[Distribution Characteristics and Influencing Factors of Abundant and Rare Planktonic Microeukaryotes in Jinsha River].

Planktonic microeukaryotes are usually composed of a few abundant species and a large number of rare species, which play an important role in maintaining the health and stability of aquatic ecosystems. At present, little is known about the biogeographical distribution patterns of these two groups of microeukaryotes in large damming rivers. This study analyzed the distribution patterns of abundant and rare planktonic microeukaryotes and the dominant factors affecting their spatial distributions in the Jinsha River, one of the largest rivers in southwestern China that is strongly regulated by cascade dams. The results showed that the alpha diversity of planktonic microeukaryotes in the Jinsha River was higher in the cascade dam reach than that in the upstream natural reach, and the increase in alpha diversity of rare species was larger than that of rich species. There were significant differences in microbial community composition among different river sections, and the relative abundances of the dominant genera such as Vermamoeba shared by them were also significantly different between the two river sections. The results of distance decay analysis revealed that the geographic distribution patterns of rare and abundant taxa were jointly influenced by environmental heterogeneity and dispersal limitation, and the results of variance decomposition analysis and partial Mantel further indicated that dispersal limitation was the dominant ecological process. The results provided data support for the distribution and ecological response of microorganisms in rivers in the areas lacking data in Southwest China.

[Effects of Reservoir Water Depth on Different Plankton Communities and Keystone Species of Network Interaction].

In order to understand the impacts of the reservoir construction on the diversity and ecological network of different microbial communities, seven sampling sites were set up in the Hengshan Reservoir in 2021. Water samples were collected from the surface and bottom of the reservoir. After filtering and extracting total DNA samples, high-throughput sequencing was carried out based on 16S and 18S rDNA to investigate the response of community structure, molecular ecological network, and keystone species of different microbial groups to water environment changes. The results showed that the Richness, Simpson, Shannon, and Pielou's Evenness indices of bacterial community in the surface and bottom layers were higher than those in the eukaryote community. The dominant community of bacteria included Proteobacteria, Actinobacteria, and Bacteroidetes, and the eukaryote community included Arthropoda, Ciliophora, Ochrophyta, etc. Moreover, the density and average clustering coefficient of the microbial networks in the surface waters of different phytoplankton communities were higher than those in the bottom waters. It was also observed that the microbial ecological networks in the surface waters were more closely related, and the number of nodes and edges, as well as the number of keystone species, of bacterial communities in the surface and bottom layers were significantly higher than those in the eukaryote microbial communities, indicating that the bacterial community network was larger, and the cooperative relationship and network connectivity between species were stronger. The interaction between bacterial community and eukaryote community in different water depths was dominated by positive correlation, and the negative correlation of the two groups in the bottom layer was slightly greater than that in the surface, indicating that the competition between bottom-layer species was greater than that between surface-layer species. In addition, the environmental impact factors of all species and keystone species of the community in surface water were basically the same, but they differed greatly in deep water, indicating that the influence mechanism of water depth change on keystone species was not the same as that of all species. The results further revealed the effects of reservoir construction on the stability and interspecific interactions of different microbial communities and provided a theoretical basis for predicting variations in microbial community and material cycling in reservoirs.

[Biogeographic Distribution Patterns and Ecological Mechanisms of Benthic Eukaryotic Microorganisms in Jinsha River].

Eukaryotic microbial communities play an important role in biogeochemical cycling and maintaining the health and stability of ecosystems. However, little is known about the geographical distribution patterns, key driving mechanisms, and interspecific interactions of eukaryotic microorganisms in large rivers. This study investigated the geographical distribution characteristics, influencing factors, and interspecific interactions of eukaryotic microorganisms in sediments from the Jinsha River, a cascade hydropower development river in southwest China. The results showed that the α-diversity indices of benthic eukaryotic microorganisms in the Jinsha River increased first and then decreased. The community structure and relative abundance of dominant genera of benthic eukaryotic microorganisms differed significantly among different reaches. The results of distance decay analysis showed that the community assembly of benthic eukaryotic microorganisms in the Jinsha River was influenced by environmental selection and dispersal limitation. The results of variance partitioning analysis and neutral model further demonstrated that the geographical distribution pattern was mainly driven by dispersal limitation. The co-occurrence network analysis revealed that the interspecific competition and network connectivity of the cascade dam reach were weaker than those of the upstream natural reach, indicating that the interactions of benthic eukaryotic microorganisms were stronger in the upstream natural reach. This study supplemented the lack of data on the diversity and geographical distribution of benthic eukaryotic microorganisms in the river of southwest China and provided data support for the ecological response of benthic eukaryotic microorganisms in the river of cascade hydropower development.

[Effects of Sulfamethazine in Soil on Rice Growth].

For the sake of investigating the effects of residual antibiotics in soil on plant growth, sulfamethazine, which is commonly detected in soil, was selected in this project. In general, the growth index of rice at the seedling and mature stages, physiological/biochemical characteristics of roots and leaves, antibiotic residues, enrichment factors, and transport coefficients in various rice organs were respectively tested and analyzed to evaluate the ecological effects of sulfamethazine residues on rice. The results revealed that the inhibitory effect of sulfamethazine on plant height and biomass was maintained during the whole growth cycle. Moreover, the effect at the seedling stage was greater than that at the growth maturity stage, and the root part was more easily influenced than the seedling section. The root activity, nitrate reductase activity, and leaf chlorophyll content at the seedling stage were hindered by the increase in antibiotic content. By contrast, the antioxidant enzyme change showed a different tendency, in which the superoxide was activated, and the catalase and peroxidase were firstly activated and then inhibited. The sulfamethazine accumulation in various rice organs was in the order of root>leaf>sti>grain. The results of antibiotic risk assessment of rice grains exhibited that EDI/ADI was less than 0.1, indicating no health risk. The effect of sulfamethazine on enrichment factors and transport coefficients at the growth maturity stage was more obvious than that at the seedling stage. Considering the adverse effects of sulfamethazine on rice, we need to take the ecological effects of sulfamethazine on plants into consideration when applying livestock manure as organic fertilizer or using aquaculture water for irrigation, to ensure crop production safety.

Coral Reef Arks: An In Situ Mesocosm and Toolkit for Assembling Reef Communities.

Coral reefs thrive and provide maximal ecosystem services when they support a multi-level trophic structure and grow in favorable water quality conditions that include high light levels, rapid water flow, and low nutrient levels. Poor water quality and other anthropogenic stressors have caused coral mortality in recent decades, leading to trophic downgrading and the loss of biological complexity on many reefs. Solutions to reverse the causes of trophic downgrading remain elusive, in part because efforts to restore reefs are often attempted in the same diminished conditions that caused coral mortality in the first place. Coral Arks, positively buoyant, midwater structures, are designed to provide improved water quality conditions and supportive cryptic biodiversity for translocated and naturally recruited corals to assemble healthy reef mesocosms for use as long-term research platforms. Autonomous Reef Monitoring Structures (ARMS), passive settlement devices, are used to translocate the cryptic reef biodiversity to the Coral Arks, thereby providing a "boost" to natural recruitment and contributing ecological support to the coral health. We modeled and experimentally tested two designs of Arks to evaluate the drag characteristics of the structures and assess their long-term stability in the midwater based on their response to hydrodynamic forces. We then installed two designs of Arks structures at two Caribbean reef sites and measured several water quality metrics associated with the Arks environment over time. At deployment and 6 months after, the Coral Arks displayed enhanced metrics of reef function, including higher flow, light, and dissolved oxygen, higher survival of translocated corals, and reduced sedimentation and microbialization relative to nearby seafloor sites at the same depth. This method provides researchers with an adaptable, long-term platform for building reef communities where local water quality conditions can be adjusted by altering deployment parameters such as the depth and site.

[Application Effect of Four Typical Submerged Macrophytes on Removing Cadmium from Polluted Sediment].

In this study, four typical submerged macrophytes, namely Hydrilla verticillata, Elodea canadensis, Potamogeton crispus, and Ceratophyllum demersum, were tested for their chlorophyll content and antioxidant enzyme activity, to analyze their cadmium tolerance. The biota-sediment accumulation factor (BSAF) and plant transport factor (TF) were utilized to understand the accumulation capacity of the plants. Finally, the distribution of cadmium in submerged macrophytes was revealed through phytohistochemical methods, to provide theoretical support for the practical application of submerged macrophytes. The results showed that three of the plants, excluding C. demersum, exhibited varying tolerances to cadmium pollution in sediments, among which the tolerance of H. verticillata and E. canadensis were the strongest. P. crispus had the strongest accumulation capacity (BSAF was 2.32) at relatively low pollution levels (≤20 mg·kg-1). In this study, because of its weak root system, the BSAF of C. demersum was less than 1.0, indicating that macrophyte roots play an important role in phytoremediation of Cd-contaminated sediments. Comparing the TF of different plants, it can be found that the roots of H. verticillata had the strongest above-ground cadmium transport capacity, while P. crispus mainly accumulated cadmium in its roots. At the same time, when the cadmium concentration was 50 mg·kg-1, cadmium was found to be evenly distributed in the stem organelles of P. crispus, in contrast to the other plants. Based on the cadmium tolerance and accumulation mechanism of the plants, and in consideration of real-world factors, H. verticillata and P. crispus were selected as ideal plants for repairing cadmium-containing sediments. Meanwhile, based on the different transport capabilities of plants, it is recommended that only the above-ground part of H. verticillate should be removed, while P. crispus should be uprooted regularly.

[Biogeographic Distribution Patterns of Diatoms in Lancang River and Their Key Drivers].

As an important primary producer, diatoms play a key role in aquatic ecosystems. However, little is known about the geographical distribution characteristics and driving factors of diatoms in large rivers. In this study, based on a high-throughput sequencing dataset of microeukaryotes, we analyzed the diversities and community compositions of planktonic and sedimentary diatoms in the 1200 km mainstream of Lancang River, a typical large river in southwestern China. The results showed that the diversities of planktonic and sedimentary diatoms in Lancang River were higher in the upstream natural section, and the community compositions of both groups were significantly different among different river sections. Dam construction had a significant effect on the dominant genera. Variance partitioning analysis showed that dispersal limitation was a major driving factor for the distribution pattern of planktonic and sedimentary diatoms, with explanation proportions of 16.7% and 29.8%. Co-occurrence network analyses showed that the interspecific competition relationship and network connectivity of the planktonic diatom network were stronger than the sedimentary ones. The network connectivity of planktonic and sedimentary diatoms in the cascade reservoir section was higher than that of the upstream natural section. This study will help to better understand the biogeographical distribution of diatoms in large rivers and provide useful information for ecological responses of diatoms to dam construction in rivers.

Estimates of environmental loading from copper alloy materials.

Metal release rates were measured from four different copper alloy-based materials used by the aquaculture industry: copper sheet machined into a diamond mesh, copper alloy mesh (CAM), silicon bronze welded wire mesh, and copper sheeting, and compared with conventional nylon aquaculture net treated with a cuprous oxide antifouling (AF) coating. Release rates were measured in situ in San Diego Bay using a Navy-developed Dome enclosure system at nine different time points over one year. As expected, copper was the predominant metal released, followed by zinc and nickel, which were fractional components of the materials tested. Release rates followed a temporal trend similar to those observed with copper AF coatings applied to vessel hulls: an initial spike in copper release was followed by a decline to an asymptotic low. Leachate toxicity was consistent with prior studies and was directly related to the metal concentrations, indicating the alloys tested had no additional toxicity above pure metals.

[Contaminant Characteristics and Ecological Risk Assessments of Heavy Metals from River Networks in the Western Area of the Wangyu River].

To study the pollution characteristics and ecological risks of heavy metals in the western area of the Wangyu River, water and surface sediment samples of five rivers were investigated. The concentration and chemical fractions of eight heavy metals (Ni, Cu, Cr, Zn, As, Cd, Pb, and Hg) were analyzed, the pollution sources of heavy metals were studied using multivariate statistical analysis, and various ecological risk assessments were applied to identify the level of heavy metal contaminants. The results showed that the concentration of heavy metals in water was low, except for Hg, which was lower than the Class I standard of Surface Water Environmental Quality Standard. The content of heavy metals in surface sediments was high, except for Hg, which was significantly higher than the environmental background values. The partition coefficient of heavy metals in water-sediments showed that Cd, As, and Hg had strong re-emission potential. The Igeo indicated that Cu, Zn, and Cd were in a high pollution state as a whole. The RI showed that Cd was the main ecological risk factor in the study area. The RRSP indicated that the degree of pollution by Ni, Zn, and As was low because of its high residual fraction ratio, which was difficult to release under natural conditions. However, the degree of pollution by Cd was high because it had the highest content of weak acid extractable fraction among all the heavy metals. Therefore, it is necessary to pay more attention to Cd contamination. The source analysis of heavy metals showed that the western area of the Wangyu River was mainly affected by the pollution emissions from the surrounding machinery factories.

How wastewater with different nutrient levels influences microbial degradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in anaerobic sediments.

While wastewater and polybrominated diphenyl ethers (PBDEs) are commonly both discharged into aquatic ecosystems, little information is known about how wastewaters with different nutrient levels impact on microbial degradation of PBDEs. In this study, we used an anaerobic microcosm experiment to examine how the removal rates of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from contaminated sediment varied when exposed to three wastewaters with different nutrient properties, namely livestock wastewater (LS), municipal sewage (MS), and shrimp pond wastewater (SP), and to determine the microbial controls on removal processes. We found that BDE-47 degraded relatively rapidly in MS, which had low carbon and nitrogen concentrations, but degraded much more slowly in LS and SP, which had relatively high nutrient concentrations. The variations in BDE-47 removal in different wastewater were related to iron reduction rates and the abundances of organohalide-respiring bacteria (OHRB). The community compositions of both total bacteria and OHRB from the family Dehalococcoidaceae differed significantly among the wastewater treatments. Compared with other treatments, some bacterial groups with PBDE degradation abilities were more abundant in MS where the PBDE-degradation efficiencies were higher. Our results should help support evaluations of the bioremediation potential of sites that are contaminated with both halogenated organic compounds and nutrient-rich wastewater.

Spatial distribution and diversity of organohalide-respiring bacteria and their relationships with polybrominated diphenyl ether concentration in Taihu Lake sediments.

It is acknowledged that organohalide-respiring bacteria (OHRB) can degrade polybrominated diphenyl ethers (PBDEs); however, very little is known about the distribution of OHRB or their response to PBDE contamination in natural sediments. We collected sediments from 28 sampling sites in Taihu Lake, China, and investigated the spatial distribution and diversity of OHRB, and the relationships between the PBDE contamination levels and the PBDE removal potential. The abundances of five typical OHRB genera, namely Dehalobacter, Dehalococcoides, Dehalogenimonas, Desulfitobacterium, and Geobacter, ranged from 0.34 × 104 to 19.4 × 107 gene copies g-1 dry sediment, and varied significantly among different areas of Taihu Lake. OHRB were more abundant in sediments from Meiliang and Zhushan Bay, where the PBDE concentrations were higher, and the phylotype diversity of the OHRB belonging to the family Dehalococcoidaceae was lower, than reported for other areas. While the sulfate concentrations explained much of the spatial distribution of OHRB, PBDE concentrations were also a strong influence on the abundance and diversity of OHRB in the sediments. For Dehalococcoides, Dehalogenimonas and Geobacter, the abundance of each genus was positively related to its own potential to remove PBDEs. The dominant OHRB genus, Dehalogenimonas, may contribute most to in situ bioremediation of PBDEs in Taihu Lake.

Effects of decabromodiphenyl ether and planting on the abundance and community composition of nitrogen-fixing bacteria and ammonia oxidizers in mangrove sediments: A laboratory microcosm study.

While nitrogen (N) fixation and ammonia oxidation by microorganisms are two important N cycling processes, little is known about how the microbes that drive these two processes respond when sediments are contaminated with persistent organic pollutants. In this study, we carried out a laboratory microcosm experiment to examine the effects of decabromodiphenyl ether (BDE-209), either on its own or combined with a common mangrove species, Avicennia marina, on the abundance, diversity, and community composition of N-fixing bacteria (NFB) and ammonia-oxidizing archaea (AOA) and bacteria (AOB) in mangrove sediments. The sediments were very N-limited after one year. The rates of N fixation and NFB abundance were significantly higher in the sediments that contaminated by BDE-209, especially in the planted sediment, indicating that both BDE-209 and planting stimulated N fixation in N-limited mangrove sediments. In contrast, the potential nitrification rate and abundance of AOA and AOB decreased significantly under BDE-209 and planting, and the inhibitory effects were stronger in the sediment with both planting and BDE-209 than in the sediments with either BDE-209 or planting. The results from pyrosequencing showed that the richness and diversity of NFB increased, while those of AOA and AOB decreased, in the sediments treated with BDE-209 only and with BDE-209 combined with planting. The community compositions of NFB, AOA, and AOB in the sediments shifted significantly because of BDE-209, either alone or particularly when combined with planting, as shown by the increases in some NFB from the Proteobacteria phylum and decreases in AOA in the Nitrosopumilus genus and AOB in the Nitrosospira genus, respectively.

The Evaluation on the Cadmium Net Concentration for Soil Ecosystems.

Yixing, known as the "City of Ceramics", is facing a new dilemma: a raw material crisis. Cadmium (Cd) exists in extremely high concentrations in soil due to the considerable input of industrial wastewater into the soil ecosystem. The in situ technique of diffusive gradients in thin film (DGT), the ex situ static equilibrium approach (HAc, EDTA and CaCl2), and the dissolved concentration in soil solution, as well as microwave digestion, were applied to predict the Cd bioavailability of soil, aiming to provide a robust and accurate method for Cd bioavailability evaluation in Yixing. Moreover, the typical local cash crops-paddy and zizania aquatica-were selected for Cd accumulation, aiming to select the ideal plants with tolerance to the soil Cd contamination. The results indicated that the biomasses of the two applied plants were sufficiently sensitive to reflect the stark regional differences of different sampling sites. The zizania aquatica could effectively reduce the total Cd concentration, as indicated by the high accumulation coefficients. However, the fact that the zizania aquatica has extremely high transfer coefficients, and its stem, as the edible part, might accumulate large amounts of Cd, led to the conclusion that zizania aquatica was not an ideal cash crop in Yixing. Furthermore, the labile Cd concentrations which were obtained by the DGT technique and dissolved in the soil solution showed a significant correlation with the Cd concentrations of the biota accumulation. However, the ex situ methods and the microwave digestion-obtained Cd concentrations showed a poor correlation with the accumulated Cd concentration in plant tissue. Correspondingly, the multiple linear regression models were built for fundamental analysis of the performance of different methods available for Cd bioavailability evaluation. The correlation coefficients of DGT obtained by the improved multiple linear regression model have not significantly improved compared to the coefficients obtained by the simple linear regression model. The results revealed that DGT was a robust measurement, which could obtain the labile Cd concentrations independent of the physicochemical features' variation in the soil ecosystem. Consequently, these findings provide stronger evidence that DGT is an effective and ideal tool for labile Cd evaluation in Yixing.

Effects of miR-338 on morphine tolerance by targeting CXCR4 in a rat model of bone cancer pain.

The present study aimed to investigate the effects of miR-338 on morphine tolerance through the targeting of CXC chemokine receptor-4 (CXCR4) in a rat model of bone cancer pain (BCP). Sprague-Dawley (SD) rats were obtained and divided into model saline (n=10), model morphine (n=50), normal saline (n=10) and normal morphine (healthy rats, n=10) groups. After BCP rat model establishment, the remaining SD rats (n=40) in the model saline group were assigned into pLV-THM-miR-338, pLV-THM-anti-miR-338, CXCR4 shRNA, blank and PBS groups. Luciferase reporter gene assay was used for luciferase activity. Quantitative real-time PCR (qRT-PCR) and Western blotting were performed to detect the miR-338 and CXCR4 mRNA and protein expression. The model saline group showed increased mRNA and protein expressions of CXCR4 but decreased miR-338 compared with the model saline group, and the model morphine group had increased mRNA and protein expressions of CXCR4 but decreased miR-338 compared with the model saline group. The mRNA and protein expressions of miR-338 in the pLV-THM-miR-338 group increased remarkably while those of the pLV-THM-anti-miR-338 group decreased significantly compared with the CXCR4 shRNA, blank and PBS groups. The pLV-THM-miR-338, pLV-THM-anti-miR-338, CXCR4 shRNA and CXCR4 mRNA groups all had lower mRNA and protein expressions of CXCR4 than those in the blank and PBS groups. miR-338 exerts significant influence in the inhibition of morphine tolerance by suppressing CXCR4 in BCP.

Evaluation of organic amendment on the effect of cadmium bioavailability in contaminated soils using the DGT technique and traditional methods.

Organic amendments have been widely proposed as a remediation technology for metal-contaminated soils, but there exist controversial results on their effectiveness. In this study, the effect of pig manure addition on cadmium (Cd) bioavailability in Cd-contaminated soils was systematically evaluated by one dynamic, in situ technique of diffusive gradients in thin films (DGT) and four traditional methods based on the equilibrium theory (soil solution concentration and the three commonly used extractants, i.e., acetic acid (HAc), ethylenediamine tetraacetic acid (EDTA), and calcium chloride (CaCl2). Wheat and maize were selected for measurement of plant Cd uptake. The results showed that pig manure addition could promote the growth of two plants, accompanied by increasing biomasses of shoots and roots with increasing doses of pig manure addition. Correspondingly, increasing additions of pig manure reduced plant Cd uptake and accumulation, as indicated by the decreases of Cd concentrations in shoots and roots. The bioavailable concentrations of Cd in Cd-contaminated soils reflected by the DGT technique obviously decreased with increasing doses of pig manure addition, following the same changing trend as plant Cd uptake. Changes in soil solution Cd concentration and extractable Cd by HAc, EDTA, and CaCl2 in soils were similar to DGT measurement. Meanwhile, the capability of Cd resupply from solid phase to soil solution decreased with increasing additions of pig manure, as reflected by the decreases in the ratio (R) value of C DGT to C sol. Positive correlations were observed between various bioavailable indicators of Cd in soils and Cd concentrations in the tissues of the two plants. These findings provide stronger evidence that pig manure amendment is effective in reducing Cd mobility and bioavailability in soils and it is an ideal organic material for remediation of Cd-contaminated soils.

The Combination of DGT Technique and Traditional Chemical Methods for Evaluation of Cadmium Bioavailability in Contaminated Soils with Organic Amendment.

Organic amendments have been proposed as a means of remediation for Cd-contaminated soils. However, understanding the inhibitory effects of organic materials on metal immobilization requires further research. In this study colza cake, a typical organic amendment material, was investigated in order to elucidate the ability of this material to reduce toxicity of Cd-contaminated soil. Available concentrations of Cd in soils were measured using an in situ diffusive gradients in thin films (DGT) technique in combination with traditional chemical methods, such as HOAc (aqua regia), EDTA (ethylene diamine tetraacetic acid), NaOAc (sodium acetate), CaCl2, and labile Cd in pore water. These results were applied to predict the Cd bioavailability after the addition of colza cake to Cd-contaminated soil. Two commonly grown cash crops, wheat and maize, were selected for Cd accumulation studies, and were found to be sensitive to Cd bioavailability. Results showed that the addition of colza cake may inhibit the growth of wheat and maize. Furthermore, the addition of increasing colza cake doses led to decreasing shoot and root biomass accumulation. However, increasing colza cake doses did lead to the reduction of Cd accumulation in plant tissues, as indicated by the decreasing Cd concentrations in shoots and roots. The labile concentration of Cd obtained by DGT measurements and the traditional chemical extraction methods, showed the clear decrease of Cd with the addition of increasing colza cake doses. All indicators showed significant positive correlations (p < 0.01) with the accumulation of Cd in plant tissues, however, all of the methods could not reflect plant growth status. Additionally, the capability of Cd to change from solid phase to become available in a soil solution decreased with increasing colza cake doses. This was reflected by the decreases in the ratio (R) value of CDGT to Csol. Our study suggests that the sharp decrease in R values could not only reflect the extremely low capability of labile Cd to be released from its solid phase, but may also be applied to evaluate the abnormal growth of the plants.

[Effects of Nutrient Inputs on Changes of Phosphorus Forms and Phytoplankton Growth in Taihu Lake].

In order to determine the effects of nutrient inputs on changes of phosphorus forms and phytoplankton growth in large shallow lakes, an enrichment bioassay was conducted using surface lake water collected from the Meiliang Bay of Taihu Lake in spring. The concentration of different phosphorus forms, phytoplankton biomass (chlorophyll a) and alkaline phosphatase activity (APA) was analyzed after the addition of different concentrations of inorganic nutrients. The results showed that the phytoplankton biomass increased significantly with the addition of phosphorus (P), but with no primary effect from nitrogen (N), which suggested the phytoplankton growth was mainly limited by P. The maximum growth rate and the highest concentration of chlorophyll both occurred in the SRP 0.015 mg x L(-1) treatment. Nitrate addition could improve the bioavailability of phosphorus, accelerate the phosphorus cycling process and promote the growth of APA. There was an induction-repression mechanism resulting in a negative relationship between APA and orthophosphate concentration. The APA was obviously stimulated under PO4(3-) -P ≤ 0.025 mg x L(-1). This paper researches the transformation and cycling process of phosphorus in water and the induction-repression mechanism between the APA and orthophosphate concentration. The result can help to reveal the compensation path of nutrients in algae growth process and provide a theoretical basis for the further reveal of the mechanism of algae outbreaks.

Prevalence of antibiotic resistance genes in antibiotic-resistant Escherichia coli isolates in surface water of Taihu Lake Basin, China.

The rapid development of antibiotic-resistant bacteria (ARB) has been of concern worldwide. In this study, antibiotic resistance genes (ARGs) were investigated in antibiotic-resistant Escherichia coli isolated from surface water samples (rivers, n = 17; Taihu Lake, n = 16) and from human, chicken, swine, and Egretta garzetta sources in the Taihu Basin. E. coli showing resistance to at least five drugs occurred in 31, 67, 58, 27, and 18% of the isolates from surface water (n = 665), chicken (n = 27), swine (n = 29), human (n = 45), and E. garzetta (n = 15) sources, respectively. The mean multi-antibiotic resistance (MAR) index of surface water samples (0.44) was lower than that of chicken (0.64) and swine (0.57) sources but higher than that of human (0.30) and E. garzetta sources (0.15). Ten tetracycline, four sulfonamide, four quinolone, five ß-lactamase, and two streptomycin resistance genes were detected in the corresponding antibiotic-resistant isolates. Most antibiotic-resistant E. coli harbored at least two similar functional ARGs. Int-I was detected in at least 57% of MAR E. coli isolates. The results of multiple correspondence analysis and Spearman correlation analysis suggest that antibiotic-resistant E. coli in water samples were mainly originated from swine, chicken, and/or human sources. Most of the ARGs detected in E. garzetta sources were prevalent in other sources. These data indicated that human activities may have contributed to the spread of ARB in the aquatic environment.

Nitric oxide supplementation alleviates ammonium toxicity in the submerged macrophyte Hydrilla verticillata (L.f.) Royle.

The likely protective effects of nitric oxide (NO) against ammonium toxicity were investigated in the submerged macrophyte Hydrilla verticillata. The plants were subjected to ammonium stress (3mM ammonium chloride) in the presence of sodium nitroprusside (SNP, 10 µM), an NO donor. Treatment with SNP significantly increased the NO content and partially reversed the ammonium-induced negative effects, including membrane damage and the decrease in levels of chlorophyll, malondialdehyde, glutathione and ascorbic acid. Further, SNP application increased the catalytic activities of ascorbate peroxidase, superoxide dismutase, guaiacol peroxidase, catalase and glutathione S-transferase, but decreased that of NADH-oxidase. Histochemical staining showed that SNP application caused a significant decrease in the levels of superoxides and hydrogen peroxide. In contrast, application of other breakdown products of SNP (10 µM sodium ferrocyanide, 10 µM sodium nitrite and 10 µM sodium nitrate) failed to show any protective effect. The results suggest that the increased intracellular NO, resulting from SNP application, improved the antioxidant capacity of H. verticillata plants in coping with ammonium-induced oxidative stress.

Effects of ammonium on the antioxidative response in Hydrilla verticillata (L.f.) Royle plants.

To investigate ammonium toxicity, the submerged plant Hydrilla verticillata (L.f.) Royle was treated with 0.1-3.0mM ammonium for 12h and 4d. After exposure to ammonium for 4d, content of O2(-) and H2O2 increased in leaves of H. verticillata exposed to 3mM ammonium compared with control (0mM NH4Cl), while the malondialdehyde content decreased. The chlorophyll (a+b) and carotenoid concentrations decreased in H. verticillata plants exposed to 1.5-3mM ammonium for 12h and 4d. Compared with controls, the activity of superoxide dismutase, peroxidase, catalase, glutathione reductase, ascorbate peroxidase, and glutathione S-transferase increased in plants treated with ammonium for 12h, and the activity of most enzymes was further enhanced at 4d. The changes in nonprotein thiols, total glutathione, ascorbic acid, and dehydroascorbate content were also assayed. Our results suggest that ammonium induced the oxidative stress and the heated antioxidant response in H. verticillata.