Phosphate-solubilizing bacteria improve the antioxidant enzyme activity of Potamogeton crispus L. and enhance the remediation effect on Cd-contaminated sediment.

Phosphorus-solubilizing bacteria (PSB) assisted phytoremediation of cadmium (Cd) pollution is an effective method, but the mechanism of PSB-enhanced in-situ remediation of Cd contaminated sediment by submerged plants is still rare. In this study, PSB (Leclercia adecarboxylata L1-5) was inoculated in the rhizosphere of Potamogeton crispus L. (P. crispus) to explore the effect of PSB on phytoremediation. The results showed that the inoculation of PSB effectively improved the Cd extraction by P. crispus under different Cd pollution and the Cd content in the aboveground and underground parts of P. crispus all increased. The µ-XRF images showed that most of the Cd was enriched in the roots of P. crispus. PSB especially showed positive effects on root development and chlorophyll synthesis. The root length of P. crispus increased by 51.7 %, 80.5 % and 74.2 % under different Cd pollution, and the Ca/Cb increased by 38.9 %, 15.2 % and 8.6 %, respectively. Furthermore, PSB enhanced the tolerance of P. crispus to Cd. The contents of soluble protein, MDA and H2O2 in 5 mg·kg-1 and 7 mg·kg-1 Cd content groups were decreased and the activities of antioxidant enzymes were increased after adding PSB. The results showed that the application of PSB was beneficial to the in-situ remediation of submerged plants.

Vertical optical complexity shaped by submerged macrophytes.

The influence of macrophytes on the optical environment of the littoral zone was assessed by studying the effect of monospecific Potamogeton perfoliatus on the quantitative and qualitative properties of light and the response of plants to this altered environment. P. perfoliatus was shown to alter the optical environment and consequently its own architecture: in high-density pondweed patches, 67 percent of incident light was absorbed in the top 10 cm, while spectral properties of light was significantly altered. Leaf morphology and photophysiology adapted to these changes, with photosynthetically active biomass concentrated in the upper water layer and stem biomass increasing in the basal parts due to self-shading. This study highlights the importance of submerged macrophytes in shaping the optical environment and ecological dynamics of littoral zones. Not only do pondweed plants from different sites show very similar vertical patterns of morphological and physiological parameters, but they also contribute to similar vertical spatial variability in water optics, thus increasing habitat complexity. This added optical heterogeneity not only increases the diversity of the littoral zone, but also enriches the entire aquatic ecosystem of shallow lakes by providing additional optical ecological niches.

The uptake, transportation, and chemical speciation of Sb(III) and Sb(V) by wetland plants Arundinoideae (Phragmites australis) and Potamogetonaceae (Potamogeton crispus).

Antimony (Sb) is increasingly released and poses a risk to the environment and human health. Antimonite (Sb(III)) oxidation can decrease Sb toxicity, but the current knowledge regarding the effects of Sb(III) and antimonate (Sb(V)) exposure is limited to wetland plants, especially the Sb speciation in plants. In this study, Phragmites australis and Potamogeton crispus were exposed to 10 and 30 mg/L Sb(III) or Sb(V) for 20 days. The total concentration, subcellular distribution, and concentration in the iron plaque of Sb were determined. The Sb speciation in plants was analyzed by HPLC-ICP-MS. It illustrated that Sb(III) exposure led to more Sb accumulation in plants than Sb(V) treatments, with the highest Sb concentration of 405.35 and 3218 mg/kg in Phragmites australis and Potamogeton crispus, respectively. In the subcellular distribution of Sb, accumulation of Sb mainly occurred in cell walls and cell cytosol. In Phragmites australis, the transport factor in the Sb(V) treatments was about 3 times higher than the Sb(III) treatments, however, it was lower in the Sb(V) treatments than Sb(III) treatments for Potamogeton crispus. Sb(V) was detected in the plants of Sb(III) treatments with different Sb(V)-total Sb vitro (Phragmites australis: 34 % and, Potamogeton crispus: 15 %), moreover, Sb(V) was also detected in the nutrient solution of Sb(III) treatments. Antimony exposure caused a reduction of the iron plaque formation, at the same time, the root aerenchyma formation was disrupted, and this phenomenon is more pronounced in the Sb(III) treatments. Moreover, the iron plaque has a higher sorption potential to Sb under Sb(III) exposure than that under Sb(V) exposure. The results can fill the gap for antinomy speciation in wetland plants and expand the current knowledge regarding the Sb translocation in wetland systems.

Analysis of diversity and function of epiphytic bacterial communities associated with macrophytes using a metagenomic approach.

Epiphytic bacteria constitute a vital component of aquatic ecosystems, pivotal in regulating elemental cycling. Despite their significance, the diversity and functions of epiphytic bacterial communities adhering to various submerged macrophytes remain largely unexplored. In this study, we employed a metagenomic approach to investigate the diversity and function of epiphytic bacterial communities associated with six submerged macrophytes: Ceratophyllum demersum, Hydrilla verticillata, Myriophyllum verticillatum, Potamogeton lucens, Stuckenia pectinata, and Najas marina. The results revealed that the predominant epiphytic bacterial species for each plant type included Pseudomonas spp., Microbacterium spp., and Stenotrophomonas rhizophila. Multiple comparisons and linear discriminant analysis effect size indicated a significant divergence in the community composition of epiphytic bacteria among the six submerged macrophytes, with 0.3-1% of species uniquely identified. Epiphytic bacterial richness associated with S. pectinata significantly differed from that of both C. demersum and H. verticillata, although no significant differences were observed in diversity and evenness. Functionally, notable variations were observed in the relative abundances of genes associated with carbon, nitrogen, and phosphorus cycling within epiphytic bacterial communities on the submerged macrophyte hosts. Among these communities, H. verticillata exhibited enrichment in genes related to the 3-hydroxypropionate bicycle and nitrogen assimilation, translocation, and denitrification. Conversely, M. verticillatum showcased enrichment in genes linked to the reductive citric acid cycle (Arnon-Buchanan cycle), reductive pentose phosphate cycle (Calvin cycle), polyphosphate degradation, and organic nitrogen metabolism. In summary, our findings offer valuable insights into the diversity and function of epiphytic bacteria on submerged macrophyte leaves, shedding light on their roles in lake ecosystems.

Response strategies of stem/leaves endophyte communities to nano-plastics regulate growth performance of submerged macrophytes.

Research on the toxicity effects of nano-plastics on submerged macrophytes has been increasing over the past several years. However, how the endophytic bacteria of submerged macrophytes respond to nano-plastics remains unknown, although they have been widely shown to help terrestrial plants cope with various environmental stressors. Here, a microcosm experiment was performed to unravel the effects of high concentration of nano-plastics (20 mg/L) on three submerged macrophyte (Vallisneria natans, Potamogeton maackianus, Myriophyllum spicatum) and their endophytic bacterial communities. Results indicated that nano-plastics induced antioxidative stress in plants, but significantly reduction in relative growth rate (RGR) only occurred in V. natans (from 0.0034 to -0.0029 day-1), accompanied by change in the stem/leaves endophyte community composition. Further analysis suggested nano-plastics caused a reduction in environmental nutrient availability and the proportion of positive interactions between endophyte communities (43%), resulting in the lowest RGR of V. natans. In contrast, endophytes may help P. maackianus and M. spicatum cope with nano-plastic stress by increasing the proportion of positive correlations among communities (70% and 75%), leaving their RGR unaffected. Collectively, our study elucidates the species-specific response strategies of submerged macrophyte-endophyte to nano-plastics, which helps to reveal the different phytoremediation potential of submerged macrophytes against nano-plastic pollution.

Comparative Plastid Genome and Phylogenomic Analyses of Potamogeton Species.

Potamogetonaceae are aquatic plants divided into six genera. The largest genus in the family is Potamogeton, which is morphologically diverse with many hybrids and polyploids. Potamogetonaceae plastomes were conserved in genome size (155,863 bp-156,669 bp), gene contents (113 genes in total, comprising 79 protein-coding genes and 30 tRNA and 4 rRNA genes), and GC content (36.5%). However, we detected a duplication of the trnH gene in the IR region of the Potamogeton crispus and P. maakianus plastomes. A comparative analysis of Alismatales indicated that the plastomes of Potamogetonaceae, Cymodaceae, and Ruppiaceae have experienced a 6-kb inversion of the rbcL-trnV region and the ndh complex has been lost in the Najas flexilis plastome. Five divergent hotspots (rps16-trnQ, atpF intron, rpoB-trnC, trnC-psbM, and ndhF-rpl32) were identified among the Potamogeton plastomes, which will be useful for species identification. Phylogenetic analyses showed that the family Potamogetonaceae is a well-defined with 100% bootstrap support and divided into two different clades, Potamogeton and Stuckenia. Compared to the nucleotide substitution rates among Alismatales, we found neutral selection in all plastid genes of Potamogeton species. Our results reveal the complete plastome sequences of Potamogeton species, and will be helpful for taxonomic identification, the elucidation of phylogenetic relationships, and the plastome structural analysis of aquatic plants.

Macrophyte communities as bioindicator of stormwater pollution in rivers: a quantitative analysis.

Macrophytes are one of the important indicators used in assessing the anthropic impact on aquatic ecosystems. The structure of macrophyte communities of two rivers were compared by species composition, dominant species and projective cover using statistical methods. It is shown that the influence of storm runoff on these rivers is manifested in the form of a change in the dominant species composition. Based on the statistical analysis carried out, it can be argued that, despite the peculiarities of the flora composition of each of the rivers, the influence of storm runoffs largely neutralizes this specificity, determining the situation in local areas immediately below the runoff. In the area of the effluent discharge the dominance of individual species and an increase in the area overgrown with macrophytes was observed. In the area of stormwater discharge on the Psel River, species were usually present: Nuphar lutea, Ceratophyllum demersum, Myriophyllum spicatum and on the Bystrica River-Glyceria maxima, Sagitaria sagittiformis, Stuckenia pectinata and Potamogeton crispus. The use of the NMDS method has been found to provide good insight into the structural rearrangements in macrophyte communities affected by runoff from stormwater systems.

Water exchange unevenness alters the species dominance and community composition of submerged macrophytes in Erhai Lake and the potential mechanisms revealed by laboratory experiment.

Water exchange unevenness (WEU) is defined as the coefficient of variation in water exchange intensity over time. Although its influence on aquatic plant characteristics has been recently investigated, there is limited understanding regarding the effects of this hydrodynamic change on submerged vegetation. This study investigated the impacts of WEU on the species dominance and community composition of submerged macrophytes in three bays with different WEU conditions in Erhai Lake, China. Subsequently, a laboratory experiment was conducted to elucidate the mechanisms underlying these effects. The field investigation showed that the dominance values of submerged macrophytes were influenced by WEU. As WEU decreased, the average dominance value decreased for Vallisneria natans (by 34.54 %), Myriophyllum spicatum (16.82 %), and Hydrilla verticillata (12.84 %); showed no significant change for Potamogeton lucens; and increased for Potamogeton maackianus (14.22 %) and Ceratophyllum demersum (17.52 %). The laboratory experiment showed that lower WEU markedly inhibited the growth of V. natans, slightly inhibited that of M. spicatum, and stimulated that of P. maackianus, consistent with the field observations. The inhibitory effect was attributed to a reduced concentration of carbon dioxide in the water; adaptive strategies, i.e., plant height, biomass allocation, and root traits, were more effective for M. spicatum than for V. natans. The stimulated growth of P. maackianus was attributed to increased dissolved oxygen concentration, which promoted root growth and nutrient uptake. Our results indicate that WEU has significant effects on the growth and community characteristics of submerged macrophytes.

Potamogeton crispus restoration increased the epiphytic microbial diversity and improved water quality in a micro-polluted urban river.

Special characterization and assembly of epiphytic microbial communities remain unclear in micro-polluted water column during submersed macrophytes restoration. In this study, an in-situ enclosure area sowing with turions of Potamogeton crispus (P. crispus) was conducted in a micro-polluted urban river to investigate the characterization of P. crispus and epiphytic microbial communities and their response to water environment under different water depths. Turions completely germinated in water column with <90 cm water depth and the germination speed decreased with increasing water depth within 18 days. There were obvious differences in morphological characteristics of P. crispus between deep and shallow water layers. P. crispus restoration decreased by 12-32%, 13-36%, 9-43% and 5-36% of COD, NH4+-N, TN and TP concentration, respectively, in enclosed overlying water compared to the river (P < 0.05) during 5 months of experiment. Illumina sequencing was employed to explore the epiphytic bacterial and microeukayotic communities at water depth 25-35 cm (shallow area) and 80-90 cm (deep area). A total of 9 bacterial and 12 microeukayotic dominant phyla were obtained in eight samples. It should be noted that the algae abundances were higher in shallow area than deep area but a reverse trend was observed for methanotrophs. Null model analysis revealed that dispersal limitation and undominated process was the most important assembly process, whereas stochastic processes gained more importance in shallow area than deep one. According to cooccurrence analysis (|r| > 0.6, P < 0.05), there were more strongly correlated edges in shallow area (456 edges) than deep area (340 edges). These results highlight that submerged macrophytes restoration can increase microbial diversity and improve water quality, and provide a "summer disease cured in winter" way by using could-resistant P. crispus for water purification in micro-polluted rivers in low-temperature season.

Effects of ROS and caspase-3-like protein on the growth and aerenchyma formation of Potamogeton perfoliatus stem.

Aerenchyma formation plays an important role in the survival of Potamogeton perfoliatus in submerged environment. To understand the regulatory role of reactive oxygen species (ROS) and caspase 3-like protein signaling molecules in aerenchyma formation, we investigated the effects of exogenous NADPH oxidase inhibitor (diphenyleneiodonium chloride, DPI), catalase inhibitor (3-amino-1,2,4-triazole, AT), and caspase-3-like protein inhibitor (AC-DEVD-CHO, DEVD) on morphological and physiological characteristics and aerenchyma formation in P. perfoliatus. The results showed that after DPI treatment, caspase-3-like protein activity decreased, ROS-related enzyme activities increased, and H2O2 content decreased, thereby inhibiting aerenchyma formation. When the concentration of DPI was approximately 1 µmol/L, the inhibitory effect was the most obvious. On the contrary, after the AT treatment, caspase-3-like protein activity increased, ROS-related enzyme activities decreased, and the H2O2 content increased, ultimately promoting aerenchyma formation, and the promotion was the most obvious under treatment with approximately 500 µmol/L AT. After DEVD treatment, the inhibition of vegetative growth caused by DPI or AT treatment was alleviated, significantly reducing caspase-3-like activity and inhibiting aerenchyma development. The results of this study show that ROS has a positive regulatory effect on aerenchyma formation, and caspase-3-like protein is activated to promote ROS-mediated aerenchyma formation. This experiment provides a new theoretical basis for further exploration of the signal transduction effects of ROS and caspase-3-like protein in plant cells and their roles in plant development.

Antioxidant Effects of Rhodoxanthin from Potamogeton crispus L. on H2 O2 -Induced RAW264.7 Macrophages Cells.

Potamogeton crispus L. (P. crispus) is the type of a widely distributed perennial herbs, which is rich in rhodoxanthin. In this research work, five antioxidant indexes in vitro were selected to study the antioxidant activity of rhodoxanthin from P. crispus (RPC). A model of hydrogen peroxide (H2 O2 ) -induced oxidative damage in RAW264.7 cells was established to analyze the antioxidant effect and potential mechanism of RPC. The levels of ROS, MDA and the activities of oxidation related enzymes by H2 O2 were determined by enzyme linked immunosorbent assay (ELISA). The mRNA expression of Nrf-2, HO-1, SOD1 and SOD2 was measured by qRT-PCR assay. According to the results, RPC had free radical scavenging ability for 2, 2-diphenyl-1-trinitrohydrazine (DPPH), 2,2'-azinobis(3-ethylbenzo-thiazoline-6-sulfonic acid radical ion) (ABTS), hydroxyl radical and superoxide anion. RPC significantly decreased the level of MDA and ROS and LDH activity, while increased GSH level and activities of SOD, GSH-Px and CAT. It was showed that RPC could increase the mRNA expression of Nrf-2, HO-1, SOD1 and SOD2 in RAW264.7 cells in a dose-dependently manner. In summary, RPC treatment could effectively attenuate the H2 O2 -induced cell damage rate, and the mechanism is related to the reduction of H2 O2 induced oxidative stress and the activation of Nrf-2 pathway.

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.

Influence of Potamogeton crispus harvesting on phosphorus composition of Lake Yimeng.

Harvesting is an important method used to control the overproduction of Potamogeton crispus in lakes. A three-year comparative field study was performed in a eutrophic lake (harvested area) and its connected lake (non-harvested area) to determine the effects of harvesting on the phosphorus (P) composition and environmental factors in the water and sediment. Results revealed that harvesting significantly reduced the dissolved total P and dissolved organic P (DOP) and increased the alkaline phosphatase activity and particulate P (PP) in the water. No significant differences were detected in the water total P (TP), soluble reactive P, chlorophyll-a, pH, and dissolved oxygen between the harvested and non-harvested areas. Sediment TP and organic P (OP) were significantly reduced in the harvested area. Harvesting changed the P composition in the water. In the non-harvested area, P was mainly formed by DOP (40%) in the water body, while in the harvested area, PP was the main water component (47%). Harvesting increased the proportion of inorganic P (IP) in the sediment and decreased the proportion of OP. In the water, the IP to TP ratio in the non-harvested and harvested areas were 58.26% and 63.51%, respectively. Our results showed that harvesting changed the P composition in the water and sediment. In the harvesting of submerged vegetation, our results can serve as a reference for the management of vegetation-rich lakes.

Climate, hydrology, and human disturbance drive long-term (1988-2018) macrophyte patterns in water diversion lakes.

Macrophytes are affected by many natural and human stressors globally but their long-term responses to these multiple stressors are not often quantified. We employed remote sensing and statistical tools to analyze datasets from both short-term (2017-2018) field investigations to explore seasonal patterns, and long-term (1988-2018) Landsat remote-sensing images to detect annual patterns of macrophyte distributions and study their responses to changes in climate, hydrology, and anthropogenic activities in a chain of water diversion lakes in eastern China. We found: 1) biomass and species richness of macrophytes peaked in summer with dominant species of submerged macrophytes Ceratophyllum demersum, Potamogeton pectinatus, and Potamogeton maackianus and floating macrophytes Trapa bispinosa, and non-native species Cabomba caroliniana spread in midstream Luoma Lake and Nansi Lake in summer, while Potamogeton crispus was dominant in all the lakes in spring; 2) water physicochemical parameters (chloride and water depth), lake characteristics (area and water storage), climate factors (air temperature and precipitation), and anthropogenic activities (commercial fishery and urban development) were significantly correlated to the seasonal distribution of macrophytes; 3) long-term data showed a significantly negative correlation between coverage of floating macrophytes and precipitation where the wettest year of 2003 had the lowest coverage of floating macrophytes; and 4) climate (air temperature) and hydrology (water level) were positively correlated with total macrophyte coverage, but human disturbance indexed by the gross domestic product was negatively driving long-term coverage of macrophytes. Our study has important implications for understanding the long-term succession of macrophytes under both natural and human stressors, and for future environmental management and ecological restoration of freshwater lakes.

The bacterial community structure in epiphytic biofilm on submerged macrophyte Potamogetom crispus L. and its contribution to heavy metal accumulation in an urban industrial area in Hangzhou.

Submerged macrophytes and their epiphytic biofilms are important media for metal transport/transformation in aquatic environment. However, the bacterial community structure and the contribution of the epiphytic biofilm to the heavy metal accumulation remain unclear. Therefore, in this study, water, sediment, submerged macrophyte (Potamogeton crispus L.) and its epiphytic biofilm samples in three sites of the moat in the industrial area of Hangzhou were collected for analyzing. The bacterial community structure was significantly impacted by the TN concentrations, and Genus Aeromonas (24.5-41.8%), Acinetobacter (16.2-29.8%) and Pseudomonas (12.6-23.6%) dominated in all epiphytic biofilm samples, which had the heavy metal pollutant resistibility. The contents of Cr in biofilms (7.4-8.3 mg/kg, DW) were significantly higher than those in leaves (1.0-2.4 mg/kg, DW), while the contents of Cu (11.0-13.9 mg/kg, DW) in leaves were significantly higher than those in biofilms (0.7-3.9 mg/kg, DW) in all the three sites. The BCF values of metals in the biofilm were followed the order of YF < IC < ETS. The results indicated that the epiphytic biofilm had positive effects on the metal bioaccumulation, and the metal accumulation ability increased with the hydrodynamic forces. Bioaccumulation by the epiphytic biofilm may be an effective way for metal (especially Cr) remediation.

How does turions production of Potamogeton crispus L. respond to parental population biomass and living environment.

Turions production is the dominant means of propagation in Potamogeton crispus L. To understand how parental population and their living environmental factors influence the turions production of P. crispus L., a field research was conducted in Nansi Lake in Yellow River Flood Plain and southwestern Shandong Province, China. This study showed that P. crispus biomass and asexual turions showed an almost uniform spatial distribution pattern. Water depth, attenuation coefficient of light, sediment water content, sediment organic matter content, and pH were significantly related to P. crispus biomass, turions weight, and turions number. Single turion weight was determined only by P. crispus biomass, while turions number was simultaneously determined by P. crispus biomass and sediment water content. Turions weight mainly depended on turions number rather than single turion weight, and maternal biomass and sediment water content determined turions weight by affected turions number rather than single turion weight.

Relationship between the coprecipitation of phosphorus-on-calcite by submerged macrophytes and the phosphorus cycle in water.

To assess potential phosphorus removal, we utilized Potamogeton crispus to determine the effects of calcium addition on phosphorus removal. Plastic film was used to block material exchange between the overlying water and the sediment, and we compared the experimental results with long-term monitoring results of Yimeng Lake, which contained a dense population of P. crispus. The results revealed that the first 10-40 days constituted a period of rapid P decrease, as P. crispus could effectively remove the phosphorus in the water through coprecipitation of CaCO3-P. The treatment groups indicated that P. crispus released calcium into the overlying water, and after the addition of calcium ions, P. crispus showed increased phosphorus removal efficiency in the water. Total phosphorus (TP) and P/Ca content increased with increasing pH in the treatment groups, and the TP and pH declined as the calcium content increased in the treatment groups. Long-term field observations showed that the calcium-to-phosphorus ratio in the coprecipitates was dependent on the pH during the crystallization process. Thus, water calcium driven by P. crispus plays an important role in the phosphorus cycle of water, due to P. crispus assisted precipitation. This study revealed the effect of P. crispus on the water purification, the migration and transformation of Ca and P in sediment and overlying water under the condition of sediment calcium addition, so as to provide a theoretical basis for the ecological restoration of shallow lakes eutrophication.

Responses of macrozoobenthos communities to changes in submerged macrophyte biomass in 19 temperate lakes in China.

Macrozoobenthos and submerged macrophytes interact closely. However, studies in China have focused on the middle and lower reaches of the Yangtze River, where shallow lakes are concentrated, rather than on temperate lakes. To clarify the responses of taxonomic and functional groups of macrozoobenthos in temperate lakes to changes in submerged macrophyte biomass (BMac) on a large scale, 19 temperate lakes within Baiyangdian Lake were investigated in this study. The BMac differed greatly across the 19 lakes, and Potamogeton crispus was the dominant species. According to the BMac, the 19 lakes were divided into 4 groups. One-way analysis of variance and Pearson correlation analysis showed that the water environmental parameters were different among the 4 groups, and the BMac was significant correlated with all the physical and chemical parameters of water bodies (except for water depth). Forty-one taxa of macrozoobenthos were identified in the 19 lakes, with oligochaetes, Hirudinea, gastropods, crustaceans, chironomid larvae, and aquatic insects (excluding chironomid larvae) represented by 9, 1, 4, 2, 19, and 6 species, respectively. Chironomid larvae and oligochaetes dominated by density, and gastropods and chironomid larvae dominated by biomass. Canonical correspondence analysis showed that the BMac was the most important factor affecting the macrozoobenthos community structure in group 1 to group 4. Macrozoobenthos with low pollution tolerance values were mainly found in areas with high BMac, while species with high pollution tolerance values were mainly distributed in areas with low BMac and high nutrient contents. Different taxonomic and functional groups of macrozoobenthos responded differently to changes in BMac. As BMac increased, density and biomass of oligochaetes and chironomid larvae tended to decrease, while those of gastropods and aquatic insects tended to first decrease and then increase. Collectors had more species than any other functional group in group 1 to group 4. As BMac increased, density and biomass of collectors gradually decreased, while density of predators, shredders, and scrapers tended to first decrease and then increase.

Effects of shining pondweed (Potamogeton lucens) on bacterial communities in water and rhizosphere sediments in Nansi Lake, China.

Submerged macrophytes and microbial communities are important parts of lake ecosystems. In this study, the bacterial community composition in rhizosphere sediments and water from areas cultivated with (PL) and without (CK) shining pondweed (Potamogeton lucens Linn.) was investigated to determine the effects of P. lucens Linn. on the structure of the bacterial communities in Nansi Lake, China. Molecular techniques, including Illumina MiSeq and qPCR targeting of the 16S rRNA gene, were used to analyze the composition and abundance of the bacterial community. We found that bacterial alpha diversity was higher in PL water than in CK water, and the opposite trend was observed in sediment. In addition, 16S rRNA gene copy number in sediment was lower in PL than in CK. We found 30 (e.g., Desulfatiglans) and 29 (e.g., Limnohabitans) significantly different genera in sediment and water, respectively. P. lucens Linn. can change chemical properties in sediment and water and thereby affect the bacterial community. At the genus level, members of bacterial community clustered according to source (water/sediment) and area (PL/CK). Our study demonstrated that submerged macrophytes can affect the bacterial community composition in both sediment and water, suggesting that submerged macrophytes affect the transportation and cycling of nutrients in lake ecosystems.

Physicochemical properties and greenhouse gas emissions of water body during the decomposition of Potamogeton crispus with different values of initial debris biomass.

A sediment-water mesocosm experiment was set up to identify the effects of different debris biomass P. crispus decomposition on water body physicochemical properties and greenhouse gas emissions in Dongping Lake, a typical shallow macrophytic lake in the north of China. The results indicated that the decomposition of high biomass (BL-2) of P. crispus could significantly affect the physicochemical properties of water bodies, especially within the first 47 days. During the experiment, DO and water pH in BL-2 were significantly lower, while NH3-N, NO2--N, DOC, and DRP in surface water and OM in sediment were significantly higher than those in the low biomass treatment (BL-1) and zero control (CK). Moreover, the DOC in BL-1 were significantly higher than CK. The decomposition of P. crispus significantly affected the emission fluxes of CH4 and CO2, but had no significant impact on N2O emission. CH4 and CO2 fluxes were generally more significantly correlated with the properties of surface water in BL-2 than in BL-1. High debris biomass decomposition significantly promoted the emission of CH4 enhancing the source effect of water body, while the decomposition of both low and high biomass notably promoted the emission of CO2 converting the water bodies from sink to source of CO2. There were significant differences in global warming potential among the three groups in which CH4 contributed most. Considering the negative impact on water environment and elevated carbon emission during the decomposition of P. crispus, it was suggested to strengthen the management of P. crispus in Dongping Lake.