Lettuce Root Growth Research Articles

Revealing the influences of organic amendment-derived dissolved organic matter on growth and nutrient accumulation in lettuce seedlings (Lactuca sativa L.)

Abstract Although the application of organic amendment (OA) is a well-established agricultural practice, the effectiveness, optimal concentration, and key characteristics of OA-derived dissolved organic matter (DOM) in promoting the growth and nutrient accumulation of lettuce are not fully understood. To gain a better understanding, the effect of OA-derived DOM that was prepared from rapeseed oil cake (ROC) on the growth of lettuce was examined. Lettuce seedlings (7 days old) were transplanted into a hydroponic nutrient solution with varying DOM concentrations (10, 20, and 30 mg C L–1) along with the control treatment (no DOM addition), and shoot and root growth of lettuce was recorded and nutrient accumulation in lettuce was analyzed after 14 days. Compared to the control treatment, the soil and plant analyzer development value, shoot fresh weight, shoot dry weight, and leaf area were significantly greater (P < 0.05) in 20 mg C L–1 DOM concentration, while the maximum leaf width was significantly higher (P < 0.05) in 10 mg C L–1 DOM concentration. The root fresh weight, root dry weight, root length, root surface area, and number of lateral roots were significantly greater (P < 0.05) in 20 mg C L–1 DOM concentration than in the control treatment. DOM concentrations of 20 and/or 10 mg C L–1 also resulted in enhanced carbon, phosphorus, potassium, sulfur, silicon, and boron contents in lettuce. Overall, these findings suggest that ROC-derived DOM can promote growth and nutrient accumulation in lettuce seedlings, with 20 and/or 10 mg C L–1 being suitable concentrations.

Xylooligosaccharides Enhance Lettuce Root Morphogenesis and Growth Dynamics.

Enhancing root development is pivotal for boosting crop yield and augmenting stress resilience. In this study, we explored the regulatory effects of xylooligosaccharides (XOSs) on lettuce root growth, comparing their impact with that of indole-3-butyric acid potassium salt (IBAP). Treatment with XOS led to a substantial increase in root dry weight (30.77%), total root length (29.40%), volume (21.58%), and surface area (25.44%) compared to the water-treated control. These enhancements were on par with those induced by IBAP. Comprehensive phytohormone profiling disclosed marked increases in indole-3-acetic acid (IAA), zeatin riboside (ZR), methyl jasmonate (JA-ME), and brassinosteroids (BRs) following XOS application. Through RNA sequencing, we identified 3807 differentially expressed genes (DEGs) in the roots of XOS-treated plants, which were significantly enriched in pathways associated with manganese ion homeostasis, microtubule motor activity, and carbohydrate metabolism. Intriguingly, approximately 62.7% of the DEGs responsive to XOS also responded to IBAP, underscoring common regulatory mechanisms. However, XOS uniquely influenced genes related to cutin, suberine, and wax biosynthesis, as well as plant hormone signal transduction, hinting at novel mechanisms of stress tolerance. Prominent up-regulation of genes encoding beta-glucosidase and beta-fructofuranosidase highlights enhanced carbohydrate metabolism as a key driver of XOS-induced root enhancement. Collectively, these results position XOS as a promising, sustainable option for agricultural biostimulation.

Onion Peel Waste Has the Potential to Be Converted into a Useful Agricultural Product to Improve Vegetable Crop Growth

The onion processing industry produces hundreds of thousands of tons of onion waste annually. Normally, onion peel waste is dumped in landfills, which creates additional sources of greenhouse gases. Research has validated that onion peel is a concentrated source of bioactive compounds; therefore, it can be turned into useful agricultural products such as soil amendments and possibly biostimulants. This study conducted three experiments to investigate the plant growth-promoting potential of an onion juice concentrate (OJC). The first experiment explored whether the application of OJC could increase plant growth of Bermuda grass, lettuce, and bok choy. The second experiment evaluated the effects of foliar and subsurface drench applications of OJC on bok choy and lettuce growth. The third experiment investigated the interaction between OJC application methods and fertilizer type on bok choy and radish growth. The results indicated that foliar applications of OJC of 1% to 2% concentrations increased the yield of bok choy and its overall growth. Subirrigation with OJC, however, enhanced the root growth of bok choy, lettuce, and radish. Notably, the combined approach of foliar and subirrigation applications further promoted the growth of both bok choy and radish. Comparing across experiments, longer OJC application periods emerged as a promising strategy for amplifying its growth-promoting benefits. Overall, our findings suggest that OJC holds promise for promoting sustainable agriculture. This potential comes from its ability to enhance both the growth and yield of vegetable crops like bok choy, lettuce, and radish while simultaneously reducing waste.

Does subjecting plants to water stress enhance biological nitrification inhibition potential of rice?

Biological nitrification inhibition (BNI) is a trait that could improve nitrogen-use efficiency of a crop. We studied varietal differences in BNI potential of rice at the vegetative phase when plants were subjected to water stress. We obtained water-soluble root exudates (RE) and water-extracts of crushed root tissues (RT) from two-week-old seedlings of five rice cultivars grown continuously under adequate water or under water stress and assessed their ability to suppress the activity of Nitrosomonas europaea and the growth of lettuce seedlings. We also investigated how growing rice under continuously saturated (TC) and unsaturated (TU) soil moisture conditions affected potential nitrification rate (PNR) and community structure of ammonia-oxidizing bacteria (AOB) in the rhizosphere compared with bulk soil. We observed that only RT at ≥ 0.50 mg ml−1 suppressed the activity of N. europaea with significant (p < 0.05) differences among rice cultivars. Subjecting rice cultivars PI312777 and PI338046 to water stress significantly (p < 0.05) increased BNI of RT. Inhibition of lettuce root growth by RT was strongly correlated with its BNI (r = 0.83, p < 0.05). In T-RFLP profiles of AOB, the relative abundance of T-RF R205 was lower in TU than in TC in all cultivars except Rexmont. The rice cultivars studied produced compounds that could inhibit ammonia oxidizers, but the degree of BNI differed based on the moisture stress experienced by the crop. Lineages of rice cultivars with known allelopathic potential would be promising candidates to consider for BNI potential.

Ex-situ biological treatment of industrial saline seafood wastewater by salt-tolerant mixed cultures and phytotoxicity evaluation

In the framework of circular economy, this study assessed the ex-situ biodegradation and desalination of saline non-sterilized seafood wastewater (SFW) by new salt-tolerant mixed bacterial cultures, followed by its phytotoxicity evaluation. These cultures were characterized through 16S amplicon sequencing, an advanced tool to process the biodiversity of samples empowering applicability to advanced bioprocessing of SFW. The mixed cultures had high relative abundance of Pseudomonas and Aeromonas, and abundance of Acinetobacter, Myroides and Chryseobacterium. The biodegradation potential, growth kinetics and specific growth rate of the mixed cultures were determined using varying concentrations of SFW (20% and 80% v/v). The process was completed in just 24 h resulting in no odour and colour. The mixed cultures were also combined. Effective Chemical Oxygen Demand (COD) removal (36.2–89.1%) was achieved by the mixed cultures and their combinations. The mixed cultures resulted in significant salt content reduction (77.5–83.3%). The considerably lower levels of COD (<900 mg/L) and salt content achieved, in most cases, is a step towards in-situ SFW treatment before entrance to the sewage system. Among all, mixed Pseudomonas sp. dominant cultures were the most promising for further in-situ bioprocessing studies. In addition, the biotreated SFW supernatant, which was not overly-diluted using freshwater, could potentially be reused in agriculture, as the germination index was higher than 50% upon seed and root growth of tomato and lettuce. It contained approximately 0.03% total nitrogen and 0.01% phosphate which may irrigate to plants providing additional nutrients.

Sustainable Soilless Cultivation Mode: Cultivation Study on Droplet Settlement of Plant Roots under Ultrasonic Aeroponic Cultivation

In order to solve the effects of environmental factors on the droplet settlement of a nutrient solution on plant roots when planting plants with ultrasonic aeroponic cultivation, this study aimed to obtain a suitable wind speed range and atomization time through a nutrient solution atomization experiment, to obtain the best control scheme through a multi-environmental parameter combination cultivation experiment. Taking an ultrasonic aeroponic cultivation device as the research object, and lettuce as the test material, experiments were carried out on two factors affecting the wind speed of an axial fan and the atomization time of the nutrient amount of ultrasonic aeroponic cultivation plants; the suitable wind speed range was 1.0–2.5 m/s. The temperatures of the lettuce root zones in the upper, middle, and lower layers of the ultrasonic aeroponic cultivation device at different time periods were obtained by atomizing the nutrient solution. When the optimum temperature for the root growth of lettuce was 15–20 °C and the wind speed was 1.0–2.5 m/s, the continuous atomization time of the nutrient solution was 66–184 min. Using a quadratic orthogonal rotation combination design method, three main factors, namely wind speed, ambient temperature, and atomization time, were selected to test droplet settlement in the lettuce roots. The droplet settlement in the lettuce root system was measured. The droplet settlement regression equation in the lettuce root system was established. The reliability of the regression model was tested according to the significance condition, and a simplified quadratic orthogonal regression equation was obtained. The main effect analysis, single factor analysis, and interaction effect analysis were used to analyze the model, and the model was further verified. The verification results showed that the relative error between the predicted value and the actual value of the average root droplet sedimentation was 5.8%. The optimum wind speed was 2.5 m/s, the ambient temperature was 16 °C, and the atomization time was 184 min when the ultrasonic aeroponic cultivation device designed in this study was used to cultivate lettuce. It could provide a theoretical reference and an experimental basis for the control of the related growth environment parameters of plants cultivated using ultrasonic aeroponic cultivation.

Root cell wall remodeling mediates copper oxide nanoparticles phytotoxicity on lettuce (Lactuca sativa L.)

Root cell wall (RCW) remodeling induced by copper oxide nanoparticles (CuO NPs) and its consequences for root growth of lettuce (Lactuca sativa L.) were investigated in this study. The results showed that a low concentration of CuO NPs (5 mg L−1) stimulated reactive oxygen species (ROS) signaling, led to the degradation of pectin by H2O2, and promoted root elongation by 22.1% by triggering RCW loosening. However, under treatment with a high concentration of CuO NPs (450 mg L−1), the unordered distribution of pectin homogalacturonan enhanced cell wall adhesion. Also, the increased xyloglucan and the decreased xyloglucan endotransglycosylase/hydrolase (XTH) activities caused cell wall stiffening, making it difficult for lettuce roots to extend. Meanwhile, the contents of hemicellulose and low-methylated pectin were increased remarkably due to the downregulation of the encoding genes XTH15, XTH17, XTH31 and the upregulation of PME3, which provided abundant binding sites of RCW with CuO NPs. In addition, the accelerated development of the apoplastic barrier and root lignification blocked the absorption of CuO NPs, and the endodermal cell walls were doubled in thickness, greatly enhancing their retention capacity to CuO NPs. Taken together, the above findings suggest that CuO NPs have concentration-dependent effects on lettuce roots, which are associated with plant tolerance and mediated by RCW remodeling.

Inoculation with Trichoderma harzianum and Azospirillum brasilense increases nutrition and yield of hydroponic lettuce.

The use of beneficial fungi and bacteria stimulate plant growth and serve to improve yield and food quality in a sustainable manner. The electrical conductivity of nutrients solution is closely linked to better nutrition of vegetable plants in a hydroponic system. Therefore, objectives of current study were to evaluate the effect of isolated and combined inoculation with Azospirillum brasilense and Trichoderma harzianum under two electrical conductivities on growth, nutrition, and yield of lettuce in hydroponic cultivation. The experiment was designed in a strip-plot block with five replications in a 4 × 2 factorial scheme. The treatments were consisted of four microbial inoculations (without, A. brasilense, T. harzianum and co-inoculation) and electrical conductivities (1.2 and 1.4 dS m-1). Inoculation with A. brasilense and T. harzianum increased lettuce root growth by 47% and 20%, respectively. The single inoculation of T. harzianum provided higher fresh leaves yield (24%) at electrical conductivity of 1.2 dS m-1, while single inoculation with A. brasilense increased fresh leaves yield by 17% at electrical conductivity 1.4 dS m-1. The lowest shoot NO3- accumulation (40%) was observed with inoculation of A. brasilense and highest (28%) with inoculation T. harzianum in both electrical conductivities. Inoculation with A. brasilense increased leaf accumulation of K, P, Ca, Mg, Fe, Mn, Cu, and Zn, which are essential for human nutrition and being recommended to improve yield of lettuce plants in hydroponics. It is recommended to use EC 1.4 dS m-1 of the nutrients solution to improve accumulation of K, Mn, Cu, and Zn, regardless of inoculations for biofortification of lettuce with application of fertilizers.

Responses of butter leaf lettuce to mixed red and blue light with extended light/dark cycle period

To investigate the effects of extended light/dark (L/D) cycle period (relative to the diurnal L/D cycle) on lettuce and explore potential advantages of abnormal L/D cycles, butter leaf lettuce were grown in a plant factory with artificial light (PFAL) and exposed to mixed red (R) and blue (B) LED light with different L/D cycles that were respectively 16 h light/8 h dark (L16/D8, as control), L24/D12, L48/D24, L96/D48 and L120/D60. The results showed that, all the abnormal L/D cycles increased shoot dry weight (DW) of lettuce (by 34–83%) compared with the control, and lettuce DW increased with the L/D cycle period prolonged. The contents of soluble sugar and crude fiber in lettuce showed an overall upward trend with the length of L/D cycle extended, and the highest vitamin C content as well as low nitrate content were both detected in lettuce treated with L120/D60. The light use efficiency (LUE) and electric use efficiency (EUE) of lettuce reached the maximum (respectively 5.37% and 1.76%) under L120/D60 treatment and so were DW, Assimilation rate (A), RC/CS, ABS/CS, TRo/CS and DIo/CS, indicating that longer L/D cycle period was beneficial for the assimilation efficiency and dry matter accumulation in lettuce leaves. The highest shoot fresh weight (FW) and nitrate content detected in lettuce subjected to L24/D12 may be related to the vigorous growth of root, specific L/D cycle seemed to strengthen root growth and water absorption of lettuce. The openness level of RC in PSII (Ψo), ETo/CS, and PIabs were all the highest in lettuce treated with L24/D12, implying that slightly extending the L/D cycle period might promote the energy flowing to the final electron transfer chain. In general, irradiation modes with extended L/D cycle period had the potential to improve energy use efficiency and biomass of lettuce in PFAL. No obvious stress or injury was detected in lettuce subjected to prolonged L/D cycles in terms of plant growth and production. From the perspective of shoot FW, the optimal treatment in this study was L24/D12, while L120/D60 was the recommended treatment as regards of the energy use efficiency and nutritional quality.

Aspergillus niger as a Biological Input for Improving Vegetable Seedling Production.

This study evaluated the potential of Aspergillus niger as an inoculant for growth promotion of vegetable seedlings. Seven vegetable species were evaluated in independent experiments carried out in 22 + 1 factorial schemes, with two doses of conidia (102 and 106 per plant) applied in two inoculation methods (seed treatment and in-furrow granular application), plus an uninoculated control. Experiments were carried out in a greenhouse. Growth parameters evaluated were shoot length, stem diameter, root volume, total root length, shoot and root fresh mass, shoot and root dry mass, and total dry mass. Regardless of the dose and inoculation method, seedlings inoculated with A. niger showed higher growth than uninoculated ones for all crops. The highest relative increase promoted by the fungus was observed for aboveground parts, increasing the production of shoot fresh mass of lettuce (61%), kale (40%), scarlet eggplant (101%), watermelon (38%), melon (16%), pepper (92%), and tomato (42%). Aspergillus niger inoculation also increased seedling root growth of lettuce, pepper, scarlet eggplant, watermelon, and tomato. This research shows that A. niger boosts the growth of all analyzed vegetables, appearing as a promising bio-input for vegetable seedling production.

Effects of surface modification on toxicity of CeO2 nanoparticles to lettuce

Phytotoxicity of nanoceria (nCeO2) has been reported, but there are few studies on how to reduce its phytotoxicity. In the present study, we modified nCeO2 with two organophosphates (nCeO2@ATMP and nCeO2@EDTMP) and compared their toxicity to lettuce with that of uncoated nCeO2. The results showed that bare nCeO2 significantly inhibited the root growth of lettuce, leading to oxidative damages and root cell death. In contrast, after surface modification, the toxicity of nCeO2@ATMP to lettuce was weakened, while nCeO2@EDTMP was nontoxic to lettuce. It was found that the surface properties of the modified materials have been changed, resulting in sharp decreases in their bioavailability. Although nCeO2 with and without surface coatings were all transformed when interacting with plants, the absolute contents of Ce(III) in roots treated with modified nCeO2 decreased significantly, which may be the main reason for the reduction of toxicity. This study indicates that it is feasible to reduce the phytotoxicity of nanomaterials through surface coating.

In vitro Bioassay of Allelopathic Activities of a Mangrove Tree, Kandelia obovata, and Fast-growing Trees, Betula platyphylla and Populus alba, Using Protoplast Co-culture Method

Allelopathic activities of a salt-tolerant and low-temperature tolerant mangrove tree, Kandelia obovata, which grows in brackish water regions of sub-tropical areas, and two fast-growing trees, Betula platyphylla and Populus alba, which grow in the temperate area, were examined by two in vitro bioassay methods, the sandwich method using dried leaves and the protoplast co-culture method using leaf protoplasts. Lettuce root growth examined by the sandwich method, was inhibited 50% by 50 mg dried mature leaves of K. obovata. In the protoplast co-culture method, inhibition rates of cell division of lettuce protoplasts were 31% and 69% by leaf protoplasts of K. obovata at densities of 1 &amp;times; 104 mL-1 and 5 &amp;times; 104 mL-1, respectively. These results were compared with the inverse relationship between allelopathic activities and salt tolerance of mangrove plants of different families. B. platyphylla showed 37% inhibition by the sandwich method using dried young leaves, but only 10% inhibition at 5 &amp;times; 104 mL-1 by the protoplast co-culture method using leaf protoplasts of B. platyphylla. Dried young leaves of P. alba showed 66% inhibition, but the leaf protoplasts at the density of 5 &amp;times; 104 mL-1 showed highly stimulatory activity. Abscisic acid, of which contents in leaf protoplasts of three tree species varies from high to low in relation to salt tolerance and recalcitrance of tissue culture, was discussed as a putative allelochemical.

Species-dependent response of food crops to polystyrene nanoplastics and microplastics

This study investigated the early responses of four common food crops (Italian lettuce, radish, wheat and corn) by exposing their seeds to suspensions of polystyrene nanoparticles (nano-PS) and microspheres (micro-PS). We found that the crop responses to exposure to nano-PS and micro-PS at different doses were dependent on the plant species. Among the four species, Italian lettuce was the most sensitive crop in terms of seed germination and its germination index after polystyrene exposure for 7 days was inhibited by 18.2%–36.0% compared with that of the control (p < 0.05). The root growth (root dry weight, root/shoot ratio and root length) of Italian lettuce and corn was significantly inhibited by the exposure treatment (p < 0.05), whereas that of radish and wheat was hardly affected. Analyses of antioxidant enzymatic activities, lipid peroxidation, and integrated biomarker indexes confirmed that the toxic effects of nano-PS and micro-PS on crops are likely due to oxidative stress. The observed distribution of fluorescent nano-PS in the roots or germs of the tested crops suggests that nanoplastics can be taken up by plants even at a very early growth stage (<7 days after sowing). Future research is needed in order to obtain more insights into their implications for agricultural sustainability and food safety.

Effects of different NO3 −: NH4 + ratios on the ultrastructure and ion flux rate of lettuce roots

Nitrogen is a vital nutrient element for plants. The two main forms of nitrogen (N) are nitrate N (NO3 −) and ammonium N (NH4 +). The effects of the different NO3 −:NH4 + ratios (0:100, 25:75, 50:50, 75:25, and 100:0) in the nutrient solution on the growth, root morphology, ultrastructure and ion flux rate of lettuce roots were studied. The results showed that the biomass and leaf area were greatest when the ratio of NO3ˉ:NH4 + was 50:50 or 75:25. The shoot NO3 − content was highest when the ratio of NO3ˉ:NH4 + was 50:50 or 75:25. The shoot NH4 +-N content was highest when the ratio of NO3ˉ:NH4 + was 50:50. The NO3 − flux was greatest when the ratio of NO3ˉ:NH4 + was 50:50 or 75:25. Superoxide dismutase (SOD) activity was lowest when the ratio of NO3ˉ:NH4 + was 0:100, and peroxidase (POD) activity was highest when the ratio of NO3ˉ:NH4 + was 100:0. The malonic dialdehyde (MDA) content was lowest when the ratio of NO3ˉ:NH4 + was 50:50, and the MDA content was higher when the ratio of NO3ˉ:NH4 + was 0:100 or 25:75. It was smooth and complete when the ratio of NO3ˉ:NH4 + was 50:50 or 75:25.

Antioxidant, allelopathic activities of leaf extracts and essential oil compositions of Acronychia pedunculata (L.) Miq.

This research aims to exploit total polyphenol, flavonoid contents, antioxidant and allelopathic activities of leaf extracts, and essential oil compositions from leaves of Acronychia pedunculata (L.) Miq. The results indicated that the leaf extract from ethanol 100% (E100) possessed a lower total polyphenol and flavonoid content than the extract from ethanol 70% (E70). In contrast, the antioxidant activity from E100 extract with IC50=612.9±12.9 μg/ml was stronger than that of E70 extract with IC50=1225.5±6.9 μg/ml. Regarding allelopathic activity, while the extracts from E100 and E70 inhibited root growth of radish, both extracts promoted root growth of lettuce. Especially, E100 extract with 3 mg/ml inhibited root growth of radish up to 48.1%. Moreover, using water solvents, the extracts reduced root growth of both the radish and lettuce. By GC-MS analyses, 33 compounds were identified from A. pedunculata essential oil. The major constituents were caryophyllene (47.09%), humulene (17.28%), α-copaene (4.98%), isoledene (3.59%), and (-)-α-panasinsen (3.51%), other compounds were accounted for lower 3%.

Allelopathic Potential and Active Substances from Wedelia Chinensis (Osbeck).

Wedelia chinensis (Asteraceae) is a wetland herb native to India, China, and Japan. It is a valuable medicinal plant recorded to have pharmaceutical properties. However, the phytotoxic potential of Wedelia chinensis has not yet been examined. Thus, we carried out this study to establish the allelopathic effects of Wedelia chinensis and to identify its phytotoxic substances. Extracts of Wedelia chinensis exhibited high inhibitory activity against the root and shoot growth of cress, alfalfa, rapeseed, lettuce, foxtail fescue, Italian ryegrass, timothy, and barnyard grass. The inhibition was varied with species and was dependent on concentrations. The extracts were separated through several purification steps, and the two effective substances were isolated and characterized as vanillic acid and gallic acid using spectral analysis. Vanillic acid and gallic acid significantly arrested the growth of cress and Italian ryegrass seedlings. The concentrations of vanillic acid and gallic acid needed for 50% inhibition (I50 values) of the seedling growth of the cress and Italian ryegrass were 0.04–15.4 and 0.45–6.6 mM, respectively. The findings suggest that vanillic acid and gallic acid may be required for the growth inhibitory activities of Wedelia chinensis.

Heavy metal pollution improves allelopathic effects of Canada goldenrod on lettuce germination.

Large amounts of heavy metals have been released into the environment. Thus, the allelopathic effects of invasive alien species on the germination performance of co-occurring indigenous species may be altered or even heightened with the rapid growth in heavy metal pollution. This study evaluated the impacts of Canada goldenrod (Solidago canadensis L.) leaf extracts at concentrations of 0, 10 or 20 gl 1 on the germination of lettuce under different forms of heavy metal pollution (Cu2+ , Pb2+ or a combination of Cu2+ and Pb2+ ; 35 mgl 1) during incubation in Petri dishes for 10 days. Goldenrod leaf extracts (high concentration) reduced growth of aboveground and belowground parts of lettuce as well as competition for light and soil nutrients. However, low concentrations of goldenrod leaf extracts dramatically improved growth of lettuce roots, competition for light, soil nutrient availability, leaf photosynthetic area and growth competitiveness. The combination of goldenrod leaf extracts and heavy metal pollution was synergistic on most lettuce germination parameters, probably because high concentrations of goldenrod leaf extracts together with heavy metal pollution had a synergistic negative impact on lettuce germination. Consequently, increased levels of heavy metal pollution may favour invasion of invasive alien species while largely suppressing germination of indigenous species.

Phytotoxic and Antimicrobial Activities of Teucrium polium and Thymus decussatus Essential Oils Extracted Using Hydrodistillation and Microwave-Assisted Techniques.

Essential oils (EOs) have been described as promising eco-friendly secondary products of aromatic plants with several biological activities. The present study aimed to characterize the chemical composition and explore phytotoxic and antimicrobial activities of Teucrium polium and Thymus decussatus EOs extracted using hydrodistillation (HD) and microwave-assisted extraction (MAE) methods. Twenty-seven and twenty-eight compounds were identified from HD and MAE extracted EOs of T. polium, respectively. The oxygenated sesquiterpenes (57.68%) were characterized as the main components of the hydrodistilled EO with a prominence of 6-epi-shyobunol (33.00%), while sesquiterpene hydrocarbons (54.48%) were the main components of the MAE method, with a prominence of delta-cadinene (25.13%). Eighteen and nineteen compounds, were characterized in T. decussatus EOs extracted using HD and MAE methods, respectively, and oxygenated monoterpenes represented the main components of both EOs with carvacrol (94.40% and 75.91%, respectively) as the main compound. The EOs extracted using the MAE method were slightly more phytotoxic than those extracted using the HD method. The T. decussatus EO extracted using the MAE method showed a higher inhibitory effect than T. polium by 16-, 32-, and 24-fold, regarding seed germination, shoot, and root growth of lettuce, respectively. Moreover, EOs extracted by HD method showed a similar pattern with 16-, 28-, and 14-fold effects. Both T. decussatus EOs exhibited potent inhibitory effect against all tested bacteria with an inhibition zone of 34–39 mm and the lowest minimum inhibitory concentration (MIC) of 0.49, 0.98, and 1.95 μg/mL against Aspergillus niger, Escherichia coli, and Staphylococcus aureus, respectively. However, the EOs of T. polium showed weak antibacterial activity and no antifungal effect. Further studies are needed for the characterization of bioactive major compounds, either singular or synergistic, at field scale and to determine their modes of action and safety.

Oyster shell-based alkalinization and photocatalytic removal of cyanide as low-cost stabilization approaches for enhanced biogas production from cassava starch wastewater

Cassava starch wastewater (CSW) poses a high polluting potential due to its high organic loading and cyanide (CN−) concentration, but this residue can be pretreated and reused. The present work proposes stabilizing the CSW pH and degrading CN- to optimize biogas production. To control the acidity of the CSW we used natural oyster shells as source of CaCO3, and the photocatalytic degradation of CN− was achieved with Degussa P25 TiO2. Natural oyster shells raised pH from 4.5 to 6.2 over 6 h of reaction, efficiently controlling the effluent acidity. After pH stabilization, the TiO2 photocatalyst tested in a degradation process under visible light was able to reduce CN− concentration by 73.02 %. After these pretreatments (pH stabilization and CN- degradation), the CSW was inoculated with sewage sludge (SS) to produce biogas. The pretreatments were proved to be efficient at favoring biogas production as this was heightened by 27.6 %. In addition, the pretreated CSW and digestate (anaerobic digestion) significantly reduced the toxicity of the effluent, assessed by investigating lettuce seeds (L. sativa) germination and root growth. Thus, pretreatments and reuse of residues may potentially provide socio-environmental and economic benefits.

Caracterização e avaliação preliminar da ecotoxicidade de resíduo de indústrias de papelão

A indústria de papel e papelão é geradora de resíduos sólidos que demandam correto tratamento e disposição. O trabalho teve por objetivo caracterizar a composição de resíduos de duas empresas de papelão de Santa Catarina e avaliar sua ecotoxicidade. A caracterização foi feita com a determinação da umidade, cinzas e celulose. A ecotoxicidade foi avaliada com ensaios de fuga com minhocas (Eisenia andrei), ensaios de reprodução com colêmbolos (Folsomia candida) e com um teste de germinação e crescimento de raízes de alface (Lactuca sativa). Para as avaliações dos ensaios de toxicidade utilizou-se a ANOVA seguida dos testes de Tukey e/ou Dunnet e o teste exato de Fisher todos à p&lt;0,05. Os Resíduos 1 e 2 apresentaram umidade de 87,23 e 60,80%, cinzas 11,18 e 55,12% e celulose 59,34 e 66,78%, respectivamente. Os ensaios de fuga e de reprodução não indicaram ecotoxicidade dos resíduos estudados para minhocas e colêmbolos quando comparados ao solo de plantio de pinus. Em relação ao crescimento de raízes, o Resíduo 1 apresentou toxicidade para as concentrações de 100, 75 e 50% do seu elutriato. Os resultados indicaram que os resíduos possuem características químicas, físicas e ecotoxicológicas que podem ser restritivas quanto a sua aplicação em solos agrícolas.