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Panax notoginseng is an important traditional medicinal plant, but the commercial value is threatened by root-rot disease caused by rhizosphere microbes and a potential health risk caused by plant arsenic (As) accumulation. Whether rhizospheric microbes isolated from P. notoginseng rhizosphere soil could impact As uptake and transport into P. notoginseng is not yet known. Among the three root-rot disease-causing pathogens Fusarium flocciferum (PG 1), Fusarium oxysporum (PG 2), and Fusarium solani (PG 3) and one root-rot disease biocontrol fungus Trichoderma koningiopsis (FC 1) and five biocontrol-exerting bacterial species Bacillus siamensis (BC 1), Delftia acidovorans (BC 2), Brevibacillus formosus (BC 3), Mortierella alpine (BC 4), and Bacillus subtilis (BC 5), one As-resistant pathogen and four biocontrol microorganisms with As-resistant ability were identified. The As-transforming ability of the identified fungi and bacteria was ranked in the order of FC 1 > PG 1 and BC 2 > BC 3 > BC 1, respectively. Then, the As-resistant biocontrol and pathogenic microbes were initiated to colonize the rhizosphere of 1-year-old P. notoginseng seedlings growing in artificially As(V)-contaminated soil to evaluate the impact of microbe inoculation on P. notoginseng As uptake and transport capacity. Concentration of As in P. notoginseng tissues decreased in the order of the sequence stem > root > leaf. Compared to treatment without colonization by microorganism, inoculation with microorganisms increased As root uptake efficiency and root As concentration, especially under treatment of inoculation by BC 2 and PG 1 + BC 2. As transport efficiency from root to stem decreased by inoculation with microorganism, especially under treatment with inoculation of BC 2 and PG 1 + BC 2. However, the impact of microorganism colonization on As stem to leaf transport efficiency was not obvious. In summary, inoculation with rhizosphere microbes may increase As accumulation in P. notoginseng root, especially when using bacteria with high As transformation ability. Therefore, it is necessary to evaluate the As transformation capacity before applying biological control microorganism to the rhizosphere of P. notoginseng.

Release of toxic cyanobacterial secondary metabolites threatens biosecurity, foodwebs and public health. Microcystis aeruginosa (Ma), the dominant species in global freshwater cyanobacterial blooms, produces exudates (MaE) that cause adverse outcomes including nerve damage. Previously, we identified300 chemicals in MaE. It is critical to investigate neurotoxicity mechanisms of active substances among this suite of Ma compounds. Here, we screened 103 neurotoxicity assays from the ToxCast database to reveal targets of action of MaE using machine learning. We then built a potential Adverse Outcome Pathway (AOP) to identify neurotoxicity mechanisms of MaE as well as key targets. Finally, we selected potential neurotoxins matched with those targets using molecular docking. We found 38 targets that were inhibited and eight targets that were activated, collectively mainly related to neurotransmission (i.e. cholinergic, dopaminergic and serotonergic neurotransmitter systems). The potential AOP of MaE neurotoxicity could be caused by blocking calcium voltage-gated channel (CACNA1A), because of antagonizing neurotransmitter receptors, or because of inhibiting solute carrier transporters. We identified nine neurotoxic MaE compounds with high affinity to those targets, including LysoPC(16:0), 2-acetyl-1-alkyl-sn-glycero-3-phosphocholine, egonol glucoside, polyoxyethylene (600) monoricinoleate, and phytosphingosine. Our study enhances understanding of neurotoxicity mechanisms and identifies neurotoxins in cyanobacterial bloom exudates, which may help identify priority compounds for cyanobacteria management.

Cyanobacterial blooms, usually dominated by Microcystis aeruginosa, pose a serious threat to global freshwater ecosystems owing to their production and release of various harmful secondary metabolites. Detection of the chemicals in M. aeruginosa exudates using metabolomics technology revealed that phytosphingosine (PHS) was one of the most abundant compounds. However, its specific toxicological mechanism remained unclear. CNE-2 cells were selected to illustrate the cytotoxic mechanism of PHS, and it was determined to cause excessive production of reactive oxygen species and subsequently damage the mitochondrial structure. Mitochondrial membrane rupture led to matrix mitochondrial membrane potential disintegration, which induced Ca

Monitoring of cyanobacterial bloom biomass in large lakes at high resolution is made possible by remote sensing. However, monitoring cyanobacterial toxins is only feasible with grab samples, which, with only sporadic sampling, results in uncertainties in the spatial distribution of toxins. To address this issue, we conducted two intensive “HABs Grabs” of microcystin (MC)-producing Microcystis blooms in the western basin of Lake Erie. These were one-day sampling events during August of 2018 and 2019 in which 100 and 172 grab samples were collected, respectively, within a six-hour window covering up to 2,270 km2 and analyzed using consistent methods to estimate the total mass of MC. The samples were analyzed for 57 parameters, including toxins, nutrients, chlorophyll, and genomics. There were an estimated 11,513 kg and 30,691 kg of MCs in the western basin during the 2018 and 2019 HABs Grabs, respectively. The bloom boundary poses substantial issues for spatial assessments because MC concentration varied by nearly two orders of magnitude over very short distances. The MC to chlorophyll ratio (MC:chl) varied by a factor up to 5.3 throughout the basin, which creates challenges for using MC:chl to predict MC concentrations. Many of the biomass metrics strongly correlated (r > 0.70) with each other except chlorophyll fluorescence and phycocyanin concentration. While MC and chlorophyll correlated well with total phosphorus and nitrogen concentrations, MC:chl correlated with dissolved inorganic nitrogen. More frequent MC data collection can overcome these issues, and models need to account for the MC:chl spatial heterogeneity when forecasting MCs.

Climate change has greatly impacted hydrological regimes of lakes in sub-trophic and trophic areas. The uncertainties surrounding conventional future hydrological simulation methods with Coupled Model Intercomparison Project phase (CMIP) climate models have long been debated. However, it is crucial to obtain an accurate assessment result to help with better decision-making. In this study, we used the Lake Dianchi Basin (LDB) as a case study to demonstrate the use of a sub-catchment scale integrated model framework to obtain detailed hydrological simulation results and a comprehensive impact assessment of climate change on hydrological regimes. The results showed that 1) For the sub trophic lake basin LDB, its hydrological regimes are significantly impacted by climate change. Precipitation change impacted greater than air temperature change. 2) The 19 hydrological indicators showed large variations among the 18 climate scenarios. Precipitation impacted much greater than air temperature, and wet season might be impacted more by climate change. Climate change might impact more on 1/3/7-day minimums/maximums than 30/90-day minimums/maximums. 3) Enormous ecological and socio-economic risk for the LDB were indicated as its hydrologic regime is vulnerable to climate change. Among all six sub-catchments, Sub_06, characterized by a hilly landscape, would be impacted the most by climate change. 4) This study showed that, in regions with complex climatic conditions and topography, it is necessary to simulate hydrological states at the sub-catchment scale and differences of responses of each indicator to climate change should be fully considered.

Cyanobacterial harmful algal blooms (cyanoHABs) in freshwater lakes across the globe are often combined with other stressors. Pharmaceutical pollution, especially antibiotics in water bodies, poses a potential hazard in aquatic ecosystems. However, how antibiotics influence the risk of cyanoHABs remains unclear. Here, we investigated the effects of norfloxacin (NOR), one of the most widely used antibiotics globally, to a bloom-forming cyanobacterium (Microcystis aeruginosa) and a common green alga (Scenedesmus quadricauda), under both mono- and coculture conditions. Taxon-specific responses to NOR were evaluated in monoculture. In addition, the growth rate and change in ratio of cyanobacteria to green algae when cocultured with exposure to NOR were determined. In monocultures of Microcystis, exposure to low concentrations of NOR resulted in decreases in biomass, chlorophyll a and soluble protein content, while superoxide anion content and superoxide dismutase activity increased. However, NOR at high concentration only slightly affected Scenedesmus. During the co-culture trials of Microcystis and Scenedesmus, the 5 μg · L-1 NOR treatment increased the ratio of Microcystis to co-cultured Scenedesmus by 47.2%. Meanwhile, although Scenedesmus growth was enhanced by 4.2% under NOR treatment in monoculture, it was conversely inhibited by 63.4% and 38.2% when co-cultured with Microcystis with and without NOR, respectively. Our results indicate that antibiotic pollution has a potential risk to enhance the perniciousness of cyanoHABs by disturbing interspecific interaction between cyanobacteria and green algae. These results reinforce the need for scientists and managers to consider the influence of xenobiotics in shaping the outcome of interactions among multiple species in aquatic ecosystems.

Climate change affects hydrological regimes by influencing precipitation and air temperature. The climate change effects on lake hydrology in the Yunnan-Guizhou Plateau of China remain unclear. Lake Dianchi, the Plateau’s largest lake subject to human interference, was selected for the study. Algorithms based on historical meteorological data produced high-resolution climate change scenarios describing climate characteristics at a local watershed scale. Integrated river and lake hydrological models simulated changes in inflow, lake volume, and hydrological extremes under different scenarios. Results showed that Lake Dianchi Basin (LDB) inflow would decrease by 1.88~2.21% if air temperature increased by 1~2 °C but increase by 1.23~16.1% if precipitation increased by 5~20%. Lake volume would change minimally (decrease of 0.87~1.15%) if air temperature increased 1~2 °C and if precipitation increased 5~20% (increase of 0.04~4.12%); thus, the hydrological regimes of LDB are more sensitive to precipitation than air temperature. Changes to 3-day and 7-day maximum hydrological extremes were double those of 3-day and 7-day minimums, indicating precipitation-affected maximum extreme hydrological events during wet season more than minimum extreme hydrological events during dry season. In conclusion, both unevenly distributed precipitation and increasing air temperature will increase wet season floods and dry-season droughts in plateau lakes like Lake Dianchi.

Eichhornia crassipes is an invasive, floating macrophyte and may have biocontrol functions on harmful cyanobacteria blooms. Eichhornia produces N-phenyl-2-naphthylamine (PNA), a compound which can inhibit algae. However, the impact of PNA on allelopathic effects of the cyanobacterium Microcystis aeruginosa on other phytoplankton species is not clear. In this study, we tested whether PNA can influence the allelopathic effect of M. aeruginosa on the green alga Scenedesmus quadricauda. S. quadricauda was more sensitive to PNA than M. aeruginosa, with 72 h-EC50 values of 0.42 and 3.66 mg L−1, respectively. In addition, PNA significantly enhanced allelopathy by M. aeruginosa on S. quadricauda. Consequently, PNA had a greater impact on the green algae when Microcystis was present. In complex ecosystems with multiple species that release allelopathic substances, unintended interspecific interactions may occur, where allelopathy plays an important role under artificial or even natural contexts. It is hard to predict the competition outcomes among allelopathic organisms in these complex ecosystems, therefore a precautionary approach is required for biological control of algae.

The widespread use of silver nanoparticles (AgNPs) is becoming a growing concern because of the risk they pose to the ecological environment and human health. Unfortunately, little is known about how AgNPs' toxicity affects the mechanisms of metabolite shift in aquatic organisms. The aim of this work is thus to study systematically the cellular metabolism of the cyanobacteria Microcystis aeruginosa upon exposure to AgNPs by using metabolomics based on non-targeted liquid chromatography and mass spectrometry. The results reveal that a total of 97 biochemical metabolites and 16 specific metabolic pathways are significantly altered by exposure to AgNPs, many of which are associated with cellular stress response. Importantly, a metabolic analysis identified some novel metabolic pathways that are specifically regulated by AgNPs, including arginine and proline metabolism, indole alkaloid biosynthesis, and phospholipid metabolism (phosphatidylinositol-4,5-bisphosphate). Further examination revealed that exposure to AgNPs elevates superoxide dismutase activity and malondialdehyde generation, damages the thylakoids, and interrupts the endocytosis process in algae cells. Together, the manifestation of differential metabolic profiles combined with the perturbation of physiological indicators upon AgNP exposure is taken as evidence of damage to photosynthesis and membranes. These results provide holistic information about complex disturbances in metabolite profiles of M. aeruginosa upon exposure to AgNPs and provide new insights into the mechanisms of AgNPs' toxicity in the aquatic environment.

Sediment heavy metal pollution in the Dianchi Lake has been a long-term environmental problem of concern. This study investigated the lake sediment heavy metal contamination level, mobility, commercial fish metal accumulation and its impact on human health. The results show high As, Hg and Cd concentration in the sediment, while Pb and Cr contamination are insignificant. Sediment sequential extraction analysis shows that Hg in sediment has the highest portion of mobile fraction, followed by As, while the portion of mobile fractions of Cd, Pb and Cr in sediment is very low. The high concentrations of Hg and As in surface water and porewater were consistent with the chemical fraction composition of the two elements in sediment. Three major commercial fish species, Culterichthys erythropterus, Carassius auratus and Hypophthalmichthys molitrix, were collected for analysis of metal concentrations in their muscles. Among the same size of fish, C. auratus has the highest As concentration due to its bottom habitat and omnivorous feeding habits. On the other hand, C. erythropterus has the highest Hg concentration due to its relatively high trophic level position. The average THQ value of metals in fish tissue decrease in the order of As > Hg > Pb > Cd > Cr and the total THQ of average metal concentration in fish species decreased in the order of C. auratus > C. erythropterus > H. molitrix. Both THQ and total THQ is below 1, suggested no non-carcinogenic human health risk of fish consumption. However, TR of As in C. auratus was above 1.00E-04 threshold value, indicated potential carcinogenic human health risk. The results from this study indicate that although moderately to heavily contamination of Hg, As, and Cd occurred in Dianchi Lake sediment, only Hg and As tend to transport to surface water and accumulate in commercial fish due to their higher mobility in sediment.

A developing body of theory and empirical evidence suggest that feeding behaviour as measured by the functional response (FR) can assist researchers in assessing the relative potential, ecological impacts and competitive abilities of native and introduced species. Here, we explored the FRs of two land snails that occur in south-western Ontario, one native (Mesodonthyroidus) and one non-indigenous (Cepaeanemoralis) to Canada. The non-indigenous species appears to have low ecological impact and inferior competitive abilities. Consistent with theory, while both species conformed to Type II functional responses, the native species had a significantly higher attack rate (5.30 vs 0.41, respectively) and slightly lower handling time (0.020 vs 0.023), and hence a higher maximum feeding rate (50.0 vs 43.5). The non-indigenous species exhibited a significantly longer time to contact for a variety of food types, and appeared less discriminating of paper that was offered as a non-food type. The non-indigenous species also ate significantly less food when in mixed species trials with the native snail. These feeding patterns match the known low ecological impact of the introduced snail and are consistent with the view that it is an inferior competitor relative to the native species. However, field experimentation is required to clarify whether the largely microallopatric distributions of the two species in south-western Ontario reflect competitive dominance by the native species or other factors such as habitat preference, feeding preferences or predator avoidance. The relative patterns of feeding behaviour and ecological impact are, however, fully in line with recent functional response theory and application.

Cyanobacteria blooms are increasing globally, with further increases predicted in association with climate change. Recently, some cyanobacteria species have been identified as a source of estrogenic effects in aquatic animals. To explore possible estrogenic effects of Microcystis aeruginosa (an often-dominant cyanobacteria species) on zooplankton, we examined effects of cyanobacteria exudates (MaE, 2 × 104 and 4 × 105 cells/ml) on reproduction in Daphnia magna. We analyzed physiological, biochemical and molecular characteristics of exposed Daphnia via both chronic and acute exposures. MaE at both low and high cell density enhanced egg number (15.4% and 23.3%, respectively) and reproduction (37.7% and 52.4%, respectively) in D. magna similar to 10 μg/L estradiol exposure. In addition, both MaE of low and high cell densities increased population growth rate (15.8% and 19.6%, respectively) and reproductive potential (60% and 83%, respectively) of D. magna. These exudates promoted D. magna reproduction by stimulating 17β-hydroxysteroid-dehydrogenase (17β-HSD) activity and production of ecdysone and juvenile hormone, and by enhancing vitellogenin biosynthesis via up-regulating expression of Vtg1 and Vtg2. However, increased expression (6.6 times higher than controls) of a detoxification gene (CYP360A8) indicated that MaE might also induce toxicity in D. magna. Reproductive interference of zooplankton by blooming cyanobacteria might negatively affect foodwebs because MaE-induced zooplankton population increase would enhance grazing and reduce abundance of edible algae, thereby adding to the list of known disruptive properties of cyanobacterial blooms.

Allelopathic interactions among phytoplankton species are regarded as one of the important factors contributing to phytoplankton species competition and succession. The role and extent of allelopathic effects of blooming freshwater cyanobacteria on other phytoplankton species in eutrophied waters, however, are still unknown. We examined the allelopathic effect of Microcystis aeruginosa on two common green algae ( Scenedesmus quadricauda , Chlorella pyrenoidosa ) and a diatom ( Cyclotella meneghiniana ) by adding exudates from different growth phases and in co-culture tests. Exudates of M. aeruginosa from the exponential growth phase and the stationary phase significantly inhibited the growth of S. quadricauda , C. pyrenoidosa and C. meneghiniana , whereas those from the decline phase increased their growth. The presence of M. aeruginosa extremely inhibited the growth of all tested species in co-cultures within 24 h. Our results indicate that under the tested environmental conditions (25 °C, light 80 μmol quanta m −2 s −1 , manual shaking twice a day), allelopathic effects of M. aeruginosa on other phytoplankton species can significantly contribute to their competitive success.

Metal-contaminated sediments in lakes is a global concern that poses toxicological risk to aquatic organisms. This study performed bioassays using the submerged macrophyte, Vallisneria natans (Lour.) Hara, exposed to contaminated sediments collected from five locations in Dianchi Lake, Yunnan, China. Among the sediments collected, Igeo showed enrichment of As and Cd in Dianchi Lake sediments. In spite of enriched toxic metals at some locations, laboratory bioassays found no significant difference in leaf biomass or leaf photosynthesis rate between the sites. Root biomass and root activity showed significant differences between locations and were negatively correlated with the concentration of As, Cd, Hg, and Pb in sediment but not related to Cr. The above correlations were strongest for Hg and As, respectively. Accumulation of Cd and Pb to leaves of bioassay plants was observed, but this was not evident for As and Cr. Overall, the results indicate that V. natans can be used as a bioassay organism and measures of root toxicity are sensitive to metal concentrations present in Dianchi Lake sediments. Furthermore, the study species holds promise for use as a biomonitor of Cd and Pb sediment metal content.

Ascidians have a recent history of species introductions globally, often with strong ecological impacts. Comparisons of per capita effects of invaders and comparable natives are useful to assess such impacts. Here, we explore ingestion rates (IR) and clearance rates (CR) of Ciona intestinalis and Ciona robusta, co-occurring native and non-native ascidians, respectively, from Brittany, France. IR was positively related to food concentration, with the invader responding more strongly to increasing food concentration. CR also differed by species, with the invader demonstrating higher values. C. robusta exhibited a higher functional response (Type I) than did C. intestinalis (Type II). Relative impact measured using seasonal abundance and IR revealed that C. robusta has a much greater impact than C. intestinalis at all food concentrations tested, though the former has a constrained distribution which limits its regional impact. Nevertheless, when abundant, we expect C. robusta to exert a greater impact on algal foods.

In the current ecological footprint (EF) calculations, the parameters of built-up land are set as equal to those of cropland, based on the assumption that built-up land is totally converted from cropland. However, built-up land may be derived from other types of land use. With the expansion of built-up area as a result of urbanization, the yield and equivalence factors of built-up land are becoming increasingly important in the EF calculation. The objective of this study was to evaluate the influence of this assumption on EF calculation. In this study, the proportions of different land types converted into built-up land were evaluated based on actual land-use conversion in two urbanized areas of Yunnan Province and Kunming City from 1980 to 2010 in the ArcGIS platform. Then, the parameters of built-up land were calculated by an area-weighting approach with the proportions. The results showed the following: (1) In both cases, the EF of Yunnan Province and Kunming City were greater than their biocapacities (BC), indicating that they were in unsustainable states. (2) The EF and BC of the two studied cases were reduced to varying degrees because the yield and equivalence factors of built-up land from land-use conversion are less than cropland factors. As the proportion of the built-up land area in Kunming City was larger than that in Yunnan Province, the reduced proportion of the EF and BC of Kunming City is greater than that of Yunnan Province. (3) The proportion of built-up land converted from cropland has a significantly positive correlation with EF and BC. Therefore, it is of great significance to revise the yield and equivalence factors of built-up land using actual land-use conversions in highly urbanized areas.

Recovery of rare aquatic plant species in eutrophic lakes often fails, and mutual allelopathic effects between cyanobacteria and submerged macrophytes are one potential reason. In this study, we investigated allelopathic interactions between cyanobacteria and Ottelia acuminata, an endangered submerged macrophyte species in China. We tested effects of Microcystis aeruginosa on germination and seedling growth of two varieties of O. acuminata (O. acuminata var. crispa, OAC; and O. acuminata var. songmingensis, OAS) and vice versa effects of culture water of young seedlings and mature macrophytes on the growth of M. aeruginosa. We found that: (1) The culture water of mature O. acuminata (both OAC and OAS) allelopathically promoted M. aeruginosa growth, while seedlings had no effect. (2) M. aeruginosa exudates and extracts significantly promoted or inhibited seed germination of O. acuminata; (3) both exudates and extracts significantly decreased the seedling vitality of OAC and OAS. (4) M. aeruginosa exudates and extracts inhibited seedlings growth of O. acuminata, especially growth of roots and the second true leaf. (5) Allelopathic effects of M. aeruginosa exudates were stronger than those of extracts, and OAC showed stronger resistance to cyanobacteria than OAS. Our results indicate that cyanobacteria can allelopathically inhibit O. acuminata mainly by their exudates, while mature O. acuminata stimulate cyanobacteria growth. Such negative effects of cyanobacteria may contribute to the disappearance of O. acuminata and also slow down their recovery in eutrophic lakes.

Cyanobacterial blooms drive water-quality and aquatic-ecosystem deterioration in eutrophic lakes worldwide, mainly owing to their harmful, secondary metabolites. The response of fish exposed to these cyanobacterial chemicals, however, remains largely unknown. In this paper, we employed an endangered fish species (Sinocyclocheilus grahami) in Dianchi Lake, China to evaluate the risks of cell-free exudates (MaE) produced by a dominant cyanobacterium (Microcystis aeruginosa) on embryo development, as well as the molecular mechanisms responsible. MaE (3d cultured) caused a reduction of fertilization (35.4%) and hatching (15.5%) rates, and increased mortality rates (≤90.0%) and malformation rate (27.6%), typically accompanied by heart failure. Proteomics analysis revealed that two greatest changed proteins - protein S100A1 (over-expressed 26 times compared with control) and myosin light chain (under-expressed 25 fold) - are closely associated with heart function. Further study revealed that heart failure was due to calcium ion imbalance and malformed cardiac structure. We conclude that harmful secondary metabolites from cyanobacteria may adversely affect embryo development in this endangered fish, and possibly contribute to its disappearance and unsuccessful recovery in Dianchi Lake. Hazardous consequences of substances released by cyanobacteria should raise concerns for managers addressing recovery of this and other imperiled species in affected lakes.

Despite recent advances in assessing lethal effects of antibiotics on freshwater organisms, little is known about their potential consequences on community composition and function, which are essential for assessing the ecological risk of these pollutants. Here, we investigated the impact of norfloxacin (NOR) on the short-term (≤ 6 days) dynamics of co-cultured Scenedesmusquadricauda-Chlorella vulgaris and Scenedesmusobliquus-C. vulgaris, and the long-term (≤ 70 days) dynamics of co-cultured S.obliquus-C. vulgaris in experiments with or without grazer Daphnia magna at sublethal antibiotic concentrations (0, 0.5, 2 and 8 mg L-1). NOR increased the relative abundance of Scenedesmus species in the absence of grazers but exerted opposite effects when Daphnia was present in both short- and long-term experiments due to reduced colony size. Meanwhile, increasing NOR concentrations led to quickly increased total algal density in the initial stage, followed by a sharp decline in the long-term experiment in the absence of grazers; when Daphnia was present, population fluctuations were even larger for both prey and predator species (e.g., grazer extinction at the highest concentration). Thus, NOR affected the outcome of species interactions and decreased temporal stability of plankton ecosystems, suggesting that antibiotics have more extensive impacts than presently recognized.

Laboratory biological simulation experiment was conducted to investigate growth disturbance of high, moderate, low concentration of aqueous extracts (i.e. the original extracts with a solid liquid ratio of 1:40 g mL-1 and its 5 times diluents and 25 times diluents) from several crops straw (residue) on Ageratina adenophora, a worldwide notorious invasive weed. The results showed: (a) aqueous extracts from several crops straw (residue) brought about different impacts on the single index for germination and growth of A. adenophora, e.g., high concentration of aqueous extracts from Brassica oleracea waste leaves showed a strong inhibition against the germination rate (GR) and germination index (GI) of A. adenophora, while high concentration of aqueous extracts from Vicia cracca straw showed a strong inhibition against radicle length (RL) and hypocotyl length (HL) of A. adenophora; (b) high concentration of aqueous extracts from B. oleracea waste leaves and high, moderate and low concentration of aqueous extracts from Oryza sativa straw and Triticum aestivum straw showed rather strong synthetic effects (inhibition) on GR and GI of A. adenophora, which could be chosen for the control over the seeds germination of A. adenophora; (c) high and moderate concentrations of aqueous extracts from V. cracca straw, high concentration of aqueous extracts from B. campestris waste leaves, and moderate and low concentrations of aqueous extracts from O. sativa straw and T. aestivum straw showed rather strong synthetic effects (inhibition) on RL and HL of A. adenophora, which could be selected as ideal materials for the control over the seedlings growth of A. adenophora; and (d) high concentrations of aqueous extracts from V. cracca straw, B. oleracea waste leaves and B. campestris waste leaves, and high, moderate and low concentrations of aqueous extracts from O. sativa straw and T. aestivum straw showed rather strong synthetic effects (inhibition) on GR, GI, RL and HL of A. adenophora, which could be selected as ideal materials for the control over the seeds germination and seedlings growth of A. adenophora. Thus, this study would provide a theoretic guidance and technical support for the resources utilization of crops straw (residue) and the prevention and control over invasive weeds as well. (C) 2013 Elsevier B.V. All rights reserved.

Submerged macrophytes are known for their positive effects on water clarity, especially in shallow lake ecosystems. Eutrophication of these systems, however, has often resulted in a decline of submerged vegetation and a dominance of cyanobacteria, producing and releasing allelopathically active substances. Whether and how these allelochemicals affect submerged macrophytes is, however, largely unknown. We tested the effect of exudates and extracts of one of the most common cyanobacteria species, Microcystis aeruginosa, on seed germination and seedling growth and photosynthesis of the submerged macrophyte Potamogeton malaianus, a common species in Chinese shallow lakes. We found that: (1) low and high exudate concentrations significantly promoted or inhibited P. malaianus seed germination, respectively, while extracts had no effect; (2) low exudate and medium extract concentrations significantly increased, whereas high concentrations decreased the biomass of P. malaianus seedlings; (3) chlorophyll content and maximum quantum yield of PS II (Fv/Fm) of the seedlings were decreased by all levels of exudates; (4) of the various responses tested, seedling leaf Fv/Fm showed the greatest sensitivity to M. aeruginosa allelochemicals; (5) the allelopathic effects of M. aeruginosa exudates were stronger than those of extracts. Our results indicate that cyanobacteria exudates can allelopathically inhibit submerged macrophytes. The early growth of seedlings rather than seed germination seems to be a sensitive phase for the impact of cyanobacterial allelochemicals.

Harmful cyanobacterial blooms and their negative impacts on water ecosystems and human health have been reported all over the world, and Microcystis aeruginosa is one of the most dominant and ecologically damaging species in eutrophic lakes such as Dianchi Lake and Taihu Lake in China. Although physical or chemical control of the blooms is possible in short period, these methods could cause other problems. Thus, there is still a need for research on biological factors controlling cyanobacteria blooms. We screened part of the Yunnan University actinomycete strain library and found that the extract of Streptomyces hebeiensis YIM 001 T exhibited obvious inhibition on M. aeruginosa . The main component – nanaomycin A methyl ester (NAME) was isolated at a level of 20 mg L −1 by scale-up fermentation. Lytic mechanism experiments of NAME on M. aeruginosa demonstrated it could effectively inhibit the growth of M. aeruginosa (EC 50 at 72 h = 2.97 mg L −1 ), hinder cell division and enlarge cell size. NAME damaged M. aeruginosa cells as evidenced by decreases in algal activity, biomass, esterase activity and chlorophyll- a content. The SOD activity of the treated cells initially increased, and then decreased together with a gradual increase in both O 2 − and malondialdehyde (MDA) content, consistent with inhibitory effects of NAME due to lipid peroxidation damage of the algal cell membrane. The results suggest that NAME is effective for controlling undesired cyanobacteria and the Chl -fluorescence is a potential endpoint to assay the NAME eco-toxicity on cyanobacteria.

Although the well-known antibiotic norfloxacin (NOR) is recognized as an important environmental pollutant, little is known about its impacts on ecological processes, particularly on species interactions. In this paper, we quantified Daphnia magna (Crustacea, Cladocera) responses in mortality rate at lethal NOR concentrations (0, 25, 50, 100, 200, 300 and 400 mg L−1), and in heartbeat rate, swimming behavior and feeding rate (on the green alga Chlorella pyrenoidosa) at sublethal NOR concentrations (0, 25, 50 and 100 mg L−1) to determine the effects of this antibiotic in plankton systems. In 96-h-long lethal experiment, mortality rates of D. magna increased significantly with increasing NOR concentration and exposure time. In sublethal experiments, heartbeat rate decreased, while time ratio of vertical to horizontal swimming (TVH) and the duration of quiescence increased in D. magna individuals exposed to increasing NOR concentrations after 4 and 12 h of exposure. These collectively led to decreases in both average swimming ability and feeding rate, consistent with the positive relationship between average swimming ability and feeding rate. Overall, results indicate that, by affecting zooplankton heartbeat rate and behavior, NOR decreased feeding efficiency of D. magna even at low doses, therefore, it might seriously compromise ecosystem health and function.

Plant-released allelopathic substances are increasingly suggested as potential natural measure to control cyanobacteria blooms in lakes. We tested whether the common cyanobacterium Microcystis aeruginosa , known to be sensitive to allelochemicals, remains suppressed when interacting with a less sensitive green alga. We investigated the effects of polyphenolic allelochemicals on single and mixed cultures of the common green alga Desmodesmus armatus and M. aeruginosa with three different inoculum compositions. Polyphenols were added as tannic acid or released by a macrophyte ( Myriophyllum verticillatum L.) in coexistence experiments with dialysis bags. Interaction with the green alga turned the inhibiting effect of allelochemicals on the cyanobacterium into an enhancement resulting in increased growth rates. The ratio between M. aeruginosa and the green alga consequently became significantly higher in treatments with allelochemicals as compared to controls after three days. When initial growth rates of M. aeruginosa and the green alga were similar, this resulted in an increasing abundance of the cyanobacterium under allelochemical presence. Interactions between phytoplankton species thus need to be taken into account when investigating the ecological relevance of macrophyte allelopathy and its potential to suppress cyanobacteria blooms.