Future CO2-induced seawater acidification mediates the physiological performance of a green alga Ulva linza in different photoperiods

Effects of photoperiod on the growth and physiological responses in Ulva prolifera under constant and diurnal temperature difference conditions

Photoperiod and temperature are two main factors in the growth of macroalgae, and changes in photoperiod and diurnal temperature difference exist in natural condition. In order to study the effects of photoperiod and diurnal temperature difference on the growth of green algae Ulva prolifera, we cultured this species under three light/dark cycles (light: dark = 10:14, 12:12 and 16:08) with constant (22 °C for light and dark period, noted as 22-22 °C) and diurnal temperature difference (22 °C and 16 °C for light and dark period, respectively, noted as 22-16 °C) conditions. The results showed that: 1) Compared with 10:14 light/dark cycle, the growth of U. prolifera under 12:12 light/dark cycle was significantly enhanced by 39% and 16% for 22-22 °C and 22-16 °C treatments, respectively, while the increase proportion decreased when the daylength increase from 12 h to 16 h. 2) The enhancement in growth induced by diurnal temperature difference was observed under 10:14 light/dark cycle, but not for 12:12 and 16:08 light/dark cycle treatments. 3) The Chl a content and photosynthetic rate increased under short light period and 22-22 °C conditions, while under 22-16 °C conditions, higher photosynthetic rate was observed under 12:12 light/dark cycle and no significant difference in Chl a content was observed. 4) Under 22-22 °C conditions, compared with 10:14 (L:D) treatment, the expression levels of proteins in light-harvesting complexes, PSII and carbon fixation were down regulated, while the photorespiration and pentose phosphate pathway (PPP) were up regulated by 16:08 light dark cycle. Then we speculate that the higher photosynthetic rate may be one compensation mechanism in short photoperiod, and under long light period condition the up regulations of photorespiration and PPP can be in charge of the decrease in enhancement growth induced by longer daylength.

A metabolomic snapshot through NMR revealed differences in phase transition during the induction of reproduction in Ulva ohnoi (Chlorophyta)

The present study deals with the metabolomic status of Ulva cells undergoing phase transition (vegetative, determination and differentiation) when exposed to different abiotic conditions. The objective was to study whether metabolite changes occurring during the phase transition reveal any commonality among differential abiotic conditions. The phase transition was followed through microscopic observations and 1H NMR characterization at 0 h, 24 h, and 48 h after the incubation of the thallus under abiotic conditions, such as different salinities (20-35 psu), temperatures (20-35 °C), photoperiods (18 : 6, 12 : 12, and 6 : 18 D/N), light intensities (220, 350, and 500 μmol photons m-2 s-1), nitrate (0.05-0.2 g L-1) and phosphate (0.05-0.2 g L-1) concentrations. Microscopic analysis revealed the role of all abiotic conditions except variable salinity and phosphate concentration in phase transition. NMR analysis revealed that glucose increased in the determination phase [7.58 to 9.62 normalized intensity (AU)] and differentiation phase (5.85 to 6.41 AU) from 20 °C to 25 °C temperature. Coniferyl aldehyde increased in vegetative (5.79 to 6.83 AU) and differentiation (6.66 to 7.40 AU) phases from 20 °C to 30 °C temperature. The highest average (22.97) was found in photoperiod (average range = 0-122.91) and the highest SD (24.73) in salinity (SD range = 1.86-57.04) in region 9 (creatinine and cysteine) of the differentiation phase. A total of 30 metabolites were identified under the categories of sugars, amino acids, and aromatic compounds. The present study will aid in understanding the mechanisms underlying cell differentiation during reproduction. The result may serve as an important reference point for future studies, besides helping in controlling seedling preparation for commercial farming as well as the management of rapid green tide formation.

Optimizing inorganic carbon and salinity for enhanced biomass and pigment production in Colaconema formosanum: Implications for sustainable carbon sequestration and stress responses

This study investigates a cultivation strategy for the macroalga Colaconema formosanum by determining optimal inorganic carbon concentration and salinity for maximizing biomass and photosynthetic pigment production while also facilitating carbon sequestration. The response surface method was used with a central composite design (CCD-RSM) to determine the optimal conditions. Results showed that adding 1.2 g/L of carbon increased the specific growth rate to 18%-19% per day. The maximum amount of pigment, including phycobiliprotein and chlorophyll, was achieved by adjusting both carbon content and salinity. This strategy enables mass pigment production and offers an eco-friendly approach to carbon sequestration while reducing culture period. This study also sheds light on algal mechanisms against enriched inorganic carbon and salinity content, contributing to an enhanced understanding of these vital processes.

Enhanced Colaconema formosanum biomass and phycoerythrin yield after manipulating inorganic carbon, irradiance, and photoperiod

Due to an increasing CO₂ concentration leading to global warming, the techniques as carbon capture utilization and storage are currently critical issues. This study aimed to investigate a cultivation strategy using optimal inorganic carbon level, irradiance, and photoperiod for producing the highest biomass and photosynthesis pigment contents (chlorophyll and phycobiliprotein) in the macroalga Colaconema formosanum. The results revealed that adding 1 g L^-1 carbon increases phycoerythrin ratio by 12.52-13.74% and decreases allophycocyanin by 10.4-9.57%. Optimal conditions can increase algal growth by 60%, providing 5-6 mg g^-1 total phycobiliprotein and 650-680 µg g^-1 total chlorophyll. The results in this study illustrate the sensitivity of photosynthesis pigment after treatment with carbon, and suggest a hypothesis explaining the mechanism. The results also provide a feasible use of carbon for high-value large-scale production of pigment in the macroalgae industry.

Climate change influences chlorophylls and bacteriochlorophylls metabolism in hypersaline microbial mat

This study aimed to determine the effect of the climatic change on the phototrophic communities of hypersaline microbial mats. Ocean acidification and warming were simulated alone and together on microbial mats placed into mesocosms. As expected, the temperature in the warming treatments increased by 4 °C from the initial temperature. Surprisingly, no significance difference was observed between the water pH of the different treatments despite of a decrease of 0.4 unit pH in the water reserves of acidification treatments. The salinity increased on the warming treatments and the dissolved oxygen concentration increased and was higher on the acidification treatments. A total of 37 pigments were identified belonging to chlorophylls, carotenes and xanthophylls families. The higher abundance of unknown chlorophyll molecules called chlorophyll derivatives was observed in the acidification alone treatment with a decrease in chlorophyll a abundance. This change in pigmentary composition was accompanied by a higher production of bound extracellular carbohydrates but didn't affect the photosynthetic efficiency of the microbial mats. A careful analysis of the absorption properties of these molecules indicated that these chlorophyll derivatives were likely bacteriochlorophyll c contained in the chlorosomes of green anoxygenic phototroph bacteria. Two hypotheses can be drawn from these results: 1/ the phototrophic communities of the microbial mats were modified under acidification treatment leading to a higher relative abundance of green anoxygenic bacteria, or 2/ the highest availability of CO₂ in the environment has led to a shift in the metabolism of green anoxygenic bacteria being more competitive than other phototrophs.

Ocean acidification exacerbates copper toxicity in both juvenile and adult stages of the green tide alga Ulva linza

The toxicity of heavy metals to coastal organisms can be modulated by changes in pH due to progressive ocean acidification (OA). We investigated the combined impacts of copper and OA on different stages of the green macroalga Ulva linza, which is widely distributed in coastal waters, by growing the alga under the addition of Cu (control, 0.125 (medium, MCu), and 0.25 (high) μM, HCu) and elevated pCO₂ of 1,000 μatm, predicted in the context of global change. The relative growth rates decreased significantly in both juvenile and adult thalli at HCu under OA conditions. The net photosynthetic and respiration rates, as well as the relative electron transfer rates for the adult thalli, also decreased under the combined impacts of HCu and OA, although no significant changes in the contents of photosynthetic pigments were detected. Our results suggest that Cu and OA act synergistically to reduce the growth and photosynthetic performance of U. linza, potentially prolonging its life cycle.

Elevated CO2 concentration alleviates UVR-induced inhibition of photosynthetic light reactions and growth in an intertidal red macroalga

The commercially important red macroalga Pyropia (formerly Porphyra) yezoensis is, in its natural intertidal environment, subjected to high levels of both photosynthetically active and ultraviolet radiation (PAR and UVR, respectively). In the present work, we investigated the effects of a plausibly increased global CO₂ concentration on quantum yields of photosystems II (PSII) and I (PSI), as well as photosynthetic and growth rates of P. yezoensis grown under natural solar irradiance regimes with or without the presence of UV-A and/or UV-B. Our results showed that the high-CO₂ treatment (~1000 μbar, which also caused a drop of 0.3 pH units in the seawater) significantly increased both CO₂ assimilation rates (by 35%) and growth (by 18%), as compared with ambient air of ~400 μbar CO₂. The inhibition of growth by UV-A (by 26%) was reduced to 15% by high-CO₂ concentration, while the inhibition by UV-B remained at ~6% under both CO₂ concentrations. Homologous results were also found for the maximal relative photosynthetic electron transport rates (rETR_max), the maximum quantum yield of PSII (F_v/F_m), as well as the midday decrease in effective quantum yield of PSII (YII) and concomitant increased non-photochemical quenching (NPQ). A two-way ANOVA analysis showed an interaction between CO₂ concentration and irradiance quality, reflecting that UVR-induced inhibition of both growth and YII were alleviated under the high-CO₂ treatment. Contrary to PSII, the effective quantum yield of PSI (YI) showed higher values under high-CO₂ condition, and was not significantly affected by the presence of UVR, indicating that it was well protected from this radiation. Both the elevated CO₂ concentration and presence of UVR significantly induced UV-absorbing compounds. These results suggest that future increasing CO₂ conditions will be beneficial for photosynthesis and growth of P. yezoensis even if UVR should remain at high levels.

Microplastics in bloom-forming macroalgae: Distribution, characteristics and impacts

Macroalgal blooms and marine microplastics (MPs), as global challenges for oceans, are both showing a rising trend. However, none is known regarding the interaction of these two important issues. The Yellow Sea suffers the world's largest green tides and severe MPs pollution as well. Therefore, we tracked the trapping of MPs by drifting Ulva prolifera in the Yellow Sea during the green-tide period. The abundance of MPs in drifting U. prolifera was 595-3917 times higher than that in seawater and increased along the drifting path from south to north in the Yellow Sea. In addition, four mechanisms of trapping plastics (twining, attachment, embedment, and wrapping) on or in U. prolifera were unmasked, which explains why the plant has such strong capacity to trap MPs. Laboratory incubation experiments showed that MPs (0.025-25 mg L^-1) did not affect relative growth rate, effective photochemical efficiency of photosystem II (PSII), or saturating irradiance of U. prolifera until reaching an extremely high concentration (100 mg L^-1), indicating a high tolerance to MPs. Due to tremendous biomass and coverage of the green tide and increased frequency as well, the plastics trap in drifting macroalgae can alter the spatio-temporal distribution of MPs in the oceans.