Light-related photosynthetic characteristics of freshwater rhodophytes

Photosynthetic characteristics in response to irradiance were analysed in 21 field and culture populations of thirteen freshwater red algal species applying two distinct techniques (chlorophyll fluorescence and oxygen evolution). Photosynthesis-irradiance (PI) curves indicated adaptations to low irradiances in all species analysed, essentially characterized by occurrence of photoinhibition, low values of the saturation parameter (I-k < 225 mu mol m(-2) s(-1)) and compensation irradiance (I-c < 20 mu mol m(-2) s(-1)) and relatively high values of the effective quantum yield of photosystem II (Delta F/F'(m) >= 45). These characteristics have been reported in freshwater red algae and were confirmed from data based on the two techniques, indicating they are typically shade-adapted plants. on the other hand, some species (e.g. Batrachospermum delicatulum) can tolerate high irradiances (up to 2400 mu mol m(-2) s(-1)), suggesting they have mechanisms that enable them to avoid photodarnage of the photosynthetic apparatus. One of these mechanisms is the increase in dissipation of excessive energy captured by reaction centres after exposure to continuous irradiance, as reflected by the non-photochemical quenching fluorescence parameter in dark/light induction curves. Photo-inhibition occurred in all algae tested by both techniques. Light acclimation was evident particularly in field populations, as revealed by lower values of the saturation parameter (Ik) and the compensation irradiance (I-c) and higher values of Delta F/F'(m) in algae under low irradiances (shaded or heavily shaded stream segments), and vice-versa. Forms living within the boundary layer (e.g. crusts), in a region of reduced current velocity, tended to be more shade-adapted than semi-erect plants (e.g. non-mucilaginous or mucilaginous filaments), as indicated by highest values of photosynthetic efficiency (alpha = 0.31) and effective quantum yield (Delta F/F'(m) = 0.88) under natural conditions. Higher photo- synthetic rates (P-max) for the same species or population were observed under culture than field conditions when measured with the oxygen evolution technique, whereas the opposite trend was observed using chlorophyll fluorescence. (c) 2005 Elsevier B.V. All rights reserved.

Photoacclimation in three species of freshwater red algae

Three freshwater Rhodophyta species (Audouinella eugenea, A. hermannii and Compsopogon coeruleus) were tested as to their responses (photosynthesis, growth and pigment concentration) to two irradiances (low light, LL, 65 μmol m -2 s-1 and high light, HL, 300 μmol m-2 s-1) and two periods (short time, ST, 4 d, and long time, LT, 28 d). Higher growth rates were consistently observed at LL but significant differences were observed only for A. hermannii. Higher values of photoinhibition at LL were found for the three species, which is consistent with the dynamic photoinhibition as a reversible photoprotective mechanism against high irradiance. Light-induced decreases of effective quantum yield (EQY) were observed in the three species consisting of pronounced decreases from LL to HL. Rapid increases of non-photochemical quenching (NPQ) were observed mainly at LL, indicating energy dissipation by reaction centers. Results revealed distinct photoacclimation strategies to deal with high irradiances: the two Audouinella species had only characteristics of shade-adapted algae: acclimation by changes of size of photosy stem units (PSU) under LT and by PSU number under ST; higher values of the photoinhibition parameter (β) and NPQ, and lower values of EQY at LL; higher recovery capacity of potential quantum yield (PQY) at LL and under ST; highly significant positive correlation of electron transport rate (ETR) with NPQ. In addition, C. coeruleus mixed some characteristics of sun-adapted algae: acclimation by changes of PSU number under LT and by PSU size under ST; higher recovery capacity of EQY than the other two species; weak or no correlation of ETR with NPQ. Thus, these characteristics indicate that C. coeruleus cope with high irradiances more efficiently than the Audouinella species.

Avaliação das respostas fotossintéticas de macroalgas lóticas sobre diferentes composições espectrais da radiação incidente

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Respostas fisiológicas de duas espécies de algas vermelhas continentais ao empobrecimento de fósforo e nitrogênio inorgânicos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Physiological performances of two populations of Compsopogon caeruleus (Rhodophyta) to inorganic nitrogen and phosphorus impoverishment

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Chlorophyll a fluorescence in Annona emarginata (Schltdl.) H. Rainer plants subjected to water stress and after rehydration

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Temperature tolerance of western Baltic Sea Fucus vesiculosus - growth, photosynthesis and survival

Fucus vesiculosus L. (Phaeophyceae) is the most abundant and hence ecologically most important primary producer, carbon sink and habitat provider in the western Baltic Sea. All F. vesiculosus L. specimens were collected on 23 April 2014 from a depth of 0.2-1 m in the non-tidal Kiel Fjord, western Baltic Sea (54°27'N; 10°12'E), where this species forms dense and almost monospecific stands on stones. After sampling the algal thalli were stored in a refrigerator box with water from the sampling site, transported to Bremerhaven and stored at 10 °C for one day in filtered seawater. Experiments were conducted with vegetative apical tips (6.7±0.5 cm length), the actively growing region of F. vesiculosus, which were randomly selected and cut from 144 different individuals prior to the experiments. These tips were acclimated to laboratory conditions for three days in filtered seawater at 10 °C before the start of the experiment. Furthermore, 30 additional vegetative apices were freeze-dried to document the initial biochemical status of F. vesiculosus in its native habitat. A temperature gradient was installed in a walk-in constant cooling chamber (15 °C) in nine water baths (5, 10, 15, 20, 24, 26, 27, 28 and 29 °C ± 0.1 °C) which were tempered by thermostats (5, 10 and 15 °C: Huber Variostat CC + Pilot ONE, Peter Huber Kältemaschinen GmbH, Offenburg, Germany; 20 and 28 °C: Haake DC3, Thermo Fisher Scientific Inc., Waltham, USA; 24, 26, 27 and 29 °C: Haake DC10). Every temperature treatment consisted of four 2 L glass beakers (n = 4). In each beaker four F. vesiculosus apices were grown in 2 µm-filtered North Sea water diluted with demineralized water in a ratio of 1:1 and enriched with nutrients after Provasoli (1968; 1/10 enrichment), leading to a salinity of about 15.6 which equaled habitat conditions. The algae were exposed to an irradiance of 130 µmol photons m-2 s-1 ±10 % (Powerstar HGI-TS 150 W, OSRAM GmbH, Bad Homburg, Germany) measured at the top of the beaker under a 16:8 h L:D cycle. The media in the beakers was changed every third or fourth day and aerated with artificial air containing 380 ppm CO2 (gas mixing device; HTK Hamburg GmbH, Hamburg, Germany). Before the experiment, the algae were acclimated to the final temperatures in steps of 5 °C for 2 days each, beginning at 10 °C. After 21 days exposure time, three out of four samples per replicate were freeze-dried for further biochemical analyses, and afterwards the thermostats were turned off to reduce the temperature to 16±0.4 °C for another 10 days permitting growth under post-culture conditions.

(Table 1) Effects of desiccation on photochemical processes and nitrogenase activity in Nostoc commune s.l. colonies

The effects of desiccation on photochemical processes and nitrogenase activity were evaluated in Nostoc commune s.l. colonies in situ from a wet thufur meadow at Petuniabukta, Billefjorden, Central Svalbard, during the 2009 arctic summer. The colonies were collected in the fully hydrated state, and were subjected to slow desiccation at ambient temperatures (5 - 8°C) and low light (30 - 80 µmol/m**2/s). For each colony the weight, area, photochemical performance, and nitrogenase activity were determined at the beginning, as well as on every day during the first four days of the experiment; thereafter, on every second day until desiccation was complete. The photochemical performance was evaluated from variable chlorophyll fluorescence parameters (FV/FM, Phi(PSII) , qP, and NPQ), and the nitrogenase activity was estimated by an acetylene-ethylene reduction assay. A significant decrease in the photochemically active area was recorded from the third day, when the colony had lost approximately 40% of its original weight indicating some changes in the extracellular matrix, and stopped on the 14th to 18th day. No effects of the desiccation on the main photochemical parameters (FV/FM, Phi(PSII), qP) were observed up to the sixth to eighth days of desiccation. Slightly lower values of FV/FM and Phi(PSII) recorded in fully-hydrated colonies could be caused by impaired diffusion of CO2 into cells. The steep reduction of photochemical activity occurred between the eighth and tenth day of the experiment, when the colony had lost approximately 80% of its fully-hydrated weight. The nitrogenase activity was highest on the first day, probably due to improved diffusion of N2 into cells, then declined, but was detectable until the sixth day of the experiment. Since Nostoc commune s.l. colonies were capable of photosynthesis and nitrogen fixation to the level of ca. 60% of its fully-hydrated weight, even partly-hydrated colonies contribute substantially to carbon and nitrogen cycling in the High Arctic wet meadow tundra ecosystem.

Photochemical responses of the diatom Skeletonema costatum grown under elevated CO2 concentrations to short-term changes in pH

Variability in pH is a common occurrence in many aquatic environments, due to physical, chemical and biological processes. In coastal waters, lagoons, estuaries and inland waters, pH can change very rapidly (within seconds or hours) in addition to daily and seasonal changes. At the same time, progressive ocean acidification caused by anthropogenic CO2 emissions is superimposed on these spatial and temporal pH changes. Photosynthetic organisms are therefore unavoidably subject to significant pH variations at the cell surface. Whether this will affect their response to long-term ocean acidification is still unknown, nor is it known whether the short-term sensitivity to pH change is affected by the pCO2 to which the cells are acclimated. We posed the latter open question as our experimental hypothesis: Does acclimation to seawater acidification affect the response of phytoplankton to acute pH variations? The diatom Skeletonema costatum, commonly found in coastal and estuarine waters where short-term acute changes in pH frequently occur, was selected to test the hypothesis. Diatoms were grown at both 390 (pH 8.2, low CO2; LC) and 1000 (pH 7.9, high CO2; HC) µatm CO2 for at least 20 generations, and photosynthetic responses to short-term and acute changes in pH (between 8.2 and 7.6) were investigated. The effective quantum yield of LC-grown cells decreased by ca. 70% only when exposed to pH 7.6; this was not observed when exposed to pH 7.9 or 8.2. HC-grown cells did not show significant responses in any pH treatment. Non-photochemical quenching showed opposite trends. In general, our results indicate that while LC-grown cells are rather sensitive to acidification, HC-grown cells are relatively unresponsive in terms of photochemical performance.

Experimental data on photophysiology and growth rates of Pararotalia calcariformata

The eastern Mediterranean is a hotspot of biological invasions. Numerous species of Indo-pacific origin have colonized the Mediterranean in recent times, including tropical symbiont-bearing foraminifera. Among these is the species Pararotalia calcariformata. Unlike other invasive foraminifera, this species has been discovered only two decades ago and is restricted to the eastern Mediterranean coast. Combining ecological, genetic and physiological observations, we attempt to explain the recent invasion of this species in the Mediterranean Sea. Using morphological and genetic data, we confirm the species attribution to P. calcariformata McCulloch 1977 and identify its symbionts as a consortium of diatom species dominated by Minutocellus polymorphus. We document photosynthetic activity of its endosymbionts using Pulse Amplitude Modulated Fluorometry and test the effects of elevated temperatures on growth rates of asexual offspring. The culturing of asexual offspring for 120 days shows a 30-day period of rapid growth followed by a period of slower growth. A subsequent 48-day temperature sensitivity experiment indicates a similar developmental pathway and high growth rate at 28°C, whereas an almost complete inhibition of growth was observed at 20°C and 35°C. This indicates that the offspring of this species may have lower tolerance to cold temperatures than what would be expected for species native to the Mediterranean. We expand this hypothesis by applying a Species Distribution Model (SDM) based on modern occurrences in the Mediterranean using three environmental variables: irradiance, turbidity and yearly minimum temperature. The model reproduces the observed restricted distribution and indicates that the range of the species will drastically expand westwards under future global change scenarios. We conclude that P. calcariformata established a population in the Levant because of the recent warming in the region. In line with observations from other groups of organisms, our results indicate that continued warming of the eastern Mediterranean will facilitate the invasion of more tropical marine taxa into the Mediterranean, disturbing local biodiversity and ecosystem structure.

Enhancement of photosynthetic carbon assimilation efficiency by phytoplankton in the future coastal ocean

A mesocosm experiment was conducted to evaluate the effects of future climate conditions on photosynthesis and productivity of coastal phytoplankton. Natural phytoplankton assemblages were incubated in field mesocosms under the ambient condition (present condition: ca. 400 ppmv CO2 and ambient temp.), and two future climate conditions (acidification condition: ca. 900 ppmv CO2 and ambient temp.; greenhouse condition: ca. 900 ppmv CO2 and 3 °C warmer than ambient). Photosynthetic parameters of steady-state light responses curves (LCs; measured by PAM fluorometer) and photosynthesis-irradiance curves (P-I curves; estimated by in situ incorporation of 14C) were compared to three conditions during the experiment period. Under acidification, electron transport efficiency (alpha LC) and photosynthetic 14C assimilation efficiency (alpha) were 10% higher than those of the present condition, but maximum rates of relative electron transport (rETRm,LC) and photosynthetic 14C assimilation (PBmax) were lower than the present condition by about 19% and 7%, respectively. In addition, rETRm,LC and alpha LC were not significantly different between and greenhouse conditions, but PBmax and alpha of greenhouse conditions were higher than those of the present condition by about 9% and 30%, respectively. In particular, the greenhouse condition has drastically higher PBmax and alpha than the present condition more than 60% during the post-bloom period. According to these results, two future ocean conditions have major positive effects on the photosynthesis in terms of energy utilization efficiency for organic carbon fixation through the inorganic carbon assimilation. Despite phytoplankton taking an advantage on photosynthesis, primary production of phytoplankton was not stimulated by future conditions. In particular, biomass of phytoplankton was depressed under both acidification and greenhouse conditions after the the pre-bloom period, and more research is required to suggest that some factors such as grazing activity could be important for regulating phytoplankton bloom in the future ocean.

Light-modulated responses of growth and photosynthetic performance to ocean acidification in the model diatom Phaeodactylum tricornutum

Ocean acidification (OA) due to atmospheric CO2 rise is expected to influence marine primary productivity. In order to investigate the interactive effects of OA and light changes on diatoms, we grew Phaeodactylum tricornutum, under ambient (390 ppmv; LC) and elevated CO2 (1000 ppmv; HC) conditions for 80 generations, and measured its physiological performance under different light levels (60 µmol/m**2/s, LL; 200 µmol/m**2/s, ML; 460 µmol/m**2/s, HL) for another 25 generations. The specific growth rate of the HC-grown cells was higher (about 12-18%) than that of the LC-grown ones, with the highest under the ML level. With increasing light levels, the effective photochemical yield of PSII (Fv'/Fm') decreased, but was enhanced by the elevated CO2, especially under the HL level. The cells acclimated to the HC condition showed a higher recovery rate of their photochemical yield of PSII compared to the LC-grown cells. For the HC-grown cells, dissolved inorganic carbon or CO2 levels for half saturation of photosynthesis (K1/2 DIC or K1/2 CO2) increased by 11, 55 and 32%, under the LL, ML and HL levels, reflecting a light dependent down-regulation of carbon concentrating mechanisms (CCMs). The linkage between higher level of the CCMs down-regulation and higher growth rate at ML under OA supports the theory that the saved energy from CCMs down-regulation adds on to enhance the growth of the diatom.

CO2-driven seawater acidification increases photochemical stress in a green alga

Increased CO2 and associated acidification in seawater, known as ocean acidification, decreases calcification of most marine calcifying organisms. However, there is little information available on how marine macroalgae would respond to the chemical changes caused by seawater acidification. We hypothesized that down-regulation of bicarbonate acquisition by algae under increased acidity and CO2 levels would lower the threshold above which photosynthetically active radiation (PAR) becomes excessive. Juveniles of Ulva prolifera derived from zoospores were grown at ambient (390 µatm) and elevated (1000 µatm) CO2 concentrations for 80 days before the hypothesis was tested. Here, the CO2-induced seawater acidification increased the quantum yield under low levels of light, but induced higher nonphotochemical quenching under high light. At the same time, the PAR level at which photosynthesis became saturated was decreased and the photosynthetic affinity for CO2 or inorganic carbon decreased in the high-CO2 grown plants. These findings indicated that ocean acidification, as an environmental stressor, can reduce the threshold above which PAR becomes excessive.

Ocean acidification alleviates low-temperature effects on growth and photosynthesis of the red alga Neosiphonia harveyi (Rhodophyta)

This study aimed to examine interactive effects between ocean acidification and temperature on the photosynthetic and growth performance of Neosiphonia harveyi. N. harveyi was cultivated at 10 and 17.5 °C at present (~380 µatm), expected future (~800 µatm), and high (~1500 µatm) pCO2. Chlorophyll a fluorescence, net photosynthesis, and growth were measured. The state of the carbon-concentrating mechanism (CCM) was examined by pH-drift experiments (with algae cultivated at 10 °C only) using ethoxyzolamide, an inhibitor of external and internal carbonic anhydrases (exCA and intCA, respectively). Furthermore, the inhibitory effect of acetazolamide (an inhibitor of exCA) and Tris (an inhibitor of the acidification of the diffusive boundary layer) on net photosynthesis was measured at both temperatures. Temperature affected photosynthesis (in terms of photosynthetic efficiency, light saturation point, and net photosynthesis) and growth at present pCO2, but these effects decreased with increasing pCO2. The relevance of the CCM decreased at 10 °C. A pCO2 effect on the CCM could only be shown if intCA and exCA were inhibited. The experiments demonstrate for the first time interactions between ocean acidification and temperature on the performance of a non-calcifying macroalga and show that the effects of low temperature on photosynthesis can be alleviated by increasing pCO2. The findings indicate that the carbon acquisition mediated by exCA and acidification of the diffusive boundary layer decrease at low temperatures but are not affected by the cultivation level of pCO2, whereas the activity of intCA is affected by pCO2. Ecologically, the findings suggest that ocean acidification might affect the biogeographical distribution of N. harveyi.