Flow velocity and light intensity combination is important for Microcystis aeruginosa physical suppression.

The cyanobacterial response to flow velocity or light intensity deviates from the combined effect of both factors. The responses of Microcystis aeruginosa to different combinations of flow velocities and light intensities were tested. Growth (OD730 and protein), stress (catalase, ascorbate peroxidase, and glutathione peroxidase), and photosynthetic ability (chlorophyll-a and fluorescence) parameters of M. aeruginosa were measured to evaluate the effects of different combinations. Exposure to different flow velocity-light combinations significantly affected the growth and physiology of M. aeruginosa. Flow velocities of 0.4 m s-1 showed a prominent influence on most of the measured parameters compared with no flow velocity or higher flow velocity conditions. The 1.2-m s-1 flow velocity and high light intensity (1200 µmol m-2  s-1 ) exposure caused a significant elevation in oxidative stress. Lower velocities are beneficial for M. aeruginosa at light stress, whereas extreme velocities are adverse and elevate the stress. Two categories of light-velocity combinations were identified as preferred and extreme categories, depending on whether they suppressed or supported M. aeruginosa growth. In controlling cyanobacteria blooms using flow or high-intensity light, it is imperative to consider the interaction of these two factors, as their combined effects can significantly vary the stress levels in cyanobacteria. A new system, designed to minimize mechanical damage on M. aeruginosa, was used to generate flow velocities. Additionally, the combined effects of flow velocities and light intensities have been considered for the first time. PRACTITIONER POINTS: Flow velocity can influence the effect of light on Microcystis aeruginosa. High light exposure effect on Microcystis aeruginosa can be reduced by low flow velocity. High flow velocity and high light exposure increase the stress on Microcystis aeruginosa. Different light intensities and flow velocity combinations changed Microcystis aeruginosa stress physiology.

Egeria densa organic extracts: an eco-friendly approach to suppress Microcystis aeruginosa growth through allelopathy.

Macrophytes play a significant role in shaping plankton communities by shading, controlling water turbulence, and nutrient availability, while also producing allelochemicals causing varying effects on different organisms. Many researchers have shown that when live macrophytes are present, they inhibit cyanobacteria. However, their widespread use is often limited due to numerous concerns, including invasive characteristics. This study focused on the applicability of Egeria densa extracts to suppress Microcystis aeruginosa. We employed pure water and dimethyl sulfoxide, to obtain compounds from E. densa. The results revealed that E. densa aqueous extracts stimulated M. aeruginosa growth, whereas organic extracts exhibited suppression. Specifically, at low concentrations of organics extracts (0.5 and 1 g/L), after day 4, the growth inhibition was confirmed by significantly higher (p < 0.05) stress levels shown in cells treated with low concentrations. The highest inhibition rate of 32% was observed at 0.5 g/L. However, high concentrations of organic extracts (3 and 6 g/L), showed increased growth compared with control. These results suggest that high concentrations of organic extracts from E. densa potentially suppress allelochemical-induced M. aeruginosa inhibition due to high nutrient availability. In comparison with an aqueous solvent, the use of organic solvent seems to be more effective in efficiently extracting allelochemicals from E. densa.

Temporal variation of 2-MIB and geosmin production by Pseudanabaena galeata and Phormidium ambiguum exposed to high-intensity light.

This study demonstrated the temporal variation of 2-methylisoborneol (2-MIB) and geosmin (GSM) production of two filamentous cyanobacteria species Pseudanabaena galeata (NIES-512; planktonic) and Phormidium ambiguum (NIES-2119; benthic) exposed to high light intensity (950-1000 µmol m-2  s-1 photosynthetically active radiation). The production of 2-MIB and GSM was quantified together with oxidative stress, chlorophyll content, and cellular protein content. The relative chlorophyll bleaching and cell degradations were compared through microscopic images. The 2-MIB production of P. galeata increased by over 42 ± 17% on the second day of exposure and remained leveled through the exposure period. P. ambiguum showed a continuous increase of 2-MIB until the 10th day, recording a 95 ± 4% increment. The GSM production was elevated until the fourth day of exposure by 46 ± 10% for P. galeata and by 74 ± 21% on the second day for P. ambiguum and reduced with prolonged exposure for both species. The chlorophyll content of P. galeata was reduced by 62 ± 7% on the second day, and that of P. ambiguum was reduced by 52 ± 9% on the fourth day and remained low. Protein and H2 O2 contents of both species were changed inconsistently. Exposure to high-intensity light can photobleach and deteriorate cells of both species, but elevations in odorous compounds can be expected.

Short-duration exposure of 3-µm polystyrene microplastics affected morphology and physiology of watermilfoil (sp. roraima).

Microplastics are one of the most widely discussed environmental issues worldwide. Several studies have shown the effect of microplastic exposure on the marine environment; however, studies on freshwater systems are lacking. This study was conducted to investigate the effect of microplastics on hydroponically growing emergent freshwater macrophytes, watermilfoil (sp. roraima) under controlled environmental conditions. Plants were exposed to 0 mg L-1 (control), 0.05 mg L-1, 0.25 mg L-1, 1.25 mg L-1, and 6 mg L-1 of 3-µm polystyrene microspheres for 7 days. The oxidative stress, antioxidant response, pigmentations, Fv/Fm, and growth parameters in the above-water and below-water parts were analyzed separately. Microscopic observations were performed to confirm the tissue absorbance of the microplastics. Exposure to microplastics altered some parameters; however, growth was not affected. The effect of microplastics was not linear with the exposure concentration for most of the parameters and between 1.25 and 6 mg L-1 concentrations. The response trends mostly followed the second-order polynomial distributions. Under the 1.25 mg L-1 exposure, there were significant changes in root length, H2O2 content, catalase activity, anthocyanin content, and Fv/Fm. There were differences in parameters between the above-water and below-water parts, and the responses of the microplastics followed different trends. Microscopic observations confirmed the attachment of microplastic particles onto newly formed roots, except for older roots or shoot tissues.

Electrode insertion generates slow propagating electric potentials in Myriophyllum aquaticum plants.

The insertion of microelectrodes into plants to record electric potentials can generate electric potential responses due to disturbance of plant tissues. Here, the electric potential triggered by Ag/AgCl glass microelectrode insertion into the stele of Myriophyllum aquaticum (parrot feather) plants was recorded. A system potential was triggered upon the electrode insertion and was propagated along the stele of the stem. The microelectrode detected this electric potential that was triggered by its own insertion and the electric potential was identical among the plants assessed. The temporal variation in electric potential registered two prominent peaks at 31.9 ± 1.8 and 17.1 ± 4.3 mV. The electric potential was repolarized after approximately 50-70 min and the stabilized electric potential was 6.5 ± 2.5 mV higher than the initial electric potential of plants. Control experiments conducted using a non-biological spongy rod wetted with distilled water or 1 M KCl confirmed that the peaks were solely due to the electric potential in the stem. These signals can be recognized as system potentials. The systematic EP could develop stimuli responses in distant locations, which is to be tested in further studies.

Nanometer-scale elongation rate fluctuations in the Myriophyllum aquaticum (Parrot feather) stem were altered by radio-frequency electromagnetic radiation.

The emission of radio-frequency electromagnetic radiation (EMR) by various wireless communication base stations has increased in recent years. While there is wide concern about the effects of EMR on humans and animals, the influence of EMR on plants is not well understood. In this study, we investigated the effect of EMR on the growth dynamics of Myriophyllum aquaticum (Parrot feather) by measuring the nanometric elongation rate fluctuation (NERF) using a statistical interferometry technique. Plants were exposed to 2 GHz EMR at a maximum of 1.42 Wm(-2) for 1 h. After continuous exposure to EMR, M. aquaticum plants exhibited a statistically significant 51 ± 16% reduction in NERF standard deviation. Temperature observations revealed that EMR exposure did not cause dielectric heating of the plants. Therefore, the reduced NERF was due to a non-thermal effect caused by EMR exposure. The alteration in NERF continued for at least 2.5 h after EMR exposure and no significant recovery was found in post-EMR NERF during the experimental period.

Short-duration exposure to radiofrequency electromagnetic radiation alters the chlorophyll fluorescence of duckweeds (Lemna minor).

Plants growing in natural environments are exposed to radiofrequency electromagnetic radiation (EMR) emitted by various communication network base stations. The environmental concentration of this radiation is increasing rapidly with the congested deployment of base stations. Although numerous scientific studies have been conducted to investigate the effects of EMR on the physiology of humans and animals, there have been few attempts to investigate the effects of EMR on plants. In this study, we attempted to evaluate the effects of EMR on photosynthesis by investigating the chlorophyll fluorescence (ChF) parameters of duckweed fronds. During the experiment, the fronds were tested with 2, 2.5, 3.5, 5.5 and 8 GHz EMR frequencies, which are not widely studied even though there is a potentially large concentration of these frequencies in the environment. The duckweed fronds were exposed to EMR for 30 min, 1 h and 24 h durations with electric field strength of 45-50 V/m for each frequency. The results indicated that exposure to EMR causes a change in the non-photochemical quenching of the duckweeds. The changes varied with the frequency of the EMR and were time-varying within a particular frequency. The temperature remained unchanged in the duckweed fronds upon exposure to EMR, which confirms that the effect is non-thermal.