Sesuvium portulacastrum-Mediated Removal of Nitrogen and Phosphorus Affected by Sulfadiazine in Aquaculture Wastewater

Plant-based removal of nitrogen (N) and phosphorus (P) from water bodies is an important method for remediation of aquaculture wastewater. In order to acquire knowledge as to how antibiotic residues in wastewater might affect the microbial community and plant uptake of N and P, this study investigated N and P removal by a coastal plant Sesuvium portulacastrum L. grown in aquaculture wastewater treated with 0, 1, 5, or 50 mg/L sulfonamide antibiotics (sulfadiazine, SD) for 28 days and compared the microbial community structure between the water and rhizosphere. Results showed that SD significantly decreased N removal rates from 87.5% to 22.1% and total P removal rates from 99.6% to 85.5%. Plant fresh weights, root numbers, and moisture contents as well as activities of some enzymes in leaves were also reduced. SD changed the microbial community structure in water, but the microbial community structure in the rhizosphere was less affected by SD. The microbial diversity in water was higher than that in the rhizosphere, indicating microbial community differences. Our results showed that the commonly used antibiotic, SD, in aquaculture can inhibit plant growth, change the structure of microbial community, and reduce the capacity of S. portulacastrum plants to remove N and P from wastewater, and also raised alarm about detrimental effects of antibiotic residues in phytoremediation of wastewater.

In Vitro Shoot Culture of Sesuvium portulacastrum: An Important Plant for Phytoremediation

Sesuvium portulacastrum L., a member of the family Aizoaceae, is an important coastal halophyte. Due to its adaptability to salinity and heavy metals, S. portulacastrum has now been widely used for the phytoremediation of saline soils and wastewater and the protection of the coast from erosion. The increasing use of this plant requires a large number of propagules. Stem cutting propagation and seed germination cannot meet this demand, and such propagations can initiate and spread diseases. A recent occurrence of Bipolaris sesuvii J.Z. Zhang and Gibbago trianthemae E.G. Simmons in S. portulacastrum resulted in the substantial loss of the plants during the remediation of aquaculture wastewater. Thus, there is an urgent need for establishing efficient methods of propagating disease-free starting materials. In the present study, we evaluated different growth regulators in the induction of axillary shoots from nodal explants cultured on Murashige and Skoog medium and identified that zeatin (ZT) and α-naphthaleneacetic acid (NAA) was an appropriate combination for inducing high numbers of axillary shoots. The nodal explants were then cultured on MS medium supplemented with different concentrations of ZT and NAA, and the combination of ZT at 1.0 mg L−1 and NAA at 0.3 mg L−1 induced more than 12 axillary shoots per explant. The axillary shoots were excised to produce microcuttings or microshoots, which were rooted on half-strength MS medium supplemented with different concentrations of indole-3-acetic acid (IAA) or indole-3-butyric acid (IBA). The results showed that IBA at 0.6 mg L−1 induced 91.7% of the microcuttings to root with root numbers of over 36 per cutting. The rooted plantlets were healthy and true-to-type and grew vigorously in plug trays or plastic containers with a 100% survey rate in a greenhouse. Thus, this established protocol could be used for the rapid propagation of genetically identical and disease-free plants of S. portulacastrum for phytoremediation and the protection of shoreline soils from erosion.

High Redox Status as the Basis for Heavy Metal Tolerance of Sesuvium portulacastrum L. Inhabiting Contaminated Soil in Jeddah, Saudi Arabia

Because sewage sludge is contaminated with heavy metals, its disposal in the soil may pose risks to the ecosystem. Thus, heavy metal remediation is necessary to reduce the associated risks. The goal of this research is to introduce a heavy metal resistant species and to assess its phytoremediation, oxidative damage markers and stress tolerance mechanisms. To this end, field research was done to compare the vegetation of polluted sites to that of a healthy site. We found 42 plant species identified in the study, Sesuvium portulacastrum L. was chosen because of its high relative density (10.3) and maximum frequency (100 percent) in the most contaminated areas. In particular, S. portulacastrum plants were characterized by strong Cu, Ni, and As uptake. At the organ level, to control growth reduction and oxidase damage, particularly in roots, increased detoxification (e.g., metallothionein, phytochelatins) and antioxidants mechanisms (e.g., tocopherols, glutathione, peroxidases). On the other hand, flavonoids content and the activity of glutathione-S transferase, glutathione reductase and dehydroascorbate reductase were increased manly in the shoots. These biochemical markers can be applied to select tolerance plant species grown under complex heavy metal contamination. Our findings also introduced S. portulacastrum to reduce soil contamination0associated risks, making the land resource available for agricultural production.

La population d’Avicennia germinans du delta du Saloum est-elle relictuelle depuis la dernière période humide ?

Dans le monde entier, les mangroves sont déboisées à un rythme plus élevé que les forêts tropicales. Dans le delta du Saloum au Sénégal, elle a connu un déclin important dans les années 1980 et 1990, mais elle se régénère spontanément depuis lors. Cet article teste l'hypothèse suivante : la population d'Avicennia germinans dans le Saloum correspondrait à une population relique établie pendant les années hyper-humides (1950 à 1967). Cet article fait la synthèse de deux campagnes botaniques différentes, espacées de 15 ans. Également, il rend compte d’une expérience sur la flottation des propagules en fonction de la salinité de l'eau. En 2003, la reproduction d'Avicennia germinans n'avait pas eu lieu dans la zone de demi-marée depuis plusieurs années déjà. Seul le piégeage par Sesuvium portulacastrum, dans la zone de haute marée, permet l'apparition de jeunes pousses. C'est donc un problème de dépôt et d'enracinement des propagules. En 2018, seuls deux individus, présents sur le même site, semblent avoir suivi un processus de régénération « normal », en zone de demi-marée, dans la boue, sans processus de piégeage des propagules. La récente diminution de la salinité permettrait à nouveau exceptionnellement aux propagules de s'enfoncer, et donc de germer comme en période humide. Une relation linéaire évidente a été observée entre la flottaison et la salinité. En Gambie et en Casamance, où les précipitations sont plus importantes et la salinité plus faible, cette espèce se reproduit normalement et n'a pas été affectée dans sa reproduction par la période de sécheresse. Cela nous permet d'estimer que des seuils de 1 000 mm de précipitations annuelles ou 20 ‰ de salinité minimale, franchis après la période hyper-humide (1950-1967), ont empêché, depuis, la reproduction de l'espèce. Si la population étudiée par la science depuis les années 1970 est bien une population relique, issue d'une période anormalement humide, toute une littérature visant à décrire et expliquer la dégradation des mangroves du Saloum aurait été basée sur un état de référence particulièrement inapproprié.