Posts Tagged 'growth'

Photosynthetic responses of the marine diatom Thalassiosira pseudonana to CO2-induced seawater acidification

Ocean acidification due to atmospheric CO2 rise is expected to influence marine phytoplankton. Diatoms are responsible for about 40% of the total primary production in the ocean. In order to investigate the physiological response of marine diatom Thalassiosira pseudonana to ocean acidification, we grew the cells under ambient CO2 level (380 µatm) versus the elevated CO2 level (800 µatm) at a light level of 180 µmol m−2 s−1 for 30 generations. Our results showed that the elevated CO2 concentration caused a decrease of the effective photochemical efficiency of PSII (F′v/F′m) and increase of the dark respiration in T. pseudonana. The intracellular carbonic anhydrase activity was suppressed and the photosynthetic affinity for CO2 was lowered in the high CO2-grown cells, reflecting a downregulation of the CO2 concentrating mechanism (CCM). PSI activity was enhanced to support an increase in ATP synthesis by cyclic electron transfer as required for transport of inorganic carbon and regulation of intracellular pH. The energetic benefit from the downregulation of CCM to growth as reported in other diatom species was not observed here in T. pseudonana.

Continue reading ‘Photosynthetic responses of the marine diatom Thalassiosira pseudonana to CO2-induced seawater acidification’

Light availability and temperature, not increased CO2, will structure future meadows of Posidonia oceanica

We evaluated the photosynthetic performance of Posidonia oceanica during short-term laboratory exposures to ambient and elevated temperatures (24–25 °C and 29–30 °C) warming and pCO2 (380, 750 and 1000 ppm pCO2) under normal and low light conditions (200 and 40 μmol photons m−2 s−1 respectively). Plant growth was measured at the low light regime and showed a negative response to warming. Light was a critical factor for photosynthetic performance, although we found no evidence of compensation of photosynthetic quantum efficiency in high light. Relative Electron Rate Transport (rETRmax) was higher in plants incubated in high light, but not affected by pCO2 or temperature. The saturation irradiance (Ik) was negatively affected by temperature. We conclude that elevated CO2 does not enhance photosynthetic activity and growth, in the short term for P. oceanica, while temperature has a direct negative effect on growth. Low light availability also negatively affected photosynthetic performance during the short experimental period examined here. Therefore increasing concentrations of CO2 may not compensate for predicted future conditions of warmer water and higher turbidity for seagrass meadows.

Continue reading ‘Light availability and temperature, not increased CO2, will structure future meadows of Posidonia oceanica’

Ocean acidification and kelp development: Reduced pH has no negative effects on meiospore germination and gametophyte development of Macrocystis pyrifera and Undaria pinnatifida

The absorption of anthropogenic CO2 by the oceans is causing a reduction in the pH of the surface waters termed ocean acidification (OA). This could have substantial effects on marine coastal environments where fleshy (non-calcareous) macroalgae are dominant primary producers and ecosystem engineers. Few OA studies have focused on the early life stages of large macroalgae such as kelps. This study evaluated the effects of seawater pH on the ontogenic development of meiospores of the native kelp Macrocystis pyrifera and the invasive kelp Undaria pinnatifida, in south-eastern New Zealand. Meiospores of both kelps were released into four seawater pH treatments (pHT 7.20, extreme OA predicted for 2300; pHT 7.65, OA predicted for 2100; pHT 8.01, ambient pH; and pHT 8.40, pre-industrial pH) and cultured for 15 d. Meiospore germination, germling growth rate, and gametophyte size and sex ratio were monitored and measured. Exposure to reduced pHT (7.20 and 7.65) had positive effects on germling growth rate and gametophyte size in both M. pyrifera and U. pinnatifida, whereas, higher pHT (8.01 and 8.40) reduced the gametophyte size in both kelps. Sex ratio of gametophytes of both kelps was biased towards females under all pHT treatments, except for U. pinnatifida at pHT 7.65. Germling growth rate under OA was significantly higher in M. pyrifera compared to U. pinnatifida but gametophyte development was equal for both kelps under all seawater pHT treatments, indicating that the microscopic stages of the native M. pyrifera and the invasive U. pinnatifida will respond similarly to OA.

Continue reading ‘Ocean acidification and kelp development: Reduced pH has no negative effects on meiospore germination and gametophyte development of Macrocystis pyrifera and Undaria pinnatifida’

Physiological response of a golden tide alga (Sargassum muticum) to the interaction of ocean acidification and phosphorus enrichment (update)

The development of golden tides is potentially influenced by global change factors, such as ocean acidification and eutrophication, but related studies are very scarce. In this study, we cultured a golden tide alga, Sargasssum muticum, at two levels of pCO2 (400 and 1000 µatm) and phosphate (0.5 and 40 µM) to investigate the interactive effects of elevated pCO2 and phosphate on the physiological properties of the thalli. Higher pCO2 and phosphate (P) levels alone increased the relative growth rate by 41 and 48 %, the net photosynthetic rate by 46 and 55 %, and the soluble carbohydrates by 33 and 62 %, respectively, while the combination of these two levels did not promote growth or soluble carbohydrates further. The higher levels of pCO2 and P alone also enhanced the nitrate uptake rate by 68 and 36 %, the nitrate reductase activity (NRA) by 89 and 39 %, and the soluble protein by 19 and 15 %, respectively. The nitrate uptake rate and soluble protein was further enhanced, although the nitrate reductase activity was reduced when the higher levels of pCO2 and P worked together. The higher pCO2 and higher P levels alone did not affect the dark respiration rate of the thalli, but together they increased it by 32 % compared to the condition of lower pCO2 and lower P. The neutral effect of the higher levels of pCO2 and higher P on growth and soluble carbohydrates, combined with the promoting effect on soluble protein and dark respiration, suggests that more energy was drawn from carbon assimilation to nitrogen assimilation under conditions of higher pCO2 and higher P; this is most likely to act against the higher pCO2 that caused acid–base perturbation via synthesizing H+ transport-related protein. Our results indicate that ocean acidification and eutrophication may not boost golden tide events synergistically, although each one has a promoting effect.

Continue reading ‘Physiological response of a golden tide alga (Sargassum muticum) to the interaction of ocean acidification and phosphorus enrichment (update)’

The most primitive metazoan animals, the placozoans, show high sensitivity to increasing ocean temperatures and acidities

The increase in atmospheric carbon dioxide (CO2) leads to rising temperatures and acidification in the oceans, which directly or indirectly affects all marine organisms, from bacteria to animals. We here ask whether the simplest—and possibly also the oldest—metazoan animals, the placozoans, are particularly sensitive to ocean warming and acidification. Placozoans are found in all warm and temperate oceans and are soft-bodied, microscopic invertebrates lacking any calcified structures, organs, or symmetry. We here show that placozoans respond highly sensitive to temperature and acidity stress. The data reveal differential responses in different placozoan lineages and encourage efforts to develop placozoans as a potential biomarker system.

Continue reading ‘The most primitive metazoan animals, the placozoans, show high sensitivity to increasing ocean temperatures and acidities’

Kelp and carbon: pathways and barriers to acquisition and transport

Large brown algae in the class Phaeophyceae (Heterokontophyta) form the structural and energetic foundation of temperate and subtropical nearshore marine forests of high productivity and ecological diversity. This dissertation examines the carbon uptake and transport physiology of large brown algae with a particular focus on the plastic or adaptive responses of these physiological traits to their abiotic environment. Chapter 1 takes an anatomical and modeling approach to investigate the structure and function of photosynthate transport networks (analogous to phloem) in diverse members of the Laminariales. To evaluate the existence of scaling and optimization of the kelp vascular system, a model of optimized transport anatomy was developed and tested with a  diverse suite of kelp species in the Laminariales. Results revealed a surprising lack of universal scaling in the kelps and the presence of optimized transport anatomy in the giant kelp (Macrocystis pyrifera) only. Chapter 2 focuses on the dynamics of carbon uptake in M. pyrifera, which can acquire both carbon dioxide and bicarbonate as carbon substrates for photosynthesis. To evaluate whether the proportion of carbon dioxide and bicarbonate utilized by M. pyrifera is constant or a variable function of their fluctuating environment, oxygen evolution experiments were carried out  n entire blades from several targeted populations in the Monterey Bay. Results indicated that M. pyrifera possesses a plastic carbon uptake physiology in which proportionally more bicarbonate is used in high irradiance and high flow conditions, but that local populations have not yet developed fixed genetic differences. Chapter 3 investigates the mechanism and patterns of carbon stable isotope discrimination in M. pyrifera. Results of a dual field and laboratory incubation approach indicate that 13C discrimination patterns are determined by a complex interaction of light intensity, dissolved inorganic carbon limitation, and fractionation occurring during transport of polysaccharides. Overall, this dissertation informs patterns and mechanisms of carbon uptake and transport in kelps, and highlights the many ways in which kelps may impact and structure their ecosystems.

Continue reading ‘Kelp and carbon: pathways and barriers to acquisition and transport’

Inter- and intraspecific phenotypic plasticity of three phytoplankton species in response to ocean acidification

Phenotypic plasticity describes the phenotypic adjustment of the same genotype to different environmental conditions and is best described by a reaction norm. We focus on the effect of ocean acidification on inter- and intraspecific reaction norms of three globally important phytoplankton species (Emiliania huxleyi, Gephyrocapsa oceanica and Chaetoceros affinis). Despite significant differences in growth rates between the species, they all showed a high potential for phenotypic buffering (similar growth rates between ambient and high CO2 conditions). Only three coccolithophore genotypes showed a reduced growth in high CO2. Diverging responses to high CO2 of single coccolithophore genotypes compared with the respective mean species responses, however, raise the question of whether an extrapolation to the population level is possible from single-genotype experiments. We therefore compared the mean response of all tested genotypes with a total species response comprising the same genotypes, which was not significantly different in the coccolithophores. Assessing species reaction norms to different environmental conditions on short time scale in a genotype-mix could thus reduce sampling effort while increasing predictive power.

Continue reading ‘Inter- and intraspecific phenotypic plasticity of three phytoplankton species in response to ocean acidification’


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