 2100 CO2 levels (1 000 μatm, pHNBS: 7.78) and predicted year 2300 CO2 levels (2 000 μatm, pHNBS: 7.49). Elevated pCO2 significantly enhanced photosynthesis (in terms of gross photosynthetic O2 evolution, effective quantum yield (ΔF/F’ m ), photosynthetic efficiency (α), maximum relative electron transport rate (rETRmax) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity) and dark respiration of D. salina, but had insignificant effects on growth. The photosynthetic O2 evolution of D. salina was significantly inhibited by the inhibitors acetazolamide (AZ), ethoxyzolamide (EZ) and 4,4’-diisothiocyanostilbene-2,2′-disulfonate (DIDS), indicating that D. salina is capable of acquiring HCOˉ 3 via extracellular carbonic anhydrase and anion-exchange proteins. Furthermore, the lower inhibition of the photosynthetic O2 evolution at high pCO2 levels by AZ, EZ and DIDS and the decreased carbonic anhydrase showed that carbon concentrating mechanisms were down-regulated at high pCO2. In conclusion, our results show that photosynthesis, dark respiration and CCMs will be affected by the increased pCO2/low pH conditions predicted for the future, but that the responses of D. salina to high pCO2/low pH might be modulated by other environmental factors such as light, nutrients and temperature. Therefore, further studies are needed to determine the interactive effects of pCO2, temperature, light and nutrients on marine microalgae.

Continue reading ‘Effects of elevated pCO2 on physiological performance of marine microalgae Dunaliella salina (Chlorophyta, Chlorophyceae)’

The effects of ocean acidification on Prochlorococcus

Prochlorococcus is the most abundant cyanobacteria in the global ocean, and is a part of the marine microbial loop. Climate change, a stressor, presents many threats to Prochlorococcus, two of which are of major concern: increased temperature and increased acidity. Both pH and temperature are not constant and vary in the ocean seasonally, diurnally, and meteorologically. This variation suggests that stress related to interactions with these variables may be complex. This present study examined the effects of lowered pH and increased temperature on Prochlorococcus in the short term. Two strains of Prochlorococcus, high-light and low-light, were manipulated to experience increased temperature, decreased pH, and a combination of the effects and both strains’ responses was observed. Photosynthetic health significantly differed in the low-light clade when the pH was lowered (p = 0.045). Extracted chlorophyll showed statistical variation in the high-light clade when pH was lowered (p = 0.036), and in the low-light clade in both treatments where pH was lowered and temperature was increased (both p < 0.001). There was no statistical difference when temperature and pH were manipulated at the same time. However, more data is needed to see if these results are replicable and to see how this would affect grazing intensity and community structure.

Continue reading ‘The effects of ocean acidification on Prochlorococcus’

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Ocean acidification in the IPCC AR5 WG II

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