The present study investigated that the potential of soil or foliar applied 15 mg/L zinc oxide quantum dots (ZnO QD, 11.7 nm) to enhance pumpkin (Cucurbita moschata Duch.) growth and biomass in comparison with the equivalent concentrations of other sizes of ZnO particles, ZnO nanoparticles (ZnO NPs, 43.3 nm) and ZnO bulk particles (ZnO BPs, 496.7 nm). In addition, ZnSO4 was used to set a Zn²⁺ ionic control. For foliar exposure, ZnO QD increased dry mass by 56% relative to the controls and values were 17.3% greater than that of the ZnO NPs particles. The cumulative water loss in the ZnO QD treatment was 10% greater than with ZnO NPs, suggesting that QD could better enhance pumpkin growth. For the root exposure, biomass and accumulative water loss equivalent across all Zn treatments. No adverse effects in terms of pigment (chlorophyll and anthocyanin) contents were evident across all Zn types regardless exposure routes. Foliar exposure to ZnO QD caused 40% increases in shoot Zn content as compared to the control; the highest Zn content was evident in the Zn²⁺ ionic treatment, although this did not lead to growth enhancement. In addition, the shoot and root content of other macro- and micro-nutrients were largely equivalent across all the treatments. The contents of other nutritional compounds, including amino acids, total protein and sugar, were also significantly increased by foliar exposure of ZnO QD. The total protein in the ZnO QD was 53% higher than the ZnO particle treatments in the root exposure group. Taken together, our findings suggest that ZnO QDs have significant potential as a novel and sustainable nano-enabled agrichemical and strategies should be developed to optimize benefit conferred to amended crops.

Arbuscular mycorrhizal fungi (AMF) are widespread and specialized soil symbiotic fungi, and the establishment of their symbiotic system is of great importance for adversity adaptation. To reveal the growth and photosynthetic characteristics of AMF–crop symbionts in response to heavy metal stress, this experiment investigated the effects of Rhizophagus irregularis (Ri) inoculation on the growth, photosynthetic gas exchange parameters, and chlorophyll fluorescence characteristics of hemp (Cannabis sativa L.) at a Cd concentration of 80 mg/kg. The results showed that (1) under Cd stress, the biomass of each plant structure in the Ri treatment was significantly higher than that in the noninoculation treatment (P < 0.05); (2) under Cd stress, the transpiration rate, stomatal conductance, net photosynthetic rate, PSII efficiency, apparent electron transport rate and photochemical quenching coefficient of the Ri inoculation group reached a maximum, with increases ranging from 1% to 28%; (3) inoculation of Ri significantly reduced Cd enrichment in leaves, which in turn significantly increased the transpiration rate, stomatal conductance, electron transfer rate, net photosynthetic rate and photosynthetic intensity, protecting PSII (P < 0.05); and (4) by measuring the light response curves of different treatments, the light saturation points of hemp inoculated with the Ri treatment reached 1448.4 μmol/m²/s, and the optical compensation point reached 24.0 μmol/m²/s under Cd stress. The Ri–hemp symbiont demonstrated high adaptability to weak light and high utilization efficiency of strong light under Cd stress. Our study showed that Ri–hemp symbiosis improves adaptation to Cd stress and promotes plant growth by regulating the photosynthetic gas exchange parameters and chlorophyll fluorescence parameters of plants. The Ri–hemp symbiosis is a promising technology for improving the productivity of Cd-contaminated soil.

Understanding of aquaporins (AQPs) facilitating the transport of water and many other small solutes including metalloids like silicon (Si) and arsenic (As) is important to develop stress tolerant cultivars. In the present study, 40 AQPs were identified in the genome of pigeonpea (Cajanus cajan), a pulse crop widely grown in semi-arid region and areas known to affected with heavy metals like As. Conserved domains, variation at NPA motifs, aromatic/arginine (ar/R) selectivity filters, and pore morphology defined here will be crucial in predicting solute specificity of pigeonpea AQPs. The study identified CcNIP2-1 as an AQP predicted to transporter Si (beneficial element) as well as As (hazardous element). Further Si quantification in different tissues showed about 1.66% Si in leaves which confirmed the predictions. Furthermore, scanning electron microscopy showed a higher level of Si accumulation in trichomes on the leaf surface. A significant alleviation in level of As, Sb and Ge stress was also observed when these heavy metals were supplemented with Si. Estimation of relative water content, H₂O₂, lipid peroxidation, proline, total chlorophyll content and other physiological parameters suggested Si derived stress tolerance. Extensive transcriptome profiling under different developmental stages from germination to senescence was performed to understand the tissue-specific regulation of different AQPs. For instance, high expression of TIP3s was observed only in reproductive tissues. Co-expression network developed using transcriptome data from 30 different conditions and tissues, showed interdependency of AQPs. Expression profiling of pigeonpea performed using real time PCR showed differential expression of AQPs after Si supplementation. The information generated about the phylogeny, distribution, molecular evolution, solute specificity, and gene expression dynamics in article will be helpful to better understand the AQP transport system in pigeonpea and other legumes.

The carcinogenic attribute of arsenic (As) has turned the world to focus more on the decontamination and declining the present level of As from the environment especially from the soil and water bodies. Phytoremediation has achieved a status of sustainable and eco-friendly approach of decontaminating pollutants, and in the present study, an attempt has been made to reveal the potential of As remediation by a halophyte plant, Acanthus ilicifolius L. Special attention has given to analyse the morphological, physiological and anatomical modulations in A. ilicifolius, developed in response to altering concentrations of Na₂AsO₄.7H₂O (0, 70, 80 and 90 μM). Growth of A. ilicifolius under As treatments were diminished as assessed from the reduction in leaf area, root length, dry matter accumulation, and tissue water status. However, the plants exhibited a comparatively higher tolerance index (44%) even when grown in the higher concentrations of As (90 μM). Arsenic treatment induced reduction in the photochemical activities as revealed by the pigment content, chlorophyll stability index (CSI) and Chlorophyll a fluorescence parameter. Interestingly, the thickness and diameter of the xylem walls in the leaf as well as root tissues of As treated samples increased upon increasing the As concentration. The adaptive strategies exhibited by A. ilicifolius towards varying concentrations of As is the result of coordinated responses of morpho-physiological and anatomical attributes, which make the plant a promising candidate for As remediation, especially in wetlands.

Eutrophication transforms clear water into turbid water in shallow lakes. Current restoration techniques focus on re-establishing the clear-water state rather than on its maintenance. We investigated the response of submerged macrophytes to temporary grass carp (Ctenopharyngodon idella) and scraping snail (Bellamya aeruginosa) introductions. We also explored the impacts of herbivores on underwater light conditions to identify their long- and short-term potential to halt regime shift from clear to turbid after clear-water state reestablishment. Herbivores reduced both the biomass of submerged macrophytes and accumulated nutrients in the tissue of submerged macrophytes. This potentially avoided the pulse of endogenous nutrient release which would have exceeded the threshold required for the regime shift from clear to turbid. However, herbivores had a non-significant impact on submerged macrophyte-reduced light attenuation coefficient, which has a positive linear relationship with water chlorophyll a. Further, grass carp and snails enhanced the inhibition ratio of submerged macrophytes to phytoplankton by 3.96 and 2.13 times, respectively. Our study provides novel findings on the potential of herbivore introduction as an indirect biomanipulation tool for halting the regime shift of shallow lakes from clear to turbid after the restoration of submerged macrophytes.

Fish community manipulation and regulation has been largely overlooked as a mitigation strategy for restoring submerged aquatic vegetation (SAV) in shallow lakes of the middle and lower Yangtze River Basin (MLYRB). An in-situ fish exclusion experiment and a large-scale lake manipulation were conducted to test the hypothesis that the reasonable removal of benthivorous and herbivorous fish would facilitate the restoration and reconstruction of SAV in shallow lakes within the MLYRB. The in-situ exclusion experiment was conducted from April to October in 2017. Electrofishing was used to remove benthivorous and herbivorous fish from the exclosures. SAV were then artificially planted in the same pattern and density in both exclosures and adjacent open sites, and responses were measured for seven consecutive months. The mean percent coverage and biomass of SAV in the exclosures increased quickly and remained significantly higher than those in open sites over the duration of the experiment. Water quality also improved as turbidity, chlorophyll-a, total phosphorus and total nitrogen in the exclosures remained significantly lower than those in the open sites. After the in-situ experiment, a larger scale manipulation of fish in the entire submerged macrophyte zone (SMZ) was implemented from 2017 to 2020. After removing more than 2/3 of the benthivorous and herbivorous fish biomass by October 2020 in the SMZ, both the species richness and spatial coverage of SAV increased from 2 to 9 and from 1.7% to 32.2%, respectively. Our results provided clear evidence that fish are strong regulators of SAV productivity and that their reasonable removal facilitates ecological recovery. Therefore, we propose that fish community manipulation as implemented in this study be given more attention in addition to the reduction of external nutrient loading when designing projects to restore SAV in shallow lakes of the MLYRB.

Wastewater containg proteinaceous ossein effluents are problematic to be treated. We studied the possibility to treat ossein effluents with the marine cyanobacterium strain Cylindrospermum stagnale. After optimizing the culture conditions of the bacterium, three different types of ossein effluents were tested: dicalcium phosphate (DCP), high total dissolved solids (HTDS) and low total dissolved (LTDS). The effluents were diluted with sea water at the following ratios 1:1, 2:1 and 3:2. The optimum operating conditions were at 3000 lux light intensity and 37 °C temperature. The highest degradation of ossein effluens by C. stagnale was attained for a dilution ratio of 1:1. However, less diluted ossein effluents reduced the growth of C. stagnale drastically. The degradation was shown by measuring the chlorophyll a content and the dry weight of bacterial cells during a seven-day incubation period degradation. Fourier Transform Infrared Spectroscopy (FT-IR) analysis verified the degradation showing the presence of the degradation products of ossein (i.e. calcium carbonate and calcite) in the culture medium. Lipid composition in fatty acids appeared to be suitable for biofuel production. The results showed that the marine cyanobacterium C. stagnale can be used to treat ossein effluents, and at the same time, to produce biofuel in a sustainable way.

The potential environmental risk of glyphosate has promoted the need for decontamination of glyphosate-polluted water bodies. These treatments should be accompanied by studies of the recovery potential of aquatic communities and ecosystems. We evaluated the potential of freshwater periphyton to recover from glyphosate exposure using microcosms under laboratory conditions. Periphyton developed on artificial substrates was exposed to 0.4 or 4 mg l⁻¹ monoisopropylamine salt of glyphosate (IPA) for 7 days, followed by translocation to herbicide-free water. We sampled the community 1, 2 and 3 weeks after the transfer. Dry weight, ash-free dry weight, chlorophyll a, and periphyton abundances were analysed. The periphyton impacted with the lowest IPA concentration recovered most of the structural parameters within 7 days in clean water, but the taxonomic structure did not entirely recover towards the control structure. Periphyton exposed to 4 mg IPA l⁻¹ could not recover during 21 days in herbicide-free water, reaching values almost four times higher in % of dead diatoms and four times lower in ash-free dry weight concerning the control at the end of the study. Results suggest a long-lasting effect of the herbicide due to the persistence within the community matrix even after translocating periphyton to decontaminated water. We conclude that the exposure concentration modulates the recovery potential of IPA-impacted periphyton. The current research is the first to study the recovery in glyphosate-free water of periphyton exposed to the most commonly used herbicide in the world. Finally, we highlight the need for more studies focused on the recovery potential of freshwater ecosystems and aquatic communities after glyphosate contamination.

The application of hydrogen peroxide (H₂O₂) to control harmful algal blooms is affected by algal density and species. In the present study, a simulation field study was carried out to evaluate the removal of cyanobacteria with high algal density (chlorophyll a of approximately 220–250 μg/L) and low algal density (chlorophyll a of approximately 30–50 μg/L) using 10, 20 mg/L H₂O₂ and 5 mg/L H₂O₂. The dynamics of algal biomass, nutrients, microcystins, phytoplankton, and zooplankton were measured within 7 d. The results showed that 5 mg/L H₂O₂ effectively eliminated algal biomass (measured as chlorophyll a and phycocyanin) and inhibited 50% of the photosynthetic activity of the cyanobacteria at 7 d in the low algal cell density group, while the same inhibition rate was observed in the high algal cell density group when the H₂O₂ was 20 mg/L. However, using a high dosage of H₂O₂, such as 10 mg/L, to suppress cyanobacteria with high biomass could result in a dramatic increase in nutrients and microcystins in the water column. The portion of eukaryotic algae, such as Chlorophyta, Bacillariophyta and Euglenophyta, in the phytoplankton community increased with increasing H₂O₂ concentrations; moreover, the dominant species of cyanobacteria changed from the nontoxic genus Dactylococcopsis to the toxic genus Oscillatoria, which may result in acute toxicity to zooplankton. Our results demonstrated that the application of H₂O₂ to control cyanobacterial blooms at the early stage when algal cell density was low posed less potential ecological risks and may have increased the diversity of the phytoplankton community.

Management of water-quality in a river ecosystem needs to be focused on susceptible regions to eutrophication based on proper measurements. The stress–response relationships between nutrients and primary productivity of phytoplankton allow the derivation of ecologically acceptable thresholds of stressors under field conditions. However, spatio-temporal variations in heterogeneous environmental conditions have hindered the development of locally applicable criteria. To address these issues, we utilized a combination of a geographically specialized artificial neural network (Geo-SOM, geo-self-organizing map) and linear mixed-effect models (LMMs). The model was applied to a 24-month dataset of 54 stations that spanned a wide spatial gradient in the Nakdong River basin. The Geo-SOM classified 1286 observations in the basin into 13 clusters that were regionally and seasonally distinct. Inclusion of the random effects of Geo-SOM clustering improved the performance of each LMM, which suggests that there were significant spatio-temporal variations in the Chla–stressor relationships. These variations arise owing to differences in background seasonality and the effects of local pollutant variables and land-use patterns. Among the 16 environmental variables, the major stressors for Chla were total phosphate (TP) as a nutrient and biological oxygen demand (BOD) as a non-nutrient according to the results of both Geo-SOM and LMM analyses. Based on LMMs with the random effect of the Geo-SOM clusters on the intercept and the slope, we can propose recommended thresholds for TP (18.5 μg L⁻¹) and BOD (1.6 mg L⁻¹) in the Nakdong River. The combined method of LMM and Geo-SOM will be useful in guiding appropriate local water-quality-management strategies and in the global development of large-scale nutrient criteria.