Investigation of the Inhibitory Effects of Mangrove Leaves and Analysis of Their Active Components on Phaeocystis globosa during Different Stages of Leaf Age

Differential allelopathic effects of mangrove plants Kandelia obovata and Aegiceras corniculatum on harmful algal species: Potential applications in algal bloom control

This study examined effects of mangrove plants Kandelia obovata and Aegiceras corniculatum on harmful algal species. While A. corniculatum leaf extract had no inhibitory effect, K. obovata leaf extract significantly inhibited the growth of two harmful algal species Alexandrium tamarense and Karenia mikimotoi. The inhibitory effect was concentration-dependent, with over 90 % inhibition at the highest concentration. Morphological changes and cell size reduction were observed in both microalgae. Excessive production of reactive oxygen species and damage to algal photosynthetic system were found. The allelopathic effect of K. obovata on K. mikimotoi with low-concentration repeated exposure was more effective than high-concentration single exposure. The EC50 of K. obovata (0.33 g L-1) was lower than reported values on other coastal plants. Higher inhibitory effects of K. obovata were found on naked algal species than the armoured ones. These findings suggest potential applications of K. obovata leaf extract in controlling harmful algal blooms.

Chemical Constituents and Biological Activities of Bruguiera Genus and Its Endophytes: A Review

The genus Bruguiera, a member of the Rhizophoraceae family, is predominantly found in coastal areas as a mangrove plant, boasting a rich and diverse community of endophytes. This review systematically compiled approximately 496 compounds derived from both the Bruguiera genus and its associated endophytes, including 152 terpenoids, 17 steroids, 16 sulfides, 44 alkaloids and peptides, 66 quinones, 68 polyketides, 19 flavonoids, 38 phenylpropanoids, 54 aromatic compounds, and 22 other compounds. Among these, 201 compounds exhibited a spectrum of activities, including cytotoxicity, antimicrobial, antioxidant, anti-inflammatory, antiviral, antidiabetic, insecticidal and mosquito repellent, and enzyme inhibitory properties, etc. These findings provided promising lead compounds for drug discovery. Certain similar or identical compounds were found to be simultaneously present in both Bruguiera plants and their endophytes, and the phenomenon of their interaction relationship was discussed.

Relationship between phytoplankton community and water parameters in planted fringing mangrove area in South China

Reforestation has been commonly adopted to increase the mangrove areas lost due to developments. A diverse phytoplankton community is critical to mangrove ecosystem functions; however, its compositions in planted mangrove habitats have seldom been reported. The present study, based on the temporal and spatial variations of phytoplankton community and water parameters, evaluated their relationships in a 20-year old artificially planted fringing mangrove in South China. Thirty-one phytoplankton taxa were identified from tidal water collected from three sites along a planted mangrove shoreline: within, and at the edge of mangroves, and at bare shoreline without mangroves. In all three sites, Bacillariophyta (diatom) was the most abundant phylum, dominated by Navicula and Nitzschia at 9.82-83.76% and 2.57-33.97%, respectively. The overall diversity ranged between 0.41 and 1.94. The temporal variations of phytoplankton and water parameters were more obvious than site differences. Higher phytoplankton diversity was found in summer, with increased green algae and cyanobacteria abundance accompanied by riverine discharge. There was site-specific dominance in some phyla between June and January, noticeably Chlorophyta, Cyanophyta, Dinophyta, and Euglenophyta. A potential toxic dinoflagellate Peridinium sp. was identified during fall and winter, serving as a warning to probable harmful bloom events. Multivariate statistical analyses revealed the abundance of major phytoplankton taxa significantly related to water physiochemical parameters, especially nitrate, ammonium, total phosphorous and orthophosphate. The present study suggests that mangrove vegetation may influence water quality and shape phytoplankton composition, but temporal differences were more significant. Compared with the protected natural mangroves in the National Nature Reserve nearby, this planted fringing mangrove habitat not only had lower nutrients, especially total nitrogen in tidal water, but also had different dominant phytoplankton species and lower species richness. The 20-year old artificially planted mangroves may still not serve the same ecological function as the protected natural mangrove forest.

Metabolomic profiling of M. speciosa champ at different growth stages

Millettia speciosa Champ (M. speciosa) is an edible food and folk medicine and extracts from its roots exhibit a hepatoprotective effect. However, its metabolic growth process and the best harvest time have not been reported. This study systematically evaluated the metabolomic profiling of M. speciosa root extracts at different growth stages through the UPLC-Q-TOF-MS, nuclear magnetic resonance (NMR) and An orthogonal partial least squares-discriminant analysis (OPLS-DA). The results revealed there were significant differences among extracts from six ages of M. speciosa, and 110 compounds were identified. Pharmacological studies showed that 5-year and 20-year old M. speciosa roots may exhibit higher fat-lowering effects, while 5-year-old (M.s-5Y) showed better hepatoprotective activity in high-fat diet (HFD)-induced nonalcoholic fatty liver disease (NAFLD) mice. Hence, our study suggested that M.s-5Y may have potent efficacy in ameliorating NAFLD, which might be useful in determining the optimum time to harvest M. speciosa.

Microcosm Study on Allelopathic Effects of Leaf Litter Leachates and Purified Condensed Tannins from Kandelia obovata on Germination and Growth of Aegiceras corniculatum

Kandelia obovata (Ko) and Aegiceras corniculatum (Ac) are common and dominant plant species in mangrove wetlands in South China, which are distributed in similar tidal zones along the coastline. The present study aimed to determine the allelopathic effects of leaf litter leachates (LLLs) from Ko and their purified condensed tannins (PCTs) on the germination and growth of Ac by mangrove microcosms. Replicate pots containing five different levels of LLLs and PCTs were separately prepared and propagules of Ac were placed in each treatment. Both LLLs and PCTs significantly inhibited the germination and growth of Ac, especially at high concentrations. The final germination rates of the roots and stems and the numbers of fine roots declined continuously, while other growth indicators, including the lengths of fine roots and nutritive roots and the biomasses of roots, stems, and leaves first increased and then decreased with increasing levels. These results indicate that LLLs from the leaf litter of Ko, in particular their PCTs, exerted an inhibition effect on propagule germination and seedling growth of Ac, and the inhibitory effects were concentration dependent. This study suggested that condensed tannins from leaf litter, acting as allelochemicals, could regulate the natural regeneration of a mangrove forest.

In vitro allelopathic effects of compounds from Cerbera manghas L. on three Dinophyta species responsible for harmful common red tides

Allelopathy is regarded as an economic and eco-friendly approach for the control of harmful algal blooms (HABs) because allelochemicals degrade easily and cause less pollution than traditional algicides. We first surveyed the inhibitory effect of the traditional medicinal plant Cerbera manghas L. on the notorious dinoflagellates Alexandrium tamarense, Scrippsiella trochoidea, and Karenia mikimotoi. Then, we identified and quantified the potential algicidal compounds by UPLC-MS and determined their activity. The aqueous extract inhibited algae with EC_{50-120 h} at 0.986, 1.567 and 1.827 g L^-1 for A. tamarense, S. trochoidea, and K. mikimotoi, respectively. Three potential allelochemicals were quantified in the stock solution: quinic acid (QA) (28.81 mg L^-1), protocatechuic acid (PA) (53.91 mg L^-1), and phloridzin (PD) (26.17 mg L^-1). Our results illustrated that 1) QA did not have an inhibitory effect, 2) PA had medium toxicity to algae (EC_50-120h: 0.22, 0.28, and 0.35 mM for A. tamarense, S. trochoidea, and K. mikimotoi), and 3) PD had low toxicity (EC_50-120h > 0.66 mM). These findings suggested that PA might be the main allelopathic compound in the aqueous extract of the studied algae. In addition, PA could have a negative effect on the photosynthesis of S. trochoidea by impeding the reduction of quinone electrons and destroying electron transfer in PSII. In summary, this was the first study to quantify allelochemicals in C. manghas fruit. Moreover, C. manghas and protocatechuic have the potential to be algicides to control and mitigate the HABs caused by dinoflagellates.

New insights into the harmful algae inhibition by Spartina alterniflora: Cellular physiology and metabolism of extracellular secretion

This study investigated the response of three toxic harmful algal blooms (HABs) species, Heterosigma akashiwo, Chattonella marina, and Alexandrium tamarense to coastal invasive plant, Spartina alterniflora. In this study, the growth of three HABs species were suppressed significantly by S. alterniflora extracts, showing a dose-response relationship. The raphidophyte H. akashiwo and C. marina exhibited higher inhibitory response with EC_50,7d decreased by 14% and 75% as compared to the dinoflagellate A. tamarense. C. marina was the most sensitive among the three species. S. alterniflora extracts disrupted algal cellular integrity and photosynthesis. Furthermore, the extracellular organic matters were detected by fluorescence excitation-emission matrix. Algal metabolites, protein-like substances (tyrosine-like peak and tryptophan-like peak) decreased as time prolonged and the humic-like substances (UVA marine humic-like peak) increased when algal cells were exposed to S. alterniflora extracts. These results provide new insights to the inhibition mechanism of S. alterniflora extracts on HABs species.

Inhibition of harmful algae Phaeocystis globosa and Prorocentrum donghaiense by extracts of coastal invasive plant Spartina alterniflora

Harmful algal blooms (HABs) and the invasion of smooth cordgrass (Spartina alterniflora) have become important environmental problems in intertidal zones of China, which caused serious damage on the coastal ecological systems. By using S. alterniflora as algaecide, this helps to utilize this invasive plant, in addition, is expected to help to control the expansion of S. alterniflora. The potential of S. alterniflora in HABs mitigation was investigated on controlling Phaeocystis globosa (haptophyceae) and Prorocentrum donghaiense (dinophyceae). The growth of both HABs species was significantly inhibited at high concentrations, and P. globosa was more sensitive than P. donghaiense. Furthermore, the extracts of S. alterniflora reduced the effective quantum yield, photosynthetic efficiency, and relative maximal electron transport rate of both algal species at high concentrations, which implies a disruption on their photosynthetic system. Flavonoids, which were previously known as antialgal chemicals, were found to be abundant in the extracts of S. alterniflora by UPLC-MS detection. Our results revealed that the potential of S. alterniflora as a novel antialgal agent for controlling HABs, simultaneously, resource utilization possibility for the invasive plant S. alterniflora.

Growth Inhibition of Phaeocystis Globosa Induced by Luteolin-7-O-glucuronide from Seagrass Enhalus acoroides

Enhalus acoroides (E. acoroides) is one of the most common species in seagrass meadows. Based on the application of allelochemicals from aquatic plants to inhibit harmful algal blooms (HABs), we used E. acoroides aqueous extract against harmful algae species Phaeocystis globosa (P. globosa). The results showed that E. acoroides aqueous extract could significantly inhibited the growth of P. globosa, decrease the chlorophyll-a content and photosynthetic efficiency (Fv/Fm) values of P. globosa, followed by vacuolization, plasmolysis, and the destruction of organelles. Twelve types of major chemical constituents were identified in E. acoroides aqueous extracts by ultraperformance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS), including six flavonoids, two homocyclic peptides, two long-chain aliphatic amides, one tannin, and one nitrogen heterocyclic compound. Flavonoids were the characteristic chemical constituents of E. acoroides aqueous extract. Furthermore, the antialgal activity of luteolin-7-O-glucuronide (68.125 μg/mL in 8 g/L E. acoroides aqueous extract) was assessed. The EC_{50–96 h} value was 34.29 μg/mL. In conclusion, the results revealed that luteolin 7-O-glucuronide was one of the antialgal compounds of E. acoroides aqueous extract, with potential application as novel algaecide.