Antarctic microalgae: physiological acclimation to environmental change

<p>Sea ice algal communities play a very significant role in primary production in the Southern Ocean, being the only source of fixed carbon for all other life in this habitat and contributing up to 22% of Antarctic primary production in ice-covered regions. Therefore it is important to understand how these organisms adapt to this highly variable and harsh environment Previous studies have described their acclimation to changes in environmental conditions but we still do not understand the physiological basis of these responses. This study examines the effects of varying levels of photosynthetically active radiation (PAR), ultraviolet-B (UV-B) radiation and temperature on bottom ice algal communities and individual algal species using pulse-amplitude modulation (PAM) fluorometry, the production of mycosporine-like amino acids (MAAs) and superoxide dismutase (SOD) activity. The experiments conducted in this thesis show that bottom ice algae are capable of acclimating to the higher levels of PAR and temperature that would likely be experienced during sea ice melt As temperature was increased past a threshold temperature of thylakoid integrity, it became the major stressor, causing decreases in photosynthetic yield at around 14°C, even at ambient PAR exposure. Similarly, a thylakoid integrity experiment independently suggested that the critical temperature for the onset of thylakoid damage was 14°C, which correlated well to the 14°C incubation observations, although this is a temperature that sea ice algae are unlikely to encounter in the polar regions. It is likely that sea ice algae produce additional MAAs, known to be cellular sunscreens, in response to increasing levels of UV-B, allowing tolerance of this stressor. This is the first study in the marine environment to demonstrate that algae can produce MAAs in response to increasing PAR and temperature, even in the absence of UV-B, indicating that MAAs may be more than just sunscreen compounds. The levels of UV-B used in this study were representative of those likely to be faced by the algae during sea ice melt. With increasing temperature, the algae maintained photosynthetic yield and decreased MAA production, implying that the rise in temperature aids the algae with another element of photoprotection such as enzymatic repair. As these results contrasted with previous studies of bottom ice algae that showed no additional MAA production in response to higher levels of PAR and UV-B, it was hypothesized that this difference was attributed to variations in species composition that could modify the productivity of the community. The short-term effects of increasing PAR and UV -B on three unialgal cultures of Thalassiosira sp., Fragilariopsis sp. (from the Ross Sea), and Chaetoceros sp. (from the Antarctic Peninsula) were therefore examined. In unialgal culture studies, these three algal species showed higher tolerance to PAR and UV-B compared to that of the mixed culture of bottom ice algae, although there remained species-specific variation. Both Ross Sea species showed increasing photosynthetic yield with increasing PAR and UV-B exposure, but there was a difference in the tolerance shown by the two species. Thalassiosira sp. tolerated higher PAR and lower UV-B and Fragilariopsis tolerated lower PAR and higher UV-B. Both species produced MAAs in response to these stressors, indicating that these compounds allowed the algae to decrease levels of photoinhibition. In comparison to the Ross Sea, the Antarctic Peninsula is an area of higher environmental variability and change, meaning that the species in both regions could have varying acclimatory capabilities. Although data from three species alone cannot conclusively demonstrate that algae from different regions have different acclimatory capabilities, they do illustrate considerable variation between species. Chaetoceros sp. from the Antarctic Peninsula region showed a higher tolerance to PAR and UV-B compared to the Ross Sea species. The former species showed an increase in photosynthetic yield in response to increasing PAR and this was accompanied by a lack of MAA production in response to the experimental levels of PAR, which indicates that the two Ross Sea species have a higher tolerance to PAR compared to the Antarctic Peninsula species. Chaetoceros sp. from the Antarctic Peninsula showed an increase in photosynthetic yield in response to high UV-B exposures, accompanied by MAA production and had no signs of photoinhibition. A further experiment was conducted to address the weaknesses in the initial methodologies, particularly related to control conditions in the short-term experiments. Common species from the Ross Sea, Antarctic Peninsula and the Arctic were exposed to a combination of increased PAR and UV-B over a period of seven days to compare acclimatory abilities using PAM and SOD activity. Thalassiosira antarctica from the Ross Sea, Chaetoceros socialis from the Antarctic Peninsula and C. socialis from the Arctic showed no significant change in quantum yield over the incubation period. This further highlights the importance of running experiments with compounding factors, as an increase in one factor could alleviate the negative effect of the other. There was an unexpected lack of change in SOD activity for all species under all treatments applied, which could indicate that the levels of PAR and UV-B used were not high enough to cause stress in these species. This work also points to the need to assay for various antioxidants, as algae are known to rely on a network of antioxidants in their defence against environmental stresses. The data from this thesis clarify the influence of PAR, UV-B and temperature on sea ice algae, and could help better evaluate the fate of these communities under various climate change scenarios. This study has made important steps towards understanding the acclimatory abilities of sea ice algae. Increasing knowledge of sea ice algal physiology, particularly of photosynthetic health in response to environmental change, will help improve predictions of productivity in the most productive ocean on this planet. Algal tolerance to increasing PAR, UV-B and temperature is remarkable, and this ability could be crucial in the context of future climate change. The productivity of these autotrophic microorganisms strongly influences secondary production that ties their fate to that of all other life in the Southern Ocean.</p>

Antarctic microalgae: physiological acclimation to environmental change

<p>Sea ice algal communities play a very significant role in primary production in the Southern Ocean, being the only source of fixed carbon for all other life in this habitat and contributing up to 22% of Antarctic primary production in ice-covered regions. Therefore it is important to understand how these organisms adapt to this highly variable and harsh environment Previous studies have described their acclimation to changes in environmental conditions but we still do not understand the physiological basis of these responses. This study examines the effects of varying levels of photosynthetically active radiation (PAR), ultraviolet-B (UV-B) radiation and temperature on bottom ice algal communities and individual algal species using pulse-amplitude modulation (PAM) fluorometry, the production of mycosporine-like amino acids (MAAs) and superoxide dismutase (SOD) activity. The experiments conducted in this thesis show that bottom ice algae are capable of acclimating to the higher levels of PAR and temperature that would likely be experienced during sea ice melt As temperature was increased past a threshold temperature of thylakoid integrity, it became the major stressor, causing decreases in photosynthetic yield at around 14°C, even at ambient PAR exposure. Similarly, a thylakoid integrity experiment independently suggested that the critical temperature for the onset of thylakoid damage was 14°C, which correlated well to the 14°C incubation observations, although this is a temperature that sea ice algae are unlikely to encounter in the polar regions. It is likely that sea ice algae produce additional MAAs, known to be cellular sunscreens, in response to increasing levels of UV-B, allowing tolerance of this stressor. This is the first study in the marine environment to demonstrate that algae can produce MAAs in response to increasing PAR and temperature, even in the absence of UV-B, indicating that MAAs may be more than just sunscreen compounds. The levels of UV-B used in this study were representative of those likely to be faced by the algae during sea ice melt. With increasing temperature, the algae maintained photosynthetic yield and decreased MAA production, implying that the rise in temperature aids the algae with another element of photoprotection such as enzymatic repair. As these results contrasted with previous studies of bottom ice algae that showed no additional MAA production in response to higher levels of PAR and UV-B, it was hypothesized that this difference was attributed to variations in species composition that could modify the productivity of the community. The short-term effects of increasing PAR and UV -B on three unialgal cultures of Thalassiosira sp., Fragilariopsis sp. (from the Ross Sea), and Chaetoceros sp. (from the Antarctic Peninsula) were therefore examined. In unialgal culture studies, these three algal species showed higher tolerance to PAR and UV-B compared to that of the mixed culture of bottom ice algae, although there remained species-specific variation. Both Ross Sea species showed increasing photosynthetic yield with increasing PAR and UV-B exposure, but there was a difference in the tolerance shown by the two species. Thalassiosira sp. tolerated higher PAR and lower UV-B and Fragilariopsis tolerated lower PAR and higher UV-B. Both species produced MAAs in response to these stressors, indicating that these compounds allowed the algae to decrease levels of photoinhibition. In comparison to the Ross Sea, the Antarctic Peninsula is an area of higher environmental variability and change, meaning that the species in both regions could have varying acclimatory capabilities. Although data from three species alone cannot conclusively demonstrate that algae from different regions have different acclimatory capabilities, they do illustrate considerable variation between species. Chaetoceros sp. from the Antarctic Peninsula region showed a higher tolerance to PAR and UV-B compared to the Ross Sea species. The former species showed an increase in photosynthetic yield in response to increasing PAR and this was accompanied by a lack of MAA production in response to the experimental levels of PAR, which indicates that the two Ross Sea species have a higher tolerance to PAR compared to the Antarctic Peninsula species. Chaetoceros sp. from the Antarctic Peninsula showed an increase in photosynthetic yield in response to high UV-B exposures, accompanied by MAA production and had no signs of photoinhibition. A further experiment was conducted to address the weaknesses in the initial methodologies, particularly related to control conditions in the short-term experiments. Common species from the Ross Sea, Antarctic Peninsula and the Arctic were exposed to a combination of increased PAR and UV-B over a period of seven days to compare acclimatory abilities using PAM and SOD activity. Thalassiosira antarctica from the Ross Sea, Chaetoceros socialis from the Antarctic Peninsula and C. socialis from the Arctic showed no significant change in quantum yield over the incubation period. This further highlights the importance of running experiments with compounding factors, as an increase in one factor could alleviate the negative effect of the other. There was an unexpected lack of change in SOD activity for all species under all treatments applied, which could indicate that the levels of PAR and UV-B used were not high enough to cause stress in these species. This work also points to the need to assay for various antioxidants, as algae are known to rely on a network of antioxidants in their defence against environmental stresses. The data from this thesis clarify the influence of PAR, UV-B and temperature on sea ice algae, and could help better evaluate the fate of these communities under various climate change scenarios. This study has made important steps towards understanding the acclimatory abilities of sea ice algae. Increasing knowledge of sea ice algal physiology, particularly of photosynthetic health in response to environmental change, will help improve predictions of productivity in the most productive ocean on this planet. Algal tolerance to increasing PAR, UV-B and temperature is remarkable, and this ability could be crucial in the context of future climate change. The productivity of these autotrophic microorganisms strongly influences secondary production that ties their fate to that of all other life in the Southern Ocean.</p>

Effects of temperature and pCO2 on the respiration, biomineralization and photophysiology of the giant clam Tridacna maxima

Such as many other reef organisms, giant clams are today confronted to global change effects and can suffer mass bleaching or mortality events mainly related to abnormally high seawater temperatures. Despite its strong ecological and socio-economical importance, its responses to the two most alarming threats linked to global change (i.e., ocean warming and acidification) still need to be explored. We investigated physiological responses of 4-years-old Tridacna maxima specimens to realistic levels of temperature and partial pressure of carbon dioxide (pCO2) (+1.5°C and +800 μatm of CO2) predicted for 2100 in French Polynesian lagoons during the warmer season. During a 65-days crossed-factor experiment, individuals were exposed to two temperatures (29.2°C; 30.7°C) and two pCO2 (430 µatm; 1212 µatm) conditions. Impact of each parameter and their potential synergetic effect were evaluated on respiration, biomineralization and photophysiology. Kinetics of thermal and acidification stress were evaluated by performing measurements at different times of exposure (29, 41, 53, 65 days). At 30.7°C, the holobiont O2 production, symbiont photosynthetic yield, and density were negatively impacted. High pCO2 had a significant negative effect on shell growth rate, symbiont photosynthetic yield and density. Shell microstructural modifications were observed from 41 days in all temperature and pCO2 conditions. No significant synergetic effect was found. Today thermal conditions (29.2°C) appeared to be sufficiently stressful to induce a host acclimatization process. All these observations indicate that temperature and pCO2 are both forcing variables affecting T. maxima physiology and jeopardize its survival under environmental conditions predicted for the end of this century.

Fruit yield and gas exchange in bell peppers after foliar application of boron, calcium, and Stimulate

ABSTRACT The objective of this study was to evaluate the effect of the isolated and combined foliar application of boron, calcium, and the plant growth regulator Stimulate on fruit yield and gas exchange in bell peppers. The evaluated treatments were boron, calcium, Stimulate, boron + calcium, boron + Stimulate, calcium + Stimulate, boron + calcium + Stimulate, and control (water). The study was performed in complete randomized block design with three replicates. The applications were performed biweekly on the plant leaves from the beginning of flowering (December 21, 2013) until March 1, 2014. The analyzed gas exchange characteristics were photosynthetic yield, internal CO2 concentration, and transpiration rate. The evaluated agronomic characteristics were number and yield of marketable and non-marketable fruits, and the average mass, volume, and firmness of commercial fruits. The foliar application of boron from the beginning of flowering increased the photosynthetic yield and the yield of marketable fruits cultivated in the field. The foliar application of calcium and Stimulate did not improve gas exchange and fruit yield. The most common effects of boron were an increase in the number of marketable fruits. Moreover, foliar spraying with calcium from the beginning of flowering increased the firmness of commercial fruits

Abundance and physiology of dominant soft corals linked to water quality in Jakarta Bay, Indonesia

Declining water quality is one of the main reasons of coral reef degradation in the Thousand Islands off the megacity Jakarta, Indonesia. Shifts in benthic community composition to higher soft coral abundances have been reported for many degraded reefs throughout the Indo-Pacific. However, it is not clear to what extent soft coral abundance and physiology are influenced by water quality. In this study, live benthic cover and water quality (i.e. dissolved inorganic nutrients (DIN), turbidity (NTU), and sedimentation) were assessed at three sites (< 20 km north of Jakarta) in Jakarta Bay (JB) and five sites along the outer Thousand Islands (20–60 km north of Jakarta). This was supplemented by measurements of photosynthetic yield and, for the first time, respiratory electron transport system (ETS) activity of two dominant soft coral genera,Sarcophytonspp. andNephtheaspp. Findings revealed highly eutrophic water conditions in JB compared to the outer Thousand Islands, with 44% higher DIN load (7.65 μM/L), 67% higher NTU (1.49 NTU) and 47% higher sedimentation rate (30.4 g m−2d−1). Soft corals were the dominant type of coral cover within the bay (2.4% hard and 12.8% soft coral cover) compared to the outer Thousand Islands (28.3% hard and 6.9% soft coral cover). Soft coral abundances, photosynthetic yield, and ETS activity were highly correlated with key water quality parameters, particularly DIN and sedimentation rates. The findings suggest water quality controls the relative abundance and physiology of dominant soft corals in JB and may thus contribute to phase shifts from hard to soft coral dominance, highlighting the need to better manage water quality in order to prevent or reverse phase shifts.

Toxicity of engineered copper (Cu0) nanoparticles to the green alga Chlamydomonas reinhardtii

Environmental context Engineered copper nanoparticles are presently under development for various uses and may thus be finally released into the aquatic environment. Copper is well known to be both an essential and a toxic element for aquatic organisms. Here, we investigate the toxicity of copper nanoparticles to a green alga and compare it with the toxicity of dissolved copper. Abstract The toxicity of carbon-coated copper nanoparticles (CuNPs) to the unicellular green alga Chlamydomonas reinhardtii was investigated and compared with effects of dissolved Cu2+. The CuNPs with an original size of 6–7nm rapidly agglomerated in the medium to average particle sizes of 140–200nm. Dissolved Cu from CuNPs increased over 2h to 1–2% of total Cu. The photosynthetic yield of C. reinhardtii strongly decreased after exposure for 1 or 2h to dissolved CuII in the concentration range 0.1–10μM, whereas this decrease occurred in the total Cu concentration range 1–100μM after exposure to CuNPs. Effects of CuNPs were compared with those of dissolved CuII on the basis of dissolution experiments. CuNP effects on photosynthetic yield were similar or somewhat stronger for the same dissolved Cu2+ concentration. Addition of EDTA as a strong ligand for CuII suppressed the toxicity of dissolved CuII and of CuNPs. These results thus indicate effects on the algae are mostly from free Cu2+.