Impacts of bisphenol A on growth and reproductive traits of submerged macrophyte Vallisneria natans.

Bisphenol A (BPA) is considered a contaminant of emerging concern and interferes with the normal activities of living organisms. The toxicity of BPA is evident in animals and terrestrial plants. However, the response of aquatic plants to low BPA concentrations is still unclear. In the present study, effects of varying BPA loadings (targeting at 0.01, 0.1, and 1 mg/L) on the growth and reproductive traits of the dioecious annual submerged macrophyte Vallisneria natans were assessed through a 5-month experiment. The results showed that BPA inhibited the elongation of V. natans leaves but resulted in an increase in leaf number and ramet number under the highest BPA loading treatment (targeting at 1 mg/L). In addition, detectable biochemical changes in the total carbon and soluble sugar contents were found, which both were significantly higher at the highest BPA loading treatment. However, the total biomass did not alter significantly after the BPA treatments, indicating that BPA did not induce direct toxic effects on the growth of V. natans. At the highest BPA loading treatment, female individuals of V. natans allocated less number for ramet than male ones, showing a clear sexual dimorphism. No significant differences between the five treatments were found for the flower or fruit traits, while the germination rate was significantly inhibited for the seeds collected from the highest BPA loading treatment. In conclusion, V. natans tolerated low concentrations of BPA by making a trade-off between ramet (leaf) number and leaf elongation, as well as modulating the total carbon and soluble sugar contents. However, serious consequence of decline in seed viability implied that the impact of BPA on plant reproduction were usually underestimated.

Responses of four submerged macrophytes to freshwater snail density (Radix swinhoei) under clear-water conditions: A mesocosm study.

Macrophytes play a key role in stabilizing clear-water conditions in shallow freshwater ecosystems. Their populations are maintained by a balance between plant grazing and plant growth. As a freshwater snail commonly found in shallow lakes, Radix swinhoei can affect the growth of submerged macrophytes by removing epiphyton from the surface of aquatic plants and by grazing directly on macrophyte organs. Thus, we conducted a long-term (11-month) experiment to explore the effects of snail density on macrophytes with distinctive structures in an outdoor clear-water mesocosm system (with relatively low total nitrogen (TN, 0.66 ± 0.27 mg/L) and total phosphorus (TP, 36 ± 20 µg/L) and a phytoplankton chlorophyll a (Chla) range of 14.8 ± 4.9 µg/L) based on two different snail densities (low and high) and four macrophyte species treatments (Myriophyllum spicatum, Potamogeton wrightii, P. crispus, and P. oxyphyllus). In the high-density treatment, snail biomass and abundance (36.5 ± 16.5 g/m2 and 169 ± 92 ind/m2, respectively) were approximately twice that observed in the low-density treatment, resulting in lower total and aboveground biomass and ramet number in the macrophytes. In addition, plant height and plant volume inhabited (PVI) showed species-specific responses to snail densities, that is, the height of P. oxyphyllus and PVI of M. spicatum were both higher under low-density treatment. Thus, compared with low-density treatment, the inhibitory effects of long-term high snail density on macrophytes by direct feeding may be greater than the positive effects resulting from epiphyton clearance when under clear-water conditions with low epiphyton biomass. Thus, under clear-water conditions, the growth and community composition of submerged macrophytes could be potentially modified by the manual addition of invertebrates (i.e., snails) to lakes if the inhibitory effects from predatory fish are minor.

Silver nanoparticles induced reactive oxygen species via photosynthetic energy transport imbalance in an aquatic plant.

The rapid growth in silver nanoparticles (AgNPs) commercialization has increased environmental exposure, including aquatic ecosystem. It has been reported that the AgNPs have damaging effects on photosynthesis and induce oxidative stress, but the toxic mechanism of AgNPs is still a matter of debate. In the present study, on the model aquatic higher plant Spirodela polyrhiza, we found that AgNPs affect photosynthesis and significantly inhibit Photosystem II (PSII) maximum quantum yield (Fv/Fm) and effective quantum yield (ΦPSII). The changes of non-photochemical fluorescence quenching (NPQ), light-induced non-photochemical fluorescence quenching [Y(NPQ)] and non-light-induced non-photochemical fluorescence quenching [Y(NO)] showed that AgNPs inhibit the photo-protective capacity of PSII. AgNPs induce reactive oxygen species (ROS) that are mainly produced in the chloroplast. The activity of ribulose-1, 5-bisphosphate carboxylase-oxygenase (Rubisco) was also very sensitive to AgNPs. The internalized Ag, regardless of whether the exposure was Ag+ or AgNPs had the same capacity to generate ROS. Our results support the hypothesis that intra-cellular AgNP dissociate into high toxic Ag+. Rubisco inhibition leads to slowing down of CO2 assimilation. Consequently, the solar energy consumption decreases and then the excess excitation energy promotes ROS generation in chloroplast.