Ecophysiological characteristics of four intertidal marine macroalgae during emersion along Shantou coast of China,with a special reference to the relationship of photosynthesis and CO_(2)

Intertidal marine macroalgae experience periodical exposures during low tide due to their zonational distribution. The duration of such emersion leads to different exposures of the plants to light and aerial CO2, which then affect the physiology of them to different extents. The ecophysiological responses to light and CO2 were investigated during emersion in two red algae Gloiopeltis furcata and Gigartina intermedia, and two brown algae Petalonia fascia and Sargassum hemiphyllum, growing along the Shantou coast of China. The light-saturated net photosynthesis in G. furcata and P. fascia showed an increase followed by slightly desiccation, whereas that in G. intermedia and S. hemiphyllumexhibited a continuous decrease with water loss. In addition, the upper-zonated G. furcata and P. fascia, exhibited higher photosynthetic tolerance to desiccation and required higher light level to saturate their photosynthesis than the lower-zonated G. intermedia and S. hemiphyllum. Desiccation had less effect on dark respiration in these four algae compared with photosynthesis. The light-saturated net photosynthesis increased with increased CO2 concentrations, being saturated at CO2 concentrations higher than the present atmospheric level in G. furcata, G. intermedia and S. hemiphyllum during emersion. It was evident that the relative enhancement of photosynthesis by elevated CO2 in those three algae increased, though the absolute values of photosynthetic enhancement owing to CO2 increase were reduced when the desiccation statuses became more severe. However, in the case of desiccated P. fascia (water loss being greater than 20 %), light saturated net photosynthesis was saturated with current ambient atmospheric CO2 level. It is proposed that increasing atmospheric CO2 will enhance the daily photosynthetic production in intertidal macroalgae by varied extents that were related to the species and zonation.

Genoprotection and metabolic benefits of marine macroalgae-Insights into the concept of functional foods through direct and indirect consumption

The consumption of marine macroalgae has been linked with health benefits,albeit some actions,including genoprotection,remain underexplored.Hence,we evaluated the genoprotective potential of a mixture of Ulva rigida,Fucus vesiculosus and Gracilaria gracilis,through direct consumption or via indirect intake using fish(Sparus aurata)as a vector of algal phytocompounds.Mice(Mus musculus)were subjected to a 1-month dietary supplementation with 5%of macroalgae mix or 10%of fillet of fish previously fed with an algae-supplemented aquafeed(for comparison purposes,10%supplementation with fillet of fish standardly fed was also considered).Thereafter,mice were challenged by the genotoxicant methyl methanesulfonate(MMS),and the genetic damage was evaluated through the micronuclei test.Complementarily,a wider evaluation was carried out encompassing the assessment of energy metabolism,haematological and histological parameters,as well as growth performance.Macroalgae unequivocally protected against MMS-induced genotoxicity.The activity profile of hepatic lactate and isocitrate dehydrogenases promoted by the supplemented diets reflected an improved energy balance.Genoprotection properties were not transferred via fish fed with the algae-supplemented aquafeed,though the transference of phytocomponents with beneficial properties(viz.energy balance improvement)should not be disregarded.Overall,these findings highlighted the genoprotection afforded by marine macroalgae,likely promoted by desmutagenic factors,reinforcing their definition as functional food.The possibility of using fish as an indirect source of algae-borne phytocomponents proved to be plausible and worthy of further investigations.

Dark respiration in the light and in darkness of three marine macroalgal species grown under ambient and elevated CO_2 concentrations

Dark respiration （non-photorespiratory mitochondrial respiration）, which occurs both in the light and in darkness, is vital for growth and survival of algae and plays a critical role in modulating the carbon balance of them. In the present study, we have investigated dark respiration in the light （RL） and in darkness （RD） in three marine macroalgal species, Hizikia fusiformis （phaeophyta）, Gracilaria lemaneiformis （Rhodophyta） and Ulva lactuca （Chlorophyta）, cultured at 20 ℃ using aeration with two CO2 conditions： current ambient （CO2 concentration about 380 μl/L） and elevated CO2 （approximately 720 μl/L） air. RL was estimated by using the Kok method, whereas RD was determined as the rate of O2 influx at zero light. The results showed that both RL and RD were unchanged for the elevated CO2-grown algae relative to ambient CO2 concentration for all the algal species tested. However, RL was significantly lower than RD across all the algal species and growth CO2 treatments, demonstrating that daytime respiration was partly depressed by the light. The percentage of inhibition of respiration by light was similar between ambient and elevated CO2- grown algae. The ratio of respiration to photosynthesis, which tended to decrease when estimated using RL instead of RD, was not altered for the elevated relative to ambient CO2 concentration. The results suggest that RL, rather than RD, is a more accurate estimate of nonphotorespiratory carbon loss in marine macroalgae during the daytime. It would not be anticipated that elevated atmospheric CO2 would exert a substantial influence on respiratory flux either in the light or in darkness in these particular marine macroalgal species.

Transcriptome sequencing of essential marine brown and red algal species in China and its significance in algal biology and phylogeny

Most phaeophytes （brown algae） and rhodophytes （red algae） dwell exclusively in marine habitats and play important roles in marine ecology and biodiversity. Many of these brown and red algae are also important resources for industries such as food, medicine and materials due to their unique metabolisms and me-tabolites. However, many fundamental questions surrounding their origins, early diversification, taxonomy, and special metabolisms remain unsolved because of poor molecular bases in brown and red algal study. As part of the 1 000 Plant Project, the marine macroalgal transcriptomes of 19 Phaeophyceae species and 21 Rhodophyta species from China＇s coast were sequenced, covering a total of 2 phyla, 3 classes, 11 orders, and 19 families. An average of 2 Gb per sample and a total 87.3 Gb of RNA-seq raw data were generated. Approxi-mately 15 000 to 25 000 unigenes for each brown algal sample and 5 000 to 10 000 unigenes for each red algal sample were annotated and analyzed. The annotation results showed obvious differences in gene expres-sion and genome characteristics between red algae and brown algae;these differences could even be seen between multicellular and unicellular red algae. The results elucidate some fundamental questions about the phylogenetic taxonomy within phaeophytes and rhodophytes, and also reveal many novel metabolic pathways. These pathways include algal CO2 fixation and particular carbohydrate metabolisms, and related gene/gene family characteristics and evolution in brown and red algae. These findings build on known algal genetic information and significantly improve our understanding of algal biology, biodiversity, evolution, and potential utilization of these marine algae.

Competition among rare earth elements on sorption onto six seaweeds

Sorption has been proposed as a promising approach towards a sustainable water decontamination and recently to the recycling of rare earth elements(REE).Although living seaweed have been shown to be capable of removing REE from contaminated solutions,no studies have yet compared the effects of REE competition on sorption onto different groups of seaweed.These effects were analysed in the present study by exposing six living seaweeds(Ulva lactuca,Ulva intestinalis,Fucus spiralis,Fucus vesiculosus,Gracilaria sp.and Osmundea pinnatifida)(3 g/L,fresh weight) to mono-element and multi-element solutions of Y,La,Ce,Pr,Nd,Eu,Gd,Tb and Dy(1 μmol/L).Results show a preference towards light REE in mono-element solutions,which is reduced when in competition with other REE.The competitive effect is less pronounced in heavy REE indicating that these are still able to bind to the macroalgae despite the presence of competing ions.Contrary to water content(%),seaweed specific surface area(cm^(2)/g) shows to be an important factor in the sorption of REE,since larger surface area is associated with higher removal and larger competitive effect.