The native submerged plant, Hydrilla verticillata outperforms its exotic confamilial with exposure to polyamide microplastic pollution: Implication for wetland revegetation and potential driving mechanism.

Microplastic pollution and biological invasion, as two by-products of human civilization, interfere the ecological function of aquatic ecosystem. The restoration of aquatic vegetation has been considered a practical approach to offset the deterioration of aquatic ecosystem. However, a lack of knowledge still lies in the species selection in the revegetation when confronting the interference from microplastic pollution and exotic counterpart. The present study subjected the native submerged species, Hydrilla verticillata and its exotic confamilial, Elodea nuttallii to the current and future scenarios of polyamide microplastic pollution. The plant performance proxies including biomass and ramet number were measured. We found that the native H. verticillata maintained its performance while the exotic E. nuttallii showed decreases in biomass and ramet number under severest pollution conditions. The restoration of native submerged plant such as H. verticillata appeared to be more effective in stabilizing aquatic vegetation in the scenario of accelerating microplastic pollution. In order to explore the underlying driving mechanism of performance differentiation, stress tolerance indicators for plants, sediment enzymatic activity and sediment fungal microbiome were investigated. We found that polyamide microplastic had weak effects on stress tolerance indicators for plants, sediment enzymatic activity and sediment fungal diversity, reflecting the decoupling between these indicators and plant performance. However, the relative abundance of sediment arbuscular mycorrhizal fungi for H. verticillata significantly increased while E. nuttallii gathered "useless" ectomycorrhizal fungi at the presence of severest polyamide microplastic pollution. We speculate that the arbuscular mycorrhizal fungi assisted the stabilization of plant performance for H. verticillata with exposure to the severest polyamide microplastic pollution.

The origins of odor (ß-cyclocitral) under different water nutrient conditions: Algae or submerged plants?

Among the problems caused by water eutrophication, the issue of odor compounds has attracted notable attention. ß-Cyclocitral, a widely distributed and versatile odor compound, is commonly derived from both algae and aquatic plants. Planting aquatic plants is a common method of water purification. However, there is limited study on their impact on ß-cyclocitral levels in water. Here, we conducted a study on the ß-cyclocitral levels in water and the submerged plant leaves under three nutrient levels and six plant density treatments. Our findings revealed the following: (1) Chlorophyll-a (Chla), ß-cyclocitral in the water (Wcyc), ß-cyclocitral in Potamogeton lucens leaves (Pcyc) and the biomass of the submerged plants increase with rising nutrient concentration, which increased about 83 %, 95 %, 450 %, 320 % from eutrophic treatment to oligotrophic treatment, respectively. (2) In water, ß-cyclocitral is influenced not only by algae but also by submerged plants, with primary influencing factors varying across different nutrient levels and plant densities. The main source of ß-cyclocitral in water becomes from plants to algae as the water eutrophication and plant density decrease. (3) As submerged plants have the capability to emit ß-cyclocitral, the release of ß-cyclocitral increases with the density of submerged plants. Hence, when considering planting submerged plants for water purification purposes, it is crucial to carefully manage submerged plant density to mitigate the risk of odor pollution emanating from aquatic plants. This study offers fresh insights into selecting optimal water density for submerged plants and their role in mitigating the release of ß-cyclocitral.

Submerged plant-biochar composite system exhibits effective control over residual organic pollutants in the benthic organisms of aquaculture ponds.

As of now, submerged plants and biochar have demonstrated significant benefits in aquaculture pond sediment remediation. However, there is limited research on the synergistic effects of biochar and submerged plants in mitigating hydrophobic organic contaminant (HOC) accumulation in aquaculture benthic organisms and in controlling the nutrient (nitrogen and phosphorus) levels in aquaculture water. This study assesses a submerged plant-biochar system's efficacy in removing HOCs from simulated freshwater aquaculture ponds. Vallisneria natans was planted in sediment with varying levels of wheat straw biochar, while Corbicula fluminea served as the targeted benthic organism. The bioaccumulation experiment identified the optimal biochar ratio for the Vallisneria natans-biochar system in controlling HOCs in aquaculture products. Analyses included final accumulation concentrations in benthic organisms, changes in freely-dissolved concentrations in aquaculture sediment, and a mass balance calculation to explore key factors in their removal from the system. Results indicated that the Vallisneria natans-1.5% biochar composite system achieved optimal control of HOCs in sediment and aquaculture products. Biochar addition to the sediment in the composite system demonstrated a "promotion with low addition, inhibition with high addition" effect on Vallisneria natans growth. Notably, the addition of 1.5% biochar (VN1.5 group) significantly promoted the growth of Vallisneria natans leaves and roots. Comparing the final pollutant proportions in different environmental media, concentrations in water (0.20%-1.8%), clam accumulation (0.032%-0.11%), and plant absorption (0.10%-0.44%) constituted a minimal portion of the overall pollutant load in the system. The majority of pollutants (24%-65%) were degraded in the aquaculture environment, with microbial degradation likely playing a predominant role. Bacterial phyla, particularly Proteobacteria and Firmicutes, were identified as potential direct contributors to pollutant degradation in the Vallisneria natans-biochar system.

Mitigated N2O emissions from submerged-plant-covered aquatic ecosystems on the Changjiang River Delta.

Submerged plants affect nitrogen cycling in aquatic ecosystems. However, whether and how submerged plants change nitrous oxide (N2O) production mechanism and emissions flux remains controversial. Current research primarily focuses on the feedback from N2O release to variation of substrate level and microbial communities. It is deficient in connecting the relative contribution of individual N2O production processes (i.e., the N2O partition). Here, we attempted to offer a comprehensive understanding of the N2O mitigation mechanism in aquatic ecosystems on the Changjiang River Delta according to stable isotopic techniques, metagenome-assembly genome analysis, and statistical analysis. We found that the submerged plant reduced 45 % of N2O emissions by slowing down the dissolved inorganic nitrogen conversion velocity to N2O in sediment (Vf-[DIN]sed). It was attributed to changing the N2O partition and suppressing the potential capacity of net N2O production (i.e., nor/nosZ). The dominated production processes showed a shift with increasing excess N2O. Meanwhile, distinct shift thresholds of planted and unplanted habitats reflected different mechanisms of stimulated N2O production. The hotspot zone of N2O production corresponded to high nor/nosZ and unsaturated oxygen (O2) in unplanted habitat. In contrast, planted habitat hotspot has lower nor/nosZ and supersaturated O2. O2 from photosynthesis critically impacted the activities of N2O producers and consumers. In summary, the presence of submerged plants is beneficial to mitigate N2O emissions from aquatic ecosystems.

Meta-analysis to identify inhibition mechanisms for the effects of submerged plants on algae.

Submerged plants inhibit algae through shading effects, nutrient competition, allelopathy, and combinations of these mechanisms. However, it is unclear which mechanism is dominant, and how the inhibition intensity results from the traits of the plant and algae. In this study, we performed meta-analysis to quantitatively identify the dominant mechanisms, evaluate the relationship between inhibition intensity and the species and functional traits of the submerged plants or algae, and reveal the influences of external environmental factors. We found that allelopathy caused stronger inhibition than the shading effect and nutrient competition and dominated the combined mechanisms. Although the leaf shapes of the submerged plants influenced light availability, this did not change the degree of algae suppression. Algal species, properties (toxic or nontoxic) and external environmental factors (e.g., lab/mesocosm experiments, co-/filtrate/extract culture, presence or absence of interspecific competition) potentially influenced inhibition strength. Cyanobacteria and Bacillariophyta were more strongly inhibited than Chlorophyta, and toxic Cyanobacteria more than non-toxic Cyanobacteria. Algae inhibition by submerged plants was species-dependent. Ceratophyllum, Vallisneria, and Potamogeton strongly inhibited Microcystis, and can potentially prevent or mitigate harmful algal blooms of this species. However, the most common submerged plant species inhibited mixed algae communities to some extent. The results from lab experiments and mesocosm experiments both confirmed the inhibition of algae by submerged plants, but more evidence from mesocosm experiments is needed to elucidate the inhibition mechanism in complex ecosystems. Submerged plants in co-cultures inhibited algae more strongly than in extract and filtrate cultures. Complex interspecific competition may strengthen or weaken algae inhibition, but the response of this inhibition to complex biological mechanisms needs to be further explored. Our meta-analysis provides insights into which mechanisms contributed most to the inhibition effect and a scientific basis for selecting suitable submerged plant species and controlling external conditions to prevent algal blooms in future ecological restoration of lakes.

Ecotoxicity of perfluorooctanoic acid and perfluorooctane sulfonate on aquatic plant Vallisneria natans.

Perfluorinated compounds (PFCs) are persistent organic contaminants that are highly toxic to the environment and bioaccumulate, but their ecotoxic effects on aquatic plants remain unclear. In this study, the submerged plant Vallisneria natans was treated with short-term (7 days) and long-term (21 days) exposures to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentrations of 0, 0.01, 0.1, 1.0, 5.0, and 10 mg/L, respectively. The results showed that both high concentrations of PFOA and PFOS inhibited the growth of V. natans and triggered the increase in photosynthetic pigment content in leaves. The oxidative damage occurred mainly in leaves, but both leaves and roots gradually built up tolerance during the stress process without serious membrane damage. Both leaves and roots replied to short-term stress by activating superoxide dismutase (SOD), catalase (CAT) and polyphenol oxidase (PPO), while peroxidase (POD) was involved under high concentration stress with increasing exposure time. Leaves showed a dose-effect relationship in integrated biomarker response (IBR) values under short-term exposure, and the sensitivity of roots and leaves to PFOS was higher than that of PFOA. Our findings help to increase knowledge of the toxic effects of PFCs and have important reference value for risk assessment and environmental remediation of PFCs in the aquatic ecosystem.

Response of a submerged macrophyte (Vallisneria natans) to water depth gradients and sediment nutrient concentrations.

Submerged plants constitute a vital component of shallow lake ecosystems, where water depth and sediment nitrogen­phosphorus content are two key factors influencing their growth. This study focuses on Vallisneria natans and investigates the morphological and physiological changes of V. natans under the interaction of three water depth gradients and two different sediment nutrient levels. It explores the mechanisms through which varying sediment nutrient conditions under different water depths affect the growth of V. natans. The results indicate that both independent and interactive effects of water depth and sediment nutrient status significantly impact the morphology, antioxidant enzyme activity, and photosynthetic pigment content of V. natans, with water depth having a greater influence. To adapt to increased water depth-induced light stress, V. natans responds morphologically by increasing leaf length, leaf width, and decreasing maximum root length. Physiologically, it enhances its antioxidant regulation capacity and photosynthetic efficiency by increasing antioxidant enzyme activity, root vitality, and photosynthetic pigment content to counter weak light stress. However, these adaptations are insufficient to cope with excessively deep waters (200 cm). Sediment nutrient levels primarily control the growth of V. natans by affecting its root system. When sediment nitrogen and phosphorus content is lower, V. natans exhibits greater total root volume and surface area to enhance nutrient absorption efficiency. Water depth not only directly influences the growth of submerged plants but may also impact the migration and transformation of phosphorus in sediments, further exacerbating its effects on the growth of these plants, thus accelerating the regime shift of shallow lakes. Therefore, this study reveals V. natans' response strategies to varying water depths and sediment nutrient levels, determining suitable water levels and sediment nutrient conditions for its growth. These research findings provide a scientific basis for water level management and ecological restoration of submerged aquatic plants in shallow lakes.

Adaptive responses and transgenerational plasticity of a submerged plant to benthivorous fish disturbance.

Submerged macrophytes play a key role in the restoration of shallow eutrophic lakes. However, in some subtropical lakes, benthivorous fishes dominate the fish assemblages and influence the growth of submerged plants. A comprehensive understanding of the direct and indirect effects of benthivorous fishes on submerged plants is important. We conducted mesocosm experiments to examine the effects of three densities of benthivorous fish, Misgurnus anguillicaudatus, on the water properties, the growth, asexual reproduction, and the germination of turions of Potamogeton crispus L. Our results showed that fish disturbance increased TN, TP, PO4-P, NH4-N, and NO3-N of the water, raising the extinction coefficient K, Chl a, and the periphyton biomass. Benthivorous fish disturbance reduced the total biomass, root length, relative growth rate (RGR), and branching number while increasing the plant height of P. crispus. The P stoichiometric homeostasis coefficient (H P) (except turions) and H N was lower in plant tissues due to fish disturbance. Benthivorous fish disturbances promoted turions formation (e.g., increased turions total numbers and biomass) of P. crispus. Moreover, P. crispus exhibited transgenerational plasticity for benthivorous fish affecting turion emergence. The maximum final germination rate occurred only when fish density in the mother plant grow experiment matched that in the turion germination experiment. Turions generated by P. crispus disturbed by low-density fish exhibited increased germination rates. Our findings suggest that controlling benthivorous fish reduces its indirect and direct effects on submerged vegetation, facilitating the successful restoration of these plants.

Investigation of water quality and aquatic ecological succession of a newly constructed river replenished by reclaimed water in Beijing.

The potential to create new ecosystems in rivers is possible through the use of reclaimed water as a replenishment source, although the long-term effects of this method are unknown. In this study, the water quality and aquatic ecological evolution of a newly constructed river replenished by reclaimed water in Beijing (the Jing River) were investigated, and the conventional water quality, phytoplankton indicators, and submerged plant growth conditions from October 2018 to December 2020 were analyzed. Spearman's correlation and redundancy analysis between possible influential environmental factors and algal indicators were conducted. The results show that the major water quality indicators could meet the water quality standards for landscape water. There were seven phyla present, including 322 species of phytoplankton. The phytoplankton density increased, followed by a decreasing trend. Phytoplankton densities at each monitoring site reached 10 × 106 to 25 × 106 cells/L in 2019 before decreasing in 2020, then ranging from 8 × 106 to 20 × 106 cells/L. Phytoplankton growth was influenced by changing water quality and ecosystems. Consequently, the submerged plant coverage rate gradually increased from 2018 (0%) to 2020 (26.27%-37.06%), as did biodiversity. Through the implementation of ecological restoration measures in the Jing River, the reclaimed water environment evolved into a more natural water environment, which could provide some reference for similar areas to use reclaimed water as a water replenishment source.

Environmental behaviors of emerging contaminants in freshwater ecosystem dominated by submerged plants: A review.

Persistent exposure of emerging contaminants (ECs) in freshwater ecosystem has initiated intense global concerns. Freshwater ecosystem dominated by submerged plants (SP-FES) has been widely constructed to control eutrophic water. However, the environmental behaviors (e.g. migration, transformation, and degradation) of ECs in SP-FES have rarely been concerned and summarized. This review briefly introduced the sources of ECs, the pathways of ECs entering into SP-FES, and the constituent elements of SP-FES. And then the environmental behaviors of dissolved ECs and refractory solid ECs in SP-FES were comprehensively summarized, and the feasibility of removing ECs from SP-FES was critically evaluated. Finally, the challenges and perspectives on the future development for ECs removal from SP-FES were prospected, giving possible research gaps and key directions. This review will provide theoretical and technical support for the effective removal of ECs in freshwater ecosystem, especially in SP-FES.

Single and combined toxicity of polystyrene nanoplastics and arsenic on submerged plant Myriophyllum verticillatum L.

The contamination of nanoplastics (NPs) and heavy metals (HM) in water bodies has caused widespread concern, while their effects on submerged plants are poorly reported. Polystyrene nanoplastics (PSNPs) and arsenic (As) were used to assess their toxicity on Myriophyllum verticillatum L. via the orthogonal experiments. PSNPs significantly reduced the accumulation of As (17.24%-66.67%) in plant. Single As and high As-PSNPs treatments significantly inhibited plant growth, with a maximum reduction of 70.09% in the growth rate. The mineral nutrient content was significantly affected by PSNPs and As treatments. The antioxidant system was significantly inhibited, which was more pronounced in the roots. Similar findings were observed for soluble protein and soluble sugar. Some organic acids and amino acids showed down-regulation at high concentrations of As, leading to a decrease in the content of the mineral element and down-regulation of antioxidant enzyme synthesis. Furthermore, PSNPs could alleviate As toxicity under 0.1 mg/L As treatment but exacerbate As toxicity at 1 mg/L As dose. This study has important implications for the study of submerged plants exposed to co-contamination of microplastics and heavy metals, as well as the possible ecological risk assessment in freshwater.

Linking fluorescent dissolved organic matters to microbial carbon metabolism in the overlying water during submerged macrophyte Potamogeton crispus L decomposition in the presence/absence of Vallisneria natans.

Multi-species submerged plants grow with succession patterns in the same habit and play an important role in the aquatic ecosystems. The decomposition of submerged plants in aquatic environments was a disturbance that affected the water quality and microbial community structures. However, the responses of the microbial community function in surface water to the disturbance remain poorly understood. In this study, the effects of submerged macrophyte Potamogeton crispus L decomposition on the water quality and microbial carbon metabolism functions (MCMF) in the overlying water were investigated in the presence/absence of Vallisneria natans. The result showed that the decomposition rapidly released a large amount of organic matter and nutrients into the overlying water. The presence of Vallisneria natans promoted the removal of dissolved organic carbon and fluorescent component C3, resulting in lower values of the percentage content of C3 (C3%). Under various decomposition processes, the MCMF changed over time and significantly negatively correlated with C3%. The functional diversity of MCMF significantly correlated with the fluorescence organic matters, such as the richness and Simpson index correlated with the amount of C1, C1+C2+C3, and C3%. But UV-visible absorption indexes and nutrients in the overlying water had no relationship with the MCMF, except for the total nitrogen correlated with the richness. These results suggested that under various decomposition conditions, the fluorescent dissolved organic matter could be used as an indicator for quick prediction of MCMF in surface water.

Allelopathic inhibitory effect on the growth of microcystis aeruginosa by improved ultrasonic-cellulase extract of Vallisneria.

The unique and efficient characteristics of allelopathy in submerged plants make it an environmentally friendly method to control harmful algal blooms. Increased research focus has been placed on the improved allelochemical extraction methods of submerged plants because of their cost-utility relationships. In this study, the growth inhibition effect of Vallisneria extract on Microcystis aeruginosa (M. aeruginosa) cells through the combination of enzyme and ultrasonic-assisted extraction method was analyzed. By establishing a co-cultivation experiment, the growth indicators, photosynthetic system, and oxidative stress system of M. aeruginosa were determined. The reactive oxygen species (ROS) and superoxide dismutase (SOD) activity, as well as the catalase (CAT) and Malondialdehyde (MDA) levels of algal cells were found to have increased significantly after co-cultivation, which indicated that the Vallisneria ultrasonic-cellulase extract could induce oxidative stress in Microcystis aeruginosa cells. The Vallisneria extract could promote at low concentrations and inhibit at high concentrations on the growth of Microcystis aeruginosa. The effective suppression of growth of algae cells with the extract was observed at 5 g/L (fresh weight). The results showed that the Vallisneria ultrasonic-cellulase extract had a significant inhibitory effect on M. aeruginosa, making the effective ingredients a useful reference for algae inhibitors.

Role of carbon and nutrient exports from different land uses in the aquatic carbon sequestration and eutrophication process.

The hydrochemical features affected by differing land uses play a key role in regulating both the primary production of aquatic photosynthetic organisms and the formation of autochthonous organic carbon (AOC); this impacts eutrophication and the global carbon cycle. In shallow water environments where phytoplankton and submerged plants coexist, the C-N-P limitations on the primary production of these aquatic organisms, and the mechanisms by which they promote the formation of AOC are poorly understood. In this study, over the hydrological year September 2018 to August 2019, a large-scale field simulation experiment at the Shawan Karst Test Site (SW China) with various types of land use was systematically conducted to investigate the C-N-P limitations on the primary production of phytoplankton and submerged plants. The results indicate that (1) phytoplankton are co-limited by nitrogen (N) and phosphorus (P) but with the N more important, while submerged plants are limited by carbon (C); (2) Chlorophyta and Bacillariophyta display a stronger competitive advantage than Cyanophyta in aqueous environments with high C but low N-P; (3) there is a seasonal difference in the contribution of phytoplankton and submerged plants to the formation of AOC, however, throughout the year, the contributions of phytoplankton (27%) and submerged plants biomass (28%) to AOC concentrations in the water were similar, combinedly accounting for approximately 17% of the formed AOC. It is concluded that natural restoration of vegetation, or injecting CO2 into water, which results in higher C but lower N-P loadings, may simultaneously help to mitigate eutrophication (with changes in biological structure and species) and increase C sequestration in surface waters.

Evaluation of mercury bioavailability and phytoaccumulation by means of a DGT technique and of submerged aquatic plants in an aquatic ecosystem situated in the vicinity of a cinnabar mine.

The ability of submerged aquatic plants (Elodea canadensis, Myriophyllum spicatum, Ceratophyllum demersum) and a natant plant (Eichhornia crassipes) to bioaccumulate mercury was evaluated in a laboratory experiment as well as in a real aquatic ecosystem situated in the vicinity of a cinnabar mine. Moreover, the ability of the diffusive gradients in the thin films technique (DGT) to predict mercury bioavailability for selected aquatic plants was tested. The submerged plants had sufficient bioaccumulation capacity for long-term phytoaccumulation of mercury in a real aquatic ecosystem. The determined bioaccumulation factor was greater than 1000. On average, the submerged plant leaves accumulated 13 times more mercury than the leaves of the natant aquatic plants. Chlorides at concentrations up to 200 mg/L had no statistically significant effect on mercury accumulation, nevertheless, the presence of humic acid in the water environment resulted in its significant (p < 0.002) decrease. A strong positive correlation (r > 0.66) was determined between mercury concentration in the input parts (leaves and/or roots) of the aquatic plants and the flow of mercury into DGT units.

[Characteristics of the rhizosphere and phyllosphere microbial community of three submerged plants in the dragon-shaped water system of Beijing].

Aquatic plants and the epiphytic microorganisms are important contributors to the purification of constructed wetlands. Taking the dragon-shaped water system of Beijing Olympic Park as a model, this study analyzed the structure and function of the microbial communities reside the sediment, the water body and the rhizosphere and phyllosphere of three submerged plants-Vallisneria natans, Myriophyllum verticillatum, and Potamogeton pectinatus using high-throughput sequencing technology. The results showed that the microbial diversity from the highest to the lowest were samples from sediment, plant rhizosphere, plant phyllosphere and water. The microbial diversity of plant phyllosphere samples were significantly higher than those of the water body. LEfSe analysis showed that different habitats enriched different microbial groups. The sediments mainly enriched anaerobic microbes, while the water body and the phyllosphere of plants mainly enriched aerobic microbes, and the rhizosphere of plants had the both. Functional prediction analysis showed that the abundance of denitrification marker genes in phyllosphere samples was higher than that in samples from rhizosphere, sediment and water body, and the abundance of denitrification marker genes in phyllosphere samples of M. verticillatum and P. pectinatus was higher than that of V. natans. This study could serve as a guidance for the selection of submerged plants and functional microorganisms for constructed wetlands.

Metagenomic insights into the effects of submerged plants on functional potential of microbial communities in wetland sediments.

Submerged plants in wetlands play important roles as ecosystem engineers to improve self-purification and promote elemental cycling. However, their effects on the functional capacity of microbial communities in wetland sediments remain poorly understood. Here, we provide detailed metagenomic insights into the biogeochemical potential of microbial communities in wetland sediments with and without submerged plants (i.e., Vallisneria natans). A large number of functional genes involved in carbon (C), nitrogen (N) and sulfur (S) cycling were detected in the wetland sediments. However, most functional genes showed higher abundance in sediments with submerged plants than in those without plants. Based on the comparison of annotated functional genes in the N and S cycling databases (i.e., NCycDB and SCycDB), we found that genes involved in nitrogen fixation (e.g., nifD/H/K/W), assimilatory nitrate reduction (e.g., nasA and nirA), denitrification (e.g., nirK/S and nosZ), assimilatory sulfate reduction (e.g., cysD/H/J/N/Q and sir), and sulfur oxidation (e.g., glpE, soeA, sqr and sseA) were significantly higher (corrected p < 0.05) in vegetated vs. unvegetated sediments. This could be mainly driven by environmental factors including total phosphorus, total nitrogen, and C:N ratio. The binning of metagenomes further revealed that some archaeal taxa could have the potential of methane metabolism including hydrogenotrophic, acetoclastic, and methylotrophic methanogenesis, which are crucial to the wetland methane budget and carbon cycling. This study opens a new avenue for linking submerged plants with microbial functions, and has further implications for understanding global carbon, nitrogen and sulfur cycling in wetland ecosystems. Supplementary Information: The online version contains supplementary material available at 10.1007/s42995-021-00100-3.

Characteristics of the rhizosphere and phyllosphere microbial community of three submerged plants in the dragon-shaped water system of Beijing / 生物工程学报

Aquatic plants and the epiphytic microorganisms are important contributors to the purification of constructed wetlands. Taking the dragon-shaped water system of Beijing Olympic Park as a model, this study analyzed the structure and function of the microbial communities reside the sediment, the water body and the rhizosphere and phyllosphere of three submerged plants-Vallisneria natans, Myriophyllum verticillatum, and Potamogeton pectinatus using high-throughput sequencing technology. The results showed that the microbial diversity from the highest to the lowest were samples from sediment, plant rhizosphere, plant phyllosphere and water. The microbial diversity of plant phyllosphere samples were significantly higher than those of the water body. LEfSe analysis showed that different habitats enriched different microbial groups. The sediments mainly enriched anaerobic microbes, while the water body and the phyllosphere of plants mainly enriched aerobic microbes, and the rhizosphere of plants had the both. Functional prediction analysis showed that the abundance of denitrification marker genes in phyllosphere samples was higher than that in samples from rhizosphere, sediment and water body, and the abundance of denitrification marker genes in phyllosphere samples of M. verticillatum and P. pectinatus was higher than that of V. natans. This study could serve as a guidance for the selection of submerged plants and functional microorganisms for constructed wetlands.

Drivers of a habitat shift by critically endangered Siberian cranes: Evidence from long-term data.

Many waterbird populations have become increasingly dependent on agricultural habitats for feeding. While habitat destruction has been proposed as a key reason forcing waterbirds to move from natural habitats to agricultural habitats, few have used long-term data to test this hypothesis. The Siberian crane (Leucogeranus leucogeranus) is an IUCN Critically Endangered species. About 98% of its global population winters at Poyang Lake, China. Recently, many cranes shifted from feeding in natural wetlands to agricultural habitats. Here, we integrate bird surveys, Vallisneria tuber (the traditional food of cranes in natural wetlands) surveys, water level data, and remotely sensed images from 1999 to 2016 to explore the drivers of this habitat shift. Changes in Siberian crane numbers in natural wetlands and agricultural fields indicated that the habitat shift occurred in the winters of 2015-2016. Analyses using generalized linear mixed models suggested that crane numbers in natural wetlands were positively related to tuber density and the interaction between dry season (October-March) water level and tuber density. The changes in tuber density and dry season water level in 2015-2016 indicated that tuber disappearance may have been the primary driver of the habitat shift, with a smaller effect of high water level. Submerged plants at Poyang Lake have degraded seriously in the past two decades. The plant degradation at Shahu Lake, a sublake of Poyang Lake, may have been caused by high spring water, high winter temperature, and low summer temperature. However, the drivers of tuber disappearance at Poyang Lake may not be restricted to these variables. Because Poyang Lake is an important refuge for many waterbirds in the Yangtze River floodplain, it is urgent to take effective measures to restore its submerged plants and ecosystem health. Agricultural fields can be important refuges for Siberian cranes, mitigating the negative impacts of wetland deterioration.

Effects of substrate and water depth of a eutrophic pond on the physiological status of a submerged plant, Vallisneria natans.

Effects of substrate and water depth on the physiological status of a submerged macrophyte, Vallisneria natans (Lour.) H. Hara, were determined by measuring biomarkers in leaves and roots, to understand factors limiting the re-establishment of V. natans in urban eutrophic ponds. Ramets of V. natans were grown in the laboratory using aquaria containing water and bottom mud from a eutrophic pond and maintained under sufficient light in an incubator. The growth and chlorophyll-a (Chl-a) content of leaves were greater in aquaria with mud than in those with sand, which was used as the reference substrate. The contents of a peroxidation product (malondialdehyde (MDA)) and three antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD)) in leaves and roots, used as stress biomarkers, changed during the experiment, although differences in these contents between mud and sand were not consistent across the experimental days. To control water depth in the field, ramets of V. natans were grown in cages with different substrates (mud and sand) installed at different depths (0.5, 1.2, and 2.0 m) in the pond. The mean light quantum during the experiment decreased with increasing depth, from 79.3 µmol/m2 s at 0.5 m to 7.9 µmol/m2 s at 2.0 m. The Chl-a content in leaves decreased, whereas the MDA content in both leaves and roots increased with increasing water depth. All enzyme activities increased at the beginning and then decreased to the end of the experiment at 2.0 m depth, suggesting deterioration of enzyme activities due to depth-related stress. The MDA content and CAT activity were higher for sand than for mud, whereas the difference in the growth and the leaf Chl-a content between substrates remained unclear in the pond. On comparing the laboratory and field experiments, the leaf Chl-a content was found to be lower and the MDA content and enzyme activities exhibited sharp increase for ramets grown in the pond, even at 0.5 m depth, when compared with those grown in the aquaria. Our results suggest that the bottom mud of the pond is not the major limiting factor in the re-establishment of V. natans. Because water depth and light attenuation exerted strong stress on V. natans, shallow areas or measures to improve water transparency are required to promote the introduction of V. natans in eutrophic ponds for successful restoration in urban areas.