Photosynthetic Oxygen Evolution Rate Research Articles

Toxicity of the sunscreen UV filter benzophenone-3 (OBZ) to the microalga Selenastrum capricornutum: An insight into OBZ’s damage to photosynthesis and respiration

Oxybenzone (OBZ; benzophenone-3, CAS# 131–57–7), as a new pollutant and ultraviolet absorbent, shows a significant threat to the survival of phytoplankton. This study aims to explore the acute toxic effects of OBZ on the growth of the microalga Selenastrum capricornutum, as well as the mechanisms for its damage to the primary metabolic pathways of photosynthesis and respiration. The results demonstrated that the concentrations for 50 % of maximal effect (EC50) of OBZ for S. capricornutum were 9.07 mg L−1 and 8.54 mg L−1 at 72 h and 96 h, respectively. A dosage of 4.56 mg L−1 OBZ significantly lowered the photosynthetic oxygen evolution rate of S. capricornutum in both light and dark conditions for a duration of 2 h, while it had no effect on the respiratory oxygen consumption rate under darkness. OBZ caused a significant decline in the efficiency of photosynthetic electron transport due to its damage to photosystem II (PSII), thereby decreasing the photosynthetic oxygen evolution rate. Over-accumulated H2O2 was produced under light due to the damage caused by OBZ to the donor and acceptor sides of PSII, resulting in increased peroxidation of cytomembranes and inhibition of algal respiration. OBZ’s damage to photosynthesis and respiration will hinder the conversion and reuse of energy in algal cells, which is an important reason that OBZ has toxic effects on S. capricornutum. The present study indicated that OBZ has an acute toxic effect on the microalga S. capricornutum. In the two most important primary metabolic pathways in algae, photosynthesis is more sensitive to the toxicity of OBZ than respiration, especially in the dark.

Effects of selective RNA processing and stabilization enzymes on carbon sequestration by photosynthesis of Synechococcus sp. PCC7002

Synechococcus is one of the most abundant prokaryotic photosynthetic organisms on Earth and plays a key role in oceanic carbon fixation and transformation. To improve the photosynthetic efficiency of synechococcus, a post-transcriptional regulatory mechanism - Selective RNA Processing and Stabilization (SRPS) was considered. We inactivated the SRPS-enzymes, executor of the SRPS mechanism, to explore their regulation rule of photosynthetic carbon fixation efficiency in Synechococcus. The results showed that the inactivation of SRPS-enzymes mainly affected the growth rate or growth phase. It significantly alters the photosynthetic oxygen evolution rate, pigment content, chlorophyll fluorescence, carbon and nitrogen content, as well as the composition and biological activity of the dissolved organic matter derived from Synechococcus (SOM). Inactivating SRPS-enzymes results in an increase in the expression level of most subunits of the Cytochrome b6-f complex, while the expression levels of most subunits of PSI, PSII, RuBisCO, and NDH decrease. All SRPS-enzymes are involved in the expression regulation of basilic protein complexes in photosynthesis, such as PSI, PSII, Cytochrome b6-f complex, ATP synthase, and RuBisCO. Our results indicate that the inactivation of SRPS-enzymes have a significant influence on carbon sequestration by photosynthesis of Synechococcus sp. PCC7002.

Inactivation of photosynthetic cyclic electron transports upregulates photorespiration for compensation of efficient photosynthesis in Arabidopsis.

Plants have multiple mechanisms to maintain efficient photosynthesis. Photosynthetic cyclic electron transports around photosystem I (CET), which includes the PGR5/PGRL1 and NDH pathways, and photorespiration play a crucial role in photosynthetic efficiency. However, how these two mechanisms are functionally linked is not clear. In this study, we revealed that photorespiration could compensate for the function of CET in efficient photosynthesis by comparison of the growth phenotypes, photosynthetic properties monitored with chlorophyll fluorescence parameters and photosynthetic oxygen evolution in leaves and photorespiratory activity monitored with the difference of photosynthetic oxygen evolution rate under high and low concentration of oxygen conditions between the deleted mutant PGR5 or PGRL1 under NDH defective background (pgr5 crr2 or pgrl1a1b crr2). Both CET mutants pgr5 crr2 and pgrl1a1b crr2 displayed similar suppression effects on photosynthetic capacities of light reaction and growth phenotypes under low light conditions. However, the total CET activity and photosynthetic oxygen evolution of pgr5 crr2 were evidently lower than those of pgrl1a1b crr2, accompanied by the upregulation of photorespiratory activity under low light conditions, resulting in severe suppression of photosynthetic capacities of light reaction and finally photodamaged phenotype under high light or fluctuating light conditions. Based on these findings, we suggest that photorespiration compensates for the loss of CET functions in the regulation of photosynthesis and that coordination of both mechanisms is essential for maintaining the efficient operation of photosynthesis, especially under stressed conditions.

Effects of calcification on air-water CO2 fluxes in tropical seagrass meadows: A mesocosm experiment

Seagrass meadows deliver a range of ecosystem services, where one of the more important is the capacity to store carbon and serve as sinks for atmospheric carbon dioxide. The capacity of seagrass meadows for carbon storage might, however, be modified and complicated by several factors; one important factor is the possible effects of calcification within the meadows. In tropical areas, seagrass meadows can contain high proportions of calcareous organisms, which through their calcification may cause release of CO2. To study this aspect of the CO2 balance within tropical seagrass systems, we investigated the air-water CO2 flux in seagrass mesocosms with different plant community compositions, i.e. mixtures of seagrass and calcifying macroalgae, having similar overall photosynthetic oxygen evolution rates. The measured CO2 fluxes changed both in rate and direction over the day and were significantly related to plant community composition. Downward fluxes of CO2 were found only over vegetation with high proportion of seagrass and in the afternoon, whereas occurrence of calcifying algae appeared to reverse the flow. A partial least squares (PLS) regression model indicated that pH, pCO2 and dissolved inorganic carbon (DIC) were the primary environmental variables predicting the CO2 fluxes. Our findings show that algal calcification might partly counteract the carbon sequestration in seagrass meadows.

Photosynthesis of Submerged and Surface Leaves of the Dwarf Water Lily (Nymphoides aquatica) Using PAM Fluorometry

Dwarf Water Lilies (Nymphoides aquatica (J.F. Gmel) Kuntze have floating and submerged leaves. Some submerged aquatic vascular plants have a form of CAM (Crassulacean Acid Metabolism) called Submerged Aquatic Macrophyte (SAM) metabolism. Blue-diode based PAM technology was used to measure the Photosynthetic Oxygen Evolution Rate (POER: 1O2 ≡ 4e– ). Optimum Irradiance (Eopt), maximum POER (POERmax) and quantum efficiency (α0) all vary on a diurnal cycle. The shape of the POER vs. E curves is different in seedling, submerged and surface leaves. Both Eopt and POERmax are very low in seedling leaves (Eopt ≈ 104 μmol photon m–2 s–1, PPFD; POERmax ≈ 4.95 µmol O2 g–1 Chl a s–1), intermediate in mature submerged leaves (Eopt ≈ 419 µmol photon m–2 s–1 PPFD, POERmax ≈ 38.1 µmol O2 g–1 Chl a s–1) and very high in surface leaves (Eopt ≈ 923 µmol photon m–2 s–1 PPFD, POERmax ≈ 76.1 µmol O2 g–1 Chl a s–1). Leaf titratable acid (C4 acid pool) is too small (≈20 to 50 mol H+ m–3) to support substantial SAM metabolism. Gross daily photosynthesis of surface leaves is ≈3.71 g C m–2 d–1 in full sun and as much as 1.4 gC m–2 d–1 in shaded submerged leaves. There is midday inhibition of photosynthesis.

Lowering pO2 Interacts with Photoperiod to Alter Physiological Performance of the Coastal Diatom Thalassiosira pseudonana.

Exacerbating deoxygenation is extensively affecting marine organisms, with no exception for phytoplankton. To probe these effects, we comparably explored the growth, cell compositions, photosynthesis, and transcriptome of a diatom Thalassiosira pseudonana under a matrix of pO2 levels and Light:Dark cycles at an optimal growth light. The growth rate (μ) of T. pseudonana under a 8:16 L:D cycle was enhanced by 34% by low pO2 but reduced by 22% by hypoxia. Under a 16:8 L:D cycle, however, the μ decreased with decreasing pO2 level. The cellular Chl a content decreased with decreasing pO2 under a 8:16 L:D cycle, whereas the protein content decreased under a 16:8 L:D cycle. The prolonged photoperiod reduced the Chl a but enhanced the protein contents. The lowered pO2 reduced the maximal PSII photochemical quantum yield (FV/FM), photosynthetic oxygen evolution rate (Pn), and respiration rate (Rd) under the 8:16 or 16:8 L:D cycles. Cellular malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were higher under low pO2 than ambient pO2 or hypoxia. Moreover, the prolonged photoperiod reduced the FV/FM and Pn among all three pO2 levels but enhanced the Rd, MDA, and SOD activity. Transcriptome data showed that most of 26 differentially expressed genes (DEGs) that mainly relate to photosynthesis, respiration, and metabolism were down-regulated by hypoxia, with varying expression degrees between the 8:16 and 16:8 L:D cycles. In addition, our results demonstrated that the positive or negative effect of lowering pO2 upon the growth of diatoms depends on the pO2 level and is mediated by the photoperiod.

Toxicity evaluation of butyl acrylate on the photosynthetic pigments, chlorophyll fluorescence parameters, and oxygen evolution activity of Phaeodactylum tricornutum and Platymonas subcordiformis.

Butyl acrylate is a hazardous and noxious substance (HNS) listed in the top 50 chemicals that is most likely to be involved in HNS spilling incident. At present, information about toxicity effect of butyl acrylate on marine organisms was insufficient, especially on marine microalgae. Phaeodactylum tricornutum (P. tricornutum) and Platymonas subcordiformis (P. subcordiformis) were used as test organism to evaluate the toxic effect of butyl acrylate on their photosynthetic system. Results showed that chlorophyll a (Chl-a) content, the net photosynthetic oxygen evolution rate (NOR), and chlorophyll fluorescence parameters including maximal photochemical efficiency (Fv/Fm), electron transfer rate (ETR), photochemical quenching (qP), and non-photochemical quenching (NPQ) were all stimulated in the toxic dose of 5,10, and 25 mg/L while those were significantly inhibited in the highest concentration of 25 mg/L groups after 96 h. Meanwhile, it was also found that Fv/Fm would be a suitable indicator for evaluating the toxicity of butyl acrylate on the photosynthetic system of two marine microalgae according to the analysis of Pearson correlation coefficient and integrated biomarker response (IBR). Once butyl acrylate enters the marine ecosystem, the toxicity data obtained in this study could be used as a reference for evaluating the effect of butyl acrylate on the photosynthetic capacity of marine microalgae.

Experimental Study of the Quantitative Impact of Flow Turbulence on Algal Growth

Flow turbulence has been widely accepted as one of the essential factors affecting phytoplankton growth. In this study, laboratory cultures of Microcystis aeruginosa in beakers were carried out under different turbulent conditions to identify the quantitative relationship between the algal growth rate and the turbulent intensity. The turbulent intensity (represented by energy dissipation rate, ε) was simulated with the software FLUENT. Daily measurement of the two parameters (algal biomass and chlorophyll-a concentration) was carried out during the experimental period to represent the algal growth rate. Meanwhile, the rates of photosynthetic oxygen evolution and chlorophyll fluorescence intensity were calculated to investigate the photosynthetic efficiency. The results indicated that the growth rate of Microcystis aeruginosa became higher in the turbulent environment than in the still water environment under the designed experimental conditions. The peak growth rate of Microcystis aeruginosa occurred when ε was 6.44 × 10−2 m2/s3, over which the rate declined, probably due to unfavorable impacts of strong turbulence. In comparison, the maximum rate of photosynthetic oxygen evolution occurred when ε was 0.19 m2/s3. Based on the findings of this study, an exponential function was proposed in order to incorporate the effect of flow turbulence into the existing algal growth models, which usually just consider the impacts of nutrient availability, illumination, and temperature.

Adaptation of a marine diatom to ocean acidification and warming reveals constraints and trade-offs

Ocean acidification and warming are recognized as two major anthropogenic perturbations of the modern ocean. However, little is known about the adaptive response of phytoplankton to them. Here we examine the adaptation of a marine diatom Thalassiosira weissflogii to ocean acidification in combination with ocean warming. Our results show that ocean warming have a greater effect than acidification on the growth of T. weissflogii over the long-term selection experiment (~380 generations), as well as many temperature response traits (e.g., optimum temperatures for photosynthesis, maximal net photosynthetic oxygen evolution rates, activation energy) in thermal reaction norm. These results suggest that ocean warming is the main driver for the evolution of the marine diatom T. weissflogii, rather than oceanacidification. However, the evolution resulting from warming can be constrained by ocean acidification, where ocean warming did not impose any effects at high CO2 level. Furthermore, adaptations to ocean warming alone or to the combination of ocean acidification and warming come with trade-offs by inhibiting photochemical performances. The constrains and trade-offs associated with the adaptation to ocean acidification and warming demonstrated in this study, should be considered for parameterizing evolutionary responses in eco-evolutionary models of phytoplankton dynamics in a future ocean.

Effects of Temperature and Light on Growth Rate and Photosynthetic Characteristics of Sargassum horneri

The changing environmental factors exerted great influences on coastal macroalgal communities. To study the responses of the brown seaweed Sargassum horneri to temperature and light, S. horneri was cultured under three temperatures (20, 25 and 30°C) and three light intensities (30, 60, and 120 µmol photonsm−2 s−1) for seven days. The growth rate, chlorophyll a (Chl a) and carotenoids (Car) contents, chlorophyll fluorescence, and photosynthetic oxygen evolution rate were measured. The results show that the highest relative growth rate (RGR), maximal electron transport rate (rETRmax); the net photosynthetic rate (Pn) were observed at the lowest temperature (20°C) and highest light intensity (120 µmol photons m−2 s−1); and the RGR and Pn were significantly inhibited by the highest temperature (30°C), especially at the lowest light intensity (30 µmol photons m−2 s−1) (P <0.05). Additionally, the highest light intensity enhanced the non-photochemical quenching (NPQ) even under the highest temperature (30°C), indicating that the higher light intensity could induce photo-protection reaction of thalli. These results suggest that the higher temperature and lower light intensity exerted negative influences on S. horneri.

Interactive effects of increasing atmospheric CO2 and copper exposure on the growth and photosynthesis in the young sporophytes of Sargassum fusiforme (Phaeophyta)

Little attention has been given to the combined effects of elevated atmospheric CO2-induced ocean acidification (OA) and heavy metal pollution on marine macroalgae at the young stage. This study investigated the mutual effects of copper (Cu) and elevated CO2 on the young sporophytes of brown macroalgae Sargassum fusiforme. A matrix of four copper concentrations, 0, 0.025, 0.075 and 0.15 mg‧L−1, and two levels of CO2 (ambient CO2: 400 μatm; elevated CO2: 1,000 μatm) were used. High concentration of copper exposure greatly depressed photosynthesis and growth of the young sporophytes of S. fusiforme by reducing the apparent photosynthetic efficiency (ɑ), maximum net photosynthetic oxygen evolution rate (Pmax), maximum photochemical quantum yield (Fv/Fm) and pigments content (Chl a and Car). While elevated CO2 alone had obscure impact on this alga. However, the inhibition of Cu stress on Fv/Fm was weakened by elevated CO2, which also decreased the light compensation point (Ic). Meanwhile, the Cu2+-induced ascent in the dark respiration rate (Rd) and superoxide dismutase (SOD) activity was mitigated under the growth with elevated CO2, suggesting an alleviated oxidative stress. Overall, we propose that, under CO2 enrichment condition, the young sporophytes of S. fusiforme may increase photosynthesis efficiency and synthesize less enzymatic antioxidants in face of increasing Cu stress.

Darkness and low nighttime temperature modulate the growth and photosynthetic performance of Ulva prolifera under lower salinity

In order to understand how darkness/irradiance and low nighttime temperature might alter physiology of Ulva prolifera under lower salinity conditions, we analyzed the growth rates, water content, superoxide dismutase (SOD) activity, total soluble proteins (SPs) and carbohydrates content at the end of dark and light period under three temperature levels (25–25 °C treatment: 25 °C for day and night; 15–15 °C treatment: 15 °C for day and night; 25–15 °C treatment: 25 °C for day with 15 °C for night) and two salinity conditions (15, 25), meanwhile, the pigment content (chlorophyll a and b), chlorophyll fluorescence and photosynthetic oxygen evolution also were determined during light phase. We found that the U. prolifera showed higher growth rate and SOD activity during dark phase at 25 °C, but this dark-induced increase could not be observed at 15 °C. The reasons for this increase varied, however, maybe not included water content and SPs for no significant difference in water content observed under all the treatments, as well as lower SPs content for dark period aside that at 15 °C and salinity 15. Compared to other two temperature treatments, the thalli grown at 25–15 °C showed higher growth rate and the photosynthetic oxygen evolution rate in light phase under salinity 15 conditions, although the maximum relative electron transport rate (rETRmax) showed higher value under 25 °C treatment. These results indicate that the darkness and the lower nighttime temperature maybe responsible reason for the rapid growth of these green tide algae.

Salinity mediates the effects of nitrogen enrichment on the growth, photosynthesis, and biochemical composition of Ulva prolifera.

To study the combined effects of multiple nitrogen (N) sources and salinity on the growth and physiology on macroalgae, we cultured Ulva prolifera under three N levels (N0, 0.1235 mg L-1; N1, 0.6 mg L-1; and N2, 4.4 mg L-1; the ratios were 18:74:8 for NH4-N, NO3-N, and NO2-N, respectively) and three salinity conditions (15, 25, and 35). Then, the growth, pigment content, photosynthetic performance, superoxide dismutase (SOD) activity, and contents of soluble protein and carbohydrates were measured. The results showed the following: (1) Compared to that grown at salinity 25, the growth of U. prolifera decreased under salinity 35, especially under the N0 and N2 levels, but there were no significant effects of salinity 15 under any of the N levels. (2) There were no significant effects of salinity on the chlorophyll a (Chla) content, but compared to the content at salinity 25, the chlorophyll b (Chlb) content was enhanced by salinity 15 and 35; lower ratio values between Chla and carotenoids (Car) occurred under the salinity 25 treatment. Under each salinity condition, the pigments were enhanced by a high N level. (3) A relatively higher salinity level decreased the photosynthetic oxygen evolution rate, while a higher N level increased this value. Compared to the rate at salinity 25, the dark respiration rate (Rd) significantly increased at salinity 15 under the N0 condition. (4) SOD activity was enhanced by a high N level, but no significant effects of salinity were observed. (5) The carbohydrate content was enhanced at salinity 35 under the N0 and N1 levels, and under salinity 15, this value increased with increasing N levels. In conclusion, although the growth of U. prolifera decreased at high N levels under high salinity conditions, a high N level induced an increase in photosynthesis, while no significant decrease in growth occurred. These findings indicate that low salinity and high N levels may be nonnegligible reasons why this species thrives, and low salinity was the better choice when this species was used for wastewater treatment.

Responses of carbonic anhydrases and Rubisco to abrupt CO2 changes of seawater in two marine diatoms.

Diatoms are experiencing striking fluctuations in seawater carbonate chemistry in the natural marine environment, especially in coastal seawaters. Here, we show that the diatoms Thalassiosira weissflogii and Phaeodactylum tricornutum, which utilize different carbon acquisition mechanisms, respond differently to short-term changes in seawater carbonate chemistry. Our results showed that T. weissflogii showed significantly higher photosynthetic oxygen evolution rates than that of P. tricornutum at low levels of CO2 or HCO3-. This suggests that T. weissflogii had higher affinities for CO2 or HCO3- when their concentrations were not sufficient to support saturated growth and photosynthesis. While the activity of Rubisco in P. tricornutum positively correlated with carbonic anhydrases (CA), we observed negative relationship between Rubisco and CA activity in the diatom T. weissflogii. These contrasting physiological responses of diatoms with varied carbon acquisition mechanisms indicate different abilities to cope up with abrupt changes in seawater carbonate chemistry. We propose that the ability to respond to varying carbonate chemistry may act as one determinant of the diatom distributions and phytoplankton community structures.

Knockdown of carbonate anhydrase elevates Nannochloropsis productivity at high CO2 level

Improving acid tolerance is pivotal to the development of microalgal feedstock for converting flue gas to biomass or oils. In the industrial oleaginous microalga Nannochloropsis oceanica, transcript knockdown of a cytosolic carbonic anhydrase (CA2), which is a key Carbon Concentrating Mechanism (CCM) component induced under 100 ppm CO2 (very low carbon, or VLC), results in ∼45%, ∼30% and ∼40% elevation of photosynthetic oxygen evolution rate, growth rate and biomass accumulation rate respectively under 5% CO2 (high carbon, or HC), as compared to the wild type. Such high-CO2-level activated biomass over-production is reproducible across photobioreactor types and cultivation scales. Transcriptomic, proteomic and physiological changes of the mutant under high CO2 (HC; 5% CO2) suggest a mechanism where the higher pH tolerance is coupled to reduced biophysical CCM, sustained pH hemostasis, stimulated energy intake and enhanced photosynthesis. Thus “inactivation of CCM” can generate hyper-CO2-assimilating and autonomously containable industrial microalgae for flue gas-based oil production.

Kinetin alleviates chromium toxicity on growth and PS II photochemistry in Nostoc muscorum by regulating antioxidant system

The present study was undertaken to evaluate the metal toxicity alleviating effects of kinetin (KN, 10 nM) on growth, photosynthetic pigments and photochemistry of PS II in the cyanobacterium Nostoc muscorum exposed to chromium (CrVI) stress (100 and 150 µM). Chromium declined growth, photosynthetic pigments (chlorophyll a, phycocyanin and carotenoids), photosynthetic oxygen evolution rate and parameters of fluorescence kinetics (ϕP0, FV/F0, ϕE0, Ψ0 and PIABS except F0/FV) in concentration dependent manner, while stimulating effects on respiration, energy flux parameters (ABS/RC, TR0/RC, ET0/RC and DI0/RC), oxidative stress biomarkers i.e., superoxide radical (SOR), hydrogen peroxide (H2O2) and lipid peroxidation (TBARS contents) and antioxidative enzymes: superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and glutathione-S-transferase (GST), were observed. However, upon addition of KN in the growth medium an alleviating effect against chromium induced toxicity on growth, photosynthetic pigments and photochemistry of PS II was recorded. This had occurred due to substantial reduction in levels of oxidative stress biomarkers: SOR, H2O2 and TBARS contents with concomitant rise in activity of antioxidative enzymes: SOD, POD, CAT and GST and appreciable lowering in the cellular accumulation of chromium. The overall results demonstrate that KN application significantly alleviated chromium induced toxicity on growth performance of the cyanobacterium N. muscorum due to significant improvement in photosynthetic pigments and photochemistry of PS II by up-regulating the activity of antioxidative enzymes, and declining cellular accumulation of chromium. Furthermore, Cr induced toxicity at lower dose (100 µM) was found to be ameliorated more efficiently in N. muscorum following supplementation of KN.

Cadmium Stress in Halophyte Thellungiella halophila: Consequences on Growth, Cadmium Accumulation, Reactive Oxygen Species and Antioxidative Systems

Cadmium (Cd) stress on the growth and antioxidant system of the halophyte Thellungiella halophila is studied to explore heavy metal tolerance and the role of antioxidants in Cd tolerance. Biomass production of both leaves and roots of four leaves T. halophila seedlings significantly decreased under 0, 0.3, 0.6, and 0.9 mmol L-1 CdCl2 for 14 days compare to no-Cd control. Meanwhile, the photosynthetic oxygen evolution rate significantly decreased and the chlorophyll content slightly decreased. The MDA and hydrogen peroxide (H2O2) contents of leaves increased as the Cd concentrations increased, and the oxidative damage in Cd-treated seedlings was greater under Cd stress than under the no-Cd controls. Though the translocation factor (TF) was always under 1, T. halophila can tolerate and accumulate more than 100 mg kg-1 Cd in shoot dry biomass. T. halophila mitigated the oxidative damage by increasing enzymatic components, glutathione (GSH), and ascorbic acid (AsA). In Cd-treated seedlings, both the leaf GSH and AsA and the activities of both peroxidase (POD) and catalase (CAT) were significantly greater under Cd stress than under no-Cd control. No significant differences were found in the activity of ascorbate peroxidase (APX), glutathione reductase (GR) and superoxide dismutase (SOD). These results critically summarize the effects of Cd stress in T. halophila and these results above indicate that the antioxidants are responsible for Cd tolerance in T. halophila.

The Interactive Effects of Elevated CO2 and Ammonium Enrichment on the Physiological Performances of Saccharina japonica (Laminariales, Phaeophyta)

Environmental challenges such as ocean acidification and eutrophication influence the physiology of kelp species. We investigated their interactive effects on Saccharina japonica (Laminariales, Phaeophyta) under two pH conditions [Low, 7.50; High (control), 8.10] and three NH 4 + concentrations (Low, 4; Medium, 60; High, 120 μM). The degree of variation of pH values in the culture medium and inhibition rate of photosynthetic oxygen evolution by acetazolamide were affected by pH treatments. Relative growth rates, carbon, nitrogen, and the C:N ratio in tissue samples were influenced by higher concentrations of NH 4 + . Rates of photosynthetic oxygen evolution were enhanced under elevated CO2 or NH 4 + conditions, independently, but these two factors did not show an interactive effect. However, rates of NH 4 + uptake were influenced by the interactive effect of increased CO2 under elevated NH 4 + treatment. Although ocean acidification and eutrophication states had an impact on physiological performance, chlorophyll fluorescence was not affected by those conditions. Our results indicated that the physiological reactions by this alga were influenced to some extent by a rise in the levels of CO2 and NH 4 + . Therefore, we expect that the biomass accumulation of S. japonica may well increase under future scenarios of ocean acidification and eutrophication.

Phytoplankton photosynthetic rate measurement using tunable pulsed light induced fluorescence kinetics.

The photosynthetic process of phytoplankton is the basis of the material circulation and energy flow of the ecosystem. The rapid and accurate measurement of phytoplankton photosynthesis rate is of great significance to water ecological environment monitoring, marine resource assessment and global climate change prediction. On the basis of "Bio-Optical" model, a photosynthetic rate measurement method based on tunable pulsed light induced fluorescence kinetics was put forward in this paper. The chlorophyll fluorescence was used as the probe of photosynthesis process, and the phytoplankton photosynthetic rate was evaluated by the photosynthetic electron transport rate. Comparative experiment results showed that the photosynthetic electron transport rate measured by fluorescence kinetic method under different conditions of DCMU, culture light and nutrients (nitrogen) were consistent with the photosynthetic oxygen evolution rate measured by oxygen evolution method, and the correlation coefficient R2 were 0.934, 0.957 and 0.955 respectively.

The short-term effects of elevated CO2 and ammonium concentrations on physiological responses in Gracilariopsis lemaneiformis (Rhodophyta)

Ocean acidification (OA) and coastal eutrophication affect coastal marine organisms. We studied the physiological responses of Gracilariopsis lemaneiformis (Gracilariales, Rhodophyta) to increased concentrations of CO2 and NH4+. Incubation treatments were applied at two different pH units (low, 7.5; high (control), 7.9) and three different NH4+ concentrations (low, 10; medium, 50; high, 100 μM). Growth, rates of photosynthetic oxygen evolution, and NH4+ uptake rates were affected by both elevated CO2 and NH4+ conditions. The changes in the pH of culture media were influenced by elevated CO2 or NH4+ treatments. However, chlorophyll fluorescence was affected only by the level of NH4+. These results indicate that the physiological responses of G. lemaneiformis might be enhanced when the concentrations of CO2 and NH4+ rise. Therefore, cultures of this alga could provide a good mitigation solution against ongoing problems with OA and coastal eutrophication.