Saturating Irradiance Research Articles

Vulnerability of kelp, Ecklonia radiata, to persistent nitrogen pollution and coastal darkening

Coastal darkening is expected to have pervasive impacts on benthic primary producers. However, the effects of nitrogen enrichment, an often-co-occurring stressor, on benthic primary producers and their functions is less clear. This study investigates the interactive effects of coastal darkening and nitrogenous eutrophication, including nitrogen source (NH4+ vs. NO3−), on the function of the kelp Ecklonia radiata. First, an in-situ experiment was used to assess the differential impacts of NH4+ and NO3− pulse enrichment on the photosynthetic performance and pH modulation capacity of E. radiata. Second, a laboratory experiment was used to assess the longer-term impacts of nitrogen enrichment under low-light conditions mimicking coastal darkening on service provisioning, including photosynthetic performance, pH modulation, nutrient uptake and growth. While pulse nitrogen enrichment had no impacts on the photosynthetic performance of E. radiata in-situ, persistent exposure to either NH4+ or NO3− acted as a stressor to sporophytes as indicated by elevated rates of dark respiration and lamina erosion and reduced photosynthetic efficiency and growth rates. Furthermore, low-light conditions elicited reduced photosynthetic capacity at saturating irradiance, which extended to a reduction in the extent of pH modulation, and significantly increased lamina erosion. While the two stressors appeared to act on distinct parameters, ultimately, both darkening and eutrophication directly reduced net primary production, especially when in combination. These results demonstrate the negative interactive effects of coastal darkening and eutrophication on E. radiata function, while suggesting a vulnerability of E. radiata to even moderate levels of persistent nitrogen enrichment. This vulnerability highlights the need to consider environmental conditions during kelp conservation and restoration, and when attempting to valorise kelp ecophysiology for nature-based solutions.

Microscale sampling of the coral gastrovascular cavity reveals a gut-like microbial community

Animal guts contain numerous microbes, which are critical for nutrient assimilation and pathogen defence. While corals and other Cnidaria lack a true differentiated gut, they possess semi-enclosed gastrovascular cavities (GVCs), where vital processes such as digestion, reproduction and symbiotic exchanges take place. The microbiome harboured in GVCs is therefore likely key to holobiont fitness, but remains severely understudied due to challenges of working in these small compartments. Here, we developed minimally invasive methodologies to sample the GVC of coral polyps and characterise the microbial communities harboured within. We used glass capillaries, low dead volume microneedles, or nylon microswabs to sample the gastrovascular microbiome of individual polyps from six species of corals, then applied low-input DNA extraction to characterise the microbial communities from these microliter volume samples. Microsensor measurements of GVCs revealed anoxic or hypoxic micro-niches, which persist even under prolonged illumination with saturating irradiance. These niches harboured microbial communities enriched in putatively microaerophilic or facultatively anaerobic taxa, such as Epsilonproteobacteria. Some core taxa found in the GVC of Lobophyllia hemprichii from the Great Barrier Reef were also detected in conspecific colonies held in aquaria, indicating that these associations are unlikely to be transient. Our findings suggest that the coral GVC is chemically and microbiologically similar to the gut of higher Metazoa. Given the importance of gut microbiomes in mediating animal health, harnessing the coral “gut microbiome” may foster novel active interventions aimed at increasing the resilience of coral reefs to the climate crisis.

A short-circuited photo-assisted electrochemical cell for wastewater treatment

An economically attractive and highly efficient electrochemical cell is fabricated by connecting a carbon felt (CF) and a steel plate (S). Using this configuration, a photo-stimulated (CF/S) arrangement promotes photo-assisted Fenton reactions that result in the degradation of recalcitrant pollutants in water. As opposed to electro-Fenton reports that describe systems with externally polarized electrodes or photo-Fenton systems that utilize iron modified carbon substrates, this work proposes a short-circuited CF/S arrangement that does not require an external potential source. By following the color removal of a dye solution and the chromatography analysis of an emergent contaminant (sulfamethoxazole (SMX)), it was found that the highest efficiencies for the production of oxidative species are observed for tests performed under O2 saturation and UV light irradiation. Under these conditions, the CF/S arrangement achieves 97 % degradation of SMX (after 60 min) and 40 % of total organic carbon (TOC) removal after 240 min. Interestingly however, the CF/S arrangement also revealed a notable efficiency when anoxic and dark conditions were employed. We postulate that in this case, •OH radicals are produced by means of Fenton-like reactions and in order to support this interpretation, cyclic voltammetry and scanning electronic microscopy (SEM) and X-ray diffraction spectroscopy (XRD) measurements were carried out. The resulting data confirmed a Fenton-like mechanism that was further supported by the detection of •OH radical species that was assessed using coumarin absorption data. This study demonstrates that the CF/S cell is a promising approach for a novel photo-assisted Fenton wastewater treatment.

The effect of irradiance versus light dose on the antioxidant activity of two strains of Ulva lacinulata

Abstract The genus Ulva, described as a good source of antioxidants known for its antibacterial properties and associated with the capacity to adapt to different environments and high growth rates, has justified the increasing interest in its large-scale production. While extensive research has been done on optimizing the extraction of Ulva’s bioactive compounds, few studies were conducted on increasing or optimizing antioxidant activity (AA) of Ulva spp. during cultivation. Our study aimed to investigate an optimization method of Ulva lacinulata by testing the impact of light dose and irradiance on its AA. Two geographically different strains (NE-Atlantic and Mediterranean) were observed for 5 days under two irradiances (70 or 185 µmol photons m−2 s−1) with the same light dose (4 mol photons m−2 d−1). Samples were collected at different times (0, 3, 24, 48 and 120 h) to evaluate their antioxidant activity (with 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) radical decolorization assay) and photosynthetic performance (with Pulse Amplitude Modulated fluorometer). A strain-dependent response was observed in the NE-Atlantic strain which had significantly higher AA after 5 days (89 %) under the photosynthetic saturating irradiance, while the Mediterranean strain was not impacted, suggesting that light dose may significantly affect AA in certain Ulva spp.

Phosphorus limitation combined with aluminum triggers synergistic responses on the freshwater microalgae Raphidocelis subcapitata (Chlorophyceae)

In the environment, algae are exposed to several stressors such as limitation of essential nutrients and excess of toxic substances. It is well known the importance of phosphorus (P) supply for healthy metabolism of algae and impacts at this level can affect the whole aquatic trophic chain. Aluminum (Al) is the most abundant metal on Earth and it is toxic to different trophic levels. Processes related to P and Al assimilation still need to be clarified and little is known about the responses of microalgae exposed to the two stressors simultaneously. We evaluated the effects of environmental concentrations of Al and P limitation, isolated and in combination, on growth, pigment production and photosynthesis of the freshwater microalga Raphidocelis subcapitata. Both stressors affected cell density, chlorophyll a, carotenoids, and maximum quantum yield. Al did not affect any other evaluated parameter, while P limitation affected parameters related to the dissipation of heat by algae and the maximum electron transport rate, decreasing the saturation irradiance. In the combination of both stressors, all parameters evaluated were affected in a synergistic way, i.e., the results were more harmful than expected considering the responses to isolated stressors. Our results indicate that photoprotection mechanisms of algae were efficient in the presence of both stressors, avoiding damages to the photosynthetic apparatus. In addition, our data highlight the higher susceptibility of R. subcapitata to Al in P-limited conditions.

Growth and photosynthetic physiology of holopelagic Sargassum (Phaeophyceae) under laboratory conditions

SummarySpecies of holopelagic Sargassum are responsible for Caribbean golden tides, commonly known as ‘Sargassum events’. These events mainly comprise Sargassum fluitans and Sargassum natans I, which are exposed to high levels of irradiance, but also self‐shading within their floating masses. In this study, we grew S. fluitans and S. natans I and acclimated them to low‐light conditions at 23°C in the laboratory to explore their responses to increasing light intensities. Photosynthesis, respiration, growth, and pigment content were evaluated over 3 weeks. S. fluitans and S. natans I photoacclimate to higher irradiances by decreasing their chlorophyll a and c contents. An increase in maximum photosynthesis and respiration rates was observed under high light, although differences occurred in the saturation irradiance and the initial slope of the photosynthesis versus irradiance curve. These adjustments were reflected in S. fluitans daily growth (from 2% to 7% d−1 at low to high light, respectively) and tissue nitrogen content (1.6–2.7%) but were absent in S. natans I (~1% d−1). The photosynthetic physiology of S. fluitans under these conditions suggests lower light requirements without compromising growth; however, under high light a higher photosynthetic performance was observed. Combining physiological and growth studies in holopelagic Sargassum species will serve as a baseline to understand and explain the success and overgrowth of these species along the Caribbean coast.

Temperature sensitivity of detrital photosynthesis.

Kelp forests are increasingly considered blue carbon habitats for ocean-based biological carbon dioxide removal, but knowledge gaps remain in our understanding of their carbon cycle. Of particular interest is the remineralization of detritus, which can remain photosynthetically active. Here, we study a widespread, thermotolerant kelp (Ecklonia radiata) to explore detrital photosynthesis as a mechanism underlying temperature and light as two key drivers of remineralization. We used meta-analysis to constrain the thermal optimum (Topt) of E. radiata. Temperature and light were subsequently controlled over a 119-day ex situ decomposition experiment. Flow-through experimental tanks were kept in darkness at 15 °C or under a subcompensating maximal irradiance of 8 µmol photons m-2 s-1 at 15, 20 or 25 °C. Photosynthesis of laterals (analogues to leaves) was estimated using closed-chamber oxygen evolution in darkness and under a saturating irradiance of 420 µmol photons m-2 s-1. T opt of E. radiata is 18 °C across performance variables (photosynthesis, growth, abundance, size, mass and fertility), life stages (gametophyte and sporophyte) and populations. Our models predict that a temperature of >15 °C reduces the potential for E. radiata detritus to be photosynthetically viable, hence detrital Topt ≤ 15 °C. Detritus is viable under subcompensating irradiance, where it performs better than in darkness. Comparison of net and gross photosynthesis indicates that elevated temperature primarily decreases detrital photosynthesis, whereas darkness primarily increases detrital respiration compared with optimal experimental conditions, in which detrital photosynthesis can persist for ≥119 days. T opt of kelp detritus is ≥3 °C colder than that of the intact plant. Given that E. radiata is one of the most temperature-tolerant kelps, this suggests that photosynthesis is generally more thermosensitive in the detrital phase, which partly explains the enhancing effect of temperature on remineralization. In contrast to darkness, even subcompensating irradiance maintains detrital viability, elucidating the accelerating effect of depth and its concomitant light reduction on remineralization to some extent. Detrital photosynthesis is a meaningful mechanism underlying at least two drivers of remineralization, even below the photoenvironment inhabited by the attached alga.

Physiological differences among cryptic species of the Mediterranean crustose coralline alga Lithophyllum stictiforme (Corallinales, Rhodophyta)

ABSTRACT The crustose coralline alga Lithophyllum stictiforme is an important reef builder, forming coralligenous concretions in the Mediterranean Sea. This algal species complex is composed of eight cryptic species (or clades). The objective of our study was to compare light-dependent physiological processes within and between the two most abundant cryptic species (C1 and C4) of L. stictiforme from the Bay of Marseille (France). Physiological rates of respiration, photosynthesis and calcification were measured using incubation chambers under various irradiance levels and in the dark during the summer period. We compared the physiology of the C1 and C4 cryptic species of L. stictiforme among three algal groups: C1 (the most common in the Marseille area) from 28 m depth, C4 from the same site and depth, and C1 from a deeper site at 45 m depth. We found both interspecific (between C1 and C4) and intraspecific (within C1) physiological differences. Photosynthetic parameters showed acclimation to light (or depth) with higher values of initial slope of photosynthetic light response curve (α) and lower values of saturating irradiance (Ek) and compensating irradiance (Ec) for C1 from 45 m than for C1 and C4 from 28 m depth. At the shallower depth, significant physiological differences were observed between C1 and C4 with a higher value of maximum rate of gross photosynthesis (Pg max) in C4, suggesting better ability to grow under high irradiance. Light and dark calcification rates differed only between C4 from 28 m and C1 from 45 m depth, being intermediate in C1 from 28 m depth. On a 24 h basis, diel net calcification rates were significantly higher in specimens from the shallower waters than from the deeper waters. Physiological differences suggest physiological plasticity within the regionally dominant cryptic species C1 and species-specific physiological traits between the cryptic species C1 and C4.

Nonuniform salinity regulate leaf characteristics and improve photosynthesis of cherry tomatoes under high salinity

Cherry tomato (Lycopersicon esculentum var. cerasiforme) is a relatively salt-tolerant fruit and vegetable widely planted worldwide. In this study, the growth and physiological responses and the different regulatory of cherry tomatoes under high, low salinity, and partial root zone salinity conditions were investigated. Cherry tomatoes grown under nonuniform salinity (0/20, 0/100 mM NaCl) conditions in a split-root pot were compared with seedlings grown under uniform salinity (20, 100 mM NaCl) conditions, and their growth and physiological parameters were determined. Our results showed that the growth was not hindered under a low salinity (20 mM NaCl), and the fruit quality was improved without a yield reduction; this was caused by promoted root growth and better leaf function maintenance. The relief effects under the higher salt stress (100 mM NaCl) conditions were more significant than those under a lower salt stress condition (20 mM NaCl). Compared with uniform high salinity conditions, nonuniform salinity conditions could improve photosynthetic characteristics and maintain better leaf function. The apparent quantum efficiency (AQE), carboxylation efficiency (CE) and light saturation irradiance (LSP) increased, while the light compensation point (LCP) and CO2 compensation point (CCP) decreased; this enhanced the light energy and CO2 utilization. Chlorophyll content (Chl), including Chl a and b and the carotenoids (Car), and the chlorophyll fluorescence parameters, including the maximum quantum efficiency of photosystem II (PSII) reaction centers (Fv/Fm), the quantum efficiency of PSII (Y(II)) and electron transport rate through PSII (ETR), were increased; this significantly promoted the net photosynthetic rate (Pn) and water use efficiency (WUE). Compared with a uniform high salt stress treatment, the leaf relative water content (RWC) and water potential (Ψ) increased by 22.57% and 13.71%, respectively, the electrolyte leakage rate decreased by 36.13%, and the final yield increased by 2.89 times under a nonuniform high salinity treatment. These results indicated that nonuniform salinity conditions regulated the leaf water relations and the antioxidant system and maintained better anatomical structure to improve photosynthesis in cherry tomato under a high salinity environment. Finally, our results can aid in the improvement of tomato productivity from salt-affected lands.

Ocean Acidification Affects the Response of the Coastal Coccolithophore Pleurochrysis carterae to Irradiance.

The ecologically important marine phytoplankton group coccolithophores have a global distribution. The impacts of ocean acidification on the cosmopolitan species Emiliania huxleyi have received much attention and have been intensively studied. However, the species-specific responses of coccolithophores and how these responses will be regulated by other environmental drivers are still largely unknown. To examine the interactive effects of irradiance and ocean acidification on the physiology of the coastal coccolithophore species Pleurochrysis carterae, we carried out a semi-continuous incubation experiment under a range of irradiances (50, 200, 500, 800 μmol photons m-2 s-1) at two CO2 concentration conditions of 400 and 800 ppm. The results suggest that the saturation irradiance for the growth rate was higher at an elevated CO2 concentration. Ocean acidification weakened the particulate organic carbon (POC) production of Pleurochrysis carterae and the inhibition rate was decreased with increasing irradiance, indicating that ocean acidification may affect the tolerating capacity of photosynthesis to higher irradiance. Our results further provide new insight into the species-specific responses of coccolithophores to the projected ocean acidification under different irradiance scenarios in the changing marine environment.

Long-term preconditioning of the coral Pocillopora acuta does not restore performance in future ocean conditions

There is overwhelming evidence that tropical coral reefs are severely impacted by human induced climate change. Assessing the capability of reef-building corals to expand their tolerance limits to survive projected climate trajectories is critical for their protection and management. Acclimation mechanisms such as developmental plasticity may provide one means by which corals could cope with projected ocean warming and acidification. To assess the potential of preconditioning to enhance thermal tolerance in the coral Pocillopora acuta, colonies were kept under three different scenarios from settlement to 17 months old: present day (0.9 °C-weeks (Degree Heating Weeks), + 0.75 °C annual, 400 ppm pCO2) mid-century (2.5 °C-weeks, + 1.5 °C annual, 685 ppm pCO2) and end of century (5 °C-weeks, + 2 °C annual, 900 ppm pCO2) conditions. Colonies from the present-day scenario were subsequently introduced to the mid-century and end of century conditions for six weeks during summer thermal maxima to examine if preconditioned colonies (reared under these elevated conditions) had a higher physiological performance compared to naive individuals. Symbiodiniaceae density and chlorophyll a concentrations were significantly lower in mid-century and end of century preconditioned groups, and declines in symbiont density were observed over the six-week accumulated heat stress in all treatments. Maximum photosynthetic rate was significantly suppressed in mid-century and end of century preconditioned groups, while minimum saturating irradiances were highest for 2050 pre-exposed individuals with parents originating from specific populations. The results of this study indicate preconditioning to elevated temperature and pCO2 for 17 months did not enhance the physiological performance in P. acuta. However, variations in trait responses and effects on tolerance found among treatment groups provides evidence for differential capacity for phenotypic plasticity among populations which could have valuable applications for future restoration efforts.

Effects of light quality and intensity on growth and bromoform content of the red seaweed Asparagopsis taxiformis

AbstractSpecies of the genus Asparagopsis are rich in halogenated bioactive compounds, particularly bromoform. Its use as a feed additive in ruminant livestock drastically decreases the animal’s methane production, thereby reducing the industry’s environmental impact. Addressing the high demand for Asparagopsis biomass requires the understanding of the culture conditions that promote higher growth rates and bromoform content. Here we evaluated how different light quality combinations (High-Blue:Red, Medium Blue:Red, High-Blue:Green:Red, and White) and four light intensities (30, 60, 90 and 120 μmol photons m−2 s−1) affect the growth and bromoform content of the Asparagopsis taxiformis tetrasporophyte in indoor tumbling cultures at two biomass densities. We also assessed the effect of light intensity on the photosynthetic response by measuring oxygen evolution rates. Light spectra containing intermediate wavelengths promoted higher growth, regardless of biomass density. Of the different light qualities tested, white light promoted the highest bromoform content. Increasing light intensity led to a positive response in A. taxiformis growth. However, the photosynthetic parameters estimated showed that the two higher light intensity treatments were above the saturation irradiance, for both culture densities. This, along with the observed development of contamination, suggests that long-term cultures of A. taxiformis should be maintained at light intensities no higher than 60 μmol photons m−2 s−1. In addition, we found that exposing cultures to higher irradiances does not guarantee a bromoform-richer biomass. These results offer valuable insights for optimizing biomass and bioactive compound production in indoor cultures of the Asparagopsis genus.

Effect of PAR irradiance intensity on Phaeocystis antarctica (Prymnesiophyceae) growth and DMSP, DMSO, and acrylate concentrations.

Phaeocystis antarctica forms extensive spring blooms in the Southern Ocean that coincide with high concentrations of dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO), dimethylsulfide (DMS), and acrylate. We determined how concentrations of these compounds changed during the growth of axenic P. antarctica cultures exposed to light-limiting, sub-saturating, and saturating PAR irradiances. Cellular DMSP concentrations per liter cell volume (CV) ranged between 199 and 403 mmol · LCV -1 , with the highest concentrations observed under light-limiting PAR. Cellular acrylate concentrations did not change appreciably with a change in irradiance level or growth, ranging between 18 and 45 mmol · LCV -1 , constituting an estimated 0.2%-2.8% of cellular carbon. Both dissolved acrylate and DMSO increased substantially with irradiance during exponential growth on a per-cell basis, ranging from 0.91 to 3.15 and 0.24 to 1.39 fmol · cell-1 , respectively, indicating substantial export of these compounds into the dissolved phase. Average cellular DMSO:DMSP ratios increased 7.6-fold between exponential and stationary phases of batch growth, with a 3- to 13-fold increase in cellular DMSO likely formed from abiotic reactions of DMSP and DMS with reactive oxygen species (ROS). At mM levels, cellular DMSP and acrylate are proposed to serve as de facto antioxidants in P. antarctica not regulated by oxidative stress or changes in ROS. Instead, cellular DMSP concentrations are likely controlled by other physiological processes including an overflow mechanism to remove excess carbon via acrylate, DMS, and DMSO during times of unbalanced growth brought on by physical stress or nutrient limitation. Together, these compounds should aid P. antarctica in adapting to a range of PAR irradiances by maintaining cellular functions and reducing oxidative stress.

Taxonomic and Morpho-Functional Photosynthetic Patterns of 18 Intertidal Macroalgal Species in the Guangdong–Hong Kong–Macao Greater Bay Area, China

Macroalgae provide food for microbial, meio- and macro-faunal communities in coastal ecosystems, thus mediating nutrient dynamics and functions in these ecosystems. Because of this vital role, it is important to clarify physiological information about macroalgae as it reflects their growth potential in the field. In this study, we examined the biomass, pigment content, and photosynthetic O2 evolution rate versus irradiance curves of 18 macroalgal species from the intertidal zone of the Guangdong–Hong Kong–Macao Greater Bay Area, China, and investigated their photosynthetic patterns in relation to phyla characteristics, morphology, and growth locations. The results showed that green algae had the highest maximum photosynthetic O2 evolution rate (Pmax), light utilization efficiency (α), and dark respiration (Rd) among the three macroalgal phyla; the sheet-like macroalgal species had the highest Pmax, α, and Rd among the four morphological categories. The macroalgal species in the upper intertidal zone showed higher Pmax and α and lower saturation irradiance (EK) and compensation irradiance (EC) than those species in the lower intertidal location. The PCA results showed that the biomass of sheet-like macroalgal species was positively correlated with factor PC1 (50.34%), and that of finely branched species was negatively correlated with factor PC2 (25.17%). In addition, our results indicate that the light absorption and utilization capabilities of macroalgae could determine whether they could dominate the intertidal zone and that their photosynthetic characteristics could be used as a potential indicator of their biomass distribution in the Greater Bay Area.

Photosynthesis-related responses of Chlorella sorokiniana (Trebouxiophyceae) to environmentally relevant concentrations of Cu nanoparticles

ABSTRACT Nanoparticles (NPs) are highly reactive particles that find a broad array of applications in society; as a result, they may accumulate in aquatic environments. Microalgae are the base of foodwebs and serve as surfaces for NPs, interacting and transporting them to higher trophic levels. We aimed at understanding the effects of environmentally significant and higher copper nanoparticles (Cu-NPs) concentrations on the photosynthetic performance of Chlorella sorokiniana, which included determining effective quantum yield (F’v/F’m), photochemical (Qp) and non-photochemical (NPQ) quenching, rapid light curves (RLC), light use efficiency (α), minimum saturation irradiance (Ek) and the maximum relative electron transport rate (ETRrmax), in addition to chlorophyll a content and cell viability. Dissolved Cu and free ionic Cu concentrations were determined, and dissolved Cu values were used as surrogate for nominal Cu-NPs concentrations. The experiments lasted 72 h and were carried out under controlled conditions. The results showed that cell viability and chlorophyll a decreased as Cu-NPs increased, but the opposite was obtained for the RLC parameters. Light saturation (Ek) and ETR increased as Cu-NPs concentrations increased in culture medium, but not the efficiency with which C. sorokiniana used the light. By showing that environmentally relevant Cu-NPs influenced C. sorokiniana metabolism, we add to the knowledge on the interactions between environmentally realistic Cu-NPs levels and phytoplankton cells.

Variation of the photosynthesis and respiration response of filamentous algae (Oedogonium) acclimated to averaged seasonal temperatures and light exposure levels

Filamentous algae (FA) have potential advantages over microalgae for wastewater treatment. However, their implementation at a large-scale is hindered by an inability to predict performance. This study compared the cellular responses (photosynthesis and respiration) and composition (pigments and photosystem proteins) of FA Oedogonium acclimatised to average summer and winter conditions (Melbourne, Australia). After seven days of acclimation the Chl a content of ‘summer acclimated’ (SA) algae was about half that of the ‘winter acclimated’ (WA) algae, which can be related to a cellular strategy to reduce photodamage under high light intensities. No statistically significant changes were observed in any identified proteins associated with photosystem PSII and the reaction centre of PSI. Transmission electron microscopy images revealed more prominent lipid bodies within the SA filaments than in WA filaments, but no discernible difference in the abundance of starch granules.Photosynthetic irradiance curves were compared for the SA and WA algae. Consistent with the differences in chlorophyll, the specific gross photosynthetic rate (μP, gross) was generally higher for the WA algae. The relative difference increased from around 2-fold at 15 °C to 3-fold at 25 °C, and then decreased to <1.5-fold at 30 °C and 35 °C. At all the tested temperatures, saturation irradiance levels were in the range of 75–500 μmol/m2·s. Photoinhibition was observed at 30 °C (above ∼300 μmol/m2·s) and was more severe at 35 °C (above ∼500 μmol/m2·s), with WA algae showing greater inhibition. In contrast, the respiration response was similar for the SA and WA algae. The study emphasises the significance of accounting for seasonal variations and their effects on biomass productivity and utilisation. The data obtained will enable the incorporation of acclimation and its effect on biochemistry and photosynthetic response into predictive models of FA performance in outdoor cultures.

A risk assessment on Zostera chilensis, the last relict of marine angiosperms in the South-East Pacific Ocean, due to the development of the desalination industry in Chile

Seagrasses, which are considered among the most ecologically valuable and endangered coastal ecosystems, have a narrowly limited distribution in the south-east Pacific, where Zostera chilensis is the only remaining relict. Due to water scarcity, desalination industry has grown in the last decades in the central-north coasts of Chile, which may be relevant to address in terms of potential impacts on benthic communities due to their associated high-salinity brine discharges to subtidal ecosystems. In this work, we assessed ecophysiological and cellular responses to desalination-extrapolable hypersalinity conditions on Z. chilensis. Mesocosms experiments were performed for 10 days, where plants were exposed to 3 different salinity treatments: 34 psu (control), 37 psu and 40 psu. Photosynthetic performance, H2O2 accumulation, and ascorbate content (reduced and oxidized) were measured, as well as relative gene expression of enzymes related to osmotic regulation and oxidative stress; these, at 1, 3, 6 and 10 days. Z. chilensis showed a decrease in photosynthetic parameters such as electron transport rate (ETRmax) and saturation irradiance (EkETR) under hypersalinity treatments, while non-photochemical quenching (NPQmax) presented an initial increment and a subsequent decline at 40 psu. H2O2 levels increased with hypersalinity, while ascorbate and dehydroascorbate only increased under 37 psu, although decreased along the experimental period. Increased salinities also triggered the expression of genes related to ion transport and osmolyte syntheses, but salinity-dependent up-regulated genes were mostly those related to the reactive oxygen species metabolism. The relict seagrass Z. chilensis has shown to withstand increased salinities that may be extrapolable to desalination effects in the short-term. As the latter is not fully clear in the long-term, and considering the restricted distribution and ecological importance, direct brine discharges to Z. chilensis meadows may not be recommended.

Species‐specific acclimatization capacity of key traits explains global vertical distribution of seagrass species

AbstractAimThe global vertical depth distribution of seagrass species remains poorly understood. Locally, the abundance and distribution of seagrasses is determined by light penetration, but at global levels each seagrass species has very distinct maximum distributional depth ranges, indicating that plant‐associated traits must also influence their specific depth ranges. Seagrass‐specific attributes, such as plant size or architecture, growth or reproductive strategy and their physiological and/or morphological acclimatization potential, have been suggested to be responsible for this variety of vertical distributions. We investigate here whether these species‐specific traits drive differences in the global maximum vertical distribution of seagrasses.LocationGlobal.Time periodPublications between 1982 and 2020.Major taxa studiedSeagrasses (order Alismatales).MethodsWe tested whether the species‐specific maximum vertical distribution of seagrasses can be predicted by (1) their rhizome diameter (a proxy for plant size); (2) their functional resilience (growth/reproductive strategy); or (3) their acclimatization capacity. For the last aspect, we used a systematic review followed by meta‐analytical approaches to select key seagrass traits that could potentially acclimatize to extreme light ranges across different seagrasses.ResultsWe found that vertical distribution is best explained by the species‐specific acclimatization capacity of various seagrass traits, including saturation irradiance (physiological trait), leaves per shoot (morphological trait) and above‐ground biomass (structural trait). In contrast, our results indicate no predictive power of seagrass size or growth/reproductive strategy on the vertical distribution of seagrasses.Main conclusionsAcross the globe, the ability of seagrass species to thrive at a wide range of depths is strongly linked to the species‐specific acclimatization capacity of key traits at different organizational levels.

Study of the growth and biochemical composition of 20 species of cyanobacteria cultured in cylindrical photobioreactors

BackgroundCyanobacteria are prokaryotic organisms with wide morphological and metabolic diversity. By means of photosynthesis, they convert inorganic compounds into biomolecules, which may have commercial interest. In this work, we evaluated 20 cyanobacterial strains regarding their physiological aspects such as growth, photosynthesis and biochemical composition, some of which are revealed here for the first time. The organisms were cultivated in cylindrical photobioreactors (CPBR) for 144 h and the biomass was obtained. The light inside cultures was constant throughout experimental time and maintained at the saturation irradiance (Ik) of each species. Culture pH was maintained within 7.8 and 8.4 by automatic CO2 bubbling. Growth rate, dry biomass, chlorophyll a, carotenoids, phycocyanin, proteins, carbohydrates, lipids, polyhydroxyalkanoate (PHA) and antioxidant activity were determined.ResultsThe proportionality of the biochemical composition varied among species, as well as the growth rates. Leptolyngbya sp. and Nostoc sp. (CCIBt3249) showed growth rates in the range of 0.7–0.8 d−1, followed by Rhabdorderma sp. (~ 0.6 d−1), and Phormidium sp. (~ 0.5 d−1). High carotenoid content was obtained in Rhabdoderma sp. (4.0 μg mL−1) and phycocyanin in Leptolyngbya sp. (60 μg mL−1). Higher total proteins were found in the genus Geitlerinema (75% DW), carbohydrates in Microcystis navacekii (30% DW) and lipids in Phormidium sp. (15% DW). Furthermore, Aphanocapsa holsatica showed the highest antioxidant activity (65%) and Sphaerocavum brasiliense, Microcystis aeruginosa, Nostoc sp. (CCIBt3249) and A. holsatica higher levels of PHA (~ 2% DW).ConclusionsThis study reports on the biochemical composition of cyanobacteria that can impact the biotechnology of their production, highlighting potential strains with high productivity of specific biomolecules.

Evaluating the effect of temperature on photosynthesis and respiration of articulated coralline algae using oxygen evolution and chlorophyll a fluorescence

Coralline algae form abundant and ecologically important submerged aquatic vegetation habitats throughout the world. However, algal performance is threatened by climate change and ocean acidification. Previous studies suggest that their photosynthetic performance will be compromised mainly at elevated temperatures. Understanding the impact of diverse climate change scenarios requires a clear and thorough comprehension of the photosynthetic response to temperature gradients. The objective of this study was to evaluate the short-term effect of temperature (10–35 °C) on the gross photosynthesis (GPS), respiration, and electron transport rates (ETRs) of 3 articulated coralline algae (Lithothrix aspergillum, Corallina officinalis, and Bossiella orbigniana) for a better understanding of their metabolism and to investigate the relationship between GPS and ETR as a function of temperature. The results showed that the coralline algal metabolism is highly sensitive to temperature, but responses were species-specific and can be related to their light adaptation/acclimation; the high-light-adapted L. aspergillum was least negatively affected. The photosynthesis to respiration ratio was optimal between 20 and 25 °C according to the local thermal regime but was significantly reduced toward higher temperatures, indicating strong carbon imbalances and highlighting the relevance of thermal stress for coralline algal performance. A strong correlation between GPS and ETR was found between 10 and 30 °C in all species, but both above saturation irradiances and at elevated temperatures (≥30 °C), a clear deviation from linearity occurred. This suggests that ETR is not a good proxy to estimate photosynthetic activity under light or thermal stress. This information should be useful for studies implementing global change scenarios and pulse amplitude modulated (PAM) fluorometry in coralline algae.