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In this study, we investigated the allelopathic interactions among five representative allelochemicals at different proportions using bloom-forming Microcystis aeruginosa as the test receptor. Binary or ternary mixtures of allelochemicals obtained three types of allelopathic interactions, i.e., synergistic, antagonistic, and additive effects. However, combinations of four or five allelochemicals only yielded antagonistic effects. Interestingly, the algal inhibition gradually increased with the tested period for all treatments. For instance, the synergistic interaction occurred with the mixture including coumarin + ρ-hydroxybenzoic acid at 80%:20%; the mixture on the 10th day showed 0.80 of algal inhibition. While the mixture comprised protocatechuic acid + stearic acid + ρ-aminobenzene-sulfonic acid at 33.3%:33.3%:33.3%, the additive interactions occurred and then the maximum algal inhibition (0.83) was acquired at the end of tested period. In conclusion, the joint effects of different allelochemicals depend on various factors such as the chemicals used, their respective proportions, the total concentration of the mixture, and the receptor species. Thus, it is necessary to consider the complexity of allelopathic interactions and the field conditions during the control and management of noxious cyanobacteria.

This study investigated the environmental restoration effects of Ranunculus sceleratus in a sewage system microcosm trial, including the removal of pollutants and algal inhibition. We compared the removal of pollutants by R. sceleratus in a eutrophic sewage system in the presence and the absence of algae. The rate of removal without algae was 16.2–20.5% of that with algae. NH 4 + – N was removed most readily by R. sceleratus . The effects of R. sceleratus on the growth of Microcystis aeruginos a were also investigated in two allelopathic modes. The level of algal inhibition after the addition of an extract of Ranunculus scleratus was 57.1–78.9% greater than that in a co-culture test. To understand the role of allelopathy interference with algal development, we also determined the total flavonoid contents of plants, which ranged from 3.57 g to 20.19 g per plant. The cell density of Microcystis aeruginosa was negatively correlated with the total flavonoids in R. sceleratus , although aquatic macrophytes may contain other allelochemicals involved with algal inhibition in addition to flavonoid compounds. The environmental effects of R. sceleratus were significantly correlated with its growth stage (or water retention time), plant height, and biomass. This study suggests that R. sceleratus has potential for the low-effort and sustainable management of freshwaters, particularly the removal of nutrient pollutants and the reduction of excessive algal growth, which may be attributable to allelochemicals such as flavonoids. The in situ environmental restoration effects of R. sceleratus require further investigation at the ecosystem level.

Summary Novozym-435-catalysed esterification of caprylic acid, capric acid and oleic acid with glycerol for the synthesis of medium- and long-chain triglycerides (MLCT) in vacuum and solvent-free system was investigated in this study. Response surface methodology with a three-level, four-factorial design was applied to optimise the enzymatic esterification for the synthesis of MLCT. The optimum conditions were as follows: reaction temperature 90 °C, 4.80 wt% enzyme load (relative to the weight of total substrates) and substrate molar ratio (fatty acids/glycerol) of 3:1 and 12.37 h. Under above-mentioned conditions, Triglycerides (TG) yield, MLCT and the residual free fatty acids (FFA) content in the product were 93.54%, 72.19% and 4.21%, respectively. The content of caprylic acid, capric acid and long-chain fatty acids of TG was 24%, 10% and 66%, respectively. Novozym 435 in the study showed no selectivity for the different fatty acids and also could be used 14 times without obvious loss of enzyme activity.

The algicidal effects of Alternanthera philoxeroides were analyzed based on a combination of a field survey and laboratory tests, as well as testing the effects of heavy metals in aquatic ecosystems. In the field investigation, a phytoplankton assemblage surrounding A. philoxeroides was significantly inhibited. A. philoxeroides also exhibited strong allelopathic potential in the laboratory. In particular, aqueous extracts significantly suppressed Chlorella pyrenoidosa and Microcystis aeruginosa . Thus, it was assumed that functional allelochemicals produced by A. philoxeroides may help it to compete and combat harmful algae. We also discovered that heavy metals (Ni, Pb, Cr, and Cu) found in an aquatic ecosystem reduced the algicidal potential of A. philoxeroides . However, certain elements other than heavy metals, i.e., the inorganic anions F − , S 2− , Cl − , and SO 4 2 − and the metallic cations K + , Na + , Ca 2+ , Mg 2+ , total Fe, Zn 2+ , and total Mn, could enhance the inhibitory rate of A. philoxeroides . Based on an analyses of these relationship, we found a significant relationship between the rate of the suppression of the tested algae by the A. philoxeroides allelopathy and the concentration of metallic cations in the aquatic habitat, but not the concentration of inorganic anions.

The present study evaluated the combined effects of four typical predatory zooplankton and allelopathic aquatic macrophytes on algal control in a microcosm system. It would determine the effects of diverse species and biological restoration on the growth of harmful water-bloom microalgae in great lakes polluted by excess nutrients. It was found that the mixtures of each zooplankton and the floating plant Nymphoides peltatum had stronger inhibitory effects on harmful water-bloom microalgae than the individual species in clean or eutrophic water bodies. In addition, a community of four zooplankton types had a synergistic effect on algal inhibition. Algal suppression by the zooplankton community was enhanced significantly when the macrophyte was co-cultured in the microcosm. Furthermore, Chlorella pyrenoidosa was more susceptible than Microcystis aeruginosa when exposed to grazing by zooplankton and the allelopathic potential of the macrophyte. Algal inhibition was also weaker in eutrophic conditions compared with the control. These findings indicate that diverse species may enhance algal inhibition. Therefore, it is necessary to restore biological diversity and rebuild an ecologically balanced food chain or web to facilitate the control of harmful algal blooms in eutrophic lakes.