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Artemisinin algaecide (AMA) had a significant inhibitory effect on algae in our previous study, but the impact on coexisting submerged plants was unclear. In this study, we investigated the impacts of AMA with varying concentrations (1‰, 5‰ and 10‰) on the growth, antioxidant response and microbial community of Vallisneria natans ( V. natans ). The results revealed a significant reduction in biomass in V. natans upon exposure to AMA, indicating an inhibitory of V. natans . Furthermore, malondialdehyde (MDA) content increased significantly in three treatment groups, and catalase (CAT) increased significantly in the 10‰ treatment group, while superoxide dismutase (SOD) had little change in all groups, indicating complex antioxidant responses to AMA. Notably, the High-throughput sequencing results showed that AMA significantly altered microbial abundance and community structure of V. natans . Alpha diversity results indicated that AMA increased the diversity of the microbial community in V. natans , but it had little impact on the dominant bacterial phylum. These results provide necessary information to assess the potential ecotoxicity of AMA to submerged plants during algal suppression and draw more attention to their use in natural water bodies.

Eutrophication of water bodies causes the disappearance of submerged macrophytes and frequent blooms of phytoplankton, which leads to changes in the underwater light environment in the aspect of light intensity and light quality. However, compared with underwater light intensity, only few studies have been concentrated in the effect of light quality on submerged macrophytes. The effect of light quality on plants is heterogeneous, and there are two absorption peaks in red and blue wavelengths. Thus, we carried out a mesocosm experiment to study the effects of a series of red and blue light ratios (red/blue light ratio = 1/8, 1/4, 1/1, 4/1, and 8/1) on two submerged macrophyte species, Hydrilla verticillata and Vallisneria natans . We hypothesized that functional traits (growth strategy, morphological, photosynthetic, and nutritional traits) of submerged macrophytes will be modified by different red/blue light ratios. With the increase of red/blue light ratio, plant height of the two submerged macrophytes decreased, while tillers number increased. We could not completely verify our hypothesis, but we found species-specific differences. The leaf area of H. verticillata under 8/1 red/blue light ratio was significantly higher than that under 1/8 red/blue light ratio, whereas the leaf area of V. natans under 4/1 red/blue light ratio was lower than that under 1/8 red/blue light ratio. Our results are helpful to understand the disappearance mechanism of submerged macrophytes in eutrophic lakes and devise more appropriate measures for the recovery of submerged macrophytes.

Native aquatic macrophytes such as American eelgrass (Vallisneria americana Michx.) are often desirable in aquatic ecosystems due to the ecological benefits they provide but are threatened by competition from invasive taxa including non-native Vallisneria taxa and hydrilla [Hydrilla verticillata (L. f.) Royle]. Identifying potential selective herbicide management options can provide tools to minimize impacts to native taxa in restoration and aquatic invasive plant management programs. Greenhouse mesocosm experiments were conducted in 2023 to investigate herbicide efficacy on two native eelgrass species (V. americana and Vallisneria neotropicalis Vict.), two non-native taxa (Vallisneria australis S.W.L. Jacobs & Les and Vallisneria spiralis L. × Vallisneria denseserrulata Makino), and H. verticillata. Herbicide applications included endothall, diquat, florpyrauxifen-benzyl, fluridone, and flumioxazin and select combinations of these herbicides used in H. verticillata management. Endothall alone provided 90% to 100% aboveground biomass reduction at 3,000 µg L–1 with at least 24 h of continuous or intermittent exposure to all native and invasive species at 6 wk after exposure, whereas florpyrauxifen-benzyl applied alone resulted in minimal aboveground biomass reduction. A 45-d of exposure of fluridone (10 µg L–1) resulted in 95% biomass reduction of V. americana and 7% to 48% of other tested taxa. The combination of flumioxazin and florpyrauxifen-benzyl resulted in 90% to 100% aboveground biomass reduction, and endothall combined with florpyrauxifen-benzyl resulted in 93% to 100% aboveground biomass reduction across taxa. Reductions in belowground biomass mirrored trends observed in aboveground biomass. No treatments selectively controlled invasive Vallisneria without injury to native Vallisneria, although efficacy was observed on H. verticillata. These insights provide an understanding for differences between these Vallisneria for researchers moving forward with selectively targeting H. verticillata in the presence of native Vallisneria species and two new aquatic invasive plants. Future research should expand treatment scenarios, increase the study period, and identify potential integrated plant management strategies for field scenarios.

Background and aims Harvesting can regulate the overgrowth of submerged macrophytes and affect interspecific competition. However, the effects of harvesting on the growth and competition of submerged macrophytes with different growth forms, remains unclear. Methods Simulation experiments were conducted to study the morphological and physiological indicators, competition intensity, and received light intensity of rosette-forming Vallisneria natans ( V.natans ) under different harvesting intensities of canopy-forming Hydrilla verticillata ( H.verticillata ). Results V. natans had greater plant height and larger leaf area at a medium-intensity (harvest 30% and 45% of the plant height) harvesting than at other intensities. Medium-intensity harvesting was the most conducive to the accumulation of chlorophyll, whereas high-intensity (harvest 60% and 75% of the plant height) harvesting had the lowest chlorophyll content and highest malondialdehyde content in V. natans . Interspecific competition was observed between H. verticillata and V. natans , and the medium harvesting intensity of H. verticillata conferred a competitive advantage to V. natans . Harvesting H. verticillata affect the growth of V. natans by increasing the underwater light intensity, with a greater harvest intensity corresponding to stronger light intensity received by V. natans . Light conditions were the most suitable for the growth of V. natans under medium-intensity harvesting. Conclusions Medium-intensity harvesting not only improved the recovery of H. verticillata but also increased the competitiveness of V. natans , thus promoting the growth of V. natans . Therefore, in practice, medium-intensity harvesting can be applied to the regulation of H. verticillata and V. natans .

Submerged macrophytes are crucial for the restoration of shallow eutrophic lake but they are diminished in coverage or lost with eutrophication. Their recovery after nutrient loading reduction depends on water and sediment nutrient levels. We studied the combined impacts of sediment fertility (low/high nitrogen and phosphorus content) and water nutrient concentrations (low/high nitrogen and phosphorus addition) on Vallisneria denseserrulata in a mesocosm experiment. We hypothesized that both the elevated external nutrient addition and high sediment nutrient contents would inhibit plant growth. We found that an increase in nutrient concentrations resulted in a significant increase in algal biomass. Furthermore, high external nutrient addition significantly reduced both the relative growth rate (RGR) and the density of V. denseserrulata growing in the nutrient-rich sediment, while in the nutrient-poor sediment treatment, RGR was not affected but the plant density decreased. Interestingly, low nutrient addition appeared to be more conducive to growth and reproduction of V. denseserrulata in the nutrient-rich sediment than in the nutrient-poor sediment. Our findings emphasize the importance of reducing external nutrient inputs is of key higher importance when restoring shallow eutrophic lakes, while the plants may benefit of the nutrient-rich sediment occurring in such lakes after eutrophication.

BackgroundResource translocation among interconnected ramets can improve the growth performance of the recipient ramets and influence soil properties and microbial communities in the rooting zone. However, scanty attention has been paid to the effect of this clonal integration on soil biotic and abiotic characteristics of neighboring species around the recipient ramets.MethodsWe conducted a soil heterogeneous experiment in which the mother ramet of the ramet pair for Vallisneria natans was planted in a high-nutrient patch, and the daughter ramet was planted in a low-nutrient patch with conspecific neighbors V. natans or heterospecific neighbors Myriophyllum spicatum. The stolons between ramet pairs were severed or left intact.ResultsOur results showed that effects of clonal integration on growth of the daughter ramet depend on the identity of neighboring species. Overall growth of neighbors V. natans was not affected by clonal integration, while growth of neighbors M. spicatum was greatly reduced. Soil properties and microbial community composition (especially bacteria) in the rhizosphere of neighboring plants were significantly influenced by clonal integration, and these effects were more obvious in the rhizosphere of neighbor V. natans than those in the rhizosphere of neighbors M. spicatum.ConclusionOur study suggests that clonal integration may play a vital role in facilitating nutrient cycling, modifying habitat heterogeneity and affecting interspecific interactions and even the community structure.

Background Interannual variation in resource abundance has become more unpredictable, and food shortages have increasingly occurred in the recent decades. However, compared to seasonal fluctuations in resource abundance, the influences of interannual variation in resource abundance on the dietary niches of consumers remain poorly understood. Poyang Lake, China, is a very important wintering ground for the globally endangered Siberian Crane ( Leucogeranus leucogeranus ), White-naped Crane ( Grus vipio ), and Hooded Crane ( G. monacha ), as well as the non-endangered Eurasian Crane ( G. grus ). Tubers of Vallisneria spp., the dominant submerged macrophytes at Poyang Lake, is an important food for cranes. Nevertheless, submerged macrophytes have experienced serious degradation recently. In this study, we used metabarcoding technology to explore the consequences of Vallisneria tuber collapse on the diet compositions, breadths, and overlaps of the four crane species based on fecal samples collected in winter 2017 (a year with tuber collapse) and winter 2018 (a year with high tuber abundance). Results Compared to previous studies, our study elucidates crane diets in an unprecedented level of detail. Vallisneria tubers was confirmed as an important food source of cranes. Surprisingly, the grassland plant Polygonum criopolitanum was also found to be an important food source in the feces of cranes. Agricultural fields were important foraging sites for Siberian Cranes, White-naped Cranes, and Hooded Cranes, providing foods that allowed them to survive in winters with natural food shortages. However, the three crane species preferred natural wetlands to agricultural fields when the abundance of natural foods was high. The abundance of Vallisneria tubers, and probably P. criopolitanum , greatly influenced the dietary compositions, breadths and overlap of cranes. During periods of preferred resource shortage, White-naped Cranes and Hooded Cranes widened their dietary niches, while Siberian Cranes maintained a stable niche width. The dietary niche overlap among crane species increased substantially under conditions of plentiful preferred food resources. Conclusions Our study emphasizes the superior quality of natural wetlands compared to agricultural fields as foraging habitats for cranes. To provide safer and better foraging areas for cranes, it is urgent to restore the submerged plants at Poyang Lake. While high dietary niche overlap is often interpreted as intense interspecific competition, our study highlights the importance of taking food abundance into account.

When restoring shallow lakes, the recovery of submerged macrophytes is of vital importance to obtain clear water conditions. However, post-restoration recovery of small omnivorous fish can increase water nutrient concentrations through excretion. The impact of these recycled nutrients on submerged macrophytes is not well-studied, and it may depend on fish food of varying nutrient contents. We studied the effects of Acheilognathus macropterus on the growth and nutrient stoichiometry of Vallisneria denseserrulata and Hydrilla verticillata . The experiment had six treatments: two controls without recycled nutrients and two nutrient treatments for each of the plant species, respectively. We found that fish released more phosphorus after consuming low N:P food and more nitrogen after high N:P food. The recycled nutrients significantly promoted the growth of both macrophyte species. Interestingly, macrophytes showed higher growth rates in treatments with nutrients from the low N:P food source. Our study, therefore, suggests that nutrient subsidy from fish excretion can significantly stimulate the growth of submerged macrophytes, the magnitude of the effect being determined by the N:P ratio of the fish food. The realization of this growth potential, however, also depends on the phytoplankton response to these nutrients, that expectedly will be weaker at high macrophyte coverage.

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.

Polycyclic aromatic hydrocarbons (PAHs) were typical environmental contaminants that accumulated continuously in sediment. Microbial degradation is the main way of PAH degradation in the natural environment. Therefore, expanding the available pool of microbial resources and investigating the molecular degrading mechanisms of PAHs are critical to the efficient control of PAH-polluted sites. Here, a strain (identified as Xanthobacteraceae bacterium ) with the ability to degrade pyrene was screened from the rhizosphere sediment of Vallisneria natans . Response surface analysis showed that the strain could degrade pyrene at pH 5–7, NaCl addition 0–1.5%, and temperature 25–40 °C, and the maximum pyrene degradation (~ 95.4%) was obtained under the optimum conditions (pH 7.0, temperature 28.5 °C, and NaCl-free addition) after 72 h. Also, it was observed that the effect of temperature on the degradation ratio was the most significant. Furthermore, eighteen metabolites were identified by mass spectrometry, among which (2Z)-2-hydroxy-3-(4-oxo-4H-phenalen-3-yl) prop-2-enoic acid, 7-(carboxymethyl)-8-formyl-1-naphthyl acetic acid, phthalic acid, naphthalene-1,2-diol, and phenol were the main metabolites. And the degradation pathway of pyrene was proposed, suggesting that pyrene undergoes initial ortho-cleavage under the catalysis of metapyrocatechase to form (2Z)-2-hydroxy-3-(4-oxo-4H-phenalen-3-yl) prop-2-enoic acid. Subsequently, this intermediate was progressively oxidized and degraded to phthalic acid or phenol, which could enter the tricarboxylic acid cycle. Furthermore, the pyrene biodegradation by the strain followed the first-order kinetic model and the degradation rate changed from fast to slow, with the rate remaining mostly slow in the later stages. The slow biodegradation rate was probably caused by a significant amount of phenol accumulation in the initial stage of degradation, which resulted in a decrease in bacterial activity or death. Graphical Abstract