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The potentially biodeteriogenic, subaerial green alga Trentepohlia umbrina is widely distributed on shaded substrates with northern aspects. This preference for low light was confirmed by a recent survey in Lazio, Italy. However, the same survey revealed an isolated occurrence of extensive growths of T. umbrina-dominated biofilms on surfaces with diverse aspects that ranged from highly exposed to shaded. Prior studies of Trentepohlia photosynthesis have been restricted to single sites, so this multi-aspect site was particularly interesting to understand the photoacclimation potential of Trentepohlia. Photosynthetic pigment concentrations and chlorophyll fluorescence (in situ and ex situ) were used to assess the photosynthetic response to changes in light exposure and humidity. Pigment contents and photoinhibition decreased, while the maximum photosynthetic rate and the level of light that saturated photosynthesis increased with an increasing light exposure duration (ranging from c. 5 to 300 min d–1 of exposure to sunlight). Laboratory tests of relative humidity (RH) on biofilm photosynthesis showed no recorded activity up to 32% RH, only 26% of the maximum activity at 77% RH, and full activity at 92% RH. When T. umbrina was in the desiccated state a lowering of basal of chlorophyll a fluorescence emission and a loss of variable fluorescence occurred. This suppression of fluorescence when cells are desiccated is known to result in photoprotection of reaction centres from continuing high irradiances, as the enhanced thermal dissipation replaces slower and potentially damaging energy transfer to the functional reaction centres. It was concluded that T. umbrina has a much wider environmental range than previously thought, but its growth is very slow and may be overlooked during cultural heritage surveillance, leading to inconspicuous chronic degradation of outdoor stone substrata. [ABSTRACT FROM AUTHOR]

Coral reefs in the Northern Straits of Malacca (NSoM), Malaysia, are frequently exposed to high concentrations of total suspended solids (TSS), thus reducing the light availability for photosynthesis. This study describes the photosynthetic performances of Porites lutea inhabiting contrasting habitats of Pulau Kendi, Pulau Songsong, and Pulau Payar in the NSoM. The light attenuation (Kd(PAR)) was significantly different between all sites, whereby highly turbid water of Pulau Kendi has the highest Kd(PAR) (m−1) = 0.8 ± 0.0 and TSS (mg/L) = 95.7 ± 2.5 in comparison to the protected reef in Pulau Payar, Kd(PAR) (m−1) = 0.5 ± 0.0 and TSS (mg/L) = 36.7 ± 0.4. Here, Pulse-Amplitude-Modulated fluorometry (PAM) and Rapid Light Curves (RLCs) indicate that P. lutea exhibits a different trend of photosynthetic performances to cope with in situ light availability. Turbid waters of Pulau Kendi were observed to provide some protection from light-induced photoinhibition whereby the maximum photosynthetic yield (Fv/Fm = 0.8 ± 0.0) was significantly higher than those in Pulau Payar and Pulau Songsong. This observation suggested that they could survive near darkness with low light availability for photosynthesis, but a significant reduction in photosynthetic capacity (rETRmax = 77.5 ± 7.4) was also observed. In contrast, greater photosynthetic capacities were observed in P. lutea inhabiting the high-light environment of Pulau Payar. This study emphasized that P. lutea can photoacclimate by maximizing light availability for photosynthesis to ensure survival in turbid nearshore environments. [ABSTRACT FROM AUTHOR]

Diatoms are a type of photosynthetic phytoplankton that can acclimate to the light level of their environment. Diatoms from different habitats exhibit different photoacclimation characteristics; those from relatively low-light intensity habitats present relatively high photosynthetic activity, high light-harvesting pigment (Chla) content, and low xanthophyll content. Conversely, diatoms from high-light intensity environments have lower photosynthetic activity, less Chla content, and efficient xanthophyll cycling. Hence, diatoms can maintain high growth and photosynthetic activity within a wide range of light intensities. Whether the mechanisms of such adaptability are a consequence of biological photoacclimation to different light intensities or interspecific differences is unknown. Here, we show that differences in photoacclimation ability are more significant than species differences. We found similar species compositions in low- and high-light habitats of the Hanjiang River, China; however, there were remarkable differences in rapid light-response curve parameters. The photoacclimation of algae and trends in their photosynthetic activity can be estimated by rapid detection techniques. We isolated three diatom species common to both habitats and grew them under various light intensities, finding that they have an excellent ability to acclimate to local light conditions. Diatoms can use physiological strategies to handle light fluctuations, but only for short periods. Our results provide a theoretical basis for controlling algal blooms through light management. With knowledge of the photoacclimation characteristics of diatoms and according to the availability of local water conservancy facilities, it is possible to use light management to control diatom blooms more efficiently than with conventional techniques, thereby reducing water usage. [ABSTRACT FROM AUTHOR]

This study characterizes the photoacclimation and photoregulation mechanisms that allow calcified macroalgae of the genus Corallina (Corallinales, Rhodophyta) to dominate rock pool habitats across the NE Atlantic despite the highly variable irradiance regimes experienced. Rapid light curves (RLCs) were performed with pulse amplitude modulation (PAM) fluorometry in situ across a full seasonal cycle in the UK intertidal with C. officinalis and C. caespitosa. Latitudinal comparisons were performed across the full extent of C. officinalis’ range in the NE Atlantic (Iceland-northern Spain), and for C. caespitosa in northern Spain. Ex situ RLCs with dark recovery were further employed to assess the optimal, as compared with actual, photophysiology across seasons and latitudes. Corallina species were shown to photoacclimate at seasonal timescales to changing irradiance, increasing light-harvesting during low-light autumn/winter periods and protecting photosystems during high-light summer conditions. Seasonal photoacclimation was achieved through alteration in the number of photosystem (PS) units (PSII and light harvesting antennae) over time. Non-photochemical quenching (NPQ) served as an important photoregulation mechanism utilized by Corallina to prevent or minimize photoinhibition over shorter time scales (seconds-hours), though the efficiency of NPQ was dependent on the seasonal-acclimated state. With increasing latitude the efficiency of photoregulation decreased, representing potential differential photoadaptation of Corallina across species ranges in the NE Atlantic. In contrast, highly conserved inter-specific patterns in photophysiological responses to irradiance were apparent. This study demonstrates the photophysiological mechanisms allowing Corallina to optimize use of the variable irradiance conditions apparent in rock pool environments, when and how they are employed, and their limitations. [ABSTRACT FROM AUTHOR]

Batrachospermum turfosumBory is one of the generalists among the few red algae that have adapted to freshwater habitats, occurring in a variety of primarily shaded, nutrient-poor micro-habitats with lotic (running) or lentic (standing) waters. Seasonal variations in water level and canopy cover can expose this sessile alga to widely fluctuating temperatures, solar irradiation and nutrient availability. Here we report on the ecophysiology ofB. turfosumcollected from an ultra-oligotrophic bog pool in the Austrian Alps. Photosynthesis as a function of photon fluence density (PFD) and temperature was studied by measuring oxygen evolution in combination with chlorophyll fluorescence. In addition, the effects of ultraviolet radiation (UVR) on photosynthetic pigments were analysed using HPLC and spectrophotometric methods, and cellular ultrastructure was studied using transmission electron microscopy. We found thatB. turfosumis adapted to low light, with a light compensation point (Ic) and a light saturation point (Ik) of 8.4 and 29.7 µmol photons m–2s–1, respectively, but also tolerates higher PFDs of ~1000 µmol photons m–2s–1, and is capable of net photosynthesis at temperatures between 5°C and 35°C. Exposure to either UV-A or UV-AB for 102 h led to a strong transient drop in effective quantum yield (ΔF/FM’), followed by an acclimation to about 70% of initial ΔF/FM’ values. Ultrastructural changes included the accumulation of plastoglobules and dilated membranes after UVR treatment. Although all photosynthetic pigments strongly decreased upon UVR exposure and no UV-photoprotectants (e.g. mycosporine-like amino acids) could be detected, the alga was capable of recovering ΔF/FM’ and phycobiliproteins after UVR treatment. In summary,B. turfosumtolerates a wide range of irradiation and temperature regimes, and these traits may be the basis for its successful adaptation to challenging environments. [ABSTRACT FROM AUTHOR]

Reaching up to 50% of the total biomass in oligotrophic waters and armed with a set of ecological and biological properties related to their small size, picophytoplankton (<3.0 µm) are a good model to address ecophysiological questions regarding phytoplankton biodiversity. Two picoplanktonic diatoms, one isolated from an upwelling ecosystem in the Pacific Ocean (Minutocellus sp., strain RCC967), and another from oceanic waters in the Indian Ocean (Minutocellus sp., strain RCC703) were used to test hypotheses on the functional relation between ecological niche adaptation and photosynthetic regulation capacity and efficiency. Cultures were subjected to five sine light climates, each one set to peak at a different photon flux density, respectively 10, 50, 100, 250 and 500 µmol photons m−2 s−1. Growth rate, photosynthesis, non-photochemical fluorescence quenching, pigment composition, and particulate organic carbon and nitrogen content were followed daily for 5 days. Growth rate and physiological response curves were different in the two species, in agreement with their distinct habitats of origin. Such differences could be related to the diverse photoacclimative strategies displayed by the two species, revealing a clear adaptive divergence despite their close taxonomic relationship. Photoacclimative strategies of the two picoplanktonic diatoms are discussed in the light of functional diversity and ecosystem adaptation. [ABSTRACT FROM PUBLISHER]

This study investigated the impact of photon flux and elevated CO2 concentrations on growth and photosynthetic electron transport on the marine diatom Chaetoceros muelleri and looked for evidence for the presence of a CO2- concentrating mechanism (CCM). pH drift experiments clearly showed that C. muelleri has the capacity to use bicarbonate to acquire inorganic carbon through one or multiple CCMs. The final pH achieved in unbuffered cultures was not changed by light intensity, even under very low photon flux, implying a low energy demand of bicarbonate use via a CCM. In short-term pH drift experiments, only treatment with the carbonic anhydrase inhibitor ethoxyzolamide (EZ) slowed down the rise in pH considerably. EZ was also the only inhibitor that altered the final pH attained, although marginally. In growth experiments, CO2 availability was manipulated by changing the pH in closed flasks at a fixed dissolved inorganic carbon (DIC) concentration. Low-light-treated samples showed lower growth rates in elevated CO2 conditions. No CO2 effect was recorded under high light exposure. The maximal photosynthetic capacity, however, increased with CO2 concentration in saturating, but not in subsaturating, light intensities. Growth and photosynthetic capacity therefore responded in opposite ways to increasing CO2 availability. The capacity to photoacclimate to high and low photon flux appeared not to be affected by CO2 treatments. However, photoacclimation was restricted to growth photon fluxes between 30 and 300 mmol photons m-2 s-1. The light saturation points for photosynthetic electron transport and for growth coincided at 100 mmol photons m-2 s-1. Below 100 mmol photons m-2 s-1the light saturation point for photosynthesis was higher than the growth photon flux (i.e. photosynthesis was not light saturated under growth conditions), whereas at higher growth photon flux, photosynthesis was saturated below growth light levels. [ABSTRACT FROM AUTHOR]

Short-term ultraviolet (UV) radiation (280-400 nm) effects on xanthophyll cycle activity and photosynthesis were assessed during fluctuating irradiance (60- and 10-min cycles - saturating irradiance to near-zero irradiance) for the marine algae Thalassiosira weissflogii (Bacillariophyceae) and Dunaliella tertiolecta (Chlorophyceae). Laboratory cultures were cycled, as above, up and down the water column for 8 h under solar radiation, during which photosystem II (PSII) quantum yield in the light [(Fm, - Ft)/Fm,] was monitored over 1-min intervals. In addition, pigment composition, xanthophyll de-epoxidation state and carbon assimilation were assessed during the fluctuating irradiance cycles. Although PSII quantum yield in the light of both species mirrored irradiance, the PSII response to irradiance fluctuations changed over time as PSII quantum yield was downregulated at midday. This coincided with maximal xanthophyll de-epoxidation that developed during the course of the day for both species. In contrast to the deepoxidation levels, nonphotochemical quenching (NPQ) and PSII quantum yield in the light fluctuated with the irradiance dynamics at noon in both species. Maximal xanthophyll de-epoxidation and NPQ at noon was lower under photosynthetically active radiation (PAR) + UV than under PAR exposure for T. weissflogii during the 10-min cycle, whereas this was not found for the 60-min cycle and in D. tertiolecta. Synthesis of xanthophyll cycle pigments occurred in both species, and was faster for D. tertiolecta during PAR + UV than during PAR exposure. Carbon incorporation and on most occasions PSII quantum yield in the light were lower during UV exposure for both species, regardless of xanthophyll de-epoxidation state. UV effects on carbon assimilation were higher during 10-min than during 60-min irradiance fluctuation cycles. However, the 10-min irradiance fluctuation cycle appeared to enhance overall carbon assimilation in D. tertiolecta but depressed productivity of T. weissflogii, as compared with the 60-min cycles. [ABSTRACT FROM AUTHOR]

A non-calcifying strain (Ply 92) of Emiliania huxleyi (Lohman) Hay et Mohler, was subjected to reciprocal step changes of photon flux density (PFD) between 50 and 800 µmol photons m-2 s-1 to establish the timescales of photoacclimation. Photoacclimation in E. huxleyi involved adjustment of cellular light harvesting pigment contents, but not cellular ribulose bisphosphate carboxylase-oxygenase (RuBisCO) or cellular RNA contents. There was considerable variability in both the magnitude and the rate of the response of physiological and biophysical variables to the step changes in PFD. The slowest response was observed in cellular chl a content, and the chl a/carbon ratio. Acclimation of these variables appeared to be due to dilution of pigment pools rather than to pigment turnover. Changes in the chl a-specific light absorption coefficient accompanied changes in cellular chl a content. Following the shifts in PFD, the efficiency of excitation energy transfer from the photosystem II antennae to reaction centres II (RCII), as assessed from [image omitted], adjusted within 12 h. The efficiency of charge separation within RCII, as assessed from [image omitted], adjusted on a similar timescale. The overall efficiency of photosystem II (PSII), as assessed from [image omitted]/ [image omitted], showed a step response to the change of PFD due to inverse changes in [image omitted], and [image omitted]. Changes in non-photochemical excitation energy quenching were correlated with the relative and absolute abundance of the xanthophyll cycle pigments diadinoxanthin and diatoxanthin, which appeared to be reversibly interconverted with fucoxanthin. Thus, acclimation to PFD involved co-ordinated adjustment of the quantum efficiency of RCII, the efficiency of excitation energy transfer from the light-harvesting pigment bed to RCII, and cellular light absorption on overlapping time scales. [ABSTRACT FROM AUTHOR]

Estuarine microphytobenthos are frequently exposed to excessively high irradiances. Photoinhibition in microalgae is prevented by various photophysiological responses. We describe here the role of the xanthophyll pigments in photoacclimation. The pigment composition of the microphytobenthos was studied in three European estuaries (Barrow, Ireland; Eden, UK; Tagus, Portugal). Using HPLC-analyses, microscale changes in biomass and pigment composition were monitored over short (hourly) and long (seasonal) time scales. In the Barrow estuary, the biomass of microphytobenthos (measured as chlorophyll a) increased significantly in the top 400-500 µm of the sediment surface within 1 h of emersion; simultaneously, the xanthophyll pool size (diadinoxanthin plus diatoxanthin, dd + dt) almost doubled. A more gradual conversion of dd into dt was observed, with the dt:dd ratio increasing from at the start of emersion to 0.3 after 3 h emersion. Similar trends in the dt:dd ratio were observed in the surface sediments of the Eden and the Tagus estuaries. Higher ratios were recorded in the Tagus estuary, which may be explained by higher incident irradiance. In addition, seasonal studies carried out in the Eden and Tagus estuaries showed that the xanthophyll pool size increased by 10% in the summer months. The pool size was highest in the Tagus estuary. Concurrently, high values for the de-epoxidation state were recorded, with values for dt/(dt + dd) > 0.35 recorded in the summer. At the Eden, the ratio never exceeded 0.3. The de-epoxidation state was higher in winter than in summer, which was ascribed to the low winter temperatures. During a vertical migration study, a negative relationship between chlorophyll a and the de-epoxidation state was observed. It is suggested that this relationship originates from 'micro-migration' within the biofilm. Migration within the euphotic zone may provide an alternative means for cells to escape photodamage. In this paper, we propose that both xanthophyll cycling and 'micro'-migration play an important role in photoacclimation and it appears that these processes operate in parallel to regulate the photosynthetic response. [ABSTRACT FROM AUTHOR]

The kelp Ecklonia radiata is found in the sublittoral zone in the Doubtful Sound complex, and is most abundant at the coastal entrance with abundance declining toward the head of the Sound. A feature of the fjord is a persistent tannin-stained, low-salinity layer (LSL) on the surface of the underlying salt water. In this unique marine environment there is an inverse relationship between the thickness of the LSL and light levels — at the head of Doubtful Sound the LSL is thicker and light reaching E. radiata at depth can be extremely low; the inverse occurs at the coastal entrance. The mountainous terrain reduces light further, particularly on the northern aspect of the fjord. To assess whether E. radiata showed evidence of photoacclimation across this light gradient, sporophytes were collected from five sites within the complex in November 2000. Pigment contents [chlorophyll (chl) a, c and fucoxanthin], photosynthetic parameters [maximum photosynthetic rate (Pmax), alpha (α), respiration rate (Rd), saturation photon-flux density (PFD) (Ek), compensation PFD (Ec) and photoinhibition (β)] and morphological parameters of E. radiata were measured. Results indicate that E. radiata acclimates to the low light at sites near the head of the fjord by increasing pigment contents, particularly chl a, as well as the surface area of the thallus. Furthermore, E. radiata increases its efficiency at capturing and transferring energy at low light by increasing a and decreasing Ek and Ec values. In doing so, E. radiata maintains similar dry weight-normalized Pmax at the five sites. It is suggested that photoacclimation may therefore be a process by which E. radiata overcomes the reduced light imposed by the LSL and extends its distribution towards the inner reaches of the fjord. [ABSTRACT FROM AUTHOR]