Higher Chlorophyll Content Research Articles

Environmental heterogeneity of a tropical river-to-sea continuum and its relationship with structure and phytoplankton dynamics – Lençóis Maranhenses National Park

β-diversity and functional traits of phytoplankton indicators associated with environmental heterogeneity were investigated as environmental quality descriptors in coastal (CS), estuarine (ES), and limnetic (LS) sectors in a tropical river-to-sea ecosystem. Results showed that environmental heterogeneity was marked by spatial differences, contributing to biological heterogeneity. Sporadic and recurrent blooms were associated with environmental spatiotemporal variations and reflected a reduction in ES α-diversity. Salinity acted as an environmental filter that governed the structure and dynamics of the community. The spatial heterogeneity and high turnover of phytoplankton resulted in reliable bioindicators selection. Colonial, bloom-forming and harmful species were associated with highly suspended particulate matter (SPM) because these species are better adapted to these conditions. Species small in size were associated with high concentrations of silicate and chlorophyll-a in the ES because of the occurrence of diatom recurrent blooms. Most flagellates indicators genera have bloom-forming potential. Integrating morphofunctional with taxonomic approaches enabled detailed observations of environmental filters, supporting the selection of priority species and areas for introducing biodiversity monitoring programs and conservation in tropical ecosystems.

Overexpression of the Wheat TaPsb28 Gene Enhances Drought Tolerance in Transgenic Arabidopsis

Psb28 is a soluble protein in the photosystem II (PSII) complex, but its role in the drought stress response of wheat remains unclear. Here, we functionally characterized the TaPsb28 gene, which positively regulates drought tolerance in wheat. When the full-length 546-bp TaPsb28 cDNA was transferred into Arabidopsis thaliana, it was located in the guard cell chloroplast around the stroma. Overexpression of TaPsb28 conferred drought tolerance, as exhibited by the increases in the survival rate. Transgenic plants maintained lower MDA content and higher chlorophyll content by inducing chlorophyll synthase (ChlG) gene transcription. The content of abscisic acid (ABA) and zeatin increased significantly in wild-type (WT) plants under drought stress, and the transcriptional expression levels of RD22, dihydroflavonol 4-reductase (DFR) and anthocyanin reductase (ANR) genes were induced, thus enhancing the contents of endogenous cyanidin, delphinidin, and proanthocyanidins. However, in transgenic plants, although anthocyanins were further aggregated, the ABA increase was inhibited, zeatin was restored to the control level under drought stress, and stomatal closure was promoted. These findings indicate ABA and zeatin have opposite synergistic effects in the process of drought tolerance caused by TaPsb28 because only after the effect of zeatin is alleviated can ABA better play its role in promoting anthocyanin accumulation and stomatal closure, thus enhancing the drought tolerance of transgenic plants. The results suggest that overexpression of TaPsb28 exerts a positive role in the drought response by influencing the functional metabolism of endogenous hormones. The understanding acquired through the research laid a foundation for further in-depth investigation of the function of TaPsb28 in drought resistance in wheat, especially its relationship with anthocyanidin accumulation.

Overexpression of LjPLT3 Enhances Salt Tolerance in Lotus japonicus.

Intracellular polyols are used as osmoprotectants by many plants under environmental stress. However, few studies have shown the role of polyol transporters in the tolerance of plants to abiotic stresses. Here, we describe the expression characteristics and potential functions of Lotus japonicus polyol transporter LjPLT3 under salt stress. Using LjPLT3 promoter-reporter gene plants showed that LjPLT3 was expressed in the vascular tissue of L. japonicus leaf, stem, root, and nodule. The expression was also induced by NaCl treatment. Overexpression of LjPLT3 in L. japonicus modified the growth rate and saline tolerance of the transgenic plants. The OELjPLT3 seedlings displayed reduced plant height under both nitrogen-sufficient and symbiotic nitrogen fixation conditions when 4 weeks old. The nodule number of OELjPLT3 plants was reduced by 6.7-27.4% when 4 weeks old. After exposure to a NaCl treatment in Petri dishes for 10 days, OELjPLT3 seedlings had a higher chlorophyll concentration, fresh weight, and survival rate than those in the wild type. For symbiotic nitrogen fixation conditions, the decrease in nitrogenase activity of OELjPLT3 plants was slower than that of the wild type after salt treatment. Compared to the wild type, both the accumulation of small organic molecules and the activity of antioxidant enzymes were higher under salt stress. Considering the concentration of lower reactive oxygen species (ROS) in transgenic lines, we speculate that overexpression of LjPLT3 in L. japonicus might improve the ROS scavenging system to alleviate the oxidative damage caused by salt stress, thereby increasing plant salinity tolerance. Our results will direct the breeding of forage legumes in saline land and also provide an opportunity for the improvement of poor and saline soils.

Selection of oat (Avena sativa L.) drought-tolerant genotypes based on multiple yield-associated traits.

Most plant breeding and agricultural practices are based on selecting genotypes for yield. However, this is inadequate to screen crop varieties for specific attributes, such as drought tolerance. In this study, we quantified the response of oat (Avena sativa L.) plant physiological and morphological traits to drought stress and selected some key traits to establish a genotype by yield*trait (GYT)-based method for ranking 30 oat genotypes. The effectiveness of this method was also evaluated under drought conditions. Water-deficit treatment significantly reduced leaf chlorophyll, root morphological traits, groat yield and associated components, such as mean grain weight. We observed that the genotypes 'JUSTICE' and 'BOLINA' had the smallest and largest yield loss, respectively, after exposure to drought stress, but showed opposite trends in the biomass allocation of roots and grains. This indicated that drought tolerance was highly dependent on the distribution of photoassimilates. Our results also illustrated that the GYT method is a trade-off approach and more effective in selecting oat ideotypes under drought conditions than the yield-related index method because it combines yield, yield stability, and related agronomic traits in the calculation process. Drought-tolerant genotypes had more biomass allocated to roots and grains with higher chlorophyll content and better root structure, e.g. longer root lengths than drought-sensitive lines. By integrating yield and yield-related traits, the GYT approach is more practical than traditional single-trait selection methods when assessing drought tolerance. © 2023 His Majesty the King in Right of Canada. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Data-Independent Acquisition Proteomics Reveals the Effects of Red and Blue Light on the Growth and Development of Moso Bamboo (Phyllostachys edulis) Seedlings

Moso bamboo is a rapidly growing species with significant economic, social, and cultural value. Transplanting moso bamboo container seedlings for afforestation has become a cost-effective method. The growth and development of the seedlings is greatly affected by the quality of light, including light morphogenesis, photosynthesis, and secondary metabolite production. Therefore, studies on the effects of specific light wavelengths on the physiology and proteome of moso bamboo seedlings are crucial. In this study, moso bamboo seedlings were germinated in darkness and then exposed to blue and red light conditions for 14 days. The effects of these light treatments on seedling growth and development were observed and compared through proteomics analysis. Results showed that moso bamboo has higher chlorophyll content and photosynthetic efficiency under blue light, while it displays longer internode and root length, more dry weight, and higher cellulose content under red light. Proteomics analysis reveals that these changes under red light are likely caused by the increased content of cellulase CSEA, specifically expressed cell wall synthetic proteins, and up-regulated auxin transporter ABCB19 in red light. Additionally, blue light is found to promote the expression of proteins constituting photosystem II, such as PsbP and PsbQ, more than red light. These findings provide new insights into the growth and development of moso bamboo seedlings regulated by different light qualities.

Male and female poplars exhibited sex-specific differences in metabolic and transcriptional responses to two levels of water deficit

Dioecious plant species exhibit sexual dimorphism in morphology and physiology under water deficit conditions, but the metabolic and molecular mechanisms underlying such differences are barely explored. In this study, we integrated metabolome and transcriptome analyses of female and male full-sibs of Populus deltoides that featured different drought tolerance in response to moderate and severe water shortage conditions. The results showed that male poplars had higher chlorophyll content and photosynthetic capacity, which result in a better growth performance than female poplars under drought conditions. The metabolome profiling revealed that both the quantification and qualification of differentially expressed metabolites in male poplars were higher than those in females. The transcriptome analysis revealed that the KEGG pathway was enriched in plant hormone signal transduction and carotenoid biosynthesis pathway in both male and female poplars under water deficiency. Moreover, the number of differentially expressed genes (DEGs) that were altered by plant sex was much lower than that by drought treatment. Simultaneously, most of these DEGs were up-regulated in male poplars, especially the key genes that involve in ABA synthetic pathway. The results revealed the metabolic and molecular mechanisms underlying the better ability of drought resistance observed in male poplar plants.

The effect of additional shading utilizing agriphotovoltaic structures on the visual qualities and metabolites of broccoli.

Agriphotovoltaic (APV) systems allow the simultaneous production of crops and electricity in the same land area. Since the reduction of yield caused by APV systems is important for food security, studies to improve the yield have been conducted steadily. However, there have been limited data on the appearance, quality, and metabolomic changes of crops. Therefore, in this study, we evaluated the visual qualities and metabolites as well as the yield of broccoli grown using an APV system during the fall season. In addition, additional shading treatment was performed, and the same qualities were evaluated. In the spring season, an additional cultivar that does not express anthocyanins was cultivated. Glucosinolate content was more sensitive to the seasonal environment and the type of cultivar than it was to treatment type. The additional shading treatment had a positive effect on the visual qualities of anthocyanin-expressing broccoli cultivar regardless of the season, and we observed that even a cultivar that does not express anthocyanins can be greener. Regardless of cultivar, higher chlorophyll content was detected in broccoli florets with additional shading treatment under the APV system. In addition, reduced anthocyanin content was observed (6.1 mg g-1 DW; about 20% of that obtained on open-field). Aspartic acid content was enhanced upon additional shading treatment. Pathway analysis revealed changes in anthocyanin, alanine, aspartic acid, and glutamic acid metabolism. Overall, our findings suggests that it is possible to produce crops with better visual qualities by utilizing APV systems.

Plant growth regulators preserved the longevity of cut stems of Chrysanthemum morifolium by orchestrating physio-biochemical and anatomical responses

The marketability of cut flowers is determined by their postharvest quality parameters. Among these parameters, vase life is most crucial and different plant growth regulators (PGRs) play a significant role in regulating vase life. With the objective, to regulate vase life and other quality parameters of commercially important cut stems of chrysanthemum cv. White Star, a study was planned to have an insight into the role of different PGRs in orchestrating underlying physio-biochemical and anatomical responses. Three PGRs viz., Benzyl adenine (50, 100, 150 and 200 μM BA), Thidiazuron (5, 10, 15 and 20 μM TDZ) and Salicylic acid (50, 100, 150 and 200 μM SA) were used as pulsing solution. The results revealed that PGR especially 10 μM TDZ delayed leaf and floret senescence as compared to control. The visual observations (retention of green colour of leaves and white of florets) were correlated to enhanced water absorption, relative water content, membrane stability index, total soluble sugars and total soluble proteins ; higher content of chlorophyll in leaves and lower content of carotenoids and anthocyanins in florets. Further, the antioxidant enzymes (peroxidase and catalase) activities were also higher in PGR-treated stems than in control. These results were further supported by anatomical studies that indicated minimum blockage in xylem and maintenance in turgidity of cells as revealed through the size of tissues (radius of pith) of treated stems (control-118.48 mm and 10 μM TDZ-177.94 mm). Although all PGR concentrations significantly maintained relative water content, membrane stability index, respiratory substrates and antioxidant activity for a longer time, the low concentrations of TDZ had the most relevant impact on longevity. The longevity of stems treated with10 μM TDZ was up to 23 days as compared to 13 days in control. So 10 μM TDZ could be used as a chemical tool to improve chrysanthemum longevity and increase its commercial potential.

The effect of shift in physiological and anatomical traits on light use efficiency under cotton domestication.

The effect of crop domestication on photosynthetic productivity has been well-studied, but at present, none examines its impacts on leaf anatomy and, consequently, light use efficiency in cotton. We investigated leaf and vein anatomy traits, light use efficiency (LUE) and gas exchange in 26 wild and 30 domesticated genotypes of cotton grown under field conditions. The results showed that domestication resulted in a higher photosynthetic rate, higher stomatal conductance, and lower lamina mass per area. Higher LUE was underpinned by the thicker leaves, greater vein volume, elongated palisade and higher chlorophyll content, although there was no difference in the apparent quantum yield. The lower vein mass per area in domesticated genotypes contributed to the reduction of lamina mass per area, but there was no decrease in vein length per area. Our study suggests that domestication has triggered a considerable shift in physiological and anatomical traits to support the increase in LUE.

Stimulating algal growth through wood ash fertilization in the Åkerberg pit lake, northern Sweden

Fifteen microcosms were installed in the Åkerberg pit lake for 15 days in the summer season (July) 2021. To stimulate algal growth, the microcosms were fertilized with two P-rich wood ashes, and KNO3. Chlorophyll-a was used as an indicator of algal growth while filtered (<0.2 μm) and particulate suspended element concentrations (>0.2 μm) were used to estimate algal metal uptake. Water quality measurements and water sampling were conducted on three occasions (every five days) and at the start of the experiment to monitor algal growth. The chlorophyll-a concentration in the microcosms fertilized with wood ash increased from 0.3-0.8 μg/L at the start of the experiment to 53–77 μg/L after 15 days. Algal element uptake of filtered concentrations (<0.2 μm) was observed for many elements including, Ni (33–36%), Zn (22–65%) and Cd (22–54%). This suggests that wood ash could be used to stimulate algal growth in pit lakes by acting as a source for P and potentially also other nutrients. The highest chlorophyll-a concentrations were seen on day 10, indicating that a breakdown of chlorophyll-a impacted the measured concentrations, which otherwise could have been higher.

Leaf Functional Traits of Zanthoxylum planispinum ‘Dintanensis’ Plantations with Different Planting Combinations and Their Responses to Soil

Leaf structural and physiological traits, nutrients, and other functional properties reflect the ability of plants to self-regulate and adapt to the environment. Species diversity can positively affect plant growth by improving the habitat, and offers mutual interspecies benefits. Therefore, optimizing the types of plants grown in a specific area is conducive to achieving sustainable development goals for plant growth. In this study, companion planting of Zanthoxylum planispinum ‘dintanensis’ (hereafter Z. planispinum) with Prunus salicina Lindl., Sophora tonkinensis Gagnep., Arachis hypogaea L. and Lonicera japonica Thunb. was investigated, along with a monoculture Z. planispinum plantation. The effect of different planting combinations on the adaptive mechanisms of Z. planispinum and its response to the soil was explored. These results revealed that Z. planispinum preferred the slow growth strategy of small specific leaf area, high leaf water content, and high chlorophyll content after combination with P. salicina. Conversely, after combination with S. tonkinensis, Z. planispinum exhibited a fast growth strategy. Combination with A. hypogaea enabled Z. planispinum to adopt a transition from slow to fast growth. Z. planispinum regulated its economy of growth through multiple functional trait combinations, indicating that planting combinations impacted its adaptive strategies. The adaptability of Z. planispinum in combination with P. salicina, L. japonica, A. hypogaea and S. tonkinensis decreased in turn, with only the adaptability of Z. planispinum + S. tonkinensis lower than that of the pure forest. Leaf functional traits were jointly influenced by soil water content, microbial biomass carbon (MBC), MB nitrogen (N), MB phosphorus (P), available N, total P and available calcium (C:N:P). The main contributors were soil water content, the different component levels and stoichiometry of elements and the MB. The results demonstrated that companion planting can promote or inhibit the growth of Z. planispinum by adjusting its functional traits.

Extraction, antioxidant activity, and hydrogel formulation of marine Cladophora glomerata

In this study, the extraction of marine algae Cladophora glomerata using acetone, methanol, and ethanol solvents was investigated. The extraction yield was in the range of 3.47–4.20 % with a total phenolic content of 2.21–3.40 mg gallic acid equivalent per gram dried weight sample (mg GAE/g DW), and an antioxidant activity IC50 of 0.15–0.39 mg/mL. High chlorophyll and carotenoid contents were observed in all extracts, ranging from 138.44 to 200.79 μg/g DW, 119.05–308.43 μg/g DW, and 15.11–43.45 mg/g DW for chlorophylls a, b, and total carotenoids, respectively. The ethanol extract was selected for further investigation because it has high extraction efficiency and is already used in pharmaceutical preparations.The gas chromatography-mass spectroscopy (GC–MS) profile of the ethanol extract showed palmitic acid (21.4 %), 2,4-di-tert-butylphenol (14.5 %), and dibutyl phthalate (7.7 %) as major compounds. The extract at concentrations of 7.8125–125 μg/mL did not affect the viability of lung fibroblast cells (MRC-5). However, at the concentrations of 250–1000 μg/mL, the extract significantly decreased cell viability. A topical C. glomerata extract hydrogel was developed. The hydrogel had a homogenous texture; was stable in terms of appearance, pH, and spreadability in a variety of low and high temperatures; light and dark storage conditions, and it retained its antioxidant activity after storage. These findings showed that C. glomerata extract hydrogels could potentially be developed as a skin care product on a manufacturing scale.

The Effects of Shading and Nutrient Management on Yield Quality of Vegetable Fern

This study investigated the optimization of shading and organic fertilizer applications on vegetable fern growth and yield quality in order to develop guidelines for farmers interested in sustainable vegetable fern production. The experiment was conducted in a split-plot design in RCBD with four replications. There were three main plots; no shading, 75% shading, and 96% shading. The five sub-plots consisted of no fertilizer application (control), chemical fertilizer at a rate of 92.80 kg N ha−1, and cow manure at rates of 92.80, 185.60, and 278.40 kg N ha−1. A comparison between different shading and fertilizer treatments, combined, demonstrated that 75% shading with the application of cow manure at the rate of 185.60 kg N ha−1 was the most appropriate management for vegetable fern production, with the highest marketable yield recorded (1128.54 kg ha−1 month−1) and a 10-fold yield increase compared to the control (no shading and no fertilizer). This treatment also resulted in good yield quality (crunchy and tender), high concentrations of chlorophyll and vitamin C, and a safe amount of nitrate accumulation for consumers.

Distribution and Biochemical Composition of Seaweeds in relation to Hydro-chemical Characters of Marine Water

The aim of this study was to determine the distribution pattern, pigments and biochemical composition of various seaweed species collected from the Gopnath coast in Gujarat, India from August 2021 to December 2021 as well as to examine physico-chemical variables in marine waters. Besides, the relationship between the pigment, biochemical content of seaweed species and hydrochemical characters was also investigated with principal component analysis (PCA). There are total of nine species with the highest number of Chlorophyta species. During the investigation period, the distribution and occurrence of the species changed greatly. Results indicate that the chlorophyta had the highest chlorophyll content, on the other hand carotenoids were found greater in Rhodophyta members. According to a statistical analysis (Correlation) computed among environmental parameters and pigment, it was observed that the chlorophyll content was positively correlated with pH, salinity and hardness whereas carotenoid shows positive correlation with temperature and dissolved oxygen of selected site. Moreover, the principal component analysis shows that the pH, electrical conductivity (EC), salinity, hardness and alkalinity are the main factor for marine water quality whereas principal component analysis of metabolites of seaweed shows that the carbohydrate and amino acids are the main principal components of Chlorophyta species. Protein is the main principal component of Rhodophyta specie. Based on the results obtained, we can conclude that the hydro-chemical characters may play a role in the biosynthetic pathways of seaweed.

Performance of constructed wetlands with different water level for treating graphene oxide wastewater: Characteristics of plants and microorganisms

Constructed wetlands (CWs) have been expected advantages in emerging pollutant removal, but with less known on their characteristic when treating wastewater containing graphene oxide (GO). In present study, we investigated characteristics of Iris pseudacorus, microorganisms, and pollutant removal in CWs with 60 cm and 37 cm water level (termed HCW and LCW). Plants in LCW had higher chlorophyll content and lower activities of antioxidant enzyme (superoxide dismutase, catalase, peroxidase) as well as malondialdehyde content. Substrate enzyme activities were affected by time and CW type. LCW increased only dehydrogenase activities, while HCW increased catalase, urease, neutral phosphatase, and arylsulfatase activities. Sequencing analysis revealed that microbial community showed higher richness and diversity in LCW, but this dissimilarity could be eased by time-effect. Proteobacteria (25.62–60.36%) and Actinobacteria (13.86–56.20%) were stable dominant phyla in CWs. Ratio of Proteobacteria/Acidobacteria indicated that trophic status of plant rhizosphere zone was lower in LCW. Nitrospirae were enriched to 0.16–0.68% and 0.75–1.42% in HCW and LCW. The enrichment of phyla Proteobacteria and Firmicutes in HCW was attributed to class Gammaproteobacteria and genus Enterococcus. GO transformation showed some reductions in CWs, which could be affected by water depth and substrate depth. Overall, HCW achieved nitrogen and phosphorus removal for 48.78–62.99% and 95.01%, which decreased by 8.41% and 7.31% in LCW. COD removal was less affected reaching 93%. This study could provide some new evidence for CWs to treat wastewater containing GO.

Constitutive expression of AtSINA2 from Arabidopsis improves grain yield, seed oil and drought tolerance in transgenic soybean

The SEVEN IN Absentia (SINA), a typical member of the RING E3 ligase family, plays a crucial role in plant growth, development and response to abiotic stress. However, its biological functions in oil crops are still unknown. Previously, we reported that overexpression of AtSINA2 in Arabidopsis positively regulated the drought tolerance of transgenic plants. In this work, we demonstrate that ectopic expression of AtSINA2 in soybean improved the shoot growth, grain yield, drought tolerance and seed oil content in transgenic plants. Compared to wild type, transgenic soybean produced greater shoot biomass and grain yield, and showed improved seed oil and drought tolerance. Physiological analyses exhibited that the increased drought tolerance of transgenic plants was accompanied with a higher chlorophyll content, and a lower malondialdehyde accumulation and water loss during drought stress. Further transcriptomic analyses revealed that the expressions of genes related to plant growth, flowering and stress response were up- or down-regulated in transgenic soybean under both normal and drought stress conditions. Our findings imply that AtSINA2 improved both agricultural production and drought tolerance, and it can be used as a candidate gene for the genetic engineering of new soybean cultivars with improved grain yield and drought resistance.

SbNAC9 Improves Drought Tolerance by Enhancing Scavenging Ability of Reactive Oxygen Species and Activating Stress-Responsive Genes of Sorghum.

Drought stress severely threatens the yield of cereal crops. Therefore, understanding the molecular mechanism of drought stress response of plants is crucial for developing drought-tolerant cultivars. NAC transcription factors (TFs) play important roles in abiotic stress of plants, but the functions of NAC TFs in sorghum are largely unknown. Here, we characterized a sorghum NAC gene, SbNAC9, and found that SbNAC9 can be highly induced by polyethylene glycol (PEG)-simulated dehydration treatments. We therefore investigated the function of SbNAC9 in drought stress response. Sorghum seedlings overexpressing SbNAC9 showed enhanced drought-stress tolerance with higher chlorophyll content and photochemical efficiency of PSII, stronger root systems, and higher reactive oxygen species (ROS) scavenging capability than wild-type. In contrast, sorghum seedlings with silenced SbNAC9 by virus-induced gene silencing (VIGS) showed weakened drought stress tolerance. Furthermore, SbNAC9 can directly activate a putative peroxidase gene SbC5YQ75 and a putative ABA biosynthesis gene SbNCED3. Silencing SbC5YQ75 and SbNCED3 led to compromised drought tolerance and reduced ABA content of sorghum seedlings, respectively. Therefore, our findings revealed the important role of SbNAC9 in response to drought stress in sorghum and may shed light on genetic improvement of other crop species under drought-stress conditions.

Phytoplankton community structure in the Western Subarctic Gyre of the Pacific Ocean during summer determined by a combined approach of HPLC-pigment CHEMTAX and metabarcoding sequencing

The Western Subarctic Gyre (WSG) is a cyclonic upwelling gyre in the northwest subarctic Pacific, which is a region with a high concentration of nutrients but low chlorophyll. We investigated the community structure and spatial distribution of phytoplankton in this area by using HPLC-pigment CHEMTAX (a chemotaxonomy program) and metabarcoding sequencing during the summer of 2021. The phytoplankton community showed significant differences between the two methods. The CHEMTAX analyses identified eight major marine phytoplankton assemblages. Cryptophytes were the major contributors (24.96%) to the total Chl a, followed by pelagophytes, prymnesiophytes, diatoms, and chlorophytes. The eukaryotic phytoplankton OTUs obtained by metabarcoding were categorized into 149 species in 96 genera of 6 major groups (diatoms, prymnesiophytes, pelagophytes, chlorophytes, cryptophytes, and dinoflagellates). Dinoflagellates were the most abundant group, accounting for 44.74% of the total OTUs obtained, followed by cryptophytes and pelagophytes. Sixteen out of the 97 identified species were annotated as harmful algal species, and Heterocapsa rotundata, Karlodinium veneficum, and Aureococcus anophagefferens were assigned to the abundant group (i.e., at least 0.1% of the total reads). Nutrients were more important in shaping the phytoplankton community than temperature and salinity. The 24 stations were divided into southern and northern regions along 44°N according to the k-means method, with the former being dominated by high Chl a and low nutrients. Although different phytoplankton assemblages analyzed by the two methods showed various relationships with environmental factors, a common feature was that the dinoflagellate proportion showed a significantly negative correlation with low nutrients and a positive correlation with Chl a.

Short-term tuning of microalgal composition by exposition to different irradiance and small doses of sulfide.

Suitability of microalgae valorization mainly depends on its biochemical composition. Overall, among all microalgal derivatives, pigments currently stand out as the major added-value component. While it is well recognized that microalgal growth conditions strongly affect biomass composition, final tuning of already grown microalgae has been scarcely studied. Herein, pigment crude extract and debris biomass composition of an already grown microalgal consortium was evaluated after a short-term exposure (90min) to different levels of irradiance (15, 50, 120μmolm-2s-1) and sulfide concentrations (0, 3.2, 16mg L-1). Although lipid, protein, and carbohydrate contents of debris biomass were not decisively modified by the short-term exposures, pigments content of the crude extracts were strongly modified after 90-min exposure at given sulfide and irradiance conditions. Particularly, a higher content of chlorophyll a, chlorophyll b, and total carotenoids was estimated at an optimal sulfide concentration of 5mg L-1, and the higher irradiance of 120μmolm-2s-1. Contrarily, the average irradiation level of 50μmolm-2s-1 and the absence of sulfide stimulated the production of phycoerythrin and phycocyanin which could be increased by 65 and 50%, respectively. Thus, a final qualitative and quantitative tuning of pigment content is plainly achievable on grown microalgal biomass, in a reduced exposure time, at given irradiance or sulfide conditions.

Charge transfer as a mechanism for chlorophyll fluorescence concentration quenching

Highly concentrated solutions of chlorophyll display rapid fluorescence quenching. The same devastating energy loss is not seen in photosynthetic light-harvesting antenna complexes, despite the need for chromophores to be in close proximity to facilitate energy transfer. A promising, though unconfirmed mechanism for the observed quenching is energy transfer from an excited chlorophyll monomer to a closely associated chlorophyll pair that subsequently undergoes rapid nonradiative decay to the ground state via a short-lived intermediate charge-transfer state. In this work, we make use of newly emerging fast methods in quantum chemistry to assess the feasibility of this proposed mechanism. We calculate rate constants for the initial charge separation, based on Marcus free-energy surfaces extracted from molecular dynamics simulations of solvated chlorophyll pairs, demonstrating that this pathway will compete with fluorescence (i.e., drive quenching) at experimentally measured quenching concentrations. We show that the rate of charge separation is highly sensitive to interchlorophyll distance and the relative orientations of chromophores within a quenching pair. We discuss possible solvent effects on the rate of charge separation (and consequently the degree of quenching), using the light-harvesting complex II (LH2) protein from rps. acidophila as a specific example of how this process might be controlled in a protein environment. Crucially, we reveal that the LH2 antenna protein prevents quenching, even at the high chlorophyll concentrations required for efficient energy transfer, by restricting the range of orientations that neighboring chlorophyll pairs can adopt.