The uptake and degradation of polychlorinated biphenyls in constructed wetlands planted with Myriophyllum aquaticum.

The unregulated dismantling and improper disposal of electronic waste lead to severe soil contamination by polychlorinated biphenyls (PCBs). Constructed wetlands (CWs) play an important role in PCBs removal as a result of the co-existence of anaerobic and aerobic conditions. However, the effects and mechanisms of different PCBs concentrations in soils on plant uptake and PCBs degradation within CWs are unclear. We evaluated the uptake and degradation of PCBs at different concentrations by Myriophyllum aquaticum (Vell.) Verdc. Planting significantly increased PCBs removal by 8.70% (p < 0.05) in soils with 1500 and 2500 µg/kg PCBs, whereas no significant effect was observed at 500 and 1000 µg/kg. PCBs levels did not significantly affect plant growth and PCBs accumulation. The contribution of plant uptake to PCBs removal was only 0.10-0.12%, indicating that microbial degradation was the dominant pathway for PCBs removal after planting with M. aquaticum. In the treatments with PCBs ≥ 1500 µg/kg, M. aquaticum increased the microbial population, altered the microbial community structure and enriched PCB-degrading bacteria. Functional prediction revealed that microbes in M. aquaticum rhizosphere secreted more peroxidase and glycosyltransferase than non-plant control, which were likely involved in PCBs metabolism.

Physiological response and tolerance of Myriophyllum aquaticum to a wide range of ammonium concentrations.

Myriophyllum aquaticum (M. aquaticum) can be used in constructed wetlands (CWs) to effectively purify swine wastewater with high-ammonia nitrogen (NH3-N and NH4+-N) concentrations. However, the understanding of its tolerance mechanism to ammonia nitrogen is limited. The physiological response and tolerance mechanism of M. aquaticum to a wide range of NH4+ concentrations (0-35 mM) were investigated in the present study. The results indicated that M. aquaticum can tolerate NH4+ concentrations of up to 30 mM for 21 days and grow well with high nutrient (N, P) uptake. A suitable concentration of NH4+ for a better growth of M. aquaticum was 0.5-20 mM. The free NH4+ content was no obviously increase at NH4+ concentration below 15 mM, indicated there was no obviously ammonium accumulation. Exogenous NH4+ inhibited K+ absorption and improved Ca2+ absorption, indicating mineral cation could mediate NH4+ homeostasis under NH4+ stress. Moreover, comparison with those in the control group, the activities of glutamine synthetase (GS), glutamate synthetase (GOGAT) in M. aquaticum increased by 52.7%-115% at 1-20 mM NH4+, and superoxide dismutase (SOD) increased by 29.2-143% at 1-35 mM NH4+. This indicated that the high NH4+ tolerance of M. aquaticum was mainly due to the balance of free NH4+ content in tissues, as well as improved nitrogen metabolism and antioxidant system. This could be attributed to the role of the GS-GOGAT cycle and SOD. In conclusion, M. aquaticum, which tolerates high NH4+ concentration and has a high N uptake ability, can be used as a good candidate specie to help develop more efficient management strategies for treating high-NH4+ wastewater in CW systems.

Fully Biodegradable Water Droplet Energy Harvester Based on Leaves of Living Plants.

Triboelectric nanogenerators (TENGs) have obtained soaring interest due to their capability for environmental energy harvesting. However, as a harvester for green energy, the frequent adoption of the hardly degradable plastic films is not desirable. Here, we report a fully biodegradable TENG (FBD-TENG) that all elements are made from natural substances, and the utilization of plastic materials is avoided. The leaf cuticle and the inside conductive tissue are utilized as the tribo-material and electrode for one part in the FBD-TENG, and water droplets are employed as the counterpart. By using water droplets to bridge the originally disconnected components into a closed-loop electrical system, we successfully collect energy from the droplet impact onto a plant leaf. The electricity generation phenomenon and the working mechanism of the FBD-TENG have been investigated. Five kinds of plants, as well as rain water droplets, are employed to demonstrate the wide availability of the proposed approach. This study provides a strategy to utilize the pervasively presented electrostatic charges in nature in an eco-friendly way.

Evaluation of cadmium hyperaccumulation and tolerance potential of Myriophyllum aquaticum.

Enrichment of the hyperaccumulator bank is important for phytoremediation, and studying new hyperaccumulators has become a research hotspot. In this study, cadmium (Cd), the main representative factor of heavy-metal-polluted water, was the research object, and the Cd bioenrichment ability and tolerance of Myriophyllum aquaticum were studied for the first time. The experiment was conducted for 28 days by establishing experimental groups with different Cd concentrations (0, 10, 20, 40, 80, and 160 mg/L). The results show that M. aquaticum is a new Cd hyperaccumulator. There was no notable damage in the 40 mg/L Cd treatment group, and the Cd enrichment ability of M. aquaticum reached 17,970 ± 1020.01 mg/kg, while the bioconcentration factor (BCF) reached 449.25. At the same time, the antioxidant system (superoxide dismutase (SOD) and peroxidase (POD)) and proline (Pro) levels of M. aquaticum maintained normal plant physiology, but there were physiological anomalies in M. aquaticum at high concentrations and under long-term treatment. The results show that M. aquaticum has a high Cd bioenrichment ability and tolerance in water and can be used for phytoremediation of river water polluted by Cd.

Comparative studies of the response of sensitive and tolerant submerged macrophytes to high ammonium concentration stress.

Three submerged macrophytes, Ceratophyllum demersum (CD), Myriophyllum spicatum (MS) and Myriophyllum aquaticum (MA), were treated with various concentrations of ammonia for different lengths of time. Ammonium ions (NH4+) in the medium severely inhibited plant growth and led to a reduction in total chlorophyll (chl a and b) in CD and MS. The addition of ammonia significantly decreased the soluble protein content and increased the free amino acid content of CD and MS in treatments with high concentrations of NH4+, but MA showed no significant physiological response. The antioxidant enzyme system of MA was activated, which in turn reduced the peroxidation level in the plant and maintained the plant's normal physiological activities when the ammonia nitrogen in the culture fluid increased. The study continued to use higher concentrations (25, 50, 100, 200 and 400 mg/L) of ammonium nitrogen to treat and observe the peroxidation level and corresponding enzyme production for this species of MA in vivo to explore its resistance mechanism. The experiments show that MA can normally live for a period of time in a high-ammonia environment of up to 100 mg/L. The results of the present study will assist in studies of the detoxification of high ammonium ion contents in submersed macrophytes and the selection of plants suitable for macrophyte recovery.

Endothall behavior in Myriophyllum spicatum and Hydrilla verticillata.

BACKGROUND: Endothall has been used to control submersed aquatic plants since 1960, providing broad-spectrum control of aquatic weeds. Although endothall is considered a contact herbicide, many field observations suggest that it might have systemic activity. The goals of this research were to determine endothall's (i) absorption characteristics, (ii) translocation from shoots to roots, and (iii) potential for desorption in Eurasian watermilfoil (EWM), monoecious and dioecious hydrilla. RESULTS: Endothall absorption was linear in dioecious hydrilla up to 192 HAT, while in EWM and monoecious hydrilla absorption data best fit an asymptotic rise function. Endothall absorption in EWM, monoecious and dioecious hydrilla was 3.3, 6.6, and 11.0 times the external herbicide concentration determined by the plant concentration factor. Translocation to EWM roots reached 7.9% of total absorbed radioactivity by 192 HAT, while translocation to monoecious and dioecious hydrilla roots reached 17.8% and 16.4% by 192 HAT, respectively. For all three species, no more than 30% of absorbed endothall moved from the plant to clean water 96 HAT. CONCLUSION: Endothall is a very water soluble compound and yet it accumulated in these three important aquatic weeds at concentrations significantly higher than the external herbicide concentration. These data provide evidence that endothall could have systemic activity in these aquatic species. Following 14 C-endothall applications, more 14 C translocated from shoots to roots compared to the translocation of 14 C for other systemic aquatic herbicides. The final confirmation of endothall's systemic behavior requires that the radioactivity found in the root system of these aquatic plants is 14 C endothall. © 2019 Society of Chemical Industry.

Are Myriophyllum alterniflorum biomarker responses to arsenic stress differentially affected by hydrodynamic conditions?

Arsenic (As) is a significant contaminant in the environment and its detection through macrophytes can provide a powerful tool. Myriophyllum alterniflorum constitutes a good candidate by virtue of its ability to accumulate contaminants, and moreover its biomarkers can respond to the presence of trace metals and metalloids. The objective of this study therefore is to evaluate the watermilfoil response to As exposure under several hydrodynamic conditions since it is well known that hydrodynamics affect plant functioning. For this purpose, fresh watermilfoil plants are subjected to three hydrodynamic conditions, namely laminar, turbulent and calm, in a synthetic medium either enriched or not by 100 µg.L-1 arsenic for 21 days. Growth, pigment content (chlorophyll a, b and carotenoids), respiratory and photosynthetic activities, osmotic potential and hydrogen peroxide concentration are all monitored. Arsenic accumulation is measured separately in the roots and shoots of Myriophyllum alterniflorum. On the one hand, it should be noted that arsenic induces: (i) a significant increase in H2O2 content; (ii) a decrease in osmotic potential, pigment content, photosynthesis and respiration rates, shoot and root growth; and (iii) an inhibition of shoot branching. Moreover, a higher accumulation of this metalloid in roots than in shoots, regardless of the hydrodynamic condition, is witnessed. While on the other hand, hydrodynamic conditions only affect watermilfoil morphology and arsenic accumulation. Also, the younger and older parts have experienced differential toxic effects. Overall, our results suggest the effective use of M. alterniflorum in both water quality biomonitoring and phytoremediation studies.

Seasonal changes in morphology govern wettability of Katsura leaves.

Deciduous broad-leaf trees survive and prepare for winter by shedding their leaves in fall. During the fall season, a change in a leaf's wettability and its impact on the leaf-fall are not well understood. In this study, we measure the surface morphology and wettability of Katsura leaves from the summer to winter, and reveal how leaf structural changes lead to wettability changes. The averaged contact angle of leaves decreases from 147° to 124° while the contact-angle hysteresis significantly increases by about 35°, which are attributed to dehydration and erosion of nano-wax. Due to such wettability changes, fall brown leaves support approximately 17 times greater water volume than summer leaves.

Cadmium accumulation and subcellular distribution in populations of Hylotelephium spectabile (Boreau) H. Ohba.

A pot experiment was conducted among six populations of Hylotelephium spectabile (Boreau) H. Ohba: four from Jiangsu province, one from Shandong province, and one from Shanxi province, China, to investigate the variation of Cd accumulation and subcellular distribution of this species (a newly reported Cd high accumulator). Under five different real Cd-contaminated soils (Cd: 0.93-97.97 mg/kg), results showed considerable differences in Cd concentration in (a) leaf (1.09-50.7 mg/kg), (b) stem (0.61-13.0 mg/kg), and (c) root (1.55-24.5 mg/kg) among the populations. Analysis of subcellular Cd distribution indicated that Cd accumulated in the leaves of H. spectabile was mainly in the cellular debris (44.1 to 53.5%), followed by heat-stable protein (HSP, 20.9 to 29.0%), Cd-rich granules (MRG, 9.9 to 19.5%), heat-denatured protein (6.0 to 8.5%), and organelle fractions (3.1 to 7.4%). The populations of H. spectabile with more Cd partitioned to cellular debris and biological detoxified metal (HSP + MRG) fractions have greater capacity to accumulate Cd, indicating the probable intrinsic mechanism to accumulate Cd. Therefore, H. spectabile has the considerable potential of phytoremediation for Cd-contaminated soils, but screening suitable populations according to soil Cd concentrations is necessary before used for phytoremediation of Cd-contaminated soils.

[Effects of Wastewater Nitrogen Concentrations and NH4+/NO3- on Nitrogen Removal Ability and the Nitrogen Component of Myriophyllum aquaticum (Vell.) Verdc].

Solution culture experiments were conducted to investigate the effect of wastewater nitrogen levels and NH4+/NO3- on nitrogen removal ability and the nitrogen component of Myriophyllum aquaticum. Experiments with three nitrogen levels and NH4+/NO3- were set up as follows:20, 100, and 200 mg·L-1and NH4+/NO3- 1:0, 0.5:0.5, and 0:1. The results showed that the biomass of plants increased fastest during the first week. The plants treated with NH4+/NO3-=1:0 with nitrogen levels of 20 and 100 mg·L-1 and those treated with NH4+/NO3-=0.5:0.5 with a nitrogen concentration of 200 mg·L-1 exhibited higher biomass than the others. The removal rates of water total nitrogen, ammonium nitrogen, and nitrate nitrogen during the first week were the maximum for all treatments and increased with water nitrogen levels. There were no significant differences in the removal rate between ammonium nitrogen and nitrate nitrogen with a nitrogen level of 20 mg/L, while with nitrogen levels of 100 and 200 mg·L-1, the nitrate removal rates were higher than those for ammonium nitrogen. The Myriophyllum aquaticum nitrogen accumulation and its contribution rate to nitrogen removal from water and sediment were all increased with water nitrogen levels and increased fastest during the first week. The contribution rate of nitrogen accumulated by plants with NH4+/NO3-=0:1 was the highest with nitrogen levels of 20 mg·L-1, while plants with NH4+/NO3-=0.5:0.5 were the highest with nitrogen levels of 100 and 200 mg·L-1. The protein, amino, and nitrate nitrogen contents in Myriophyllum aquaticum plants were all increased by increasing water nitrogen levels with a ranking of protein content > amino nitrogen content > nitrate nitrogen content. The protein concentrations in plants with NH4+/NO3-=1:0 and NH4+/NO3-=0.5:0.5 were higher regardless of water nitrogen levels, while the amino nitrogen concentration in plants with NH4+/NO3-=1:0 and the nitrate nitrogen content in plants with NH4+/NO3-=0:1 were higher than the others. It was concluded that the nitrogen removal ability of Myriophyllum aquaticum was improved by raising water nitrogen levels under the tested condition, which indicates that Myriophyllum aquaticum could purify high nitrogen wastewater. Myriophyllum aquaticum is an ammonium-nitrophile, but had the strongest capacity for growing and removing wastewater nitrogen exhibited with higher than 100 mg·L-1 nitrogen levels only with equal NH4+ to NO3-. The nitrogen component concentrations of protein, amino, and nitrate in Myriophyllum aquaticum plant were all affected by the ratio of NH4+/NO3-.

Transfer kinetics of phosphorus (P) in macrophyte rhizosphere and phytoremoval performance for lake sediments using DGT technique.

DGT (diffusive gradients in thin films) technique and DIFS (DGT induced fluxes in sediment) model are firstly designed for macrophyte-rhizobox system and in-situ macrophytes in Lake Erhai. Dynamics of phosphorus (P) transfer in Zizania latifolia (ZL) and Myriophyllum verticiilatur (MV) rhizosphere is revealed and phytoremediation performance for P in sediment is evaluated. Dynamic transfer process of P at DGT/sediment interface includes (i) diffusion flux and concentration gradients at DGT(root)/porewater interface leading to porewater concentration (C0) depletion and (ii) P desorption from labile P pool in sediment solid to resupply C0 depletion. Fe-redox controlled P release from Fe-bound P (BD-P2) and then NH4Cl-P1 in rhizosphere sediment resupplies porewater depletion due to DGT (root) sink. Kd (labile P pool size in solid phase), r (resupply ratio) and kinetic exchange (Tc and k-1) lead to change characters of DIFS curves of (1) r against deployment time and (2) Csolu (dissolved concentration) against distance at 24 h. They include two opposite types of "fast" and "slow" rate of resupplies. Sediment properties and DIFS parameters control P diffusion and resupply in rhizosphere sediment. Phytoremoval ability for sediment P in lake is estimated to be 23.4 (ZL) or 15.0 t a-1 (MV) by "DGT-flux" method.

[Physiological Characteristics and Nitrogen and Phosphorus Uptake of Myriophyllum aquaticum Under High Ammonium Conditions].

Ammonium nitrogen (NH4+-N) at high concentrations is toxic to plants. In order to explore the NH4+-N tolerance of Myriophyllum aquaticum (M. aquaticum) and its ability of nitrogen (N) and phosphorus (P) uptake, this study used a nutrient solution with three NH4+-N levels (70, 210, 420 mg·L-1) to incubate M. aquaticum for 21 d. The characteristics of plant physiology and N and P uptake of M. aquaticum were measured. At NH4+-N of 70 mg·L-1, M. aquaticum grew healthily, and shoot height and biomass linearly increased with the increase incubation time. Relative shoot height and biomass of M. aquaticum were 40.56 cm and 17.82 g·hole-1 on day 21, respectively. Compared to the control with 70 mg·L-1 ammonium, malondialdehyde (MDA) content of M. aquaticum was significantly increased; chlorophyll and soluble sugar contents were also high at NH4+-N of 210 mg·L-1. M. aquaticum suffered from the NH4+-N stress. However, the stress of 210 mg·L-1 NH4+-N did not affect its normal growth and there was no significant difference in the relative growth rate of the shoot height and biomass compared with the control. At NH4+-N of 420 mg·L-1, MDA contents of M. aquaticum doubled and the shoot height and biomass growth rate were only 27.4% and 17.9% of those for 70 mg·L-1 NH4+-N, indicating that M. aquaticum was subjected to serious stress that caused unhealthy growth or even death. At three NH4+-N levels, the ranges of N and P content of M. aquaticum were 30.7-53.4 mg·g-1 and 3.8-7.7 mg·g-1, respectively, which indicated that M. aquaticum had a high uptake capacity of N and P. M. aquaticum is an ideal wetland plant that has a good application prospect for constructed wetlands in biological treatment of high-ammonia wastewater.