Photosynthesis Irradiance Research Articles

Phenology and the response of photosynthesis to irradiance and temperature gradient in the herbal drug red alga, Chondria armata (Rhodomelaceae, Ceramiales) from Kagoshima, Japan

Seasonal changes in the size of the herbal drug red alga Chondria armata (Rhodomelaceae, Ceramiales) were investigated in Kagoshima, Japan, which is near the northern distributional limit in the western Pacific. Additionally, its photosynthetic response to irradiance and temperature was examined using dissolved oxygen sensors and a pulse amplitude modulation (PAM)-chlorophyll fluorometer. This alga was observed in tidepools throughout the year; its height and weight were greatest in December and the lowest in April and May. The net photosynthesis of the photosynthesis–irradiance (P–E) curve determined at 28°C quickly saturated at 113 µmol photons m-2 s-1, with minimal inhibition even at 1000 µmol photons m-2 s-1. The gross photosynthesis of the photosynthesis–temperature (P–T) curved over 8 to 40°C, measured at 500 µmol photons m-2 s-1, peaked at 30.1°C and decreased rapidly below 20°C and above 36°C, respectively. Similarly, the effective quantum yield (ΔF/Fm') after a 3-day culture during 4–40°C at 50 µmol photons m-2 s-1 remained stable between 16°C and 32°C but decreased outside of this range. The combined effect of irradiance (200 [low] and 1000 [high] µmol photons m-2 s-1) and temperature (28, 22, and 16°C) revealed that ΔF/Fm' declined during exposure to high irradiance at all temperature treatments. However, it mostly recovered after a subsequent 12-hour period of dim-light acclimation at 28°C and 22°C. In contrast, those at 16°C could not recover, indicating the occurrence of low-temperature light stress. This alga appears to be well-adapted to the irradiance and temperature environment at the study site. However, the winter temperature appears to approach its threshold level, and the occurrence of strong light during the winter might adversely affect the abundance of this alga near its northern distributional limit.

Assessing the impact of atmospheric attributes on the effectiveness of solar irradiance for photosynthesis of urban vegetation in Attica, Greece

Assessing the impact of atmospheric attributes on the effectiveness of solar irradiance for photosynthesis of urban vegetation in Attica, Greece

The response of photosynthesis to temperature and irradiance in a green alga, Ryuguphycus kuaweuweu (Ulvales) reveals adaptation to a subtidal environment in the northern Ryukyu Islands

We investigated the photosynthetic response of Ryuguphycus kuaweuweu (=Umbraulva kuaweuweu, Ulvales), a subtidal green alga from the northern Ryukyu Islands (35–40 m deep), Kagoshima, Japan, to temperature, irradiance, and light spectral limitation using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. The photochemical efficiency in photosystem II (maximum quantum yield, Fv/Fm and effective quantum yield, ΔF/Fm′) response during 3-day temperature exposure (8–40 °C) revealed that Fv/Fm, measured in darkness, was not significantly affected by temperatures below 32 °C. In contrast, ΔF/Fm′ measured at 50 μmol photons m−2 s−1 was sensitive to temperature and showed an optimum temperature of 26.1 °C. The gross photosynthesis (GP rate, 8–40 °C) at 200 μmol photons m−2 s−1 showed that the maximum GP rate occurred at 29.5 °C. The photosynthesis–irradiance (P–E) responses (0–1000 μmol photons m−2 s−1) measured at 12, 20, and 28 °C showed that the net photosynthesis quickly saturated at low irradiance levels. However, as temperature increased, the irradiances required for photosynthetic saturation also increased. Additionally, the P–E curves obtained under blue (450 nm), green (525 nm), red (660 nm), and white (metal halide lamp) lights indicated that this alga exhibited higher levels of maximum photosynthetic output under blue and green lights. We further observed that during continuous 6-h exposure to irradiance levels of 100, 200, 500, and 1000 μmol photons m−2 s−1 at 20 °C, ΔF/Fm′ decreased progressively as the irradiance levels increased. At 100 μmol photons m−2 s−1 and 12, 20, and 28 °C, the ΔF/Fm′ was stable at 20 and 28 °C but declined at 12 °C, suggesting the occurrence of low temperature-light stress. In conclusion, the results suggest that R. kuaweuweu is adapted to the study site's subtidal temperature and light environments where green and blue wavelengths can effectively penetrate.

Going under: The implications of sea‐level rise and reduced light availability on intertidal primary production

AbstractEstuarine intertidal flats are known for high rates of primary production, however, globally these ecosystems are under threat from rising sea‐level and accelerated inputs of terrestrial sediments. These stressors simultaneously alter the duration of submersion/emersion periods and water‐column turbidity impacting seafloor photoperiods. To assess how changes in submergence time and water‐clarity can affect benthic primary production, we derived in situ seasonal photosynthesis‐irradiance (P‐I) curves over 2 yr. These were conducted during submerged and emerged periods in a seagrass meadow (Zostera muelleri) and an unvegetated sandflat (dominated by microphytobenthos). P‐I curves showed strong light responses during submergence in both habitats and seagrass during emergence, but in the exposed sandflat there was little relationship between light availability and photosynthesis. Light‐saturated measures of gross primary production (GPPsat) were 2.1 (submerged) and 4.1 times (emerged) higher in the seagrass than the sandflat habitat. Submerged GPPsat was always higher than emerged GPPsat, but this difference was much more pronounced in the sandflat habitat (2.4 vs. 1.3 times for seagrass). Integrating seasonally averaged P‐I curves for both tidal states into a simple model suggests that increasing submergence time could increase primary production in both habitats. However, reductions in water‐clarity will decrease submerged primary production; an effect that will be exacerbated with sea‐level rise. The sandflat trophic state was more sensitive to these environmental stressors because emerged production could not compensate for reductions during submergence. Collectively, regional management of water‐clarity may be key to providing resilience to intertidal habitats, against the inevitable effects of sea‐level rise.

The effect of temperature, light‐spectrum, desiccation and salinity gradients on the photosynthetic performance of a subtidal brown alga, Sargassum macrocarpum, from Japan

SUMMARYThe effect of temperature, light‐spectrum, desiccation and salinity gradients on the photosynthesis of a Japanese subtidal brown alga, Sargassum macrocarpum (Fucales), was determined using a pulse amplitude modulation‐chlorophyll fluorometer and dissolved oxygen sensors. Temperature responses of the maximum (Fv/Fm in darkness) and effective (ΔF/Fm′ at 50 μmol photons m−2 s−1; = ΦPSII) quantum yields during 6‐day culture (4–36°C) remained high at 12–28°C, but decreased at higher temperatures. Nevertheless, ΔF/Fm′ also dropped at temperatures below 8°C, suggesting light sensitivity under chilling temperatures because Fv/Fm remained high. Photosynthesis–irradiance responses at 24°C under red (660 nm), green (525 nm), blue (450 nm) and white light (metal halide lamp) showed that maximum net photosynthesis under blue and white light was greater than under red and green light, indicating the sensitivity and photosynthetic availability of blue light in the subtidal light environment. In the desiccation experiment, samples under aerial exposure of up to 8 h under dim‐light at 24°C and 50% humidity showed that ΔF/Fm′ quickly declined after more than 45 min of emersion; furthermore, ΔF/Fm′ also failed to recover to initial levels even after 1 day of rehydration in seawater. Under the emersion state, the ΔF/Fm′ remained high when the relative water content (RWC) was greater than 50%; in contrast, it quickly dropped when the RWC was less than 50%. When the RWC was reduced below 50%, ΔF/Fm′ did not return to initial levels, regardless of subsequent re‐hydration, suggesting a low capacity of photosynthesis to recover from desiccation. The stenohaline response of photosynthesis under 3‐day culture is evident, given that ΔF/Fm′ declined when salinity was beyond 20–40 psu. Adaptation to subtidal environments in temperate waters of Japan can be linked to these traits.

Variation in seagrass meadow respiration measured by aquatic eddy covariance

AbstractAccurate daily metabolic estimates of respiration, gross primary production, and net ecosystem metabolism are necessary to assess ecosystem health and blue carbon contributions of vegetated coastal ecosystems. Using our database of 2115 hourly benthic oxygen (O2) fluxes measured by aquatic eddy covariance, we examine how respiration for a Zostera marina seagrass meadow varies through night and day, and how this affects commonly performed metabolic estimates. Respiration decreased linearly by 29% through the night and a corresponding linear increase in daytime respiration coupled with production described by a standard photosynthesis–irradiance curve accurately predicted measured daytime O2 fluxes. Many studies have questioned the widely used assumption in metabolic estimates that nighttime and daytime respiration are constant and equal. However, if respiration can be approximated as we found here by linear relationships, standard means for calculating daily metabolic numbers remain valid if estimates are based on full 24‐h records of flux data.

Linking Thallus Morphology with P-I Curves of 50 Macrobenthic Algae from Bolinao, Pangasinan, Philippines

This study demonstrated that thallus morphology could affect a species’ capacity to utilize light for photosynthesis and, hence, will affect its productivity. Fifty (50) macroalgal species collected from an intertidal habitat in Bolinao, Pangasinan, Philippines were grouped into five “functional-forms” based on their inferred productivity: functional-form group (FFG) A: very thin tubes/sheets/strips, FFG B: thin sheets/delicately branched, FFG C: medium-thick blade/coarsely branched with dense ramuli, FFG D: heavily thick branches/segments or with moderate calcification, and FFG E: heavily calcified. Their photosynthesis-irradiance (P-I) curves were determined through the measurement of oxygen evolved in a closed system after 1-h incubation under six different light treatments. P-I curve parameters such as Pnmax, Ik, Ic, α, and Rd were assessed to determine the groups’ physiological responses to light. The thickness of thallus blades, coarseness of branches, complex branching, and calcification appeared to lessen photosynthetic capacity, as shown by the significantly decreasing trend of Pnmax from FFGs A–E. FFG A also showed the steepest slope (highest mean α value) compared with the rest of the functional-form groups, indicating their efficiency to utilize low light for photosynthesis. Light saturation and compensation values were less distinct in differentiating the functional form groups, probably because the seaweeds examined were all collected from the same shallow intertidal zone, suggesting their acclimation to similar photon flux densities. Results from this study fit the prediction of the function form hypothesis for seaweeds quite well.

Photosynthetic, Respirational, and Growth Responses of Six Benthic Diatoms from the Antarctic Peninsula as Functions of Salinity and Temperature Variations.

Temperature and salinity are some of the most influential abiotic parameters shaping biota in aquatic ecosystems. In recent decades, climate change has had a crucial impact on both factors—especially around the Antarctic Peninsula—with increasing air and water temperature leading to glacial melting and the accompanying freshwater increase in coastal areas. Antarctic soft and hard bottoms are typically inhabited by microphytobenthic communities, which are often dominated by benthic diatoms. Their physiology and primary production are assumed to be negatively affected by increased temperatures and lower salinity. In this study, six representative benthic diatom strains were isolated from different aquatic habitats at King George Island, Antarctic Peninsula, and comprehensively identified based on molecular markers and morphological traits. Photosynthesis, respiration, and growth response patterns were investigated as functions of varying light availability, temperature, and salinity. Photosynthesis–irradiance curve measurements pointed to low light requirements, as light-saturated photosynthesis was reached at <70 µmol photons m−2 s−1. The marine isolates exhibited the highest effective quantum yield between 25 and 45 SA (absolute salinity), but also tolerance to lower and higher salinities at 1 SA and 55 SA, respectively, and in a few cases even <100 SA. In contrast, the limnic isolates showed the highest effective quantum yield at salinities ranging from 1 SA to 20 SA. Almost all isolates exhibited high effective quantum yields between 1.5 °C and 25 °C, pointing to a broad temperature tolerance, which was supported by measurements of the short-term temperature-dependent photosynthesis. All studied Antarctic benthic diatoms showed activity patterns over a broader environmental range than they usually experience in situ. Therefore, it is likely that their high ecophysiological plasticity represents an important trait to cope with climate change in the Antarctic Peninsula.

Interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga Saccharina japonica (Laminariales) from Hokkaido, Japan

The interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga, Saccharina japonica (var. japonica, Laminariales) from Hokkaido, Japan were examined using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. Assessment of maximum quantum yields (in darkness) and effective quantum yields (at 50 μmol photons m−2 s−1) at nine temperatures (4–36 °C, four increments) during 3-d culture indicated a temperature threshold at 24 °C, with early decline of maximum quantum yields at such temperature, which could probably be due to exhaustion of carbohydrate reserves by respiration in prolonged darkness. Unlike maximum quantum yields that was relatively stable through 4–20 °C, effective quantum yields under 50 μmol photons m−2 s−1 gradually declined at low temperatures, revealing light sensitivity under chilling temperatures. Chronic 6-h exposures under 200 (low) and 1000 (high) μmol photons m−2 s−1 at 4, 16, and 24 °C generated a significant decline in effective quantum yields at 4 °C under both irradiances; however, only treatments under low irradiance fully recovered after a subsequent 12-h dim light treatment. Moreover, post-dim light acclimation effective quantum yields of treatments at 16 and 24 °C under high irradiance returned to initial levels, suggesting accelerated photoinhibition at low temperature. Photosynthesis–irradiance responses at 16 °C under blue (450 nm), green (525 nm), red (660 nm), and white light (metal halide lamp) showed that the maximum photosynthetic output occurred under blue and white lights. The photoinhibitory sensitivity to chilling-light stress and the enhanced photosynthesis under blue light of S. japonica presented additional evidence of their physiological adaptation to cold-temperate subtidal waters.

Biomass Production and Predicted Ethanol Yield Are Linked with Optimum Photosynthesis in Phragmites karka under Salinity and Drought Conditions.

Plant photosynthesis and biomass production are closely associated traits but critical to unfavorable environmental constraints such as salinity and drought. The relationships among stress tolerance, photosynthetic mechanisms, biomass and ethanol yield were assessed in Phragmites karka. The growth parameters, leaf gas exchange and chlorophyll fluorescence of P. karka were studied when irrigated with the control and 100 and 300 mM NaCl in a nutrient solution and water deficit conditions (drought, at 50% water holding capacity). The plant shoot fresh biomass was increased in the low NaCl concentration; however, it significantly declined in high salinity and drought. Interestingly the addition of low salinity increased the shoot biomass and ethanol yield. The number of tillers was increased at 100 mM NaCl in comparison to the control treatment. High salinity increased the photosynthetic performance, but there were no significant changes in drought-treated plants. The saturated irradiance (Is) for photosynthesis increased significantly in low salinity, but it declined (about 50%) in high salt-stressed and (about 20%) in drought-treated plants compared to the control. The rates of dark respiration (Rd) and compensation irradiance (Ic) were decreased significantly under all treatments of salinity and drought, with the exception of unchanged Rd values in the control and drought treatments. A-Ci curve analyses revealed a significant improvement in the Jmax, Vc, max, and triose-phosphate utilization (TPU) at lower salinity levels but decreased at 300 mM NaCl and drought treatments compared to the control. In the chlorophyll fluorescence parameters (Fv/Fm, maximum photochemical quantum yield of PSII, and Y(NO)), the non-photochemical yields were not affected under the salt and drought treatments, although an effective photochemical quantum yield (YII) and electron transport rate (ETR) were significantly enhanced in water deficit compared to control plants. P. karka regulates an efficient photosynthesis mechanism to grow in saline and arid areas and can therefore be used as a sustainable biofuel crop.

Primary productivity measurements in the Ross Sea, Antarctica: a regional synthesis

Abstract. Polar systems are undersampled due to the difficulty of sampling remote and challenging environments; however, these systems are critical components of global biogeochemical cycles. Measurements on primary productivity in specific areas can quantify the input of organic matter to food webs and so are of critical ecological importance as well. However, long-term measurements using the same methodology are available only for a few polar systems. Primary productivity measurements using 14C-uptake incubations from the Ross Sea, Antarctica, are synthesized, along with chlorophyll concentrations at the same depths and locations. A total of 19 independent cruises were completed and 449 stations occupied where measurements of primary productivity (each with seven depths) were completed. The incubations used the same basic simulated in situ methodology for all. Integrated water column productivity for all stations averaged 1.10 ± 1.20 g C m−2 d−1, and the maximum was 13.1 g C m−2 d−1. Annual productivity calculated from the means throughout the growing season equalled 146 g C m−2 yr−1. The mean chlorophyll concentration in the euphotic zone (the 1 % irradiance level) was 2.85 ± 2.68 mg m−3 (maximum observed concentration was 19.1 mg m−3). Maximum photosynthetic rates above the 30 % isolume (normalized to chlorophyll) averaged 0.98 ± 0.71 mg C (mg chl)−1 h−1, similar to the maximum rate found in photosynthesis–irradiance measurements. Productivity measurements are consistent with the temporal patterns of biomass found previously, with biomass and productivity peaking in late December; mixed layers were at a minimum at this time as well. Estimates of plankton composition also suggest that pre-January productivity was largely driven by the haptophyte Phaeocystis antarctica and summer productivity by diatoms. The data set (https://doi.org/10.26008/1912/bco-dmo.863815.2, Smith, 2021) will be useful for a comparison to other Antarctic regions and provide a basis for refined bio-optical models of regional primary productivity and biogeochemical models for the Southern Ocean.

Shining Light on Photosynthesis in the Harmful Dinoflagellate Karenia mikimotoi–Responses to Short-Term Changes in Temperature, Nitrogen Form, and Availability

Karenia mikimotoi is a toxic bloom-forming dinoflagellate that sometimes co-blooms with Karenia brevis in the Gulf of Mexico, especially on the West Florida Shelf where strong vertical temperature gradients and rapid changes in nitrogen (N) can be found. Here, the short-term interactions of temperature, N form, and availability on photosynthesis–irradiance responses were examined using rapid light curves and PAM fluorometry in order to understand their interactions, and how they may affect photosynthetic yields. Cultures of K. mikimotoi were enriched with either nitrate (NO3−), ammonium (NH4+), or urea with varying amounts (1, 5, 10, 20, 50 µM-N) and then incubated at temperatures of 15, 20, 25, 30 °C for 1 h. At 15–25 °C, fluorescence parameters (Fv/Fm, rETR) when averaged for all N treatments were comparable. Within a given light intensity, increasing all forms of N concentrations generally led to higher photosynthetic yields. Cells appeared to dynamically balance the “push” due to photon flux pressure and reductant generation, with consumption in overall metabolism (“pull” due to demand). However, at 30 °C, all fluorescence parameters declined precipitously, but differential responses were observed depending on N form. Cells enriched with urea at 30 °C showed a smaller decline in fluorescence parameters than cells treated with NO3− or NH4+, implying that urea might induce a photoprotective mechanism by increasing metabolic “pull”.

Differential acclimation responses to irradiance and temperature in two co-occurring seaweed species in Arctic fjords

Arctic fjord systems experience large amplitudes of change in temperature and radiation regime due to climate warming and the related decrease in sea ice. The resultant increase in irradiance entering the water column influences photosynthetic activity of benthic and pelagic primary producers. The subtidal brown alga&nbsp;Desmarestia aculeata&nbsp;and the intertidal red alga&nbsp;Palmaria palmata&nbsp;populate the cold-temperate coasts of the North Atlantic, reaching the polar zone. To evaluate their acclimation potential, we collected both species in Kongsfjorden, Svalbard (78.9°N, 11.9°E), during the Arctic summer and exposed specimens to two different PAR levels (50 and 500 μmol photons m−2&nbsp;s−1) and temperatures (0, 4 and 8 °C) for 21 days. Photosynthetic parameters and biochemical features (pigment concentration and antioxidants) were assessed. In general, high irradiance was the factor that generated a negative effect for&nbsp;D. aculeata&nbsp;and&nbsp;P. palmata&nbsp;in the photosynthetic parameters of the photosynthesis–irradiance curve and&nbsp;Fv/Fm. The pigment concentration in both species tended to decrease with increasing irradiance. Antioxidant level showed different trends for both species: in&nbsp;D. aculeata, antioxidant potential increased with high irradiance and temperature, while in&nbsp;P. palmata, it only increased with high irradiance. Both species showed responses to the interaction of irradiance and temperature, although&nbsp;D. aculeata&nbsp;was more sensitive to high irradiance than&nbsp;P. palmata. Our study shows how these species, which have similar geographical distribution in the North Atlantic and the Arctic but belong to different taxonomic lineages, have similar strategies of acclimation, although they respond differently to ecophysiological parameters.

Examining the size-specific photosynthesis-irradiance parameters and relationship with phytoplankton types in a subtropical marginal sea

Through photosynthesis, phytoplankton initiate material cycling and the flow of energy through marine ecosystems. The structure of marine ecosystems is sensitive to the size of primary producers, and size-specific photosynthesis-irradiance (P-I) parameters are required for modeling the size-specific primary production. We defined a phytoplankton type to be a group of phytoplankton communities with similar compositions and hypothesized that a function of phytoplankton types might be used to quantify systematic differences of P-I parameters between size classes (structural effects) and variations of the magnitudes of those parameters if the overlap between habitats was small (environmental effects). To test this hypothesis, we conducted a study to measure the size-specific P-I parameters of two size classes (<2 μm and >2 μm) and pigment-based phytoplankton community structure in a marginal sea, the Taiwan Strait. Three phytoplankton types were classified, and type-based and size-specific P-I parameters were derived. The results demonstrated the potential of a type-based model to estimate P-I parameters for two phytoplankton size classes as well as different habitats.

Novel photo-microrespirometric method for the rapid determination of photosynthesis-irradiance (PI) curves in microalgal-bacterial systems

Photoreactors are now largely used in a span of applications but are complex systems that would still benefit from a better constraint of their kinetic behaviour. Among others, the determination of the Photosynthetic-Irradiance (PI) curve in photoreactors, which describes the correlation between light irradiance and activity of the algal or algal-bacterial culture, is of utmost importance for modelling, optimization, and control purposes. Habitually, PI curves in photoreactors are determined through incubation done under a range of irradiance, and even if many remarkable advances have been achieved in the methods applied, there is still a need for a simple, robust, polyvalent and fast method. We present here a method based on a modified respirometer, commercially available, that allows to measure the dissolved oxygen production/uptake, simultaneously in 24 replicates under a controlled irradiance. This so-called photo-microrespirometric method, was applied successfully to the determination of PI curves of a microalgal-bacterial culture obtained from a pilot-scale pond treating the liquid fraction of an anaerobic digestate. The PI curves obtained, in a few hours of experimental work, were well fitted by the Bernard-Rémond's kinetic model. In addition to PI curves, the method allowed for the quantification of the inhibitory effect of dissolved oxygen as well as the response time of the photoactivation and photoinhibition.

The effects of four stressors, irradiance, temperature, desiccation, and salinity on the photosynthesis of a red alga, Agarophyton vermiculophyllum (Gracilariales) from a native distributional range in Japan

We examined the effects of four stressors, irradiance, temperature, desiccation, and salinity on the photosynthesis of a red alga, Agarophyton vermiculophyllum (= Gracilaria vermiculophylla, Gracilariales, Rhodophyta) from its native distributional range in Hokkaido and Kagoshima, Japan. Photosynthesis–irradiance (P–E) curves at 8, 16, and 28°C showed that the maximum net-photosynthetic rates (NPmax) and saturation irradiance (Ek) were highest at 28°C for both strains. Gross-photosynthesis determined at 8–40°C at 200 μmol photons m-2 s-1 showed that the maximum gross-photosynthetic rate (GPmax) occurred at 25.3°C for Hokkaido and 28.0°C for Kagoshima ( $$ {T}_{opt}^{GP} $$ ), which is almost consistent with the summer-time seawater temperature at each habitat. The temperature responses (4–40°C) of effective quantum yields (ΔF/Fm') of photosystem II during 7-day exposures were similar to that of oxygenic photosynthesis and the optimum temperature ( $$ {T}_{opt}^{\varDelta F/ Fm\prime } $$ ) was 20.0°C for Hokkaido and 30.1°C for Kagoshima. In the desiccation experiment, the ΔF/Fm' decreased with decreasing absolute water content (AWC); nevertheless, for samples with an AWC above 20%, ΔF/Fm' retuned to initial levels after subsequent 1-day rehydration in seawater, suggesting relatively strong tolerance to desiccation. This alga also showed a broad range of tolerance to salinity ranging from 20 to 60 psu in 7-day exposures, and the ΔF/Fm' tolerated 0 psu at 3-day exposure. The adaptations of A. vermiculophyllum from its native range in Japan to relatively high irradiance, a broad range of temperature, and strong osmotic (desiccation and salinity) tolerance explain its potentially high invasive capacity.

The photosynthetic performance of a cultivated Japanese green alga Caulerpa lentillifera in response to three different stressors, temperature, irradiance, and desiccation

The effects of temperature, irradiance, and desiccation on the photosynthesis of a cultivated Japanese green alga Caulerpa lentillifera (Caulerpaceae) were determined by a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. The photochemical efficiency in the photosystem II (Fv/Fm and ΔF/Fm') during the 72-h temperature exposures (8, 12, 16, 20, 24, 28, 32, 36, and 40°C) was generally stable at 16–32°C but quickly dropped at lower and higher temperatures. The photosynthesis–temperature curve at 200 μmol photons m−2 s−1 also revealed that the maximum gross photosynthesis (GPmax) occurred at 30.7°C (30.5–30.9, 95% highest density credible intervals). Photosynthesis–irradiance curves at 16, 24, and 32°C quickly saturated, then expressed photoinhibition, and revealed that the maximum net photosynthetic rates (NPmax) and saturation irradiance (Ek) were highest at 32°C and lowest at 16°C. Continuous 6-h exposure to irradiances of 200 (low) and 400 (high) μmol photons m−2 s−1 at 16, 24, and 32°C expressed greater declines in their ΔF/Fm' at 16°C, revealing chronic chilling-light stress. The response to continuous desiccation (~480 min) under 50% humidity at 24°C showed that ΔF/Fm' dropped to zero at 480-min aerial exposure, and the treatments of more than 60-min desiccation did not return to the initial level even after 24-h subsequent rehydration in seawater. Likewise, ΔF/Fm' fell when the absolute water content (AWC) of the frond dropped below AWC of 90% and mostly did not return to the initial level even after 24-h subsequent rehydration in seawater, signifying a low tolerance to desiccation.

Two versions of short-term phytoplankton ecophysiology and taxonomic assemblages in the Arctic Ocean’s North Water (Canada, Greenland)

Abstract Photosynthetic performance in open marine waters is determined by how well phytoplankton species are adapted to their immediate environment and available light. Although there is light for 24 h a day during the Arctic summer, little is known about short-term (h) temporal variability of phytoplankton photosynthetic performance in Arctic waters. To address this, we sampled the North Water (76.5°N) every 4 h over 24 h at two stations on the East and West sides that are influenced by different water masses and current conditions. We specifically investigated phytoplankton pigments, the xanthophyll cycle (XC), which is an indication of photoprotective capacity, and photosynthesis–irradiance (PE) response curves, at the surface and 20 m depth. The photophysiological parameters on the two sides differed along with the taxonomic signal derived from accessory pigments. On both sides, surface XC pigments showed high photoprotection capacity with the dinodinoxanthin–diatoxanthin (DD) and the violaxanthin, antheraxanthin and zeaxanthin cycles correlated with incoming radiation. The PE results showed that communities dominated by small flagellates on the western side performed better compared to diatom dominated communities on the eastern side. We conclude that phytoplankton and photosynthetic capacity differed consistent with known hydrography, with implications for a changing Arctic.

The effects of irradiance, temperature, and desiccation on the photosynthesis of a brown alga, Sargassum muticum (Fucales), from a native distributional range in Japan

We determined the effects of irradiance, temperature, and desiccation on the photosynthesis of a brown alga, Sargassum muticum (Fucales), from its native distributional range in Japan by using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and optical dissolved oxygen sensors. Photosynthesis–irradiance curves at three temperatures (8, 20, and 28°C) showed that the maximum net photosynthetic rates (NPmax) and saturation irradiance were highest at 28°C. Gross photosynthesis determined at 8–36°C (every four increments) and 300 μmol photons m−2 s−1 showed that the maximum gross photosynthetic rate (GPmax) occurred at 19.5°C ( $$ {T}_{\mathrm{opt}}^{\mathrm{GP}} $$ ), which is consistent with the seawater temperature at its peaked abundance in Japan. The maximum quantum yields (Fv/Fm) of photosystem II (PSII) during the 72-h temperature exposures were above 0.60 at 8–28°C but dropped at higher temperatures. Continuous exposure (12 h) to irradiance of 200 (low) and 1000 (high) μmol photons m−2 s−1 at three temperatures showed remarkable decline in the effective quantum yields (ΔF/Fm') of PSII under high irradiance at 8°C only; the Fv/Fm measured after 12-h dark acclimation also did not recover to initial values, signifying its sensitivity to photoinhibition at 8°C. Furthermore, the alga exhibited tolerance to 2 h of desiccation with 80% of water loss from the thallus, and ΔF/Fm' recovered after 24 h of rehydration in seawater, suggesting potential of photosynthetic recovery of this alga at such low hydration threshold. In conclusion, the adaptation of S. muticum to relatively high irradiance, to broad range of temperature (8–28°C), and to desiccation explains its potentially high invasive capacity.

Temperature characteristics on the growth and photosynthesis of a red alga Phycocalidia tanegashimensis (= Pyropia tanegashimensis, Bangiales) reveal adaptation to subtropical environments due to year-round occurrence of the macroscopic gametophyte

The effects of temperature on the photosynthesis and growth of a subtropical red alga, Phycocalidia tanegashimensis (= Pyropia tanegashimensis, Bangiaceae, Bangiales) from Tanegashima Island, Japan, were determined to better understand the ecology of the macroscopic gametophyte. Net photosynthesis–irradiance (P–E) curves, determined at 12, 20, and 28°C, revealed that the maximum net photosynthetic rates occurred at 28°C. A gross photosynthesis–temperature (P–T) curve, determined at temperatures between 8 and 36°C, supported this result and indicated that optimal temperature ( $$ {T}_{opt}^{GP} $$ ) for maximum gross photosynthetic rates was 27.3°C (25.9–28.8 95% highest density credible intervals, HDCI). However, after 4 days of incubation at constant temperature, the effective quantum yields (ΔF/Fm') of photosystem II, determined between 4 and 40°C under 50 μmol photons m−2 s−1 (12L:12D), were greatest at 22.1°C (20.9–23.4 HDCI) and declined quickly below 20°C and 32°C. The relative growth rate (RGR) was highest at 25.8°C (22.5–28.1 HDCI) at the conclusion of a 6-day culture (4 to 36°C) under 50 μmol photons m−2 s−1 (12L:12D). Compared to other temperate species of Bangiaceae, P. tanegashimensis appears to be well adapted to relatively high temperatures. The macroscopic gametophyte stage of Bangiaceae is regarded to be adapted to cold temperatures to overwinter; nevertheless, the significance of our study is that a year-round occurrence of P. tanegashimensis is enabled by its high optimal temperatures for photosynthesis and growth.