Saturating Irradiance Research Articles

Photochemical Efficiencies of Diatom Symbionts in Hospite in Amphistegina Gibbosa (foraminifera) Across Seasons in the Florida Keys, Usa

Abstract Benthic foraminiferal taxa that host algal endosymbionts can serve as model organisms in understanding photo-oxidative stress in environments where algal symbioses are prevalent. This study examined photochemical performance of the diatom symbionts within the foraminifer Amphistegina gibbosa. Data on bleaching prevalence and photochemical efficiency for photosystem II (PSII) were obtained from specimens collected at Tennessee Reef, Florida reef tract, USA, as close as logistically feasible to each equinox and solstice in 2012 and 2013. Specimens were collected at 6 m and 18 m depths, isolated, visually characterized, and assessed for maximum quantum yield of PSII using a pulse-amplitude modulated (PAM) fluorometer. Rapid-light curves (RLCs) were performed in the laboratory on specimens within a few hours of collection. Trials examined the effects of depth, sampling date, and degree of host bleaching. Consistent with field studies in the 1990s, proportions of A. gibbosa populations exhibiting visible loss of symbionts (i.e., “bleaching”) were lowest in December, with between-season and between-year differences in maxima. Maximum quantum yields ranged from 0.66–0.76. Significant differences between sampling dates were found at the 6 m site, with highest yields in winter and lowest in summer. At the 18 m site, maximum quantum yields differed both by sampling date and by degree of bleaching. Rapid light curves revealed that relative electron transport rates were highest in specimens exhibiting no visible symbiont loss; derived-photosynthetic parameters of α (initial slope of the RLC) and Ek (minimum saturating irradiance) did not differ significantly across different degrees of symbiont loss. Overall results indicate that even individuals exhibiting substantial symbiont loss retain some fully functional symbionts.

Individual and combined effects of fluoranthene, phenanthrene, mannitol and sulfuric acid on marigold (Calendula officinalis)

A study was conducted to characterize marigold stress response to polycyclic aromatic hydrocarbons (PAHs) (oxidative stress inducers) with and without sulfuric acid (S.Acid; pH 3) (acid-stress inducer), and to evaluate reactive oxygen species (ROS) scavenging activity of mannitol (Mann). Marigold (Calendula officinalis) seedlings were grown in a greenhouse and fumigated with fluoranthene (FLU), phenanthrene (PHE), Mann, and S.Acid individually and in various combinations for 40 days. Various physiological and biochemical parameters among others were analyzed using standard methods. The results revealed that fumigation of FLU induced oxidative stress to the plants via ROS generation leading to negative effects on photosynthesis at near saturating irradiance (Amax), stomatal conductance (Gs), internal carbon dioxide concentration (Ci), leaf water relations and chlorophyll pigments. Significant per cent inhibition of Amax (54%), Gs (86%) and Ci (32%), as well as per cent reductions in chlorophyll a (Chl.a) (33%), Chl.b (34%), and total chlorophyll (Tot. Chl) (48%) contents were recorded in FLU fumigated treatment in comparison to control. Combination of Mann with FLU scavenged the generated ROS and substantially lowered the oxidative stress on the plants hence all the measured parameters were not significantly different from control. PHE fumigation had varied effects on marigold plants and was not as deleterious as FLU. Combined fumigation of S.Acid with both the PAHs had significant negative effect on leaf water relations, and positive effect on fresh and turgid weight of the plants but had no effect on the other measured parameters. The lowest proline contents and highest catalase and ascorbate peroxidase activities in FLU fumigated plants further confirmed that oxidative stress was imposed via the generation of ROS. From the results, it is evident that Mann could be an efficient scavenger of ROS-generated by FLU in the marigold plants. We recommend Mann to be widely used for the protection of higher plants from FLU-generated stress in the urban areas.

Physiological Effects of Light Intensity on the Opportunistic Algae Ulva rigida C. Agardh (Chlorophyta)

Intertidal seaweeds exposed to strong fluctuation in light quantity and spectral light quality. Light plays an important role controlling seaweed growth and physiology. Therefore, we conducted a culture experiment to determine the physiological effects of light intensity on the opportunistic algae Ulva rigida C. Agardh. For this reason, samples were exposed to two different light intensities (55 µmol photons m -2 s -1 and 100 µmol photons m -2 s -1 ) and their some physiological features including photosynthetic performance, growth rate, pigment content, total protein and nitrate reductase activity were measured. According to our results, the maximum relative electron transport rate and saturation irradiance point were not significantly different between the treatments. On the other hand, relative growth rate, nitrate reductase activity and chlorophyll- a concentrations of U. rigida were significantly decreased under low light condition. Consequently, our data indicated that photosynthetic perfomance of Ulva rigida was not affected to treated light intensity, while growth and nitrogen metabolism were primarily controlled by light.

Moderate Increase in TCO2 Enhances Photosynthesis of Seagrass Zostera japonica, but Not Zostera marina: Implications for Acidification Mitigation

Photosynthesis and respiration are vital biological processes that shape the diurnal variability of carbonate chemistry in nearshore waters, presumably ameliorating (daytime) or exacerbating (nighttime) short-term acidification events, which are expected to increase in severity with ocean acidification (OA). Biogenic habitats such as seagrass beds have the capacity to reduce CO2 concentration and potentially provide refugia from OA. Further, some seagrasses have been shown to increase their photosynthetic rate in response to enriched total CO2 (TCO2). Therefore, the ability of seagrass to mitigate OA may increase as concentrations of TCO2 increase. In this study, we exposed native Zostera marina and non-native Zostera japonica seagrasses from Padilla Bay, WA (USA) to various levels of irradiance and TCO2. Our results indicate that the average maximum net photosynthetic rate (Pmax) for Z. japonica as a function of irradiance and TCO2 was 3x greater than Z. marina when standardized to chlorophyll (360 ± 33 μmol TCO2 mg chl-1 h-1 and 113 ± 10 μmol TCO2 mg chl-1 h-1, respectively). Additionally, Z. japonica increased its Pmax ~50% when TCO2 increased from ~1770 to 2051 μmol TCO2 kg-1. In contrast, Z. marina did not display an increase in Pmax with higher TCO2, possibly due to the variance of photosynthetic rates at saturating irradiance within TCO2 treatments (coefficient of variation: 30–60%) relative to the range of TCO2 tested. Our results suggest that Z. japonica can affect the OA mitigation potential of seagrass beds, and its contribution may increase relative to Z. marina as oceanic TCO2 rises. Further, we extended our empirical results to incorporate various biomass to water volume ratios in order to conceptualize how these additional attributes affect changes in carbonate chemistry. Estimates show that the change in TCO2 via photosynthetic carbon uptake as modeled in this study can produce positive diurnal changes in pH and aragonite saturation state that are on the same order of magnitude as those estimated for whole seagrass systems. Based on our results, we predict that seagrasses Z. marina and Z. japonica both have the potential to produce short-term changes in carbonate chemistry thus offsetting anthropogenic acidification when irradiance is saturating.

Light response in alpine species: Different patterns of physiological plasticity

Light is one of the major stress factors that alpine plants face. Phenotypic plasticity of photoprotection mechanisms was analyzed in six alpine species growing in the Teide National Park (Canary Islands, Spain) at two different light exposures: full sunlight and 50% shading. Measurements of absorptance and chlorophyll fluorescence parameters obtained from induction kinetics and rapid light curves were performed. The studied species displayed high modulation capacity in most of the analyzed physiological traits, such as avoidance of light absorption, partitioning of the absorbed energy into consumption and/or dissipation, and its resultant resistance to high light, although in some cases opposite directions were observed. Three different response patterns were reported: 1) high adaptive plasticity response to light exposure, such as in Spartocytisus supranubius and Scrophularia glabrata, which could develop a high non-photochemical quenching or face higher levels of saturating irradiation at full sunlight exposure, 2) high modulation response in a non-adaptive direction, as found in Adenocarpus viscosus, which decreased its non-photochemical quenching at high irradiation, and in Pterocephalus lasiospermus, which increased photodamage of PSII and started decreasing ETR at low PPFD when developing at high light exposition, and 3) low physiological plasticity, as in Echium wildpretii, which could only modulate its leaf absorptance. Our data suggest that phenotypic plasticity should not always be considered as an adaptive response in nature.

Effects of temperature and PAR on the photosynthesis of Kappaphycus sp. (Solieriaceae, Rhodophyta) from Okinawa, Japan, at the northern limit of native Kappaphycus distribution in the western Pacific

:The successful cultivation of the Japanese Kappaphycus sp. (K. striatus auctorum japonicorum) in Okinawa, Japan, requires the detailed understanding of its physiological response to environmental factors. The photosynthetic performance of this native red alga was investigated under a variety of temperature and photosynthetic active radiation (PAR) conditions by employing methods based on pulse amplitude modulation–chlorophyll fluorometry and dissolved oxygen sensors. The net photosynthesis–irradiance (P–E) curve at 24°C revealed that the compensation (Ec) and saturation (Ek) irradiances were 26 [95% Bayesian prediction interval (BPI), 11–29 μmol photons m−2 s−1] and 140 (95% BPI, 98–192) μmol photons m−2 s−1, respectively. No inhibition in oxygenic evolution and quantum yield was observed at the highest PAR of 1000 μmol photons m−2 s−1. However, the ability of the seaweed to recover from photoinhibition was complicated following long-term PAR exposures at 18°C but not at 28°C. The Japanese Kappaphycus sp. showed photosynthetic optima at 17.4–29.1°C, derived from the Fv/Fm and gross photosynthesis–temperature models, respectively. These characteristic results were closely related to the depth of its habitat and its northern limit of distribution in Okinawa as influenced primarily by seawater temperature. Findings of this study should be useful to the development of culture systems adapted for subtropical waters, whether for commercial purpose or for conservation of natural communities.

PHOTOPHYSIOLOGICAL TOLERANCE OF ALGAL SYMBIONTS OFARCHAIAS ANGULATUSTO TEMPERATURE EXTREMES

Larger benthic foraminifers that host algal symbionts are abundant in the meiobenthos of coral-reef environments in tropical and subtropical regions worldwide. This study investigated photophysiological responses of chlorophyte endosymbionts of Archaias angulatus , both in hospite and in cytoplasm extracted from the host shell, across a range of temperature conditions (4.4–33.9°C) using pulse amplitude modulated chlorophyll fluorometry and chlorophyll a measurements. Typical mean yields (F v /F m ) for symbionts in hospite were 0.6–0.7, and for extracted symbionts were 0.5–0.6. The trends in all of the photophysiological parameters measured or calculated (yield [F v /F m ], photoefficiency [α], maximum electron transport rate [ETR max ], and minimum saturating irradiance [E k ]) were similar between in hospite and extracted symbionts. With the exception of E k , the in hospite values were somewhat higher than those for the extracted symbionts. Though chlorophyll a negatively correlated with temperature, individual variability was high. Light curves based on median relative Electron Transport Rate (rETR) and associated photophysiologically-derived parameters were consistent with results from previous studies of the A. angulatus holobiont based on O 2 and CO 2 production or consumption, with ETR max at ∼200 μmol photon m −2 s −1 and photoinhibition >500 μmol photon m −2 s −1 . Photoinhibition occurred at temperatures >31.0°C. We observed survival of the holobiont and minimal reduction in symbiont photoefficiency at 4.4°C, revealing a lower thermal-tolerance range than had been previously reported for A. angulatus .

Spring phytoplankton communities of the Labrador Sea (2005–2014): pigment signatures, photophysiology and elemental ratios

Abstract. The Labrador Sea is an ideal region to study the biogeographical, physiological, and biogeochemical implications of phytoplankton community composition due to sharp transitions between distinct water masses across its shelves and central basin. We have investigated the multi-year (2005–2014) distributions of late spring and early summer (May to June) phytoplankton communities in the various hydrographic settings of the Labrador Sea. Our analysis is based on pigment markers (using CHEMTAX analysis), and photophysiological and biogeochemical characteristics associated with each phytoplankton community. Diatoms were the most abundant group, blooming first in shallow mixed layers of haline-stratified Arctic shelf waters. Along with diatoms, chlorophytes co-dominated at the western end of the section (particularly in the polar waters of the Labrador Current (LC)), whilst Phaeocystis co-dominated in the east (modified polar waters of the West Greenland Current (WGC)). Pre-bloom conditions occurred in deeper mixed layers of the central Labrador Sea in May, where a mixed assemblage of flagellates (dinoflagellates, prasinophytes, prymnesiophytes, particularly coccolithophores, and chrysophytes/pelagophytes) occurred in low-chlorophyll areas, succeeding to blooms of diatoms and dinoflagellates in thermally stratified Atlantic waters in June. Light-saturated photosynthetic rates and saturation irradiance levels were highest at stations where diatoms were the dominant phytoplankton group ( > 70 % of total chlorophyll a), as opposed to stations where flagellates were more abundant (from 40 up to 70 % of total chlorophyll a). Phytoplankton communities from the WGC (Phaeocystis and diatoms) had lower light-limited photosynthetic rates, with little evidence of photoinhibition, indicating greater tolerance to a high light environment. By contrast, communities from the central Labrador Sea (dinoflagellates and diatoms), which bloomed later in the season (June), appeared to be more sensitive to high light levels. Ratios of accessory pigments (AP) to total chlorophyll a (TChl a) varied according to phytoplankton community composition, with polar phytoplankton (cold-water related) having lower AP : TChl a. Polar waters (LC and WGC) also had higher and more variable particulate organic carbon (POC) to particulate organic nitrogen (PON) ratios, suggesting the influence of detritus from freshwater input, derived from riverine, glacial, and/or sea ice meltwater. Long-term observational shifts in phytoplankton communities were not assessed in this study due to the short temporal frame (May to June) of the data. Nevertheless, these results add to our current understanding of phytoplankton group distribution, as well as an evaluation of the biogeochemical role (in terms of C : N ratios) of spring phytoplankton communities in the Labrador Sea, which will assist our understanding of potential long-term responses of phytoplankton communities in high-latitude oceans to a changing climate.

Behavioral and physiological photoresponses to light intensity by intertidal microphytobenthos

Behavioral and physiological responses to light are the two major mechanisms by which natural microphytobenthic assemblages adapt to the intertidal environment and protect themselves from light stress. The present study investigated these photoresponses with different light intensities over 8 h of illumination, and used a specific inhibitor (Latrunculin A, Lat A) for migration to compare migratory and non-migratory microphytobenthos (MPB). Photosynthetic activity was detected using rapid light curves and induction curves by chlorophyll fluorescence. It showed distinct variation in migratory responses to different light intensities; high light induced downward migration to avoid photoinhibition, and low and medium light (50–250 μmol/(m2·s)) promoted upward migration followed by downward migration after certain period of light exposure. No significant difference in non-photochemical quenching (NPQ) or PSII maximal quantum yield (Fv/Fm) was detected between low and medium light irradiance, possibly indicating that only high light influences the photosynthetic capability of MPB. Decreased photosynthetic activity, indicated by three parameters, the maximum relative electron transport rate (rETR max), minimum saturating irradiance (Ek) and light utilization coefficient (α), was observed in MPB after exposure to prolonged illumination under low and medium light. Lat A effectively inhibited the migration of MPB in all light treatments and induced lower Fv/Fm under high light (500 and 100 μmol/(m2·s)) and prolonged illumination at 250 μmol/(m2·s), but did not significantly influence Fv/Fm under low light (0–100 μmol/(m2·s)) or NPQ. The increase of NPQ in Lat A treatments with time implied that the MPB assemblages can recover their physiological photoprotection capacity to adapt to light stress. Non-migratory MPB exhibited lower light use efficiency (lower α) and lower maximum photosynthetic capacity (lower rETR max) than migratory MPB under light intensities above 250 μmol/(m2·s) after 4.0 h illumination.

Nutrients influence the thermal ecophysiology of an intertidal macroalga: multiple stressors or multiple drivers?

Urbanization of coastlines is leading to increased introduction of nutrients from the terrestrial environment to nearshore habitats. While such nutrient influxes can be detrimental to coastal marine organisms due to increased eutrophication and subsequent reduced oxygen, they could also have positive effects (i.e., increased food availability) on species that are nitrogen-limited such as macroalgae. Nutrient enrichment in this environment thus has the potential to counteract some of the negative impacts of increasing temperatures, at least for some species. Characterizing the physiological response of organisms to simultaneous changes in multiple drivers such as these is an important first step in predicting how global climate change may lead to ecological responses at more local levels. We evaluated how nutrient enrichment (i.e., nitrogen availability) affected the growth of Fucus vesiculosus, a foundational macroalgal species in the North Atlantic rocky intertidal zone, and found that nutrient-enriched algal blades showed a significant increase in tissue growth compared to individuals grown under ambient conditions. We further quantified net photosynthesis by ambient and nutrient-enriched tissues at saturating irradiance over a range of temperature conditions (6-30°C). Respiration was unaffected by nutrient treatment; however, there was a significant increase in photosynthetic oxygen production for nutrient-enriched tissue compared to ambient, but only at elevated (≥18°C) temperatures. This study contributes to a growing body of literature showing the complexity of responses to changes in multiple drivers, and highlights the importance of studying the impacts of global climate change within the context of more local environmental conditions.

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 1000ppm pCO2) under normal and low light conditions (200 and 40μmol photons m−2s−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.

Proteome Analysis Reveals Extensive Light Stress-Response Reprogramming in the Seagrass Zostera muelleri (Alismatales, Zosteraceae) Metabolism.

Seagrasses are marine ecosystem engineers that are currently declining in abundance at an alarming rate due to both natural and anthropogenic disturbances in ecological niches. Despite reports on the morphological and physiological adaptations of seagrasses to extreme environments, little is known of the molecular mechanisms underlying photo-acclimation, and/or tolerance in these marine plants. This study applies the two-dimensional isoelectric focusing (2D-IEF) proteomics approach to identify photo-acclimation/tolerance proteins in the marine seagrass Zostera muelleri. For this, Z. muelleri was exposed for 10 days in laboratory mesocosms to saturating (control, 200 μmol photons m−2 s−1), super-saturating (SSL, 600 μmol photons m−2 s−1), and limited light (LL, 20 μmol photons m−2 s−1) irradiance conditions. Using LC-MS/MS analysis, 93 and 40 protein spots were differentially regulated under SSL and LL conditions, respectively, when compared to the control. In contrast to the LL condition, Z. muelleri robustly tolerated super-saturation light than control conditions, evidenced by their higher relative maximum electron transport rate and minimum saturating irradiance values. Proteomic analyses revealed up-regulation and/or appearances of proteins belonging to the Calvin-Benson and Krebs cycle, glycolysis, the glycine cleavage system of photorespiration, and the antioxidant system. These proteins, together with those from the inter-connected glutamate-proline-GABA pathway, shaped Z. muelleri photosynthesis and growth under SSL conditions. In contrast, the LL condition negatively impacted the metabolic activities of Z. muelleri by down-regulating key metabolic enzymes for photosynthesis and the metabolism of carbohydrates and amino acids, which is consistent with the observation with lower photosynthetic performance under LL condition. This study provides novel insights into the underlying molecular photo-acclimation mechanisms in Z. muelleri, in addition to identifying protein-based biomarkers that could be used as early indicators to detect acute/chronic light stress in seagrasses to monitor seagrass health.

Response to experimental warming in northern eelgrass populations: comparison across a range of temperature adaptations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 589:59-72 (2018) - DOI: https://doi.org/10.3354/meps12439 Response to experimental warming in northern eelgrass populations: comparison across a range of temperature adaptations P. Beca-Carretero1,2,*, B. Olesen3, N. Marbà1, D. Krause-Jensen4,5 1Department of Global Change Research, IMEDEA (CSIC-UIB), Institut Mediterrani d’Estudis Avancats, Miquel Marques 21, 07190 Esporles (Illes Balears), Spain 2Botany and Plant Science, School of Natural Sciences, and Ryan Institute, National University of Ireland Galway, University Road, Galway H91 TK33, Ireland 3Department of Bioscience, Aarhus University, Ole Worms Allé 1, Building 1135, 8000 Aarhus C, Denmark 4Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark 5Arctic Research Centre, Aarhus University, Ny Munkegade 114, Building 1540, 8000 Aarhus C, Denmark *Corresponding author: pedropersiobk@hotmail.es ABSTRACT: Global warming may exert diverging effects on eelgrass (Zostera marina L.) populations originating from the northern versus the central part of the distribution range and on populations growing at saturating versus limiting light. We experimentally examined growth and physiological temperature responses of 3 eelgrass populations adapted to different temperature regimes in subarctic Greenland (2 populations) and in Denmark (1 population). Shoots were incubated at 5 different temperatures (10, 15, 20, 25 and 28°C) for 15 to 16 d at a saturating irradiance (200 µmol m-2 s-1) and one of the populations was also incubated at a limited irradiance of 50 µmol m-2 s-1. All populations exhibited optimum temperatures of 20 to 25°C for photosynthesis and growth under saturating light, while light limitation reduced the optimum by 5 to 10°C. When compared at their respective in situ summer temperature (i.e. 10, 15 and 20°C), all populations exhibited similar relative growth rates, indicating a capacity for local adaptation. The 2 subarctic populations exhibited higher activation energy for growth and, hence, greater responsiveness to warming than the centrally located population. However, subarctic populations were also more sensitive to extreme high temperatures, showing faster increases in respiration rates and declines in photosynthesis. Sensitivity to warming varied across light conditions with light-limited plants being most vulnerable to extreme temperatures, causing a negative carbon budget. In conclusion, projected warming would stimulate the performance of subarctic eelgrass populations but could eventually compromise populations in the center of the distribution range, which currently grow close to their temperature optimum. KEY WORDS: Experimental warming · Latitude comparison · Production · Energy activation · Photosynthetic response · Greenland · Denmark · Seagrass · Zostera marina Full text in pdf format Supplementary material PreviousNextCite this article as: Beca-Carretero P, Olesen B, Marbà N, Krause-Jensen D (2018) Response to experimental warming in northern eelgrass populations: comparison across a range of temperature adaptations. Mar Ecol Prog Ser 589:59-72. https://doi.org/10.3354/meps12439 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 589. Online publication date: February 23, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Interactive effects of nutrient availability, temperature, and irradiance on photosynthetic pigments and color of the brown alga Undaria pinnatifida

Color is one of the important factors that determine the commercial value of cultivated marine macroalgae such as the brown alga Undaria pinnatifida (Laminariales; Phaeophyta) in Japan. Macroalgal color is fundamentally derived from the algal photosynthetic pigment content, which is affected by abiotic factors. However, little is known about the quantitative relationship between pigment content and color and the direct effects of abiotic factors on the color of marine macroalgae. We conducted a 24-day indoor culture experiment to assess the combined effects of nutrient availability (enriched and nonenriched seawater), seawater temperature (15 and 5 °C), and irradiance (180 and 30 μmol photons m−2 s−1) on the concentrations of six pigments (chlorophyll (Chl) a, Chl c 1, Chl c 2, fucoxanthin, violaxanthin, and zeaxanthin) and three color values (lightness L*, redness a*, and yellowness b*) of U. pinnatifida sporophytes. Negative correlations between pigment content and color values of the cultured algae were detected. Reduced nutrient availability, decrease in temperature, and elevated irradiance resulted in decreased pigment contents and increased color values. Moreover, a significant interaction between nutrient availability and temperature indicated that the positive effect of nutrient enrichment was antagonized by a decrease in temperature. These results suggest that U. pinnatifida can discolor under nutrient-poor, winter temperature, and saturated irradiance conditions. To increase the commercial value of this species, artificial nutrient enrichment during spring or cultivation from a deeper depth may be effective.

Light and temperature effects on photosynthetic activity of Eucheuma denticulatum and Kappaphycus alvarezii (brown and green color morphotypes) from Sulawesi Utara, Indonesia

SUMMARYKnowledge concerning the effects of several abiotic factors on the physiology of carrageenophytes is essential both in ecological and economic standpoints, to ensure their sufficient supply for the sustainability of seaweed‐based industries. This paper presents the photosynthetic characteristics of farmed carrageenophytes, E ucheuma denticulatum and K appaphycus alvarezii [brown (BRN) and green (GRN) color morphotypes] from Sulawesi Utara (Sulawesi Island), Indonesia, as determined by examining their photosynthetic response across different temperatures and irradiances using dissolved oxygen measurements and pulse‐amplitude modulated fluorometer. Net photosynthesis–irradiance ( P – E ) curves at 26°C revealed that net photosynthetic rates of the three seaweeds gradually increased until the estimated saturation irradiances ( E k ) of 58 μmol photons m− 2 s−1 (49–68 μmol photons m− 2 s−1, 95% Bayesian prediction intervals; BPI) for E . denticulatum, and 158 and 143 μmol photons m− 2 s−1 (134–185 and 99–203 μmol photons m− 2 s−1, 95% BPI) for BRN and GRN K . alvarezii, respectively; and that no photoinhibition was observed at the highest irradiance of 1000 μmol photons m− 2 s−1. All seaweed samples exhibited photosynthetic tolerance to high PAR as shown by their recovery in maximum quantum yields (Fv / Fm ) following chronic exposures; as well as tolerance over a broad range of temperature, which is from 19 to 33°C for E . denticulatum, 20–29°C for BRN K . alvarezii, and 17–32°C for GRN K . alvarezii. Temperature responses of these carrageenophytes indicated that they were well‐adapted to the annual seawater temperatures in the cultivation site; however, they are also likely close to threshold levels for thermal inhibition, given the decline in Fv / Fm above 30°C.

Abiotic influences on bicarbonate use in the giant kelp, Macrocystis pyrifera, in the Monterey Bay.

In the Monterey Bay region of central California, the giant kelp Macrocystis pyrifera experiences broad fluctuations in wave forces, temperature, light availability, nutrient availability, and seawater carbonate chemistry, all of which may impact their productivity. In particular, current velocities and light intensity may strongly regulate the supply and demand of inorganic carbon (Ci) as substrates for photosynthesis. Macrocystispyrifera can acquire and utilize both CO2 and bicarbonate (HCO3- ) as Ci substrates for photosynthesis and growth. Given the variability in carbon delivery (due to current velocities and varying [DIC]) and demand (in the form of saturating irradiance), we hypothesized that the proportion of CO2 and bicarbonate utilized is not constant for M.pyrifera, but a variable function of their fluctuating environment. We further hypothesized that populations acclimated to different wave exposure and irradiance habitats would display different patterns of bicarbonate uptake. To test these hypotheses, we carried out oxygen evolution trials in the laboratory to measure the proportion of bicarbonate utilized by M.pyrifera via external CA under an orthogonal cross of velocity, irradiance, and acclimation treatments. Our Monterey Bay populations of M.pyrifera exhibited proportionally higher external bicarbonate utilization in high irradiance and high flow velocity conditions than in sub-saturating irradiance or low flow velocity conditions. However, there was no significant difference in proportional bicarbonate use between deep blades and canopy blades, nor between individuals from wave-exposed versus wave-protected sites. This study contributes a new field-oriented perspective on the abiotic controls of carbon utilization physiology in macroalgae.

Differential photosynthetic and morphological adaptations to low light affect depth distribution of two submersed macrophytes in lakes

To evaluate the relative importance of photosynthetic versus morphological adaptations of submersed macrophytes to low light intensity in lakes, rapid light curves (RLCs), morphological parameters, relative growth rate (RGR), clonal reproduction and abundance of two submersed macrophytes (Potamogeton maackianus and Vallisneria natans) were examined under 2.8%, 7.1%, 17.1% and 39.5% ambient light in a field and outdoor experimental study. The plants increased their initial slope of RLCs (α) and decreased their minimum saturating irradiance (Ek) and maximum relative electron transport rate (ETRm) of RLCs under low light stress, but V. natans was more sensitive in RLCs than P. maackianus. Accordingly, the RGR, plant height and abundance of P. maackianus were higher in the high light regimes (shallow water) but lower in the low light regimes than those of V. natans. At the 2.8% ambient light, V. natans produced ramets and thus fulfilled its population expansion, in contrast to P. maackianus. The results revealed that P. maackianus as a canopy-former mainly elongated its shoot length towards the water surface to compensate for the low light conditions, however, it became limited in severe low light stress conditions. V. natans as a rosette adapted to low light stress mainly through photosynthetic adjustments and superior to severely low light than shoot elongation.

Effect of temperature, salinity and irradiance on growth and photosynthesis of Ulva prolifera

Intensive Pyropia aquaculture in the coast of southwestern Yellow Sea and its subsequent waste, including disposed Ulva prolifera, was speculated to be one of the major sources for the large-scale green tide proceeding in the Yellow Sea since 2007. It was, however, unclear how the detached U. prolifera responded and resumed growing after they detached from its original habitat. In this study, we investigated the growth and photosynthetic response of the detached U. prolifera to various temperature, salinity and irradiance in the laboratory. The photosynthetic rate of the detached U. prolifera was significantly higher at moderate temperature levels (14–27°C) and high salinity (26–32), with optimum at 23°C and 32. Both low (<14°C) and highest temperature (40°C), as well as low salinity (8) had adverse effects on the photosynthesis. Compared with the other Ulva species, U. prolifera showed higher saturated irradiance and no significant photoinhibition at high irradiance, indicating the great tolerance of U. prolifera to the high irradiance. The dense branch and complex structure of floating mats could help protect the thalli and reduce photoinhibition in field. Furthermore, temperature exerted a stronger influence on the growth rate of the detached U. prolifera compared to salinity. Overall, the high growth rate of this detached U. prolifera (10.6%–16.7% d–1) at a wide range of temperature (5–32°C) and salinity (14–32) implied its blooming tendency with fluctuated salinity and temperature during floating. The environmental parameters in the southwestern Yellow Sea at the beginning of green tide were coincident with the optimal conditions for the detached U. prolifera.

Seasonal patterns in phytoplankton photosynthetic parameters and primary production at a coastal NW Mediterranean site

We carried out monthly photosynthesis-irradiance (P-E) experiments with the 14 C-method for 12 years (2003–2014) to determine the photosynthetic parameters and primary production of surface phytoplankton in the Blanes Bay Microbial Observatory, a coastal sampling station in the NW Mediterranean Sea. Our goal was to obtain seasonal trends and to establish the basis for detecting future changes of primary production in this oligotrophic area. The maximal photosynthetic rate P B max ranged 30-fold (0.5-15 mg C mg Chl a –1 h –1 ), averaged 3.7 mg C mg Chl a –1 h –1 (±0.25 SE) and was highest in August and lowest in April and December. We only observed photoinhibition twice. The initial or light-limited slope of the P-E relationship, α B , was low, averaging 0.007 mg C mg Chl a –1 h –1 (μmol photons m –2 s –1 ) –1 (±0.001 SE, range 0.001-0.045) and showed the lowest values in spring (April-June). The light saturation parameter or saturation irradiance, E K , averaged 711 μmol photons m –2 s –1 (± 58.4 SE) and tended to be higher in spring and lower in winter. Phytoplankton assemblages were typically dominated by picoeukaryotes in early winter, diatoms in late autumn and late winter, dinoflagellates in spring and cyanobacteria in summer. Total particulate primary production averaged 1.45 mg C m -3 h –1 (±0.13 SE) with highest values in winter (up to 8.50 mg C m -3 h –1 ) and lowest values in summer (summer average, 0.30 mg C m -3 h –1 ), while chlorophyll-specific primary production averaged 2.49 mg C mg Chl a –1 h –1 (±0.19, SE) and peaked in summer (up to 12.0 mg C mg Chl a –1 h –1 in August). 14 C-determined phytoplankton growth rates varied between ca. 0.3 d –1 in winter and 0.5 d –1 in summer and were within 60-80% of the maximal rates of growth, based on P B max . Chlorophyll a was a good predictor of primary production only in the winter and autumn. Seasonality appeared to explain most of the variability in the studied variables, while phytoplankton composition played a minor role. Daily integrated primary production was fairly constant throughout the year: similar to previous oxygen-based estimates in winter but considerably lower than these in summer. The difference between 14 C- and oxygen-based estimates of primary production could be explained by community respiration. Annually integrated primary production amounted to a rather modest 48 g C m –2 yr –1 (equivalent to 130 mg C m –2 d –1 ). Although no interannual patterns were detected, our work soundly establishes the seasonal trends for the coastal NW Mediterranean, therefore setting the basis for future detection of change.

Photosynthetic activity detected in the seed epidermis of Thalassia testudinum

Seagrasses are marine angiosperms that have evolved from terrestrial ancestors. Photosynthetic activity on seed has been studied before in Posidonia genus. T. testudinum and P. oceanica share some evolutionary aspects as they live in more stable environments. As in P. oceanica, T. testudinim seed is also green-coloured suggesting the presence of photosynthetic pigments. Here, the photosynthetic activity in the T. testudinum seed was examined. Measurements of photosynthetic production, pigment content and maximum PSII photochemical efficiency (Fv: Fm) were determined. Epifluorescence microscopy analysis was used to obtain evidence of photosynthetic structures within the seed. This study revealed photosynthetic activity in seed epidermis which increased linearly with increasing irradiance. T. testudinum seed displayed a higher Photosynthetic efficiency (α), and lower light saturated photosynthesis (P. max), saturation irradiance (Ek), and compensation irradiance (Ec) compared to adult leaves. Epifluorescence microscopy images of the seeds showed an epidermis composed of relatively small, regular cells, tending towards a rectangular shape, containing abundant chloroplasts. The photobiological behaviour results in the T. testudinum seed being strongly adapted to colonize environments with reduced light availability. Photosynthetic activity in T. testudinum seed shed some light on seagrass dispersal and expansion mechanisms.